+ * This method is caller sensitive, which means that it may return different + * values to different callers. + *
+ * For any given caller class {@code C}, the lookup object returned by this call + * has equivalent capabilities to any lookup object + * supplied by the JVM to the bootstrap method of an + * invokedynamic instruction + * executing in the same caller class {@code C}. + * @return a lookup object for the caller of this method, with private access + */ + @CallerSensitive + @ForceInline // to ensure Reflection.getCallerClass optimization + public static Lookup lookup() { + return new Lookup(Reflection.getCallerClass()); + } + + /** + * This reflected$lookup method is the alternate implementation of + * the lookup method when being invoked by reflection. + */ + @CallerSensitive + private static Lookup reflected$lookup() { + Class caller = Reflection.getCallerClass(); + if (caller.getClassLoader() == null) { + throw newIllegalArgumentException("illegal lookupClass: "+caller); + } + return new Lookup(caller); + } + + /** + * Returns a {@link Lookup lookup object} which is trusted minimally. + * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes. + * It can only be used to create method handles to public members of + * public classes in packages that are exported unconditionally. + *
+ * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class} + * of this lookup object will be {@link java.lang.Object}. + * + * @apiNote The use of Object is conventional, and because the lookup modes are + * limited, there is no special access provided to the internals of Object, its package + * or its module. Consequently, the lookup context of this lookup object will be the + * bootstrap class loader, which means it cannot find user classes. + * + *
+ * Discussion: + * The lookup class can be changed to any other class {@code C} using an expression of the form + * {@link Lookup#in publicLookup().in(C.class)}. + * but may change the lookup context by virtue of changing the class loader. + * A public lookup object is always subject to + * security manager checks. + * Also, it cannot access + * caller sensitive methods. + * @return a lookup object which is trusted minimally + * + * @revised 9 + * @spec JPMS + */ + public static Lookup publicLookup() { + return Lookup.PUBLIC_LOOKUP; + } + + /** + * Returns a {@link Lookup lookup object} with full capabilities to emulate all + * supported bytecode behaviors, including + * private access, on a target class. + * This method checks that a caller, specified as a {@code Lookup} object, is allowed to + * do deep reflection on the target class. If {@code m1} is the module containing + * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing + * the target class, then this check ensures that + *
+ * If there is a security manager, its {@code checkPermission} method is called to + * check {@code ReflectPermission("suppressAccessChecks")}. + * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object + * was created by code in the caller module (or derived from a lookup object originally + * created by the caller). A lookup object with the {@code MODULE} lookup mode can be + * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE} + * access to the caller. + * @param targetClass the target class + * @param lookup the caller lookup object + * @return a lookup object for the target class, with private access + * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class + * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null} + * @throws IllegalAccessException if the access check specified above fails + * @throws SecurityException if denied by the security manager + * @since 9 + * @spec JPMS + * @see Lookup#dropLookupMode + */ + public static Lookup privateLookupIn(Class targetClass, Lookup lookup) throws IllegalAccessException { + SecurityManager sm = System.getSecurityManager(); + if (sm != null) sm.checkPermission(ACCESS_PERMISSION); + if (targetClass.isPrimitive()) + throw new IllegalArgumentException(targetClass + " is a primitive class"); + if (targetClass.isArray()) + throw new IllegalArgumentException(targetClass + " is an array class"); + Module targetModule = targetClass.getModule(); + Module callerModule = lookup.lookupClass().getModule(); + if (!callerModule.canRead(targetModule)) + throw new IllegalAccessException(callerModule + " does not read " + targetModule); + if (targetModule.isNamed()) { + String pn = targetClass.getPackageName(); + assert pn.length() > 0 : "unnamed package cannot be in named module"; + if (!targetModule.isOpen(pn, callerModule)) + throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule); + } + if ((lookup.lookupModes() & Lookup.MODULE) == 0) + throw new IllegalAccessException("lookup does not have MODULE lookup mode"); + if (!callerModule.isNamed() && targetModule.isNamed()) { + IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger(); + if (logger != null) { + logger.logIfOpenedForIllegalAccess(lookup, targetClass); + } + } + return new Lookup(targetClass); + } + + /** + * Performs an unchecked "crack" of a + * direct method handle. + * The result is as if the user had obtained a lookup object capable enough + * to crack the target method handle, called + * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect} + * on the target to obtain its symbolic reference, and then called + * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs} + * to resolve the symbolic reference to a member. + *
+ * If there is a security manager, its {@code checkPermission} method
+ * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
+ * @param
+ * A lookup class which needs to create method handles will call
+ * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
+ * When the {@code Lookup} factory object is created, the identity of the lookup class is
+ * determined, and securely stored in the {@code Lookup} object.
+ * The lookup class (or its delegates) may then use factory methods
+ * on the {@code Lookup} object to create method handles for access-checked members.
+ * This includes all methods, constructors, and fields which are allowed to the lookup class,
+ * even private ones.
+ *
+ *
+ * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
+ * as if by {@code ldc CONSTANT_Class}.
+ * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
+ *
+ * In cases where the given member is of variable arity (i.e., a method or constructor)
+ * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
+ * In all other cases, the returned method handle will be of fixed arity.
+ *
+ * Discussion:
+ * The equivalence between looked-up method handles and underlying
+ * class members and bytecode behaviors
+ * can break down in a few ways:
+ *
+ * All access checks start from a {@code Lookup} object, which
+ * compares its recorded lookup class against all requests to
+ * create method handles.
+ * A single {@code Lookup} object can be used to create any number
+ * of access-checked method handles, all checked against a single
+ * lookup class.
+ *
+ * A {@code Lookup} object can be shared with other trusted code,
+ * such as a metaobject protocol.
+ * A shared {@code Lookup} object delegates the capability
+ * to create method handles on private members of the lookup class.
+ * Even if privileged code uses the {@code Lookup} object,
+ * the access checking is confined to the privileges of the
+ * original lookup class.
+ *
+ * A lookup can fail, because
+ * the containing class is not accessible to the lookup class, or
+ * because the desired class member is missing, or because the
+ * desired class member is not accessible to the lookup class, or
+ * because the lookup object is not trusted enough to access the member.
+ * In any of these cases, a {@code ReflectiveOperationException} will be
+ * thrown from the attempted lookup. The exact class will be one of
+ * the following:
+ *
+ * In general, the conditions under which a method handle may be
+ * looked up for a method {@code M} are no more restrictive than the conditions
+ * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
+ * Where the JVM would raise exceptions like {@code NoSuchMethodError},
+ * a method handle lookup will generally raise a corresponding
+ * checked exception, such as {@code NoSuchMethodException}.
+ * And the effect of invoking the method handle resulting from the lookup
+ * is exactly equivalent
+ * to executing the compiled, verified, and resolved call to {@code M}.
+ * The same point is true of fields and constructors.
+ *
+ * Discussion:
+ * Access checks only apply to named and reflected methods,
+ * constructors, and fields.
+ * Other method handle creation methods, such as
+ * {@link MethodHandle#asType MethodHandle.asType},
+ * do not require any access checks, and are used
+ * independently of any {@code Lookup} object.
+ *
+ * If the desired member is {@code protected}, the usual JVM rules apply,
+ * including the requirement that the lookup class must be either be in the
+ * same package as the desired member, or must inherit that member.
+ * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
+ * In addition, if the desired member is a non-static field or method
+ * in a different package, the resulting method handle may only be applied
+ * to objects of the lookup class or one of its subclasses.
+ * This requirement is enforced by narrowing the type of the leading
+ * {@code this} parameter from {@code C}
+ * (which will necessarily be a superclass of the lookup class)
+ * to the lookup class itself.
+ *
+ * The JVM imposes a similar requirement on {@code invokespecial} instruction,
+ * that the receiver argument must match both the resolved method and
+ * the current class. Again, this requirement is enforced by narrowing the
+ * type of the leading parameter to the resulting method handle.
+ * (See the Java Virtual Machine Specification, section 4.10.1.9.)
+ *
+ * The JVM represents constructors and static initializer blocks as internal methods
+ * with special names ({@code "
+ * In some cases, access between nested classes is obtained by the Java compiler by creating
+ * an wrapper method to access a private method of another class
+ * in the same top-level declaration.
+ * For example, a nested class {@code C.D}
+ * can access private members within other related classes such as
+ * {@code C}, {@code C.D.E}, or {@code C.B},
+ * but the Java compiler may need to generate wrapper methods in
+ * those related classes. In such cases, a {@code Lookup} object on
+ * {@code C.E} would be unable to those private members.
+ * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
+ * which can transform a lookup on {@code C.E} into one on any of those other
+ * classes, without special elevation of privilege.
+ *
+ * The accesses permitted to a given lookup object may be limited,
+ * according to its set of {@link #lookupModes lookupModes},
+ * to a subset of members normally accessible to the lookup class.
+ * For example, the {@link MethodHandles#publicLookup publicLookup}
+ * method produces a lookup object which is only allowed to access
+ * public members in public classes of exported packages.
+ * The caller sensitive method {@link MethodHandles#lookup lookup}
+ * produces a lookup object with full capabilities relative to
+ * its caller class, to emulate all supported bytecode behaviors.
+ * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
+ * with fewer access modes than the original lookup object.
+ *
+ *
+ *
+ * Discussion of private access:
+ * We say that a lookup has private access
+ * if its {@linkplain #lookupModes lookup modes}
+ * include the possibility of accessing {@code private} members.
+ * As documented in the relevant methods elsewhere,
+ * only lookups with private access possess the following capabilities:
+ *
+ * Each of these permissions is a consequence of the fact that a lookup object
+ * with private access can be securely traced back to an originating class,
+ * whose bytecode behaviors and Java language access permissions
+ * can be reliably determined and emulated by method handles.
+ *
+ *
+ * If a security manager is present, member and class lookups are subject to
+ * additional checks.
+ * From one to three calls are made to the security manager.
+ * Any of these calls can refuse access by throwing a
+ * {@link java.lang.SecurityException SecurityException}.
+ * Define {@code smgr} as the security manager,
+ * {@code lookc} as the lookup class of the current lookup object,
+ * {@code refc} as the containing class in which the member
+ * is being sought, and {@code defc} as the class in which the
+ * member is actually defined.
+ * (If a class or other type is being accessed,
+ * the {@code refc} and {@code defc} values are the class itself.)
+ * The value {@code lookc} is defined as not present
+ * if the current lookup object does not have
+ * private access.
+ * The calls are made according to the following rules:
+ *
+ * If a method handle for a caller-sensitive method is requested,
+ * the general rules for bytecode behaviors apply,
+ * but they take account of the lookup class in a special way.
+ * The resulting method handle behaves as if it were called
+ * from an instruction contained in the lookup class,
+ * so that the caller-sensitive method detects the lookup class.
+ * (By contrast, the invoker of the method handle is disregarded.)
+ * Thus, in the case of caller-sensitive methods,
+ * different lookup classes may give rise to
+ * differently behaving method handles.
+ *
+ * In cases where the lookup object is
+ * {@link MethodHandles#publicLookup() publicLookup()},
+ * or some other lookup object without
+ * private access,
+ * the lookup class is disregarded.
+ * In such cases, no caller-sensitive method handle can be created,
+ * access is forbidden, and the lookup fails with an
+ * {@code IllegalAccessException}.
+ *
+ * Discussion:
+ * For example, the caller-sensitive method
+ * {@link java.lang.Class#forName(String) Class.forName(x)}
+ * can return varying classes or throw varying exceptions,
+ * depending on the class loader of the class that calls it.
+ * A public lookup of {@code Class.forName} will fail, because
+ * there is no reasonable way to determine its bytecode behavior.
+ *
+ * If an application caches method handles for broad sharing,
+ * it should use {@code publicLookup()} to create them.
+ * If there is a lookup of {@code Class.forName}, it will fail,
+ * and the application must take appropriate action in that case.
+ * It may be that a later lookup, perhaps during the invocation of a
+ * bootstrap method, can incorporate the specific identity
+ * of the caller, making the method accessible.
+ *
+ * The function {@code MethodHandles.lookup} is caller sensitive
+ * so that there can be a secure foundation for lookups.
+ * Nearly all other methods in the JSR 292 API rely on lookup
+ * objects to check access requests.
+ *
+ * @revised 9
+ */
+ public static final
+ class Lookup {
+ /** The class on behalf of whom the lookup is being performed. */
+ private final Class lookupClass;
+
+ /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
+ private final int allowedModes;
+
+ /** A single-bit mask representing {@code public} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x01}, happens to be the same as the value of the
+ * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
+ */
+ public static final int PUBLIC = Modifier.PUBLIC;
+
+ /** A single-bit mask representing {@code private} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x02}, happens to be the same as the value of the
+ * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
+ */
+ public static final int PRIVATE = Modifier.PRIVATE;
+
+ /** A single-bit mask representing {@code protected} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x04}, happens to be the same as the value of the
+ * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
+ */
+ public static final int PROTECTED = Modifier.PROTECTED;
+
+ /** A single-bit mask representing {@code package} access (default access),
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value is {@code 0x08}, which does not correspond meaningfully to
+ * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
+ */
+ public static final int PACKAGE = Modifier.STATIC;
+
+ /** A single-bit mask representing {@code module} access (default access),
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value is {@code 0x10}, which does not correspond meaningfully to
+ * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
+ * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
+ * with this lookup mode can access all public types in the module of the
+ * lookup class and public types in packages exported by other modules
+ * to the module of the lookup class.
+ * @since 9
+ * @spec JPMS
+ */
+ public static final int MODULE = PACKAGE << 1;
+
+ /** A single-bit mask representing {@code unconditional} access
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value is {@code 0x20}, which does not correspond meaningfully to
+ * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
+ * A {@code Lookup} with this lookup mode assumes {@linkplain
+ * java.lang.Module#canRead(java.lang.Module) readability}.
+ * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
+ * with this lookup mode can access all public members of public types
+ * of all modules where the type is in a package that is {@link
+ * java.lang.Module#isExported(String) exported unconditionally}.
+ * @since 9
+ * @spec JPMS
+ * @see #publicLookup()
+ */
+ public static final int UNCONDITIONAL = PACKAGE << 2;
+
+ private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
+ private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
+ private static final int TRUSTED = -1;
+
+ private static int fixmods(int mods) {
+ mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
+ return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
+ }
+
+ /** Tells which class is performing the lookup. It is this class against
+ * which checks are performed for visibility and access permissions.
+ *
+ * The class implies a maximum level of access permission,
+ * but the permissions may be additionally limited by the bitmask
+ * {@link #lookupModes lookupModes}, which controls whether non-public members
+ * can be accessed.
+ * @return the lookup class, on behalf of which this lookup object finds members
+ */
+ public Class lookupClass() {
+ return lookupClass;
+ }
+
+ // This is just for calling out to MethodHandleImpl.
+ private Class lookupClassOrNull() {
+ return (allowedModes == TRUSTED) ? null : lookupClass;
+ }
+
+ /** Tells which access-protection classes of members this lookup object can produce.
+ * The result is a bit-mask of the bits
+ * {@linkplain #PUBLIC PUBLIC (0x01)},
+ * {@linkplain #PRIVATE PRIVATE (0x02)},
+ * {@linkplain #PROTECTED PROTECTED (0x04)},
+ * {@linkplain #PACKAGE PACKAGE (0x08)},
+ * {@linkplain #MODULE MODULE (0x10)},
+ * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
+ *
+ * A freshly-created lookup object
+ * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
+ * all possible bits set, except {@code UNCONDITIONAL}. The lookup can be used to
+ * access all members of the caller's class, all public types in the caller's module,
+ * and all public types in packages exported by other modules to the caller's module.
+ * A lookup object on a new lookup class
+ * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
+ * may have some mode bits set to zero.
+ * Mode bits can also be
+ * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
+ * Once cleared, mode bits cannot be restored from the downgraded lookup object.
+ * The purpose of this is to restrict access via the new lookup object,
+ * so that it can access only names which can be reached by the original
+ * lookup object, and also by the new lookup class.
+ * @return the lookup modes, which limit the kinds of access performed by this lookup object
+ * @see #in
+ * @see #dropLookupMode
+ *
+ * @revised 9
+ * @spec JPMS
+ */
+ public int lookupModes() {
+ return allowedModes & ALL_MODES;
+ }
+
+ /** Embody the current class (the lookupClass) as a lookup class
+ * for method handle creation.
+ * Must be called by from a method in this package,
+ * which in turn is called by a method not in this package.
+ */
+ Lookup(Class lookupClass) {
+ this(lookupClass, FULL_POWER_MODES);
+ // make sure we haven't accidentally picked up a privileged class:
+ checkUnprivilegedlookupClass(lookupClass);
+ }
+
+ private Lookup(Class lookupClass, int allowedModes) {
+ this.lookupClass = lookupClass;
+ this.allowedModes = allowedModes;
+ }
+
+ /**
+ * Creates a lookup on the specified new lookup class.
+ * The resulting object will report the specified
+ * class as its own {@link #lookupClass() lookupClass}.
+ *
+ * However, the resulting {@code Lookup} object is guaranteed
+ * to have no more access capabilities than the original.
+ * In particular, access capabilities can be lost as follows:
+ * The resulting lookup's capabilities for loading classes
+ * (used during {@link #findClass} invocations)
+ * are determined by the lookup class' loader,
+ * which may change due to this operation.
+ *
+ * @param requestedLookupClass the desired lookup class for the new lookup object
+ * @return a lookup object which reports the desired lookup class, or the same object
+ * if there is no change
+ * @throws NullPointerException if the argument is null
+ *
+ * @revised 9
+ * @spec JPMS
+ */
+ public Lookup in(Class requestedLookupClass) {
+ Objects.requireNonNull(requestedLookupClass);
+ if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
+ return new Lookup(requestedLookupClass, FULL_POWER_MODES);
+ if (requestedLookupClass == this.lookupClass)
+ return this; // keep same capabilities
+ int newModes = (allowedModes & FULL_POWER_MODES);
+ if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
+ // Need to drop all access when teleporting from a named module to another
+ // module. The exception is publicLookup where PUBLIC is not lost.
+ if (this.lookupClass.getModule().isNamed()
+ && (this.allowedModes & UNCONDITIONAL) == 0)
+ newModes = 0;
+ else
+ newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
+ }
+ if ((newModes & PACKAGE) != 0
+ && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
+ newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
+ }
+ // Allow nestmate lookups to be created without special privilege:
+ if ((newModes & PRIVATE) != 0
+ && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
+ newModes &= ~(PRIVATE|PROTECTED);
+ }
+ if ((newModes & PUBLIC) != 0
+ && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
+ // The requested class it not accessible from the lookup class.
+ // No permissions.
+ newModes = 0;
+ }
+
+ checkUnprivilegedlookupClass(requestedLookupClass);
+ return new Lookup(requestedLookupClass, newModes);
+ }
+
+
+ /**
+ * Creates a lookup on the same lookup class which this lookup object
+ * finds members, but with a lookup mode that has lost the given lookup mode.
+ * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
+ * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
+ * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
+ * dropped and so the resulting lookup mode will never have these access capabilities.
+ * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
+ * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
+ * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
+ * is dropped then the resulting lookup has no access.
+ * @param modeToDrop the lookup mode to drop
+ * @return a lookup object which lacks the indicated mode, or the same object if there is no change
+ * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
+ * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
+ * @see MethodHandles#privateLookupIn
+ * @since 9
+ */
+ public Lookup dropLookupMode(int modeToDrop) {
+ int oldModes = lookupModes();
+ int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
+ switch (modeToDrop) {
+ case PUBLIC: newModes &= ~(ALL_MODES); break;
+ case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
+ case PACKAGE: newModes &= ~(PRIVATE); break;
+ case PROTECTED:
+ case PRIVATE:
+ case UNCONDITIONAL: break;
+ default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
+ }
+ if (newModes == oldModes) return this; // return self if no change
+ return new Lookup(lookupClass(), newModes);
+ }
+
+ /**
+ * Defines a class to the same class loader and in the same runtime package and
+ * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
+ * {@linkplain #lookupClass() lookup class}.
+ *
+ * The {@linkplain #lookupModes() lookup modes} for this lookup must include
+ * {@link #PACKAGE PACKAGE} access as default (package) members will be
+ * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
+ * that the lookup object was created by a caller in the runtime package (or derived
+ * from a lookup originally created by suitably privileged code to a target class in
+ * the runtime package). The {@code bytes} parameter is the class bytes of a valid class file (as defined
+ * by the The Java Virtual Machine Specification) with a class name in the
+ * same package as the lookup class. This method does not run the class initializer. The class initializer may
+ * run at a later time, as detailed in section 12.4 of the The Java Language
+ * Specification. If there is a security manager, its {@code checkPermission} method is first called
+ * to check {@code RuntimePermission("defineClass")}.
+ * (It may seem strange that protected access should be
+ * stronger than private access. Viewed independently from
+ * package access, protected access is the first to be lost,
+ * because it requires a direct subclass relationship between
+ * caller and callee.)
+ * @see #in
+ *
+ * @revised 9
+ * @spec JPMS
+ */
+ @Override
+ public String toString() {
+ String cname = lookupClass.getName();
+ switch (allowedModes) {
+ case 0: // no privileges
+ return cname + "/noaccess";
+ case PUBLIC:
+ return cname + "/public";
+ case PUBLIC|UNCONDITIONAL:
+ return cname + "/publicLookup";
+ case PUBLIC|MODULE:
+ return cname + "/module";
+ case PUBLIC|MODULE|PACKAGE:
+ return cname + "/package";
+ case FULL_POWER_MODES & ~PROTECTED:
+ return cname + "/private";
+ case FULL_POWER_MODES:
+ return cname;
+ case TRUSTED:
+ return "/trusted"; // internal only; not exported
+ default: // Should not happen, but it's a bitfield...
+ cname = cname + "/" + Integer.toHexString(allowedModes);
+ assert(false) : cname;
+ return cname;
+ }
+ }
+
+ /**
+ * Produces a method handle for a static method.
+ * The type of the method handle will be that of the method.
+ * (Since static methods do not take receivers, there is no
+ * additional receiver argument inserted into the method handle type,
+ * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
+ * The method and all its argument types must be accessible to the lookup object.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * If the returned method handle is invoked, the method's class will
+ * be initialized, if it has not already been initialized.
+ * Example:
+ *
+ * When called, the handle will treat the first argument as a receiver
+ * and dispatch on the receiver's type to determine which method
+ * implementation to enter.
+ * (The dispatching action is identical with that performed by an
+ * {@code invokevirtual} or {@code invokeinterface} instruction.)
+ *
+ * The first argument will be of type {@code refc} if the lookup
+ * class has full privileges to access the member. Otherwise
+ * the member must be {@code protected} and the first argument
+ * will be restricted in type to the lookup class.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * Because of the general equivalence between {@code invokevirtual}
+ * instructions and method handles produced by {@code findVirtual},
+ * if the class is {@code MethodHandle} and the name string is
+ * {@code invokeExact} or {@code invoke}, the resulting
+ * method handle is equivalent to one produced by
+ * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
+ * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
+ * with the same {@code type} argument.
+ *
+ * If the class is {@code VarHandle} and the name string corresponds to
+ * the name of a signature-polymorphic access mode method, the resulting
+ * method handle is equivalent to one produced by
+ * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
+ * the access mode corresponding to the name string and with the same
+ * {@code type} arguments.
+ *
+ * Example:
+ *
+ * The requested type must have a return type of {@code void}.
+ * (This is consistent with the JVM's treatment of constructor type descriptors.)
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * If the returned method handle is invoked, the constructor's class will
+ * be initialized, if it has not already been initialized.
+ * Example:
+ *
+ * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
+ * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
+ * load the requested class, and then determines whether the class is accessible to this lookup object.
+ *
+ * @param targetName the fully qualified name of the class to be looked up.
+ * @return the requested class.
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws LinkageError if the linkage fails
+ * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
+ * @throws IllegalAccessException if the class is not accessible, using the allowed access
+ * modes.
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @since 9
+ */
+ public Class findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
+ Class targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
+ return accessClass(targetClass);
+ }
+
+ /**
+ * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
+ * static initializer of the class is not run.
+ *
+ * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
+ * {@linkplain #lookupModes() lookup modes}.
+ *
+ * @param targetClass the class to be access-checked
+ *
+ * @return the class that has been access-checked
+ *
+ * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
+ * modes.
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @since 9
+ */
+ public Class accessClass(Class targetClass) throws IllegalAccessException {
+ if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
+ throw new MemberName(targetClass).makeAccessException("access violation", this);
+ }
+ checkSecurityManager(targetClass, null);
+ return targetClass;
+ }
+
+ /**
+ * Produces an early-bound method handle for a virtual method.
+ * It will bypass checks for overriding methods on the receiver,
+ * as if called from an {@code invokespecial}
+ * instruction from within the explicitly specified {@code specialCaller}.
+ * The type of the method handle will be that of the method,
+ * with a suitably restricted receiver type prepended.
+ * (The receiver type will be {@code specialCaller} or a subtype.)
+ * The method and all its argument types must be accessible
+ * to the lookup object.
+ *
+ * Before method resolution,
+ * if the explicitly specified caller class is not identical with the
+ * lookup class, or if this lookup object does not have
+ * private access
+ * privileges, the access fails.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * (Note: JVM internal methods named {@code " Example:
+ *
+ * Access checking is performed immediately on behalf of the lookup
+ * class.
+ *
+ * Certain access modes of the returned VarHandle are unsupported under
+ * the following conditions:
+ *
+ * If the field is declared {@code volatile} then the returned VarHandle
+ * will override access to the field (effectively ignore the
+ * {@code volatile} declaration) in accordance to its specified
+ * access modes.
+ *
+ * If the field type is {@code float} or {@code double} then numeric
+ * and atomic update access modes compare values using their bitwise
+ * representation (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @apiNote
+ * Bitwise comparison of {@code float} values or {@code double} values,
+ * as performed by the numeric and atomic update access modes, differ
+ * from the primitive {@code ==} operator and the {@link Float#equals}
+ * and {@link Double#equals} methods, specifically with respect to
+ * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
+ * Care should be taken when performing a compare and set or a compare
+ * and exchange operation with such values since the operation may
+ * unexpectedly fail.
+ * There are many possible NaN values that are considered to be
+ * {@code NaN} in Java, although no IEEE 754 floating-point operation
+ * provided by Java can distinguish between them. Operation failure can
+ * occur if the expected or witness value is a NaN value and it is
+ * transformed (perhaps in a platform specific manner) into another NaN
+ * value, and thus has a different bitwise representation (see
+ * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
+ * details).
+ * The values {@code -0.0} and {@code +0.0} have different bitwise
+ * representations but are considered equal when using the primitive
+ * {@code ==} operator. Operation failure can occur if, for example, a
+ * numeric algorithm computes an expected value to be say {@code -0.0}
+ * and previously computed the witness value to be say {@code +0.0}.
+ * @param recv the receiver class, of type {@code R}, that declares the
+ * non-static field
+ * @param name the field's name
+ * @param type the field's type, of type {@code T}
+ * @return a VarHandle giving access to non-static fields.
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ * @since 9
+ */
+ public VarHandle findVarHandle(Class recv, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName getField = resolveOrFail(REF_getField, recv, name, type);
+ MemberName putField = resolveOrFail(REF_putField, recv, name, type);
+ return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
+ }
+
+ /**
+ * Produces a method handle giving read access to a static field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * The method handle will take no arguments.
+ * Access checking is performed immediately on behalf of the lookup class.
+ *
+ * If the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can load values from the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findStaticGetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
+ return getDirectField(REF_getStatic, refc, field);
+ }
+
+ /**
+ * Produces a method handle giving write access to a static field.
+ * The type of the method handle will have a void return type.
+ * The method handle will take a single
+ * argument, of the field's value type, the value to be stored.
+ * Access checking is performed immediately on behalf of the lookup class.
+ *
+ * If the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can store values into the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findStaticSetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
+ return getDirectField(REF_putStatic, refc, field);
+ }
+
+ /**
+ * Produces a VarHandle giving access to a static field {@code name} of
+ * type {@code type} declared in a class of type {@code decl}.
+ * The VarHandle's variable type is {@code type} and it has no
+ * coordinate types.
+ *
+ * Access checking is performed immediately on behalf of the lookup
+ * class.
+ *
+ * If the returned VarHandle is operated on, the declaring class will be
+ * initialized, if it has not already been initialized.
+ *
+ * Certain access modes of the returned VarHandle are unsupported under
+ * the following conditions:
+ *
+ * If the field is declared {@code volatile} then the returned VarHandle
+ * will override access to the field (effectively ignore the
+ * {@code volatile} declaration) in accordance to its specified
+ * access modes.
+ *
+ * If the field type is {@code float} or {@code double} then numeric
+ * and atomic update access modes compare values using their bitwise
+ * representation (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @apiNote
+ * Bitwise comparison of {@code float} values or {@code double} values,
+ * as performed by the numeric and atomic update access modes, differ
+ * from the primitive {@code ==} operator and the {@link Float#equals}
+ * and {@link Double#equals} methods, specifically with respect to
+ * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
+ * Care should be taken when performing a compare and set or a compare
+ * and exchange operation with such values since the operation may
+ * unexpectedly fail.
+ * There are many possible NaN values that are considered to be
+ * {@code NaN} in Java, although no IEEE 754 floating-point operation
+ * provided by Java can distinguish between them. Operation failure can
+ * occur if the expected or witness value is a NaN value and it is
+ * transformed (perhaps in a platform specific manner) into another NaN
+ * value, and thus has a different bitwise representation (see
+ * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
+ * details).
+ * The values {@code -0.0} and {@code +0.0} have different bitwise
+ * representations but are considered equal when using the primitive
+ * {@code ==} operator. Operation failure can occur if, for example, a
+ * numeric algorithm computes an expected value to be say {@code -0.0}
+ * and previously computed the witness value to be say {@code +0.0}.
+ * @param decl the class that declares the static field
+ * @param name the field's name
+ * @param type the field's type, of type {@code T}
+ * @return a VarHandle giving access to a static field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ * @since 9
+ */
+ public VarHandle findStaticVarHandle(Class decl, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
+ MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
+ return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
+ }
+
+ /**
+ * Produces an early-bound method handle for a non-static method.
+ * The receiver must have a supertype {@code defc} in which a method
+ * of the given name and type is accessible to the lookup class.
+ * The method and all its argument types must be accessible to the lookup object.
+ * The type of the method handle will be that of the method,
+ * without any insertion of an additional receiver parameter.
+ * The given receiver will be bound into the method handle,
+ * so that every call to the method handle will invoke the
+ * requested method on the given receiver.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set
+ * and the trailing array argument is not the only argument.
+ * (If the trailing array argument is the only argument,
+ * the given receiver value will be bound to it.)
+ *
+ * This is almost equivalent to the following code, with some differences noted below:
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * If m is static, and
+ * if the returned method handle is invoked, the method's class will
+ * be initialized, if it has not already been initialized.
+ * @param m the reflected method
+ * @return a method handle which can invoke the reflected method
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflect(Method m) throws IllegalAccessException {
+ if (m.getDeclaringClass() == MethodHandle.class) {
+ MethodHandle mh = unreflectForMH(m);
+ if (mh != null) return mh;
+ }
+ if (m.getDeclaringClass() == VarHandle.class) {
+ MethodHandle mh = unreflectForVH(m);
+ if (mh != null) return mh;
+ }
+ MemberName method = new MemberName(m);
+ byte refKind = method.getReferenceKind();
+ if (refKind == REF_invokeSpecial)
+ refKind = REF_invokeVirtual;
+ assert(method.isMethod());
+ @SuppressWarnings("deprecation")
+ Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
+ return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
+ }
+ private MethodHandle unreflectForMH(Method m) {
+ // these names require special lookups because they throw UnsupportedOperationException
+ if (MemberName.isMethodHandleInvokeName(m.getName()))
+ return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
+ return null;
+ }
+ private MethodHandle unreflectForVH(Method m) {
+ // these names require special lookups because they throw UnsupportedOperationException
+ if (MemberName.isVarHandleMethodInvokeName(m.getName()))
+ return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
+ return null;
+ }
+
+ /**
+ * Produces a method handle for a reflected method.
+ * It will bypass checks for overriding methods on the receiver,
+ * as if called from an {@code invokespecial}
+ * instruction from within the explicitly specified {@code specialCaller}.
+ * The type of the method handle will be that of the method,
+ * with a suitably restricted receiver type prepended.
+ * (The receiver type will be {@code specialCaller} or a subtype.)
+ * If the method's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class,
+ * as if {@code invokespecial} instruction were being linked.
+ *
+ * Before method resolution,
+ * if the explicitly specified caller class is not identical with the
+ * lookup class, or if this lookup object does not have
+ * private access
+ * privileges, the access fails.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * @param m the reflected method
+ * @param specialCaller the class nominally calling the method
+ * @return a method handle which can invoke the reflected method
+ * @throws IllegalAccessException if access checking fails,
+ * or if the method is {@code static},
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle unreflectSpecial(Method m, Class specialCaller) throws IllegalAccessException {
+ checkSpecialCaller(specialCaller, null);
+ Lookup specialLookup = this.in(specialCaller);
+ MemberName method = new MemberName(m, true);
+ assert(method.isMethod());
+ // ignore m.isAccessible: this is a new kind of access
+ return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
+ }
+
+ /**
+ * Produces a method handle for a reflected constructor.
+ * The type of the method handle will be that of the constructor,
+ * with the return type changed to the declaring class.
+ * The method handle will perform a {@code newInstance} operation,
+ * creating a new instance of the constructor's class on the
+ * arguments passed to the method handle.
+ *
+ * If the constructor's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ *
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
+ *
+ * If the returned method handle is invoked, the constructor's class will
+ * be initialized, if it has not already been initialized.
+ * @param c the reflected constructor
+ * @return a method handle which can invoke the reflected constructor
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectConstructor(Constructor c) throws IllegalAccessException {
+ MemberName ctor = new MemberName(c);
+ assert(ctor.isConstructor());
+ @SuppressWarnings("deprecation")
+ Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
+ return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
+ }
+
+ /**
+ * Produces a method handle giving read access to a reflected field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * If the field is static, the method handle will take no arguments.
+ * Otherwise, its single argument will be the instance containing
+ * the field.
+ * If the field's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ *
+ * If the field is static, and
+ * if the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param f the reflected field
+ * @return a method handle which can load values from the reflected field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
+ return unreflectField(f, false);
+ }
+ private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
+ MemberName field = new MemberName(f, isSetter);
+ assert(isSetter
+ ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
+ : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
+ @SuppressWarnings("deprecation")
+ Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
+ return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
+ }
+
+ /**
+ * Produces a method handle giving write access to a reflected field.
+ * The type of the method handle will have a void return type.
+ * If the field is static, the method handle will take a single
+ * argument, of the field's value type, the value to be stored.
+ * Otherwise, the two arguments will be the instance containing
+ * the field, and the value to be stored.
+ * If the field's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ *
+ * If the field is static, and
+ * if the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param f the reflected field
+ * @return a method handle which can store values into the reflected field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
+ return unreflectField(f, true);
+ }
+
+ /**
+ * Produces a VarHandle giving access to a reflected field {@code f}
+ * of type {@code T} declared in a class of type {@code R}.
+ * The VarHandle's variable type is {@code T}.
+ * If the field is non-static the VarHandle has one coordinate type,
+ * {@code R}. Otherwise, the field is static, and the VarHandle has no
+ * coordinate types.
+ *
+ * Access checking is performed immediately on behalf of the lookup
+ * class, regardless of the value of the field's {@code accessible}
+ * flag.
+ *
+ * If the field is static, and if the returned VarHandle is operated
+ * on, the field's declaring class will be initialized, if it has not
+ * already been initialized.
+ *
+ * Certain access modes of the returned VarHandle are unsupported under
+ * the following conditions:
+ *
+ * If the field is declared {@code volatile} then the returned VarHandle
+ * will override access to the field (effectively ignore the
+ * {@code volatile} declaration) in accordance to its specified
+ * access modes.
+ *
+ * If the field type is {@code float} or {@code double} then numeric
+ * and atomic update access modes compare values using their bitwise
+ * representation (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @apiNote
+ * Bitwise comparison of {@code float} values or {@code double} values,
+ * as performed by the numeric and atomic update access modes, differ
+ * from the primitive {@code ==} operator and the {@link Float#equals}
+ * and {@link Double#equals} methods, specifically with respect to
+ * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
+ * Care should be taken when performing a compare and set or a compare
+ * and exchange operation with such values since the operation may
+ * unexpectedly fail.
+ * There are many possible NaN values that are considered to be
+ * {@code NaN} in Java, although no IEEE 754 floating-point operation
+ * provided by Java can distinguish between them. Operation failure can
+ * occur if the expected or witness value is a NaN value and it is
+ * transformed (perhaps in a platform specific manner) into another NaN
+ * value, and thus has a different bitwise representation (see
+ * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
+ * details).
+ * The values {@code -0.0} and {@code +0.0} have different bitwise
+ * representations but are considered equal when using the primitive
+ * {@code ==} operator. Operation failure can occur if, for example, a
+ * numeric algorithm computes an expected value to be say {@code -0.0}
+ * and previously computed the witness value to be say {@code +0.0}.
+ * @param f the reflected field, with a field of type {@code T}, and
+ * a declaring class of type {@code R}
+ * @return a VarHandle giving access to non-static fields or a static
+ * field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ * @since 9
+ */
+ public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
+ MemberName getField = new MemberName(f, false);
+ MemberName putField = new MemberName(f, true);
+ return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
+ f.getDeclaringClass(), getField, putField);
+ }
+
+ /**
+ * Cracks a direct method handle
+ * created by this lookup object or a similar one.
+ * Security and access checks are performed to ensure that this lookup object
+ * is capable of reproducing the target method handle.
+ * This means that the cracking may fail if target is a direct method handle
+ * but was created by an unrelated lookup object.
+ * This can happen if the method handle is caller sensitive
+ * and was created by a lookup object for a different class.
+ * @param target a direct method handle to crack into symbolic reference components
+ * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
+ * @exception NullPointerException if the target is {@code null}
+ * @see MethodHandleInfo
+ * @since 1.8
+ */
+ public MethodHandleInfo revealDirect(MethodHandle target) {
+ MemberName member = target.internalMemberName();
+ if (member == null || (!member.isResolved() &&
+ !member.isMethodHandleInvoke() &&
+ !member.isVarHandleMethodInvoke()))
+ throw newIllegalArgumentException("not a direct method handle");
+ Class defc = member.getDeclaringClass();
+ byte refKind = member.getReferenceKind();
+ assert(MethodHandleNatives.refKindIsValid(refKind));
+ if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
+ // Devirtualized method invocation is usually formally virtual.
+ // To avoid creating extra MemberName objects for this common case,
+ // we encode this extra degree of freedom using MH.isInvokeSpecial.
+ refKind = REF_invokeVirtual;
+ if (refKind == REF_invokeVirtual && defc.isInterface())
+ // Symbolic reference is through interface but resolves to Object method (toString, etc.)
+ refKind = REF_invokeInterface;
+ // Check SM permissions and member access before cracking.
+ try {
+ checkAccess(refKind, defc, member);
+ checkSecurityManager(defc, member);
+ } catch (IllegalAccessException ex) {
+ throw new IllegalArgumentException(ex);
+ }
+ if (allowedModes != TRUSTED && member.isCallerSensitive()) {
+ Class callerClass = target.internalCallerClass();
+ if (!hasPrivateAccess() || callerClass != lookupClass())
+ throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
+ }
+ // Produce the handle to the results.
+ return new InfoFromMemberName(this, member, refKind);
+ }
+
+ /// Helper methods, all package-private.
+
+ MemberName resolveOrFail(byte refKind, Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ checkSymbolicClass(refc); // do this before attempting to resolve
+ Objects.requireNonNull(name);
+ Objects.requireNonNull(type);
+ return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
+ NoSuchFieldException.class);
+ }
+
+ MemberName resolveOrFail(byte refKind, Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ checkSymbolicClass(refc); // do this before attempting to resolve
+ Objects.requireNonNull(name);
+ Objects.requireNonNull(type);
+ checkMethodName(refKind, name); // NPE check on name
+ return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
+ NoSuchMethodException.class);
+ }
+
+ MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
+ checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
+ Objects.requireNonNull(member.getName());
+ Objects.requireNonNull(member.getType());
+ return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
+ ReflectiveOperationException.class);
+ }
+
+ void checkSymbolicClass(Class refc) throws IllegalAccessException {
+ Objects.requireNonNull(refc);
+ Class caller = lookupClassOrNull();
+ if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
+ throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
+ }
+
+ /** Check name for an illegal leading "<" character. */
+ void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
+ if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
+ throw new NoSuchMethodException("illegal method name: "+name);
+ }
+
+
+ /**
+ * Find my trustable caller class if m is a caller sensitive method.
+ * If this lookup object has private access, then the caller class is the lookupClass.
+ * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
+ */
+ Class findBoundCallerClass(MemberName m) throws IllegalAccessException {
+ Class callerClass = null;
+ if (MethodHandleNatives.isCallerSensitive(m)) {
+ // Only lookups with private access are allowed to resolve caller-sensitive methods
+ if (hasPrivateAccess()) {
+ callerClass = lookupClass;
+ } else {
+ throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
+ }
+ }
+ return callerClass;
+ }
+
+ /**
+ * Returns {@code true} if this lookup has {@code PRIVATE} access.
+ * @return {@code true} if this lookup has {@code PRIVATE} access.
+ * @since 9
+ */
+ public boolean hasPrivateAccess() {
+ return (allowedModes & PRIVATE) != 0;
+ }
+
+ /**
+ * Perform necessary access checks.
+ * Determines a trustable caller class to compare with refc, the symbolic reference class.
+ * If this lookup object has private access, then the caller class is the lookupClass.
+ */
+ void checkSecurityManager(Class refc, MemberName m) {
+ SecurityManager smgr = System.getSecurityManager();
+ if (smgr == null) return;
+ if (allowedModes == TRUSTED) return;
+
+ // Step 1:
+ boolean fullPowerLookup = hasPrivateAccess();
+ if (!fullPowerLookup ||
+ !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
+ ReflectUtil.checkPackageAccess(refc);
+ }
+
+ if (m == null) { // findClass or accessClass
+ // Step 2b:
+ if (!fullPowerLookup) {
+ smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
+ }
+ return;
+ }
+
+ // Step 2a:
+ if (m.isPublic()) return;
+ if (!fullPowerLookup) {
+ smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
+ }
+
+ // Step 3:
+ Class defc = m.getDeclaringClass();
+ if (!fullPowerLookup && defc != refc) {
+ ReflectUtil.checkPackageAccess(defc);
+ }
+ }
+
+ void checkMethod(byte refKind, Class refc, MemberName m) throws IllegalAccessException {
+ boolean wantStatic = (refKind == REF_invokeStatic);
+ String message;
+ if (m.isConstructor())
+ message = "expected a method, not a constructor";
+ else if (!m.isMethod())
+ message = "expected a method";
+ else if (wantStatic != m.isStatic())
+ message = wantStatic ? "expected a static method" : "expected a non-static method";
+ else
+ { checkAccess(refKind, refc, m); return; }
+ throw m.makeAccessException(message, this);
+ }
+
+ void checkField(byte refKind, Class refc, MemberName m) throws IllegalAccessException {
+ boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
+ String message;
+ if (wantStatic != m.isStatic())
+ message = wantStatic ? "expected a static field" : "expected a non-static field";
+ else
+ { checkAccess(refKind, refc, m); return; }
+ throw m.makeAccessException(message, this);
+ }
+
+ /** Check public/protected/private bits on the symbolic reference class and its member. */
+ void checkAccess(byte refKind, Class refc, MemberName m) throws IllegalAccessException {
+ assert(m.referenceKindIsConsistentWith(refKind) &&
+ MethodHandleNatives.refKindIsValid(refKind) &&
+ (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
+ int allowedModes = this.allowedModes;
+ if (allowedModes == TRUSTED) return;
+ int mods = m.getModifiers();
+ if (Modifier.isProtected(mods) &&
+ refKind == REF_invokeVirtual &&
+ m.getDeclaringClass() == Object.class &&
+ m.getName().equals("clone") &&
+ refc.isArray()) {
+ // The JVM does this hack also.
+ // (See ClassVerifier::verify_invoke_instructions
+ // and LinkResolver::check_method_accessability.)
+ // Because the JVM does not allow separate methods on array types,
+ // there is no separate method for int[].clone.
+ // All arrays simply inherit Object.clone.
+ // But for access checking logic, we make Object.clone
+ // (normally protected) appear to be public.
+ // Later on, when the DirectMethodHandle is created,
+ // its leading argument will be restricted to the
+ // requested array type.
+ // N.B. The return type is not adjusted, because
+ // that is *not* the bytecode behavior.
+ mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
+ }
+ if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
+ // cannot "new" a protected ctor in a different package
+ mods ^= Modifier.PROTECTED;
+ }
+ if (Modifier.isFinal(mods) &&
+ MethodHandleNatives.refKindIsSetter(refKind))
+ throw m.makeAccessException("unexpected set of a final field", this);
+ int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
+ if ((requestedModes & allowedModes) != 0) {
+ if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
+ mods, lookupClass(), allowedModes))
+ return;
+ } else {
+ // Protected members can also be checked as if they were package-private.
+ if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
+ && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
+ return;
+ }
+ throw m.makeAccessException(accessFailedMessage(refc, m), this);
+ }
+
+ String accessFailedMessage(Class refc, MemberName m) {
+ Class defc = m.getDeclaringClass();
+ int mods = m.getModifiers();
+ // check the class first:
+ boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
+ (defc == refc ||
+ Modifier.isPublic(refc.getModifiers())));
+ if (!classOK && (allowedModes & PACKAGE) != 0) {
+ classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
+ (defc == refc ||
+ VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
+ }
+ if (!classOK)
+ return "class is not public";
+ if (Modifier.isPublic(mods))
+ return "access to public member failed"; // (how?, module not readable?)
+ if (Modifier.isPrivate(mods))
+ return "member is private";
+ if (Modifier.isProtected(mods))
+ return "member is protected";
+ return "member is private to package";
+ }
+
+ private static final boolean ALLOW_NESTMATE_ACCESS = false;
+
+ private void checkSpecialCaller(Class specialCaller, Class refc) throws IllegalAccessException {
+ int allowedModes = this.allowedModes;
+ if (allowedModes == TRUSTED) return;
+ if (!hasPrivateAccess()
+ || (specialCaller != lookupClass()
+ // ensure non-abstract methods in superinterfaces can be special-invoked
+ && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
+ && !(ALLOW_NESTMATE_ACCESS &&
+ VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
+ throw new MemberName(specialCaller).
+ makeAccessException("no private access for invokespecial", this);
+ }
+
+ private boolean restrictProtectedReceiver(MemberName method) {
+ // The accessing class only has the right to use a protected member
+ // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
+ if (!method.isProtected() || method.isStatic()
+ || allowedModes == TRUSTED
+ || method.getDeclaringClass() == lookupClass()
+ || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
+ || (ALLOW_NESTMATE_ACCESS &&
+ VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
+ return false;
+ return true;
+ }
+ private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class caller) throws IllegalAccessException {
+ assert(!method.isStatic());
+ // receiver type of mh is too wide; narrow to caller
+ if (!method.getDeclaringClass().isAssignableFrom(caller)) {
+ throw method.makeAccessException("caller class must be a subclass below the method", caller);
+ }
+ MethodType rawType = mh.type();
+ if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
+ MethodType narrowType = rawType.changeParameterType(0, caller);
+ assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
+ assert(mh.viewAsTypeChecks(narrowType, true));
+ return mh.copyWith(narrowType, mh.form);
+ }
+
+ /** Check access and get the requested method. */
+ private MethodHandle getDirectMethod(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
+ final boolean doRestrict = true;
+ final boolean checkSecurity = true;
+ return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
+ }
+ /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
+ private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
+ final boolean doRestrict = false;
+ final boolean checkSecurity = true;
+ return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerClass);
+ }
+ /** Check access and get the requested method, eliding security manager checks. */
+ private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
+ final boolean doRestrict = true;
+ final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
+ return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
+ }
+ /** Common code for all methods; do not call directly except from immediately above. */
+ private MethodHandle getDirectMethodCommon(byte refKind, Class refc, MemberName method,
+ boolean checkSecurity,
+ boolean doRestrict, Class callerClass) throws IllegalAccessException {
+ checkMethod(refKind, refc, method);
+ // Optionally check with the security manager; this isn't needed for unreflect* calls.
+ if (checkSecurity)
+ checkSecurityManager(refc, method);
+ assert(!method.isMethodHandleInvoke());
+
+ if (refKind == REF_invokeSpecial &&
+ refc != lookupClass() &&
+ !refc.isInterface() &&
+ refc != lookupClass().getSuperclass() &&
+ refc.isAssignableFrom(lookupClass())) {
+ assert(!method.getName().equals("
+ * Certain access modes of the returned VarHandle are unsupported under
+ * the following conditions:
+ *
+ * If the component type is {@code float} or {@code double} then numeric
+ * and atomic update access modes compare values using their bitwise
+ * representation (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @apiNote
+ * Bitwise comparison of {@code float} values or {@code double} values,
+ * as performed by the numeric and atomic update access modes, differ
+ * from the primitive {@code ==} operator and the {@link Float#equals}
+ * and {@link Double#equals} methods, specifically with respect to
+ * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
+ * Care should be taken when performing a compare and set or a compare
+ * and exchange operation with such values since the operation may
+ * unexpectedly fail.
+ * There are many possible NaN values that are considered to be
+ * {@code NaN} in Java, although no IEEE 754 floating-point operation
+ * provided by Java can distinguish between them. Operation failure can
+ * occur if the expected or witness value is a NaN value and it is
+ * transformed (perhaps in a platform specific manner) into another NaN
+ * value, and thus has a different bitwise representation (see
+ * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
+ * details).
+ * The values {@code -0.0} and {@code +0.0} have different bitwise
+ * representations but are considered equal when using the primitive
+ * {@code ==} operator. Operation failure can occur if, for example, a
+ * numeric algorithm computes an expected value to be say {@code -0.0}
+ * and previously computed the witness value to be say {@code +0.0}.
+ * @param arrayClass the class of an array, of type {@code T[]}
+ * @return a VarHandle giving access to elements of an array
+ * @throws NullPointerException if the arrayClass is null
+ * @throws IllegalArgumentException if arrayClass is not an array type
+ * @since 9
+ */
+ public static
+ VarHandle arrayElementVarHandle(Class arrayClass) throws IllegalArgumentException {
+ return VarHandles.makeArrayElementHandle(arrayClass);
+ }
+
+ /**
+ * Produces a VarHandle giving access to elements of a {@code byte[]} array
+ * viewed as if it were a different primitive array type, such as
+ * {@code int[]} or {@code long[]}.
+ * The VarHandle's variable type is the component type of
+ * {@code viewArrayClass} and the list of coordinate types is
+ * {@code (byte[], int)}, where the {@code int} coordinate type
+ * corresponds to an argument that is an index into a {@code byte[]} array.
+ * The returned VarHandle accesses bytes at an index in a {@code byte[]}
+ * array, composing bytes to or from a value of the component type of
+ * {@code viewArrayClass} according to the given endianness.
+ *
+ * The supported component types (variables types) are {@code short},
+ * {@code char}, {@code int}, {@code long}, {@code float} and
+ * {@code double}.
+ *
+ * Access of bytes at a given index will result in an
+ * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
+ * or greater than the {@code byte[]} array length minus the size (in bytes)
+ * of {@code T}.
+ *
+ * Access of bytes at an index may be aligned or misaligned for {@code T},
+ * with respect to the underlying memory address, {@code A} say, associated
+ * with the array and index.
+ * If access is misaligned then access for anything other than the
+ * {@code get} and {@code set} access modes will result in an
+ * {@code IllegalStateException}. In such cases atomic access is only
+ * guaranteed with respect to the largest power of two that divides the GCD
+ * of {@code A} and the size (in bytes) of {@code T}.
+ * If access is aligned then following access modes are supported and are
+ * guaranteed to support atomic access:
+ *
+ * Misaligned access, and therefore atomicity guarantees, may be determined
+ * for {@code byte[]} arrays without operating on a specific array. Given
+ * an {@code index}, {@code T} and it's corresponding boxed type,
+ * {@code T_BOX}, misalignment may be determined as follows:
+ *
+ * If the variable type is {@code float} or {@code double} then atomic
+ * update access modes compare values using their bitwise representation
+ * (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @param viewArrayClass the view array class, with a component type of
+ * type {@code T}
+ * @param byteOrder the endianness of the view array elements, as
+ * stored in the underlying {@code byte} array
+ * @return a VarHandle giving access to elements of a {@code byte[]} array
+ * viewed as if elements corresponding to the components type of the view
+ * array class
+ * @throws NullPointerException if viewArrayClass or byteOrder is null
+ * @throws IllegalArgumentException if viewArrayClass is not an array type
+ * @throws UnsupportedOperationException if the component type of
+ * viewArrayClass is not supported as a variable type
+ * @since 9
+ */
+ public static
+ VarHandle byteArrayViewVarHandle(Class viewArrayClass,
+ ByteOrder byteOrder) throws IllegalArgumentException {
+ Objects.requireNonNull(byteOrder);
+ return VarHandles.byteArrayViewHandle(viewArrayClass,
+ byteOrder == ByteOrder.BIG_ENDIAN);
+ }
+
+ /**
+ * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
+ * viewed as if it were an array of elements of a different primitive
+ * component type to that of {@code byte}, such as {@code int[]} or
+ * {@code long[]}.
+ * The VarHandle's variable type is the component type of
+ * {@code viewArrayClass} and the list of coordinate types is
+ * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
+ * corresponds to an argument that is an index into a {@code byte[]} array.
+ * The returned VarHandle accesses bytes at an index in a
+ * {@code ByteBuffer}, composing bytes to or from a value of the component
+ * type of {@code viewArrayClass} according to the given endianness.
+ *
+ * The supported component types (variables types) are {@code short},
+ * {@code char}, {@code int}, {@code long}, {@code float} and
+ * {@code double}.
+ *
+ * Access will result in a {@code ReadOnlyBufferException} for anything
+ * other than the read access modes if the {@code ByteBuffer} is read-only.
+ *
+ * Access of bytes at a given index will result in an
+ * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
+ * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
+ * {@code T}.
+ *
+ * Access of bytes at an index may be aligned or misaligned for {@code T},
+ * with respect to the underlying memory address, {@code A} say, associated
+ * with the {@code ByteBuffer} and index.
+ * If access is misaligned then access for anything other than the
+ * {@code get} and {@code set} access modes will result in an
+ * {@code IllegalStateException}. In such cases atomic access is only
+ * guaranteed with respect to the largest power of two that divides the GCD
+ * of {@code A} and the size (in bytes) of {@code T}.
+ * If access is aligned then following access modes are supported and are
+ * guaranteed to support atomic access:
+ *
+ * Misaligned access, and therefore atomicity guarantees, may be determined
+ * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
+ * {@code index}, {@code T} and it's corresponding boxed type,
+ * {@code T_BOX}, as follows:
+ *
+ * If the variable type is {@code float} or {@code double} then atomic
+ * update access modes compare values using their bitwise representation
+ * (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @param viewArrayClass the view array class, with a component type of
+ * type {@code T}
+ * @param byteOrder the endianness of the view array elements, as
+ * stored in the underlying {@code ByteBuffer} (Note this overrides the
+ * endianness of a {@code ByteBuffer})
+ * @return a VarHandle giving access to elements of a {@code ByteBuffer}
+ * viewed as if elements corresponding to the components type of the view
+ * array class
+ * @throws NullPointerException if viewArrayClass or byteOrder is null
+ * @throws IllegalArgumentException if viewArrayClass is not an array type
+ * @throws UnsupportedOperationException if the component type of
+ * viewArrayClass is not supported as a variable type
+ * @since 9
+ */
+ public static
+ VarHandle byteBufferViewVarHandle(Class viewArrayClass,
+ ByteOrder byteOrder) throws IllegalArgumentException {
+ Objects.requireNonNull(byteOrder);
+ return VarHandles.makeByteBufferViewHandle(viewArrayClass,
+ byteOrder == ByteOrder.BIG_ENDIAN);
+ }
+
+
+ /// method handle invocation (reflective style)
+
+ /**
+ * Produces a method handle which will invoke any method handle of the
+ * given {@code type}, with a given number of trailing arguments replaced by
+ * a single trailing {@code Object[]} array.
+ * The resulting invoker will be a method handle with the following
+ * arguments:
+ *
+ * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
+ * the indicated {@code type}.
+ * That is, if the target is exactly of the given {@code type}, it will behave
+ * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
+ * is used to convert the target to the required {@code type}.
+ *
+ * The type of the returned invoker will not be the given {@code type}, but rather
+ * will have all parameters except the first {@code leadingArgCount}
+ * replaced by a single array of type {@code Object[]}, which will be
+ * the final parameter.
+ *
+ * Before invoking its target, the invoker will spread the final array, apply
+ * reference casts as necessary, and unbox and widen primitive arguments.
+ * If, when the invoker is called, the supplied array argument does
+ * not have the correct number of elements, the invoker will throw
+ * an {@link IllegalArgumentException} instead of invoking the target.
+ *
+ * This method is equivalent to the following code (though it may be more efficient):
+ *
+ * This method is equivalent to the following code (though it may be more efficient):
+ * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
+ *
+ *
+ * Discussion:
+ * Invoker method handles can be useful when working with variable method handles
+ * of unknown types.
+ * For example, to emulate an {@code invokeExact} call to a variable method
+ * handle {@code M}, extract its type {@code T},
+ * look up the invoker method {@code X} for {@code T},
+ * and call the invoker method, as {@code X.invoke(T, A...)}.
+ * (It would not work to call {@code X.invokeExact}, since the type {@code T}
+ * is unknown.)
+ * If spreading, collecting, or other argument transformations are required,
+ * they can be applied once to the invoker {@code X} and reused on many {@code M}
+ * method handle values, as long as they are compatible with the type of {@code X}.
+ *
+ * (Note: The invoker method is not available via the Core Reflection API.
+ * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
+ * on the declared {@code invokeExact} or {@code invoke} method will raise an
+ * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)
+ *
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @return a method handle suitable for invoking any method handle of the given type
+ * @throws IllegalArgumentException if the resulting method handle's type would have
+ * too many parameters
+ */
+ public static
+ MethodHandle exactInvoker(MethodType type) {
+ return type.invokers().exactInvoker();
+ }
+
+ /**
+ * Produces a special invoker method handle which can be used to
+ * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
+ * The resulting invoker will have a type which is
+ * exactly equal to the desired type, except that it will accept
+ * an additional leading argument of type {@code MethodHandle}.
+ *
+ * Before invoking its target, if the target differs from the expected type,
+ * the invoker will apply reference casts as
+ * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
+ * Similarly, the return value will be converted as necessary.
+ * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
+ * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
+ *
+ * This method is equivalent to the following code (though it may be more efficient):
+ * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
+ *
+ * Discussion:
+ * A {@linkplain MethodType#genericMethodType general method type} is one which
+ * mentions only {@code Object} arguments and return values.
+ * An invoker for such a type is capable of calling any method handle
+ * of the same arity as the general type.
+ *
+ * (Note: The invoker method is not available via the Core Reflection API.
+ * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
+ * on the declared {@code invokeExact} or {@code invoke} method will raise an
+ * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)
+ *
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @return a method handle suitable for invoking any method handle convertible to the given type
+ * @throws IllegalArgumentException if the resulting method handle's type would have
+ * too many parameters
+ */
+ public static
+ MethodHandle invoker(MethodType type) {
+ return type.invokers().genericInvoker();
+ }
+
+ /**
+ * Produces a special invoker method handle which can be used to
+ * invoke a signature-polymorphic access mode method on any VarHandle whose
+ * associated access mode type is compatible with the given type.
+ * The resulting invoker will have a type which is exactly equal to the
+ * desired given type, except that it will accept an additional leading
+ * argument of type {@code VarHandle}.
+ *
+ * @param accessMode the VarHandle access mode
+ * @param type the desired target type
+ * @return a method handle suitable for invoking an access mode method of
+ * any VarHandle whose access mode type is of the given type.
+ * @since 9
+ */
+ static public
+ MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
+ return type.invokers().varHandleMethodExactInvoker(accessMode);
+ }
+
+ /**
+ * Produces a special invoker method handle which can be used to
+ * invoke a signature-polymorphic access mode method on any VarHandle whose
+ * associated access mode type is compatible with the given type.
+ * The resulting invoker will have a type which is exactly equal to the
+ * desired given type, except that it will accept an additional leading
+ * argument of type {@code VarHandle}.
+ *
+ * Before invoking its target, if the access mode type differs from the
+ * desired given type, the invoker will apply reference casts as necessary
+ * and box, unbox, or widen primitive values, as if by
+ * {@link MethodHandle#asType asType}. Similarly, the return value will be
+ * converted as necessary.
+ *
+ * This method is equivalent to the following code (though it may be more
+ * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
+ *
+ * @param accessMode the VarHandle access mode
+ * @param type the desired target type
+ * @return a method handle suitable for invoking an access mode method of
+ * any VarHandle whose access mode type is convertible to the given
+ * type.
+ * @since 9
+ */
+ static public
+ MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
+ return type.invokers().varHandleMethodInvoker(accessMode);
+ }
+
+ static /*non-public*/
+ MethodHandle basicInvoker(MethodType type) {
+ return type.invokers().basicInvoker();
+ }
+
+ /// method handle modification (creation from other method handles)
+
+ /**
+ * Produces a method handle which adapts the type of the
+ * given method handle to a new type by pairwise argument and return type conversion.
+ * The original type and new type must have the same number of arguments.
+ * The resulting method handle is guaranteed to report a type
+ * which is equal to the desired new type.
+ *
+ * If the original type and new type are equal, returns target.
+ *
+ * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
+ * and some additional conversions are also applied if those conversions fail.
+ * Given types T0, T1, one of the following conversions is applied
+ * if possible, before or instead of any conversions done by {@code asType}:
+ *
+ * The given array controls the reordering.
+ * Call {@code #I} the number of incoming parameters (the value
+ * {@code newType.parameterCount()}, and call {@code #O} the number
+ * of outgoing parameters (the value {@code target.type().parameterCount()}).
+ * Then the length of the reordering array must be {@code #O},
+ * and each element must be a non-negative number less than {@code #I}.
+ * For every {@code N} less than {@code #O}, the {@code N}-th
+ * outgoing argument will be taken from the {@code I}-th incoming
+ * argument, where {@code I} is {@code reorder[N]}.
+ *
+ * No argument or return value conversions are applied.
+ * The type of each incoming argument, as determined by {@code newType},
+ * must be identical to the type of the corresponding outgoing parameter
+ * or parameters in the target method handle.
+ * The return type of {@code newType} must be identical to the return
+ * type of the original target.
+ *
+ * The reordering array need not specify an actual permutation.
+ * An incoming argument will be duplicated if its index appears
+ * more than once in the array, and an incoming argument will be dropped
+ * if its index does not appear in the array.
+ * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
+ * incoming arguments which are not mentioned in the reordering array
+ * may be of any type, as determined only by {@code newType}.
+ *
+ * Note: The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ * @param target the method handle to invoke after arguments are reordered
+ * @param newType the expected type of the new method handle
+ * @param reorder an index array which controls the reordering
+ * @return a method handle which delegates to the target after it
+ * drops unused arguments and moves and/or duplicates the other arguments
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if the index array length is not equal to
+ * the arity of the target, or if any index array element
+ * not a valid index for a parameter of {@code newType},
+ * or if two corresponding parameter types in
+ * {@code target.type()} and {@code newType} are not identical,
+ */
+ public static
+ MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
+ reorder = reorder.clone(); // get a private copy
+ MethodType oldType = target.type();
+ permuteArgumentChecks(reorder, newType, oldType);
+ // first detect dropped arguments and handle them separately
+ int[] originalReorder = reorder;
+ BoundMethodHandle result = target.rebind();
+ LambdaForm form = result.form;
+ int newArity = newType.parameterCount();
+ // Normalize the reordering into a real permutation,
+ // by removing duplicates and adding dropped elements.
+ // This somewhat improves lambda form caching, as well
+ // as simplifying the transform by breaking it up into steps.
+ for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
+ if (ddIdx > 0) {
+ // We found a duplicated entry at reorder[ddIdx].
+ // Example: (x,y,z)->asList(x,y,z)
+ // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
+ // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
+ // The starred element corresponds to the argument
+ // deleted by the dupArgumentForm transform.
+ int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
+ boolean killFirst = false;
+ for (int val; (val = reorder[--dstPos]) != dupVal; ) {
+ // Set killFirst if the dup is larger than an intervening position.
+ // This will remove at least one inversion from the permutation.
+ if (dupVal > val) killFirst = true;
+ }
+ if (!killFirst) {
+ srcPos = dstPos;
+ dstPos = ddIdx;
+ }
+ form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
+ assert (reorder[srcPos] == reorder[dstPos]);
+ oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
+ // contract the reordering by removing the element at dstPos
+ int tailPos = dstPos + 1;
+ System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
+ reorder = Arrays.copyOf(reorder, reorder.length - 1);
+ } else {
+ int dropVal = ~ddIdx, insPos = 0;
+ while (insPos < reorder.length && reorder[insPos] < dropVal) {
+ // Find first element of reorder larger than dropVal.
+ // This is where we will insert the dropVal.
+ insPos += 1;
+ }
+ Class ptype = newType.parameterType(dropVal);
+ form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
+ oldType = oldType.insertParameterTypes(insPos, ptype);
+ // expand the reordering by inserting an element at insPos
+ int tailPos = insPos + 1;
+ reorder = Arrays.copyOf(reorder, reorder.length + 1);
+ System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
+ reorder[insPos] = dropVal;
+ }
+ assert (permuteArgumentChecks(reorder, newType, oldType));
+ }
+ assert (reorder.length == newArity); // a perfect permutation
+ // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
+ form = form.editor().permuteArgumentsForm(1, reorder);
+ if (newType == result.type() && form == result.internalForm())
+ return result;
+ return result.copyWith(newType, form);
+ }
+
+ /**
+ * Return an indication of any duplicate or omission in reorder.
+ * If the reorder contains a duplicate entry, return the index of the second occurrence.
+ * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
+ * Otherwise, return zero.
+ * If an element not in [0..newArity-1] is encountered, return reorder.length.
+ */
+ private static int findFirstDupOrDrop(int[] reorder, int newArity) {
+ final int BIT_LIMIT = 63; // max number of bits in bit mask
+ if (newArity < BIT_LIMIT) {
+ long mask = 0;
+ for (int i = 0; i < reorder.length; i++) {
+ int arg = reorder[i];
+ if (arg >= newArity) {
+ return reorder.length;
+ }
+ long bit = 1L << arg;
+ if ((mask & bit) != 0) {
+ return i; // >0 indicates a dup
+ }
+ mask |= bit;
+ }
+ if (mask == (1L << newArity) - 1) {
+ assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
+ return 0;
+ }
+ // find first zero
+ long zeroBit = Long.lowestOneBit(~mask);
+ int zeroPos = Long.numberOfTrailingZeros(zeroBit);
+ assert(zeroPos <= newArity);
+ if (zeroPos == newArity) {
+ return 0;
+ }
+ return ~zeroPos;
+ } else {
+ // same algorithm, different bit set
+ BitSet mask = new BitSet(newArity);
+ for (int i = 0; i < reorder.length; i++) {
+ int arg = reorder[i];
+ if (arg >= newArity) {
+ return reorder.length;
+ }
+ if (mask.get(arg)) {
+ return i; // >0 indicates a dup
+ }
+ mask.set(arg);
+ }
+ int zeroPos = mask.nextClearBit(0);
+ assert(zeroPos <= newArity);
+ if (zeroPos == newArity) {
+ return 0;
+ }
+ return ~zeroPos;
+ }
+ }
+
+ private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
+ if (newType.returnType() != oldType.returnType())
+ throw newIllegalArgumentException("return types do not match",
+ oldType, newType);
+ if (reorder.length == oldType.parameterCount()) {
+ int limit = newType.parameterCount();
+ boolean bad = false;
+ for (int j = 0; j < reorder.length; j++) {
+ int i = reorder[j];
+ if (i < 0 || i >= limit) {
+ bad = true; break;
+ }
+ Class src = newType.parameterType(i);
+ Class dst = oldType.parameterType(j);
+ if (src != dst)
+ throw newIllegalArgumentException("parameter types do not match after reorder",
+ oldType, newType);
+ }
+ if (!bad) return true;
+ }
+ throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
+ }
+
+ /**
+ * Produces a method handle of the requested return type which returns the given
+ * constant value every time it is invoked.
+ *
+ * Before the method handle is returned, the passed-in value is converted to the requested type.
+ * If the requested type is primitive, widening primitive conversions are attempted,
+ * else reference conversions are attempted.
+ * The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
+ * @param type the return type of the desired method handle
+ * @param value the value to return
+ * @return a method handle of the given return type and no arguments, which always returns the given value
+ * @throws NullPointerException if the {@code type} argument is null
+ * @throws ClassCastException if the value cannot be converted to the required return type
+ * @throws IllegalArgumentException if the given type is {@code void.class}
+ */
+ public static
+ MethodHandle constant(Class type, Object value) {
+ if (type.isPrimitive()) {
+ if (type == void.class)
+ throw newIllegalArgumentException("void type");
+ Wrapper w = Wrapper.forPrimitiveType(type);
+ value = w.convert(value, type);
+ if (w.zero().equals(value))
+ return zero(w, type);
+ return insertArguments(identity(type), 0, value);
+ } else {
+ if (value == null)
+ return zero(Wrapper.OBJECT, type);
+ return identity(type).bindTo(value);
+ }
+ }
+
+ /**
+ * Produces a method handle which returns its sole argument when invoked.
+ * @param type the type of the sole parameter and return value of the desired method handle
+ * @return a unary method handle which accepts and returns the given type
+ * @throws NullPointerException if the argument is null
+ * @throws IllegalArgumentException if the given type is {@code void.class}
+ */
+ public static
+ MethodHandle identity(Class type) {
+ Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
+ int pos = btw.ordinal();
+ MethodHandle ident = IDENTITY_MHS[pos];
+ if (ident == null) {
+ ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
+ }
+ if (ident.type().returnType() == type)
+ return ident;
+ // something like identity(Foo.class); do not bother to intern these
+ assert (btw == Wrapper.OBJECT);
+ return makeIdentity(type);
+ }
+
+ /**
+ * Produces a constant method handle of the requested return type which
+ * returns the default value for that type every time it is invoked.
+ * The resulting constant method handle will have no side effects.
+ * The returned method handle is equivalent to {@code empty(methodType(type))}.
+ * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
+ * since {@code explicitCastArguments} converts {@code null} to default values.
+ * @param type the expected return type of the desired method handle
+ * @return a constant method handle that takes no arguments
+ * and returns the default value of the given type (or void, if the type is void)
+ * @throws NullPointerException if the argument is null
+ * @see MethodHandles#constant
+ * @see MethodHandles#empty
+ * @see MethodHandles#explicitCastArguments
+ * @since 9
+ */
+ public static MethodHandle zero(Class type) {
+ Objects.requireNonNull(type);
+ return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
+ }
+
+ private static MethodHandle identityOrVoid(Class type) {
+ return type == void.class ? zero(type) : identity(type);
+ }
+
+ /**
+ * Produces a method handle of the requested type which ignores any arguments, does nothing,
+ * and returns a suitable default depending on the return type.
+ * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
+ * The returned method handle is equivalent to
+ * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
+ *
+ * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
+ * {@code guardWithTest(pred, target, empty(target.type())}.
+ * @param type the type of the desired method handle
+ * @return a constant method handle of the given type, which returns a default value of the given return type
+ * @throws NullPointerException if the argument is null
+ * @see MethodHandles#zero
+ * @see MethodHandles#constant
+ * @since 9
+ */
+ public static MethodHandle empty(MethodType type) {
+ Objects.requireNonNull(type);
+ return dropArguments(zero(type.returnType()), 0, type.parameterList());
+ }
+
+ private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
+ private static MethodHandle makeIdentity(Class ptype) {
+ MethodType mtype = methodType(ptype, ptype);
+ LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
+ return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
+ }
+
+ private static MethodHandle zero(Wrapper btw, Class rtype) {
+ int pos = btw.ordinal();
+ MethodHandle zero = ZERO_MHS[pos];
+ if (zero == null) {
+ zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
+ }
+ if (zero.type().returnType() == rtype)
+ return zero;
+ assert(btw == Wrapper.OBJECT);
+ return makeZero(rtype);
+ }
+ private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
+ private static MethodHandle makeZero(Class rtype) {
+ MethodType mtype = methodType(rtype);
+ LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
+ return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
+ }
+
+ private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
+ // Simulate a CAS, to avoid racy duplication of results.
+ MethodHandle prev = cache[pos];
+ if (prev != null) return prev;
+ return cache[pos] = value;
+ }
+
+ /**
+ * Provides a target method handle with one or more bound arguments
+ * in advance of the method handle's invocation.
+ * The formal parameters to the target corresponding to the bound
+ * arguments are called bound parameters.
+ * Returns a new method handle which saves away the bound arguments.
+ * When it is invoked, it receives arguments for any non-bound parameters,
+ * binds the saved arguments to their corresponding parameters,
+ * and calls the original target.
+ *
+ * The type of the new method handle will drop the types for the bound
+ * parameters from the original target type, since the new method handle
+ * will no longer require those arguments to be supplied by its callers.
+ *
+ * Each given argument object must match the corresponding bound parameter type.
+ * If a bound parameter type is a primitive, the argument object
+ * must be a wrapper, and will be unboxed to produce the primitive value.
+ *
+ * The {@code pos} argument selects which parameters are to be bound.
+ * It may range between zero and N-L (inclusively),
+ * where N is the arity of the target method handle
+ * and L is the length of the values array.
+ *
+ * Note: The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ * @param target the method handle to invoke after the argument is inserted
+ * @param pos where to insert the argument (zero for the first)
+ * @param values the series of arguments to insert
+ * @return a method handle which inserts an additional argument,
+ * before calling the original method handle
+ * @throws NullPointerException if the target or the {@code values} array is null
+ * @see MethodHandle#bindTo
+ */
+ public static
+ MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
+ int insCount = values.length;
+ Class[] ptypes = insertArgumentsChecks(target, insCount, pos);
+ if (insCount == 0) return target;
+ BoundMethodHandle result = target.rebind();
+ for (int i = 0; i < insCount; i++) {
+ Object value = values[i];
+ Class ptype = ptypes[pos+i];
+ if (ptype.isPrimitive()) {
+ result = insertArgumentPrimitive(result, pos, ptype, value);
+ } else {
+ value = ptype.cast(value); // throw CCE if needed
+ result = result.bindArgumentL(pos, value);
+ }
+ }
+ return result;
+ }
+
+ private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
+ Class ptype, Object value) {
+ Wrapper w = Wrapper.forPrimitiveType(ptype);
+ // perform unboxing and/or primitive conversion
+ value = w.convert(value, ptype);
+ switch (w) {
+ case INT: return result.bindArgumentI(pos, (int)value);
+ case LONG: return result.bindArgumentJ(pos, (long)value);
+ case FLOAT: return result.bindArgumentF(pos, (float)value);
+ case DOUBLE: return result.bindArgumentD(pos, (double)value);
+ default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
+ }
+ }
+
+ private static Class[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
+ MethodType oldType = target.type();
+ int outargs = oldType.parameterCount();
+ int inargs = outargs - insCount;
+ if (inargs < 0)
+ throw newIllegalArgumentException("too many values to insert");
+ if (pos < 0 || pos > inargs)
+ throw newIllegalArgumentException("no argument type to append");
+ return oldType.ptypes();
+ }
+
+ /**
+ * Produces a method handle which will discard some dummy arguments
+ * before calling some other specified target method handle.
+ * The type of the new method handle will be the same as the target's type,
+ * except it will also include the dummy argument types,
+ * at some given position.
+ *
+ * The {@code pos} argument may range between zero and N,
+ * where N is the arity of the target.
+ * If {@code pos} is zero, the dummy arguments will precede
+ * the target's real arguments; if {@code pos} is N
+ * they will come after.
+ *
+ * Example:
+ *
+ * This method is also equivalent to the following code:
+ *
+ * The {@code pos} argument may range between zero and N,
+ * where N is the arity of the target.
+ * If {@code pos} is zero, the dummy arguments will precede
+ * the target's real arguments; if {@code pos} is N
+ * they will come after.
+ * @apiNote
+ *
+ * This method is also equivalent to the following code:
+ *
+ * The resulting handle will have the same return type as the target handle.
+ *
+ * In more formal terms, assume these two type lists:
+ * The pre-processing is performed by one or more method handles,
+ * specified in the elements of the {@code filters} array.
+ * The first element of the filter array corresponds to the {@code pos}
+ * argument of the target, and so on in sequence.
+ *
+ * Null arguments in the array are treated as identity functions,
+ * and the corresponding arguments left unchanged.
+ * (If there are no non-null elements in the array, the original target is returned.)
+ * Each filter is applied to the corresponding argument of the adapter.
+ *
+ * If a filter {@code F} applies to the {@code N}th argument of
+ * the target, then {@code F} must be a method handle which
+ * takes exactly one argument. The type of {@code F}'s sole argument
+ * replaces the corresponding argument type of the target
+ * in the resulting adapted method handle.
+ * The return type of {@code F} must be identical to the corresponding
+ * parameter type of the target.
+ *
+ * It is an error if there are elements of {@code filters}
+ * (null or not)
+ * which do not correspond to argument positions in the target.
+ * Example:
+ * Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * denotes the return type of both the {@code target} and resulting adapter.
+ * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
+ * of the parameters and arguments that precede and follow the filter position
+ * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
+ * values of the filtered parameters and arguments; they also represent the
+ * return types of the {@code filter[i]} handles. The latter accept arguments
+ * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
+ * the resulting adapter.
+ *
+ * Note: The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ *
+ * @param target the method handle to invoke after arguments are filtered
+ * @param pos the position of the first argument to filter
+ * @param filters method handles to call initially on filtered arguments
+ * @return method handle which incorporates the specified argument filtering logic
+ * @throws NullPointerException if the target is null
+ * or if the {@code filters} array is null
+ * @throws IllegalArgumentException if a non-null element of {@code filters}
+ * does not match a corresponding argument type of target as described above,
+ * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
+ * or if the resulting method handle's type would have
+ * too many parameters
+ */
+ public static
+ MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
+ filterArgumentsCheckArity(target, pos, filters);
+ MethodHandle adapter = target;
+ int curPos = pos-1; // pre-incremented
+ for (MethodHandle filter : filters) {
+ curPos += 1;
+ if (filter == null) continue; // ignore null elements of filters
+ adapter = filterArgument(adapter, curPos, filter);
+ }
+ return adapter;
+ }
+
+ /*non-public*/ static
+ MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
+ filterArgumentChecks(target, pos, filter);
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ BoundMethodHandle result = target.rebind();
+ Class newParamType = filterType.parameterType(0);
+ LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
+ MethodType newType = targetType.changeParameterType(pos, newParamType);
+ result = result.copyWithExtendL(newType, lform, filter);
+ return result;
+ }
+
+ private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
+ MethodType targetType = target.type();
+ int maxPos = targetType.parameterCount();
+ if (pos + filters.length > maxPos)
+ throw newIllegalArgumentException("too many filters");
+ }
+
+ private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ if (filterType.parameterCount() != 1
+ || filterType.returnType() != targetType.parameterType(pos))
+ throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing
+ * a sub-sequence of its arguments with a filter (another method handle).
+ * The pre-processed arguments are replaced by the result (if any) of the
+ * filter function.
+ * The target is then called on the modified (usually shortened) argument list.
+ *
+ * If the filter returns a value, the target must accept that value as
+ * its argument in position {@code pos}, preceded and/or followed by
+ * any arguments not passed to the filter.
+ * If the filter returns void, the target must accept all arguments
+ * not passed to the filter.
+ * No arguments are reordered, and a result returned from the filter
+ * replaces (in order) the whole subsequence of arguments originally
+ * passed to the adapter.
+ *
+ * The argument types (if any) of the filter
+ * replace zero or one argument types of the target, at position {@code pos},
+ * in the resulting adapted method handle.
+ * The return type of the filter (if any) must be identical to the
+ * argument type of the target at position {@code pos}, and that target argument
+ * is supplied by the return value of the filter.
+ *
+ * In all cases, {@code pos} must be greater than or equal to zero, and
+ * {@code pos} must also be less than or equal to the target's arity.
+ * Example:
+ * Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * represents the return type of the {@code target} and resulting adapter.
+ * {@code V}/{@code v} stand for the return type and value of the
+ * {@code filter}, which are also found in the signature and arguments of
+ * the {@code target}, respectively, unless {@code V} is {@code void}.
+ * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
+ * and values preceding and following the collection position, {@code pos},
+ * in the {@code target}'s signature. They also turn up in the resulting
+ * adapter's signature and arguments, where they surround
+ * {@code B}/{@code b}, which represent the parameter types and arguments
+ * to the {@code filter} (if any).
+ *
+ * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
+ * one which first "folds" the affected arguments, and then drops them, in separate
+ * steps as follows:
+ *
+ * Note: The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ *
+ * @param target the method handle to invoke after filtering the subsequence of arguments
+ * @param pos the position of the first adapter argument to pass to the filter,
+ * and/or the target argument which receives the result of the filter
+ * @param filter method handle to call on the subsequence of arguments
+ * @return method handle which incorporates the specified argument subsequence filtering logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if the return type of {@code filter}
+ * is non-void and is not the same as the {@code pos} argument of the target,
+ * or if {@code pos} is not between 0 and the target's arity, inclusive,
+ * or if the resulting method handle's type would have
+ * too many parameters
+ * @see MethodHandles#foldArguments
+ * @see MethodHandles#filterArguments
+ * @see MethodHandles#filterReturnValue
+ */
+ public static
+ MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
+ MethodType newType = collectArgumentsChecks(target, pos, filter);
+ MethodType collectorType = filter.type();
+ BoundMethodHandle result = target.rebind();
+ LambdaForm lform;
+ if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
+ lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
+ if (lform != null) {
+ return result.copyWith(newType, lform);
+ }
+ }
+ lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
+ return result.copyWithExtendL(newType, lform, filter);
+ }
+
+ private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ Class rtype = filterType.returnType();
+ List
+ * If the target returns a value, the filter must accept that value as
+ * its only argument.
+ * If the target returns void, the filter must accept no arguments.
+ *
+ * The return type of the filter
+ * replaces the return type of the target
+ * in the resulting adapted method handle.
+ * The argument type of the filter (if any) must be identical to the
+ * return type of the target.
+ * Example:
+ * Here is pseudocode for the resulting adapter. In the code,
+ * {@code T}/{@code t} represent the result type and value of the
+ * {@code target}; {@code V}, the result type of the {@code filter}; and
+ * {@code A}/{@code a}, the types and values of the parameters and arguments
+ * of the {@code target} as well as the resulting adapter.
+ *
+ * Note: The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ * @param target the method handle to invoke before filtering the return value
+ * @param filter method handle to call on the return value
+ * @return method handle which incorporates the specified return value filtering logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if the argument list of {@code filter}
+ * does not match the return type of target as described above
+ */
+ public static
+ MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ filterReturnValueChecks(targetType, filterType);
+ BoundMethodHandle result = target.rebind();
+ BasicType rtype = BasicType.basicType(filterType.returnType());
+ LambdaForm lform = result.editor().filterReturnForm(rtype, false);
+ MethodType newType = targetType.changeReturnType(filterType.returnType());
+ result = result.copyWithExtendL(newType, lform, filter);
+ return result;
+ }
+
+ private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
+ Class rtype = targetType.returnType();
+ int filterValues = filterType.parameterCount();
+ if (filterValues == 0
+ ? (rtype != void.class)
+ : (rtype != filterType.parameterType(0) || filterValues != 1))
+ throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing
+ * some of its arguments, and then calling the target with
+ * the result of the pre-processing, inserted into the original
+ * sequence of arguments.
+ *
+ * The pre-processing is performed by {@code combiner}, a second method handle.
+ * Of the arguments passed to the adapter, the first {@code N} arguments
+ * are copied to the combiner, which is then called.
+ * (Here, {@code N} is defined as the parameter count of the combiner.)
+ * After this, control passes to the target, with any result
+ * from the combiner inserted before the original {@code N} incoming
+ * arguments.
+ *
+ * If the combiner returns a value, the first parameter type of the target
+ * must be identical with the return type of the combiner, and the next
+ * {@code N} parameter types of the target must exactly match the parameters
+ * of the combiner.
+ *
+ * If the combiner has a void return, no result will be inserted,
+ * and the first {@code N} parameter types of the target
+ * must exactly match the parameters of the combiner.
+ *
+ * The resulting adapter is the same type as the target, except that the
+ * first parameter type is dropped,
+ * if it corresponds to the result of the combiner.
+ *
+ * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
+ * that either the combiner or the target does not wish to receive.
+ * If some of the incoming arguments are destined only for the combiner,
+ * consider using {@link MethodHandle#asCollector asCollector} instead, since those
+ * arguments will not need to be live on the stack on entry to the
+ * target.)
+ * Example:
+ * Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * represents the result type of the {@code target} and resulting adapter.
+ * {@code V}/{@code v} represent the type and value of the parameter and argument
+ * of {@code target} that precedes the folding position; {@code V} also is
+ * the result type of the {@code combiner}. {@code A}/{@code a} denote the
+ * types and values of the {@code N} parameters and arguments at the folding
+ * position. {@code B}/{@code b} represent the types and values of the
+ * {@code target} parameters and arguments that follow the folded parameters
+ * and arguments.
+ *
+ * Note: The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ * @param target the method handle to invoke after arguments are combined
+ * @param combiner method handle to call initially on the incoming arguments
+ * @return method handle which incorporates the specified argument folding logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if {@code combiner}'s return type
+ * is non-void and not the same as the first argument type of
+ * the target, or if the initial {@code N} argument types
+ * of the target
+ * (skipping one matching the {@code combiner}'s return type)
+ * are not identical with the argument types of {@code combiner}
+ */
+ public static
+ MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
+ return foldArguments(target, 0, combiner);
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
+ * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
+ * before the folded arguments.
+ *
+ * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
+ * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
+ * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
+ * 0.
+ *
+ * @apiNote Example:
+ * Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * represents the result type of the {@code target} and resulting adapter.
+ * {@code V}/{@code v} represent the type and value of the parameter and argument
+ * of {@code target} that precedes the folding position; {@code V} also is
+ * the result type of the {@code combiner}. {@code A}/{@code a} denote the
+ * types and values of the {@code N} parameters and arguments at the folding
+ * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
+ * and values of the {@code target} parameters and arguments that precede and
+ * follow the folded parameters and arguments starting at {@code pos},
+ * respectively.
+ *
+ * Note: The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ *
+ * @param target the method handle to invoke after arguments are combined
+ * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
+ * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
+ * @param combiner method handle to call initially on the incoming arguments
+ * @return method handle which incorporates the specified argument folding logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if either of the following two conditions holds:
+ * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
+ * {@code pos} of the target signature;
+ * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
+ * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
+ *
+ * @see #foldArguments(MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
+ MethodType targetType = target.type();
+ MethodType combinerType = combiner.type();
+ Class rtype = foldArgumentChecks(pos, targetType, combinerType);
+ BoundMethodHandle result = target.rebind();
+ boolean dropResult = rtype == void.class;
+ LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
+ MethodType newType = targetType;
+ if (!dropResult) {
+ newType = newType.dropParameterTypes(pos, pos + 1);
+ }
+ result = result.copyWithExtendL(newType, lform, combiner);
+ return result;
+ }
+
+ /**
+ * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
+ * added capability of selecting the arguments from the targets parameters
+ * to call the combiner with. This allows us to avoid some simple cases of
+ * permutations and padding the combiner with dropArguments to select the
+ * right argument, which may ultimately produce fewer intermediaries.
+ */
+ static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
+ MethodType targetType = target.type();
+ MethodType combinerType = combiner.type();
+ Class rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
+ BoundMethodHandle result = target.rebind();
+ boolean dropResult = rtype == void.class;
+ LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
+ MethodType newType = targetType;
+ if (!dropResult) {
+ newType = newType.dropParameterTypes(pos, pos + 1);
+ }
+ result = result.copyWithExtendL(newType, lform, combiner);
+ return result;
+ }
+
+ private static Class foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
+ int foldArgs = combinerType.parameterCount();
+ Class rtype = combinerType.returnType();
+ int foldVals = rtype == void.class ? 0 : 1;
+ int afterInsertPos = foldPos + foldVals;
+ boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
+ if (ok) {
+ for (int i = 0; i < foldArgs; i++) {
+ if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
+ ok = false;
+ break;
+ }
+ }
+ }
+ if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
+ ok = false;
+ if (!ok)
+ throw misMatchedTypes("target and combiner types", targetType, combinerType);
+ return rtype;
+ }
+
+ private static Class foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
+ int foldArgs = combinerType.parameterCount();
+ if (argPos.length != foldArgs) {
+ throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
+ }
+ Class rtype = combinerType.returnType();
+ int foldVals = rtype == void.class ? 0 : 1;
+ boolean ok = true;
+ for (int i = 0; i < foldArgs; i++) {
+ int arg = argPos[i];
+ if (arg < 0 || arg > targetType.parameterCount()) {
+ throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
+ }
+ if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
+ throw newIllegalArgumentException("target argument type at position " + arg
+ + " must match combiner argument type at index " + i + ": " + targetType
+ + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
+ }
+ }
+ if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
+ ok = false;
+ }
+ if (!ok)
+ throw misMatchedTypes("target and combiner types", targetType, combinerType);
+ return rtype;
+ }
+
+ /**
+ * Makes a method handle which adapts a target method handle,
+ * by guarding it with a test, a boolean-valued method handle.
+ * If the guard fails, a fallback handle is called instead.
+ * All three method handles must have the same corresponding
+ * argument and return types, except that the return type
+ * of the test must be boolean, and the test is allowed
+ * to have fewer arguments than the other two method handles.
+ *
+ * Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * represents the uniform result type of the three involved handles;
+ * {@code A}/{@code a}, the types and values of the {@code target}
+ * parameters and arguments that are consumed by the {@code test}; and
+ * {@code B}/{@code b}, those types and values of the {@code target}
+ * parameters and arguments that are not consumed by the {@code test}.
+ *
+ * The target and handler must have the same corresponding
+ * argument and return types, except that handler may omit trailing arguments
+ * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
+ * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
+ *
+ * Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * represents the return type of the {@code target} and {@code handler},
+ * and correspondingly that of the resulting adapter; {@code A}/{@code a},
+ * the types and values of arguments to the resulting handle consumed by
+ * {@code handler}; and {@code B}/{@code b}, those of arguments to the
+ * resulting handle discarded by {@code handler}.
+ *
+ * The target and handler must return the same type, even if the handler
+ * always throws. (This might happen, for instance, because the handler
+ * is simulating a {@code finally} clause).
+ * To create such a throwing handler, compose the handler creation logic
+ * with {@link #throwException throwException},
+ * in order to create a method handle of the correct return type.
+ * @param target method handle to call
+ * @param exType the type of exception which the handler will catch
+ * @param handler method handle to call if a matching exception is thrown
+ * @return method handle which incorporates the specified try/catch logic
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code handler} does not accept
+ * the given exception type, or if the method handle types do
+ * not match in their return types and their
+ * corresponding parameters
+ * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
+ */
+ public static
+ MethodHandle catchException(MethodHandle target,
+ Class exType,
+ MethodHandle handler) {
+ MethodType ttype = target.type();
+ MethodType htype = handler.type();
+ if (!Throwable.class.isAssignableFrom(exType))
+ throw new ClassCastException(exType.getName());
+ if (htype.parameterCount() < 1 ||
+ !htype.parameterType(0).isAssignableFrom(exType))
+ throw newIllegalArgumentException("handler does not accept exception type "+exType);
+ if (htype.returnType() != ttype.returnType())
+ throw misMatchedTypes("target and handler return types", ttype, htype);
+ handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
+ if (handler == null) {
+ throw misMatchedTypes("target and handler types", ttype, htype);
+ }
+ return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
+ }
+
+ /**
+ * Produces a method handle which will throw exceptions of the given {@code exType}.
+ * The method handle will accept a single argument of {@code exType},
+ * and immediately throw it as an exception.
+ * The method type will nominally specify a return of {@code returnType}.
+ * The return type may be anything convenient: It doesn't matter to the
+ * method handle's behavior, since it will never return normally.
+ * @param returnType the return type of the desired method handle
+ * @param exType the parameter type of the desired method handle
+ * @return method handle which can throw the given exceptions
+ * @throws NullPointerException if either argument is null
+ */
+ public static
+ MethodHandle throwException(Class returnType, Class exType) {
+ if (!Throwable.class.isAssignableFrom(exType))
+ throw new ClassCastException(exType.getName());
+ return MethodHandleImpl.throwException(methodType(returnType, exType));
+ }
+
+ /**
+ * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
+ * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
+ * delivers the loop's result, which is the return value of the resulting handle.
+ *
+ * Intuitively, every loop is formed by one or more "clauses", each specifying a local iteration variable and/or a loop
+ * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
+ * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
+ * terms of method handles, each clause will specify up to four independent actions:
+ * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
+ * this case. See below for a detailed description.
+ *
+ * Parameters optional everywhere:
+ * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
+ * As an exception, the init functions cannot take any {@code v} parameters,
+ * because those values are not yet computed when the init functions are executed.
+ * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
+ * In fact, any clause function may take no arguments at all.
+ *
+ * Loop parameters:
+ * A clause function may take all the iteration variable values it is entitled to, in which case
+ * it may also take more trailing parameters. Such extra values are called loop parameters,
+ * with their types and values notated as {@code (A...)} and {@code (a...)}.
+ * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
+ * (Since init functions do not accept iteration variables {@code v}, any parameter to an
+ * init function is automatically a loop parameter {@code a}.)
+ * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
+ * These loop parameters act as loop-invariant values visible across the whole loop.
+ *
+ * Parameters visible everywhere:
+ * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
+ * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
+ * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
+ * Most clause functions will not need all of this information, but they will be formally connected to it
+ * as if by {@link #dropArguments}.
+ *
+ * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
+ * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
+ * In that notation, the general form of an init function parameter list
+ * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
+ *
+ * Checking clause structure:
+ * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
+ * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
+ * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
+ * met by the inputs to the loop combinator.
+ *
+ * Effectively identical sequences:
+ *
+ * A parameter list {@code A} is defined to be effectively identical to another parameter list {@code B}
+ * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
+ * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
+ * as a whole if the set contains a longest list, and all members of the set are effectively identical to
+ * that longest list.
+ * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
+ * and the same is true if more sequences of the form {@code (V... A*)} are added.
+ *
+ * Step 0: Determine clause structure.
+ * Step 1A: Determine iteration variable types {@code (V...)}.
+ * Step 1B: Determine loop parameters {@code (A...)}.
+ * Step 1C: Determine loop return type.
+ * Step 1D: Check other types.
+ * Step 2: Determine parameter lists.
+ * Step 3: Fill in omitted functions.
+ * Step 4: Fill in missing parameter types.
+ * Final observations.
+ * Example. As a consequence of step 1A above, the {@code loop} combinator has the following property:
+ *
+ * Loop execution.
+ * Usage tips.
+ *
+ * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
+ * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
+ * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
+ *
+ * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
+ * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
+ * evaluates to {@code true}).
+ * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
+ *
+ * The {@code init} handle describes the initial value of an additional optional loop-local variable.
+ * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
+ * and updated with the value returned from its invocation. The result of loop execution will be
+ * the final value of the additional loop-local variable (if present).
+ *
+ * The following rules hold for these argument handles:
+ * The resulting loop handle's result type and parameter signature are determined as follows:
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
+ * passed to the loop.
+ *
+ * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
+ * method will, in each iteration, first execute its body and then evaluate the predicate.
+ * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
+ *
+ * The {@code init} handle describes the initial value of an additional optional loop-local variable.
+ * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
+ * and updated with the value returned from its invocation. The result of loop execution will be
+ * the final value of the additional loop-local variable (if present).
+ *
+ * The following rules hold for these argument handles:
+ * The resulting loop handle's result type and parameter signature are determined as follows:
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
+ * passed to the loop.
+ *
+ * The number of iterations is determined by the {@code iterations} handle evaluation result.
+ * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
+ * It will be initialized to 0 and incremented by 1 in each iteration.
+ *
+ * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
+ * of that type is also present. This variable is initialized using the optional {@code init} handle,
+ * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
+ *
+ * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
+ * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
+ * iteration variable.
+ * The result of the loop handle execution will be the final {@code V} value of that variable
+ * (or {@code void} if there is no {@code V} variable).
+ *
+ * The following rules hold for the argument handles:
+ * The resulting loop handle's result type and parameter signature are determined as follows:
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
+ * arguments passed to the loop.
+ *
+ * The loop counter {@code i} is a loop iteration variable of type {@code int}.
+ * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
+ * values of the loop counter.
+ * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
+ * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
+ *
+ * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
+ * of that type is also present. This variable is initialized using the optional {@code init} handle,
+ * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
+ *
+ * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
+ * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
+ * iteration variable.
+ * The result of the loop handle execution will be the final {@code V} value of that variable
+ * (or {@code void} if there is no {@code V} variable).
+ *
+ * The following rules hold for the argument handles:
+ * The resulting loop handle's result type and parameter signature are determined as follows:
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
+ * arguments passed to the loop.
+ *
+ * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
+ * Each value it produces will be stored in a loop iteration variable of type {@code T}.
+ *
+ * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
+ * of that type is also present. This variable is initialized using the optional {@code init} handle,
+ * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
+ *
+ * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
+ * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
+ * iteration variable.
+ * The result of the loop handle execution will be the final {@code V} value of that variable
+ * (or {@code void} if there is no {@code V} variable).
+ *
+ * The following rules hold for the argument handles:
+ * The type {@code T} may be either a primitive or reference.
+ * Since type {@code Iterator
+ * The resulting loop handle's result type and parameter signature are determined as follows:
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
+ * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
+ *
+ * The {@code cleanup} handle will be passed one or two additional leading arguments.
+ * The first is the exception thrown during the
+ * execution of the {@code target} handle, or {@code null} if no exception was thrown.
+ * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
+ * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
+ * The second argument is not present if the {@code target} handle has a {@code void} return type.
+ * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
+ * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
+ *
+ * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
+ * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
+ * two extra leading parameters:
+ * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
+ * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
+ * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
+ * the cleanup.
+ *
+ * Note that the saved arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the target, and so are passed unchanged
+ * from the caller to the cleanup, if it is invoked.
+ *
+ * The target and cleanup must return the same type, even if the cleanup
+ * always throws.
+ * To create such a throwing cleanup, compose the cleanup logic
+ * with {@link #throwException throwException},
+ * in order to create a method handle of the correct return type.
+ *
+ * Note that {@code tryFinally} never converts exceptions into normal returns.
+ * In rare cases where exceptions must be converted in that way, first wrap
+ * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
+ * to capture an outgoing exception, and then wrap with {@code tryFinally}.
+ *
+ * @param target the handle whose execution is to be wrapped in a {@code try} block.
+ * @param cleanup the handle that is invoked in the finally block.
+ *
+ * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code cleanup} does not accept
+ * the required leading arguments, or if the method handle types do
+ * not match in their return types and their
+ * corresponding trailing parameters
+ *
+ * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
+ ListLookup Factory Methods
+ * The factory methods on a {@code Lookup} object correspond to all major
+ * use cases for methods, constructors, and fields.
+ * Each method handle created by a factory method is the functional
+ * equivalent of a particular bytecode behavior.
+ * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
+ * Here is a summary of the correspondence between these factory methods and
+ * the behavior of the resulting method handles:
+ *
+ *
+ *
+ * Access checking
+ * Access checks are applied in the factory methods of {@code Lookup},
+ * when a method handle is created.
+ * This is a key difference from the Core Reflection API, since
+ * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
+ * performs access checking against every caller, on every call.
+ *
+ *
+ *
+ *
+ * Security manager interactions
+ * Although bytecode instructions can only refer to classes in
+ * a related class loader, this API can search for methods in any
+ * class, as long as a reference to its {@code Class} object is
+ * available. Such cross-loader references are also possible with the
+ * Core Reflection API, and are impossible to bytecode instructions
+ * such as {@code invokestatic} or {@code getfield}.
+ * There is a {@linkplain java.lang.SecurityManager security manager API}
+ * to allow applications to check such cross-loader references.
+ * These checks apply to both the {@code MethodHandles.Lookup} API
+ * and the Core Reflection API
+ * (as found on {@link java.lang.Class Class}).
+ *
+ *
+ * Security checks are performed after other access checks have passed.
+ * Therefore, the above rules presuppose a member or class that is public,
+ * or else that is being accessed from a lookup class that has
+ * rights to access the member or class.
+ *
+ * Caller sensitive methods
+ * A small number of Java methods have a special property called caller sensitivity.
+ * A caller-sensitive method can behave differently depending on the
+ * identity of its immediate caller.
+ *
+ *
+ *
+ *
+ * If none of the above cases apply, it is the case that full
+ * access (public, module, package, private, and protected) is allowed.
+ * In this case, no suffix is added.
+ * This is true only of an object obtained originally from
+ * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
+ * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
+ * always have restricted access, and will display a suffix.
+ *
+ * @param refc the class from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails,
+ * or if the method is not {@code static},
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public
+ MethodHandle findStatic(Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
+ return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
+ }
+
+ /**
+ * Produces a method handle for a virtual method.
+ * The type of the method handle will be that of the method,
+ * with the receiver type (usually {@code refc}) prepended.
+ * The method and all its argument types must be accessible to the lookup object.
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
+ "asList", methodType(List.class, Object[].class));
+assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
+ * }
+ *
+ * @param refc the class or interface from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method, with the receiver argument omitted
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails,
+ * or if the method is {@code static},
+ * or if the method is {@code private} method of interface,
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findVirtual(Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ if (refc == MethodHandle.class) {
+ MethodHandle mh = findVirtualForMH(name, type);
+ if (mh != null) return mh;
+ } else if (refc == VarHandle.class) {
+ MethodHandle mh = findVirtualForVH(name, type);
+ if (mh != null) return mh;
+ }
+ byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
+ MemberName method = resolveOrFail(refKind, refc, name, type);
+ return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
+ }
+ private MethodHandle findVirtualForMH(String name, MethodType type) {
+ // these names require special lookups because of the implicit MethodType argument
+ if ("invoke".equals(name))
+ return invoker(type);
+ if ("invokeExact".equals(name))
+ return exactInvoker(type);
+ assert(!MemberName.isMethodHandleInvokeName(name));
+ return null;
+ }
+ private MethodHandle findVirtualForVH(String name, MethodType type) {
+ try {
+ return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
+ } catch (IllegalArgumentException e) {
+ return null;
+ }
+ }
+
+ /**
+ * Produces a method handle which creates an object and initializes it, using
+ * the constructor of the specified type.
+ * The parameter types of the method handle will be those of the constructor,
+ * while the return type will be a reference to the constructor's class.
+ * The constructor and all its argument types must be accessible to the lookup object.
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle MH_concat = publicLookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
+ "hashCode", methodType(int.class));
+MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
+ "hashCode", methodType(int.class));
+assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
+assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
+assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
+// interface method:
+MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
+ "subSequence", methodType(CharSequence.class, int.class, int.class));
+assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
+// constructor "internal method" must be accessed differently:
+MethodType MT_newString = methodType(void.class); //()V for new String()
+try { assertEquals("impossible", lookup()
+ .findVirtual(String.class, "
+ * @param refc the class or interface from which the method is accessed
+ * @param type the type of the method, with the receiver argument omitted, and a void return type
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the constructor does not exist
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findConstructor(Class refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ if (refc.isArray()) {
+ throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
+ }
+ String name = "{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle MH_newArrayList = publicLookup().findConstructor(
+ ArrayList.class, methodType(void.class, Collection.class));
+Collection orig = Arrays.asList("x", "y");
+Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
+assert(orig != copy);
+assertEquals(orig, copy);
+// a variable-arity constructor:
+MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
+ ProcessBuilder.class, methodType(void.class, String[].class));
+ProcessBuilder pb = (ProcessBuilder)
+ MH_newProcessBuilder.invoke("x", "y", "z");
+assertEquals("[x, y, z]", pb.command().toString());
+ * }
+ *
+ * @param refc the class or interface from which the method is accessed
+ * @param name the name of the method (which must not be "<init>")
+ * @param type the type of the method, with the receiver argument omitted
+ * @param specialCaller the proposed calling class to perform the {@code invokespecial}
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails,
+ * or if the method is {@code static},
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findSpecial(Class refc, String name, MethodType type,
+ Class specialCaller) throws NoSuchMethodException, IllegalAccessException {
+ checkSpecialCaller(specialCaller, refc);
+ Lookup specialLookup = this.in(specialCaller);
+ MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
+ return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
+ }
+
+ /**
+ * Produces a method handle giving read access to a non-static field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * The method handle's single argument will be the instance containing
+ * the field.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can load values from the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ * @see #findVarHandle(Class, String, Class)
+ */
+ public MethodHandle findGetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName field = resolveOrFail(REF_getField, refc, name, type);
+ return getDirectField(REF_getField, refc, field);
+ }
+
+ /**
+ * Produces a method handle giving write access to a non-static field.
+ * The type of the method handle will have a void return type.
+ * The method handle will take two arguments, the instance containing
+ * the field, and the value to be stored.
+ * The second argument will be of the field's value type.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can store values into the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ * @see #findVarHandle(Class, String, Class)
+ */
+ public MethodHandle findSetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
+ MemberName field = resolveOrFail(REF_putField, refc, name, type);
+ return getDirectField(REF_putField, refc, field);
+ }
+
+ /**
+ * Produces a VarHandle giving access to a non-static field {@code name}
+ * of type {@code type} declared in a class of type {@code recv}.
+ * The VarHandle's variable type is {@code type} and it has one
+ * coordinate type, {@code recv}.
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+static class Listie extends ArrayList {
+ public String toString() { return "[wee Listie]"; }
+ static Lookup lookup() { return MethodHandles.lookup(); }
+}
+...
+// no access to constructor via invokeSpecial:
+MethodHandle MH_newListie = Listie.lookup()
+ .findConstructor(Listie.class, methodType(void.class));
+Listie l = (Listie) MH_newListie.invokeExact();
+try { assertEquals("impossible", Listie.lookup().findSpecial(
+ Listie.class, "
+ *
+ *
+ *
+ *
+ * where {@code defc} is either {@code receiver.getClass()} or a super
+ * type of that class, in which the requested method is accessible
+ * to the lookup class.
+ * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
+ * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
+ * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
+ * the receiver is restricted by {@code findVirtual} to the lookup class.)
+ * @param receiver the object from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method, with the receiver argument omitted
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * refuses access
+ * @throws NullPointerException if any argument is null
+ * @see MethodHandle#bindTo
+ * @see #findVirtual
+ */
+ public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ Class refc = receiver.getClass(); // may get NPE
+ MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
+ MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
+ if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
+ throw new IllegalAccessException("The restricted defining class " +
+ mh.type().leadingReferenceParameter().getName() +
+ " is not assignable from receiver class " +
+ receiver.getClass().getName());
+ }
+ return mh.bindArgumentL(0, receiver).setVarargs(method);
+ }
+
+ /**
+ * Makes a direct method handle
+ * to m, if the lookup class has permission.
+ * If m is non-static, the receiver argument is treated as an initial argument.
+ * If m is virtual, overriding is respected on every call.
+ * Unlike the Core Reflection API, exceptions are not wrapped.
+ * The type of the method handle will be that of the method,
+ * with the receiver type prepended (but only if it is non-static).
+ * If the method's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * If m is not public, do not share the resulting handle with untrusted parties.
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle mh0 = lookup().findVirtual(defc, name, type);
+MethodHandle mh1 = mh0.bindTo(receiver);
+mh1 = mh1.withVarargs(mh0.isVarargsCollector());
+return mh1;
+ * }
+ *
+ *
+ *
+ *
+ *
+ * {@code
+ * int sizeOfT = T_BOX.BYTES; // size in bytes of T
+ * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
+ * alignmentOffset(0, sizeOfT);
+ * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
+ * boolean isMisaligned = misalignedAtIndex != 0;
+ * }
+ *
+ *
+ * {@code
+ * int sizeOfT = T_BOX.BYTES; // size in bytes of T
+ * ByteBuffer bb = ...
+ * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
+ * boolean isMisaligned = misalignedAtIndex != 0;
+ * }
+ *
+ *
+ *
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
+ * @return a method handle suitable for invoking any method handle of the given type
+ * @throws NullPointerException if {@code type} is null
+ * @throws IllegalArgumentException if {@code leadingArgCount} is not in
+ * the range from 0 to {@code type.parameterCount()} inclusive,
+ * or if the resulting method handle's type would have
+ * too many parameters
+ */
+ public static
+ MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
+ if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
+ throw newIllegalArgumentException("bad argument count", leadingArgCount);
+ type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
+ return type.invokers().spreadInvoker(leadingArgCount);
+ }
+
+ /**
+ * Produces a special invoker method handle which can be used to
+ * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
+ * The resulting invoker will have a type which is
+ * exactly equal to the desired type, except that it will accept
+ * an additional leading argument of type {@code MethodHandle}.
+ * {@code
+MethodHandle invoker = MethodHandles.invoker(type);
+int spreadArgCount = type.parameterCount() - leadingArgCount;
+invoker = invoker.asSpreader(Object[].class, spreadArgCount);
+return invoker;
+ * }
+ *
+ * @param target the method handle to invoke after arguments are retyped
+ * @param newType the expected type of the new method handle
+ * @return a method handle which delegates to the target after performing
+ * any necessary argument conversions, and arranges for any
+ * necessary return value conversions
+ * @throws NullPointerException if either argument is null
+ * @throws WrongMethodTypeException if the conversion cannot be made
+ * @see MethodHandle#asType
+ */
+ public static
+ MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
+ explicitCastArgumentsChecks(target, newType);
+ // use the asTypeCache when possible:
+ MethodType oldType = target.type();
+ if (oldType == newType) return target;
+ if (oldType.explicitCastEquivalentToAsType(newType)) {
+ return target.asFixedArity().asType(newType);
+ }
+ return MethodHandleImpl.makePairwiseConvert(target, newType, false);
+ }
+
+ private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
+ if (target.type().parameterCount() != newType.parameterCount()) {
+ throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
+ }
+ }
+
+ /**
+ * Produces a method handle which adapts the calling sequence of the
+ * given method handle to a new type, by reordering the arguments.
+ * The resulting method handle is guaranteed to report a type
+ * which is equal to the desired new type.
+ *
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodType intfn1 = methodType(int.class, int.class);
+MethodType intfn2 = methodType(int.class, int.class, int.class);
+MethodHandle sub = ... (int x, int y) -> (x-y) ...;
+assert(sub.type().equals(intfn2));
+MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
+MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
+assert((int)rsub.invokeExact(1, 100) == 99);
+MethodHandle add = ... (int x, int y) -> (x+y) ...;
+assert(add.type().equals(intfn2));
+MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
+assert(twice.type().equals(intfn1));
+assert((int)twice.invokeExact(21) == 42);
+ * }
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
+MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
+assertEquals(bigType, d0.type());
+assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
+ * }
+ * @param target the method handle to invoke after the arguments are dropped
+ * @param valueTypes the type(s) of the argument(s) to drop
+ * @param pos position of first argument to drop (zero for the leftmost)
+ * @return a method handle which drops arguments of the given types,
+ * before calling the original method handle
+ * @throws NullPointerException if the target is null,
+ * or if the {@code valueTypes} list or any of its elements is null
+ * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
+ * or if {@code pos} is negative or greater than the arity of the target,
+ * or if the new method handle's type would have too many parameters
+ */
+ public static
+ MethodHandle dropArguments(MethodHandle target, int pos, List
+ * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
+ *
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodHandle d0 = dropArguments(cat, 0, String.class);
+assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
+MethodHandle d1 = dropArguments(cat, 1, String.class);
+assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
+MethodHandle d2 = dropArguments(cat, 2, String.class);
+assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
+MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
+assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
+ * }
+ * @param target the method handle to invoke after the arguments are dropped
+ * @param valueTypes the type(s) of the argument(s) to drop
+ * @param pos position of first argument to drop (zero for the leftmost)
+ * @return a method handle which drops arguments of the given types,
+ * before calling the original method handle
+ * @throws NullPointerException if the target is null,
+ * or if the {@code valueTypes} array or any of its elements is null
+ * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
+ * or if {@code pos} is negative or greater than the arity of the target,
+ * or if the new method handle's type would have
+ * too many parameters
+ */
+ public static
+ MethodHandle dropArguments(MethodHandle target, int pos, Class... valueTypes) {
+ return dropArguments0(target, pos, copyTypes(valueTypes));
+ }
+
+ // private version which allows caller some freedom with error handling
+ private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List
+ * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
+ *
+ *
+ * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
+ * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
+ * {@link #dropArguments(MethodHandle, int, Class[])}.
+ *
+ * @apiNote
+ * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
+ * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
+ *
+ * @param target the method handle to adapt
+ * @param skip number of targets parameters to disregard (they will be unchanged)
+ * @param newTypes the list of types to match {@code target}'s parameter type list to
+ * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
+ * @return a possibly adapted method handle
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
+ * or if {@code skip} is negative or greater than the arity of the target,
+ * or if {@code pos} is negative or greater than the newTypes list size,
+ * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
+ * {@code pos}.
+ * @since 9
+ */
+ public static
+ MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+...
+MethodHandle h0 = constant(boolean.class, true);
+MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
+MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
+MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
+if (h1.type().parameterCount() < h2.type().parameterCount())
+ h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
+else
+ h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
+MethodHandle h3 = guardWithTest(h0, h1, h2);
+assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
+ * }
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle upcase = lookup().findVirtual(String.class,
+ "toUpperCase", methodType(String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodHandle f0 = filterArguments(cat, 0, upcase);
+assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
+MethodHandle f1 = filterArguments(cat, 1, upcase);
+assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
+MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
+assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
+ * }
+ * {@code
+ * T target(P... p, A[i]... a[i], B... b);
+ * A[i] filter[i](V[i]);
+ * T adapter(P... p, V[i]... v[i], B... b) {
+ * return target(p..., filter[i](v[i])..., b...);
+ * }
+ * }
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle deepToString = publicLookup()
+ .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
+
+MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
+assertEquals("[strange]", (String) ts1.invokeExact("strange"));
+
+MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
+assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
+
+MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
+MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
+assertEquals("[top, [up, down], strange]",
+ (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
+
+MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
+assertEquals("[top, [up, down], [strange]]",
+ (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
+
+MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
+assertEquals("[top, [[up, down, strange], charm], bottom]",
+ (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
+ * }
+ * {@code
+ * T target(A...,V,C...);
+ * V filter(B...);
+ * T adapter(A... a,B... b,C... c) {
+ * V v = filter(b...);
+ * return target(a...,v,c...);
+ * }
+ * // and if the filter has no arguments:
+ * T target2(A...,V,C...);
+ * V filter2();
+ * T adapter2(A... a,C... c) {
+ * V v = filter2();
+ * return target2(a...,v,c...);
+ * }
+ * // and if the filter has a void return:
+ * T target3(A...,C...);
+ * void filter3(B...);
+ * T adapter3(A... a,B... b,C... c) {
+ * filter3(b...);
+ * return target3(a...,c...);
+ * }
+ * }
+ * If the target method handle consumes no arguments besides than the result
+ * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
+ * is equivalent to {@code filterReturnValue(coll, mh)}.
+ * If the filter method handle {@code coll} consumes one argument and produces
+ * a non-void result, then {@code collectArguments(mh, N, coll)}
+ * is equivalent to {@code filterArguments(mh, N, coll)}.
+ * Other equivalences are possible but would require argument permutation.
+ * {@code
+ * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
+ * mh = MethodHandles.foldArguments(mh, coll); //step 1
+ * }
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle length = lookup().findVirtual(String.class,
+ "length", methodType(int.class));
+System.out.println((String) cat.invokeExact("x", "y")); // xy
+MethodHandle f0 = filterReturnValue(cat, length);
+System.out.println((int) f0.invokeExact("x", "y")); // 2
+ * }
+ * {@code
+ * T target(A...);
+ * V filter(T);
+ * V adapter(A... a) {
+ * T t = target(a...);
+ * return filter(t);
+ * }
+ * // and if the target has a void return:
+ * void target2(A...);
+ * V filter2();
+ * V adapter2(A... a) {
+ * target2(a...);
+ * return filter2();
+ * }
+ * // and if the filter has a void return:
+ * T target3(A...);
+ * void filter3(V);
+ * void adapter3(A... a) {
+ * T t = target3(a...);
+ * filter3(t);
+ * }
+ * }
+ * {@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
+ "println", methodType(void.class, String.class))
+ .bindTo(System.out);
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
+MethodHandle catTrace = foldArguments(cat, trace);
+// also prints "boo":
+assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
+ * }
+ * {@code
+ * // there are N arguments in A...
+ * T target(V, A[N]..., B...);
+ * V combiner(A...);
+ * T adapter(A... a, B... b) {
+ * V v = combiner(a...);
+ * return target(v, a..., b...);
+ * }
+ * // and if the combiner has a void return:
+ * T target2(A[N]..., B...);
+ * void combiner2(A...);
+ * T adapter2(A... a, B... b) {
+ * combiner2(a...);
+ * return target2(a..., b...);
+ * }
+ * }
+ * {@code
+ import static java.lang.invoke.MethodHandles.*;
+ import static java.lang.invoke.MethodType.*;
+ ...
+ MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
+ "println", methodType(void.class, String.class))
+ .bindTo(System.out);
+ MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+ assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
+ MethodHandle catTrace = foldArguments(cat, 1, trace);
+ // also prints "jum":
+ assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
+ * }
+ * {@code
+ * // there are N arguments in A...
+ * T target(Z..., V, A[N]..., B...);
+ * V combiner(A...);
+ * T adapter(Z... z, A... a, B... b) {
+ * V v = combiner(a...);
+ * return target(z..., v, a..., b...);
+ * }
+ * // and if the combiner has a void return:
+ * T target2(Z..., A[N]..., B...);
+ * void combiner2(A...);
+ * T adapter2(Z... z, A... a, B... b) {
+ * combiner2(a...);
+ * return target2(z..., a..., b...);
+ * }
+ * }
+ * Note that the test arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the test, and so are passed unchanged
+ * from the caller to the target or fallback as appropriate.
+ * @param test method handle used for test, must return boolean
+ * @param target method handle to call if test passes
+ * @param fallback method handle to call if test fails
+ * @return method handle which incorporates the specified if/then/else logic
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code test} does not return boolean,
+ * or if all three method types do not match (with the return
+ * type of {@code test} changed to match that of the target).
+ */
+ public static
+ MethodHandle guardWithTest(MethodHandle test,
+ MethodHandle target,
+ MethodHandle fallback) {
+ MethodType gtype = test.type();
+ MethodType ttype = target.type();
+ MethodType ftype = fallback.type();
+ if (!ttype.equals(ftype))
+ throw misMatchedTypes("target and fallback types", ttype, ftype);
+ if (gtype.returnType() != boolean.class)
+ throw newIllegalArgumentException("guard type is not a predicate "+gtype);
+ List{@code
+ * boolean test(A...);
+ * T target(A...,B...);
+ * T fallback(A...,B...);
+ * T adapter(A... a,B... b) {
+ * if (test(a...))
+ * return target(a..., b...);
+ * else
+ * return fallback(a..., b...);
+ * }
+ * }
+ * Note that the saved arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the target, and so are passed unchanged
+ * from the caller to the handler, if the handler is invoked.
+ * {@code
+ * T target(A..., B...);
+ * T handler(ExType, A...);
+ * T adapter(A... a, B... b) {
+ * try {
+ * return target(a..., b...);
+ * } catch (ExType ex) {
+ * return handler(ex, a...);
+ * }
+ * }
+ * }
+ *
+ * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
+ * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
+ * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
+ * to their full length, even though individual clause functions may neglect to take them all.
+ * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
+ *
+ * @apiNote Example:
+ * {@code
+ * V... init...(A...);
+ * boolean pred...(V..., A...);
+ * V... step...(V..., A...);
+ * R fini...(V..., A...);
+ * R loop(A... a) {
+ * V... v... = init...(a...);
+ * for (;;) {
+ * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
+ * v = s(v..., a...);
+ * if (!p(v..., a...)) {
+ * return f(v..., a...);
+ * }
+ * }
+ * }
+ * }
+ * }
+ * The same example, dropping arguments and using combinators:
+ * {@code
+ * // iterative implementation of the factorial function as a loop handle
+ * static int one(int k) { return 1; }
+ * static int inc(int i, int acc, int k) { return i + 1; }
+ * static int mult(int i, int acc, int k) { return i * acc; }
+ * static boolean pred(int i, int acc, int k) { return i < k; }
+ * static int fin(int i, int acc, int k) { return acc; }
+ * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
+ * // null initializer for counter, should initialize to 0
+ * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
+ * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
+ * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
+ * assertEquals(120, loop.invoke(5));
+ * }
+ * A similar example, using a helper object to hold a loop parameter:
+ * {@code
+ * // simplified implementation of the factorial function as a loop handle
+ * static int inc(int i) { return i + 1; } // drop acc, k
+ * static int mult(int i, int acc) { return i * acc; } //drop k
+ * static boolean cmp(int i, int k) { return i < k; }
+ * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
+ * // null initializer for counter, should initialize to 0
+ * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
+ * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
+ * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
+ * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
+ * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
+ * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
+ * assertEquals(720, loop.invoke(6));
+ * }
+ *
+ * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
+ *
+ * @return a method handle embodying the looping behavior as defined by the arguments.
+ *
+ * @throws IllegalArgumentException in case any of the constraints described above is violated.
+ *
+ * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle loop(MethodHandle[]... clauses) {
+ // Step 0: determine clause structure.
+ loopChecks0(clauses);
+
+ List{@code
+ * // instance-based implementation of the factorial function as a loop handle
+ * static class FacLoop {
+ * final int k;
+ * FacLoop(int k) { this.k = k; }
+ * int inc(int i) { return i + 1; }
+ * int mult(int i, int acc) { return i * acc; }
+ * boolean pred(int i) { return i < k; }
+ * int fin(int i, int acc) { return acc; }
+ * }
+ * // assume MH_FacLoop is a handle to the constructor
+ * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
+ * // null initializer for counter, should initialize to 0
+ * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
+ * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
+ * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
+ * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
+ * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
+ * assertEquals(5040, loop.invoke(7));
+ * }
+ *
+ *
+ *
+ *
+ *
+ * @apiNote Example:
+ * {@code
+ * V init(A...);
+ * boolean pred(V, A...);
+ * V body(V, A...);
+ * V whileLoop(A... a...) {
+ * V v = init(a...);
+ * while (pred(v, a...)) {
+ * v = body(v, a...);
+ * }
+ * return v;
+ * }
+ * }
+ *
+ *
+ * @apiNote The implementation of this method can be expressed as follows:
+ * {@code
+ * // implement the zip function for lists as a loop handle
+ * static List
+ *
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
+ * above for other constraints.
+ * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
+ * See above for other constraints.
+ *
+ * @return a method handle implementing the {@code while} loop as described by the arguments.
+ * @throws IllegalArgumentException if the rules for the arguments are violated.
+ * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
+ *
+ * @see #loop(MethodHandle[][])
+ * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
+ whileLoopChecks(init, pred, body);
+ MethodHandle fini = identityOrVoid(body.type().returnType());
+ MethodHandle[] checkExit = { null, null, pred, fini };
+ MethodHandle[] varBody = { init, body };
+ return loop(checkExit, varBody);
+ }
+
+ /**
+ * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
+ * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
+ * {@code
+ * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
+ * MethodHandle fini = (body.type().returnType() == void.class
+ * ? null : identity(body.type().returnType()));
+ * MethodHandle[]
+ * checkExit = { null, null, pred, fini },
+ * varBody = { init, body };
+ * return loop(checkExit, varBody);
+ * }
+ * }
+ *
+ *
+ *
+ *
+ *
+ * @apiNote Example:
+ * {@code
+ * V init(A...);
+ * boolean pred(V, A...);
+ * V body(V, A...);
+ * V doWhileLoop(A... a...) {
+ * V v = init(a...);
+ * do {
+ * v = body(v, a...);
+ * } while (pred(v, a...));
+ * return v;
+ * }
+ * }
+ *
+ *
+ * @apiNote The implementation of this method can be expressed as follows:
+ * {@code
+ * // int i = 0; while (i < limit) { ++i; } return i; => limit
+ * static int zero(int limit) { return 0; }
+ * static int step(int i, int limit) { return i + 1; }
+ * static boolean pred(int i, int limit) { return i < limit; }
+ * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
+ * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
+ * assertEquals(23, loop.invoke(23));
+ * }
+ *
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
+ * See above for other constraints.
+ * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
+ * above for other constraints.
+ *
+ * @return a method handle implementing the {@code while} loop as described by the arguments.
+ * @throws IllegalArgumentException if the rules for the arguments are violated.
+ * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
+ *
+ * @see #loop(MethodHandle[][])
+ * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
+ whileLoopChecks(init, pred, body);
+ MethodHandle fini = identityOrVoid(body.type().returnType());
+ MethodHandle[] clause = {init, body, pred, fini };
+ return loop(clause);
+ }
+
+ private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
+ Objects.requireNonNull(pred);
+ Objects.requireNonNull(body);
+ MethodType bodyType = body.type();
+ Class returnType = bodyType.returnType();
+ List{@code
+ * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
+ * MethodHandle fini = (body.type().returnType() == void.class
+ * ? null : identity(body.type().returnType()));
+ * MethodHandle[] clause = { init, body, pred, fini };
+ * return loop(clause);
+ * }
+ * }
+ *
+ *
+ *
+ *
+ *
+ * @apiNote Example with a fully conformant body method:
+ * {@code
+ * int iterations(A...);
+ * V init(A...);
+ * V body(V, int, A...);
+ * V countedLoop(A... a...) {
+ * int end = iterations(a...);
+ * V v = init(a...);
+ * for (int i = 0; i < end; ++i) {
+ * v = body(v, i, a...);
+ * }
+ * return v;
+ * }
+ * }
+ *
+ * @apiNote Example with the simplest possible body method type,
+ * and passing the number of iterations to the loop invocation:
+ * {@code
+ * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
+ * // => a variation on a well known theme
+ * static String step(String v, int counter, String init) { return "na " + v; }
+ * // assume MH_step is a handle to the method above
+ * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
+ * MethodHandle start = MethodHandles.identity(String.class);
+ * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
+ * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
+ * }
+ *
+ * @apiNote Example that treats the number of iterations, string to append to, and string to append
+ * as loop parameters:
+ * {@code
+ * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
+ * // => a variation on a well known theme
+ * static String step(String v, int counter ) { return "na " + v; }
+ * // assume MH_step is a handle to the method above
+ * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
+ * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
+ * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
+ * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
+ * }
+ *
+ * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
+ * to enforce a loop type:
+ * {@code
+ * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
+ * // => a variation on a well known theme
+ * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
+ * // assume MH_step is a handle to the method above
+ * MethodHandle count = MethodHandles.identity(int.class);
+ * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
+ * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
+ * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
+ * }
+ *
+ * @apiNote The implementation of this method can be expressed as follows:
+ * {@code
+ * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
+ * // => a variation on a well known theme
+ * static String step(String v, int counter, String pre) { return pre + " " + v; }
+ * // assume MH_step is a handle to the method above
+ * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
+ * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
+ * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
+ * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
+ * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
+ * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
+ * }
+ *
+ * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
+ * result type must be {@code int}. See above for other constraints.
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param body body of the loop, which may not be {@code null}.
+ * It controls the loop parameters and result type in the standard case (see above for details).
+ * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
+ * and may accept any number of additional types.
+ * See above for other constraints.
+ *
+ * @return a method handle representing the loop.
+ * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
+ * @throws IllegalArgumentException if any argument violates the rules formulated above.
+ *
+ * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
+ return countedLoop(empty(iterations.type()), iterations, init, body);
+ }
+
+ /**
+ * Constructs a loop that counts over a range of numbers.
+ * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
+ * {@code
+ * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
+ * return countedLoop(empty(iterations.type()), iterations, init, body);
+ * }
+ * }
+ *
+ *
+ *
+ *
+ *
+ * @apiNote The implementation of this method can be expressed as follows:
+ * {@code
+ * int start(A...);
+ * int end(A...);
+ * V init(A...);
+ * V body(V, int, A...);
+ * V countedLoop(A... a...) {
+ * int e = end(a...);
+ * int s = start(a...);
+ * V v = init(a...);
+ * for (int i = s; i < e; ++i) {
+ * v = body(v, i, a...);
+ * }
+ * return v;
+ * }
+ * }
+ *
+ * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
+ * See above for other constraints.
+ * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
+ * {@code end-1}). The result type must be {@code int}. See above for other constraints.
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param body body of the loop, which may not be {@code null}.
+ * It controls the loop parameters and result type in the standard case (see above for details).
+ * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
+ * and may accept any number of additional types.
+ * See above for other constraints.
+ *
+ * @return a method handle representing the loop.
+ * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
+ * @throws IllegalArgumentException if any argument violates the rules formulated above.
+ *
+ * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
+ countedLoopChecks(start, end, init, body);
+ Class counterType = start.type().returnType(); // int, but who's counting?
+ Class limitType = end.type().returnType(); // yes, int again
+ Class returnType = body.type().returnType();
+ MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
+ MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
+ MethodHandle retv = null;
+ if (returnType != void.class) {
+ incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
+ pred = dropArguments(pred, 1, returnType); // ditto
+ retv = dropArguments(identity(returnType), 0, counterType);
+ }
+ body = dropArguments(body, 0, counterType); // ignore the limit variable
+ MethodHandle[]
+ loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
+ bodyClause = { init, body }, // v = init(); v = body(v, i)
+ indexVar = { start, incr }; // i = start(); i = i + 1
+ return loop(loopLimit, bodyClause, indexVar);
+ }
+
+ private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
+ Objects.requireNonNull(start);
+ Objects.requireNonNull(end);
+ Objects.requireNonNull(body);
+ Class counterType = start.type().returnType();
+ if (counterType != int.class) {
+ MethodType expected = start.type().changeReturnType(int.class);
+ throw misMatchedTypes("start function", start.type(), expected);
+ } else if (end.type().returnType() != counterType) {
+ MethodType expected = end.type().changeReturnType(counterType);
+ throw misMatchedTypes("end function", end.type(), expected);
+ }
+ MethodType bodyType = body.type();
+ Class returnType = bodyType.returnType();
+ List{@code
+ * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
+ * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
+ * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
+ * // the following semantics:
+ * // MH_increment: (int limit, int counter) -> counter + 1
+ * // MH_predicate: (int limit, int counter) -> counter < limit
+ * Class counterType = start.type().returnType(); // int
+ * Class returnType = body.type().returnType();
+ * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
+ * if (returnType != void.class) { // ignore the V variable
+ * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
+ * pred = dropArguments(pred, 1, returnType); // ditto
+ * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
+ * }
+ * body = dropArguments(body, 0, counterType); // ignore the limit variable
+ * MethodHandle[]
+ * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
+ * bodyClause = { init, body }, // v = init(); v = body(v, i)
+ * indexVar = { start, incr }; // i = start(); i = i + 1
+ * return loop(loopLimit, bodyClause, indexVar);
+ * }
+ * }
+ *
+ *
+ *
+ *
+ *
+ * @apiNote Example:
+ * {@code
+ * Iterator
+ *
+ * @apiNote The implementation of this method can be expressed approximately as follows:
+ * {@code
+ * // get an iterator from a list
+ * static List
+ *
+ * @param iterator an optional handle to return the iterator to start the loop.
+ * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
+ * See above for other constraints.
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param body body of the loop, which may not be {@code null}.
+ * It controls the loop parameters and result type in the standard case (see above for details).
+ * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
+ * and may accept any number of additional types.
+ * See above for other constraints.
+ *
+ * @return a method handle embodying the iteration loop functionality.
+ * @throws NullPointerException if the {@code body} handle is {@code null}.
+ * @throws IllegalArgumentException if any argument violates the above requirements.
+ *
+ * @since 9
+ */
+ public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
+ Class iterableType = iteratedLoopChecks(iterator, init, body);
+ Class returnType = body.type().returnType();
+ MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
+ MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
+ MethodHandle startIter;
+ MethodHandle nextVal;
+ {
+ MethodType iteratorType;
+ if (iterator == null) {
+ // derive argument type from body, if available, else use Iterable
+ startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
+ iteratorType = startIter.type().changeParameterType(0, iterableType);
+ } else {
+ // force return type to the internal iterator class
+ iteratorType = iterator.type().changeReturnType(Iterator.class);
+ startIter = iterator;
+ }
+ Class ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
+ MethodType nextValType = nextRaw.type().changeReturnType(ttype);
+
+ // perform the asType transforms under an exception transformer, as per spec.:
+ try {
+ startIter = startIter.asType(iteratorType);
+ nextVal = nextRaw.asType(nextValType);
+ } catch (WrongMethodTypeException ex) {
+ throw new IllegalArgumentException(ex);
+ }
+ }
+
+ MethodHandle retv = null, step = body;
+ if (returnType != void.class) {
+ // the simple thing first: in (I V A...), drop the I to get V
+ retv = dropArguments(identity(returnType), 0, Iterator.class);
+ // body type signature (V T A...), internal loop types (I V A...)
+ step = swapArguments(body, 0, 1); // swap V <-> T
+ }
+
+ MethodHandle[]
+ iterVar = { startIter, null, hasNext, retv },
+ bodyClause = { init, filterArgument(step, 0, nextVal) };
+ return loop(iterVar, bodyClause);
+ }
+
+ private static Class iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
+ Objects.requireNonNull(body);
+ MethodType bodyType = body.type();
+ Class returnType = bodyType.returnType();
+ List{@code
+ * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
+ * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
+ * Class returnType = body.type().returnType();
+ * Class ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
+ * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
+ * MethodHandle retv = null, step = body, startIter = iterator;
+ * if (returnType != void.class) {
+ * // the simple thing first: in (I V A...), drop the I to get V
+ * retv = dropArguments(identity(returnType), 0, Iterator.class);
+ * // body type signature (V T A...), internal loop types (I V A...)
+ * step = swapArguments(body, 0, 1); // swap V <-> T
+ * }
+ * if (startIter == null) startIter = MH_getIter;
+ * MethodHandle[]
+ * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
+ * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
+ * return loop(iterVar, bodyClause);
+ * }
+ * }
+ *
+ *
+ * {@code
+ * V target(A..., B...);
+ * V cleanup(Throwable, V, A...);
+ * V adapter(A... a, B... b) {
+ * V result = (zero value for V);
+ * Throwable throwable = null;
+ * try {
+ * result = target(a..., b...);
+ * } catch (Throwable t) {
+ * throwable = t;
+ * throw t;
+ * } finally {
+ * result = cleanup(throwable, result, a...);
+ * }
+ * return result;
+ * }
+ * }