30  * Cracking (reflecting) method handles back into their constituent symbolic parts.

    35  * A symbolic reference obtained by cracking a method handle into its consitutent symbolic parts.

    31  *

    36  * To crack a direct method handle, call {@link Lookup#revealDirect Lookup.revealDirect}.

    37  * <p>

    38  * A <em>direct method handle</em> represents a method, constructor, or field without

    39  * any intervening argument bindings or other transformations.

    40  * The method, constructor, or field referred to by a direct method handle is called

    41  * its <em>underlying member</em>.

    42  * Direct method handles may be obtained in any of these ways:

    43  * <ul>

    44  * <li>By executing an {@code ldc} instruction on a {@code CONSTANT_MethodHandle} constant.

    45  *     (See the Java Virtual Machine Specification, sections 4.4.8 and 5.4.3.)

    46  * <li>By calling one of the <a href="MethodHandles.Lookup.html#lookups">Lookup Factory Methods</a>,

    47  *     such as {@link Lookup#findVirtual Lookup.findVirtual},

    48  *     to resolve a symbolic reference into a method handle.

    49  *     A symbolic reference consists of a class, name string, and type.

    50  * <li>By calling the factory method {@link Lookup#unreflect Lookup.unreflect}

    51  *     or {@link Lookup#unreflectSpecial Lookup.unreflectSpecial}

    52  *     to convert a {@link Method} into a method handle.

    53  * <li>By calling the factory method {@link Lookup#unreflectConstructor Lookup.unreflectConstructor}

    54  *     to convert a {@link Constructor} into a method handle.

    55  * <li>By calling the factory method {@link Lookup#unreflectGetter Lookup.unreflectGetter}

    56  *     or {@link Lookup#unreflectSetter Lookup.unreflectSetter}

    57  *     to convert a {@link Field} into a method handle.

    58  * </ul>

    59  * In all of these cases, it is possible to crack the resulting direct method handle

    60  * to recover a symbolic reference for the underlying method, constructor, or field.

    61  * Cracking must be done via a {@code Lookup} object equivalent to that which created

    62  * the target method handle, or which has enough access permissions to recreate

    63  * an equivalent method handle.

    64  *

    65  * <h1><a name="refkinds"></a>Reference kinds</h1>

    66  * The <a href="MethodHandles.Lookup.html#lookups">Lookup Factory Methods</a>

    67  * correspond to all major use cases for methods, constructors, and fields.

    68  * These use cases may be distinguished using small integers as follows:

    69  * <table border=1 cellpadding=5 summary="reference kinds">

    70  * <tr><th>reference kind</th><th>descriptive name</th><th>scope</th><th>member</th><th>behavior</th></tr>

    71  * <tr>

    72  *     <td>{@code 1}</td><td>{@code REF_getField}</td><td>{@code class}</td>

    73  *     <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>

    74  * </tr>

    75  * <tr>

    76  *     <td>{@code 2}</td><td>{@code REF_getStatic}</td><td>{@code class} or {@code interface}</td>

    77  *     <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>

    78  * </tr>

    79  * <tr>

    80  *     <td>{@code 3}</td><td>{@code REF_putField}</td><td>{@code class}</td>

    81  *     <td>{@code FT f;}</td><td>{@code this.f = x;}</td>

    82  * </tr>

    83  * <tr>

    84  *     <td>{@code 4}</td><td>{@code REF_putStatic}</td><td>{@code class}</td>

    85  *     <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>

    86  * </tr>

    87  * <tr>

    88  *     <td>{@code 5}</td><td>{@code REF_invokeVirtual}</td><td>{@code class}</td>

    89  *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>

    90  * </tr>

    91  * <tr>

    92  *     <td>{@code 6}</td><td>{@code REF_invokeStatic}</td><td>{@code class} or {@code interface}</td>

    93  *     <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>

    94  * </tr>

    95  * <tr>

    96  *     <td>{@code 7}</td><td>{@code REF_invokeSpecial}</td><td>{@code class} or {@code interface}</td>

    97  *     <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>

    98  * </tr>

    99  * <tr>

   100  *     <td>{@code 8}</td><td>{@code REF_newInvokeSpecial}</td><td>{@code class}</td>

   101  *     <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>

   102  * </tr>

   103  * <tr>

   104  *     <td>{@code 9}</td><td>{@code REF_invokeInterface}</td><td>{@code interface}</td>

   105  *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>

   106  * </tr>

   107  * </table>

   108  * @since 1.8

    33 final class MethodHandleInfo {

   110 public

    34    public static final int

   111 interface MethodHandleInfo {

    35        REF_getField                = Constants.REF_getField,

   112     /**

    36        REF_getStatic               = Constants.REF_getStatic,

   113      * A direct method handle reference kind,

    37        REF_putField                = Constants.REF_putField,

   114      * as defined in the <a href="MethodHandleInfo.html#refkinds">table above</a>.

    38        REF_putStatic               = Constants.REF_putStatic,

   115      */

    39        REF_invokeVirtual           = Constants.REF_invokeVirtual,

   116     public static final int

    40        REF_invokeStatic            = Constants.REF_invokeStatic,

   117         REF_getField                = Constants.REF_getField,

    41        REF_invokeSpecial           = Constants.REF_invokeSpecial,

   118         REF_getStatic               = Constants.REF_getStatic,

    42        REF_newInvokeSpecial        = Constants.REF_newInvokeSpecial,

   119         REF_putField                = Constants.REF_putField,

    43        REF_invokeInterface         = Constants.REF_invokeInterface;

   120         REF_putStatic               = Constants.REF_putStatic,

    44 

   121         REF_invokeVirtual           = Constants.REF_invokeVirtual,

    45    private final Class<?> declaringClass;

   122         REF_invokeStatic            = Constants.REF_invokeStatic,

    46    private final String name;

   123         REF_invokeSpecial           = Constants.REF_invokeSpecial,

    47    private final MethodType methodType;

   124         REF_newInvokeSpecial        = Constants.REF_newInvokeSpecial,

    48    private final int referenceKind;

   125         REF_invokeInterface         = Constants.REF_invokeInterface;

    49 

   126 

    50    public MethodHandleInfo(MethodHandle mh) {

   127     /**

    51        MemberName mn = mh.internalMemberName();

   128      * Returns the reference kind of the cracked method handle, which in turn

    52        if (mn == null)  throw new IllegalArgumentException("not a direct method handle");

   129      * determines whether the method handle's underlying member was a constructor, method, or field.

    53        this.declaringClass = mn.getDeclaringClass();

   130      * See the <a href="MethodHandleInfo.html#refkinds">table above</a> for definitions.

    54        this.name = mn.getName();

   131      * @return the integer code for the kind of reference used to access the underlying member

    55        this.methodType = mn.getMethodOrFieldType();

   132      */

    56        byte refKind = mn.getReferenceKind();

   133     public int getReferenceKind();

    57        if (refKind == REF_invokeSpecial && !mh.isInvokeSpecial())

   134 

    58            // Devirtualized method invocation is usually formally virtual.

   135     /**

    59            refKind = REF_invokeVirtual;

   136      * Returns the class in which the cracked method handle's underlying member was defined.

    60        this.referenceKind = refKind;

   137      * @return the declaring class of the underlying member

    61    }

   138      */

    62 

   139     public Class<?> getDeclaringClass();

    63    public Class<?> getDeclaringClass() {

   140 

    64        return declaringClass;

   141     /**

    65    }

   142      * Returns the name of the cracked method handle's underlying member.

    66 

   143      * This is {@code "<init>"} if the underlying member was a constructor,

    67    public String getName() {

   144      * else it is a simple method name or field name.

    68        return name;

   145      * @return the simple name of the underlying member

    69    }

   146      */

    70 

   147     public String getName();

    71    public MethodType getMethodType() {

   148 

    72        return methodType;

   149     /**

    73    }

   150      * Returns the nominal type of the cracked symbolic reference, expressed as a method type.

    74 

   151      * If the reference is to a constructor, the return type will be {@code void}.

    75    public int getModifiers() {

   152      * If it is to a non-static method, the method type will not mention the {@code this} parameter.

    76        return -1; //TODO

   153      * If it is to a field and the requested access is to read the field,

    77    }

   154      * the method type will have no parameters and return the field type.

    78 

   155      * If it is to a field and the requested access is to write the field,

    79    public int getReferenceKind() {

   156      * the method type will have one parameter of the field type and return {@code void}.

    80        return referenceKind;

   157      * <p>

    81    }

   158      * Note that original direct method handle may include a leading {@code this} parameter,

    82 

   159      * or (in the case of a constructor) will replace the {@code void} return type

    83    static String getReferenceKindString(int referenceKind) {

   160      * with the constructed class.

    84         switch (referenceKind) {

   161      * The nominal type does not include any {@code this} parameter,

    85             case REF_getField: return "getfield";

   162      * and (in the case of a constructor) will return {@code void}.

    86             case REF_getStatic: return "getstatic";

   163      * @return the type of the underlying member, expressed as a method type

    87             case REF_putField: return "putfield";

   164      */

    88             case REF_putStatic: return "putstatic";

   165     public MethodType getMethodType();

    89             case REF_invokeVirtual: return "invokevirtual";

   166 

    90             case REF_invokeStatic: return "invokestatic";

   167     // Utility methods.

    91             case REF_invokeSpecial: return "invokespecial";

   168     // NOTE: class/name/type and reference kind constitute a symbolic reference

    92             case REF_newInvokeSpecial: return "newinvokespecial";

   169     // member and modifiers are an add-on, derived from Core Reflection (or the equivalent)

    93             case REF_invokeInterface: return "invokeinterface";

   170 

    94             default: return "UNKNOWN_REFENCE_KIND" + "[" + referenceKind + "]";

   171     /**

    95         }

   172      * Reflects the underlying member as a method, constructor, or field object.

   173      * If the underlying member is public, it is reflected as if by

   174      * {@code getMethod}, {@code getConstructor}, or {@code getField}.

   175      * Otherwise, it is reflected as if by

   176      * {@code getDeclaredMethod}, {@code getDeclaredConstructor}, or {@code getDeclaredField}.

   177      * The underlying member must be accessible to the given lookup object.

   178      * @param <T> the desired type of the result, either {@link Member} or a subtype

   179      * @param expected a class object representing the desired result type {@code T}

   180      * @param lookup the lookup object that created this MethodHandleInfo, or one with equivalent access privileges

   181      * @return a reference to the method, constructor, or field object

   182      * @exception ClassCastException if the member is not of the expected type

   183      * @exception NullPointerException if either argument is {@code null}

   184      * @exception IllegalArgumentException if the underlying member is not accessible to the given lookup object

   185      */

   186     public <T extends Member> T reflectAs(Class<T> expected, Lookup lookup);

   187 

   188     /**

   189      * Returns the access modifiers of the underlying member.

   190      * @return the Java language modifiers for underlying member,

   191      *         or -1 if the member cannot be accessed

   192      * @see Modifier

   193      * @see reflectAs

   194      */

   195     public int getModifiers();

   196 

   197     /**

   198      * Determines if the underlying member was a variable arity method or constructor.

   199      * Such members are represented by method handles that are varargs collectors.

   200      * @implSpec

   201      * This produces a result equivalent to:

   202      * <pre>{@code

   203      *     getReferenceKind() >= REF_invokeVirtual && Modifier.isTransient(getModifiers())

   204      * }</pre>

   205      *

   206      *

   207      * @return {@code true} if and only if the underlying member was declared with variable arity.

   208      */

   209     // spelling derived from java.lang.reflect.Executable, not MethodHandle.isVarargsCollector

   210     public default boolean isVarArgs()  {

   211         // fields are never varargs:

   212         if (MethodHandleNatives.refKindIsField((byte) getReferenceKind()))

   213             return false;

   214         // not in the public API: Modifier.VARARGS

   215         final int ACC_VARARGS = 0x00000080;  // from JVMS 4.6 (Table 4.20)

   216         assert(ACC_VARARGS == Modifier.TRANSIENT);

   217         return Modifier.isTransient(getModifiers());

    98     @Override

   220     /**

    99     public String toString() {

   221      * Returns the descriptive name of the given reference kind,

   100         return String.format("%s %s.%s:%s", getReferenceKindString(referenceKind),

   222      * as defined in the <a href="MethodHandleInfo.html#refkinds">table above</a>.

   101                              declaringClass.getName(), name, methodType);

   223      * The conventional prefix "REF_" is omitted.

   224      * @param referenceKind an integer code for a kind of reference used to access a class member

   225      * @return a mixed-case string such as {@code "getField"}

   226      * @exception IllegalArgumentException if the argument is not a valid

   227      *            <a href="MethodHandleInfo.html#refkinds">reference kind number</a>

   228      */

   229     public static String referenceKindToString(int referenceKind) {

   230         if (!MethodHandleNatives.refKindIsValid(referenceKind))

   231             throw newIllegalArgumentException("invalid reference kind", referenceKind);

   232         return MethodHandleNatives.refKindName((byte)referenceKind);

   233     }

   234 

   235     /**

   236      * Returns a string representation for a {@code MethodHandleInfo},

   237      * given the four parts of its symbolic reference.

   238      * This is defined to be of the form {@code "RK C.N:MT"}, where {@code RK} is the

   239      * {@linkplain #referenceKindToString reference kind string} for {@code kind},

   240      * {@code C} is the {@linkplain java.lang.Class#getName name} of {@code defc}

   241      * {@code N} is the {@code name}, and

   242      * {@code MT} is the {@code type}.

   243      * These four values may be obtained from the

   244      * {@linkplain #getReferenceKind reference kind},

   245      * {@linkplain #getDeclaringClass declaring class},

   246      * {@linkplain #getName member name},

   247      * and {@linkplain #getMethodType method type}

   248      * of a {@code MethodHandleInfo} object.

   249      *

   250      * @implSpec

   251      * This produces a result equivalent to:

   252      * <pre>{@code

   253      *     String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type)

   254      * }</pre>

   255      *

   256      * @param kind the {@linkplain #getReferenceKind reference kind} part of the symbolic reference

   257      * @param defc the {@linkplain #getDeclaringClass declaring class} part of the symbolic reference

   258      * @param name the {@linkplain #getName member name} part of the symbolic reference

   259      * @param type the {@linkplain #getMethodType method type} part of the symbolic reference

   260      * @return a string of the form {@code "RK C.N:MT"}

   261      * @exception IllegalArgumentException if the first argument is not a valid

   262      *            <a href="MethodHandleInfo.html#refkinds">reference kind number</a>

   263      * @exception NullPointerException if any reference argument is {@code null}

   264      */

   265     public static String toString(int kind, Class<?> defc, String name, MethodType type) {

   266         Objects.requireNonNull(name); Objects.requireNonNull(type);

   267         return String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type);