1 /*

     2  * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package java.lang.invoke;

    27 

    28 import sun.invoke.util.Wrapper;

    29 import java.lang.ref.WeakReference;

    30 import java.lang.ref.Reference;

    31 import java.lang.ref.ReferenceQueue;

    32 import java.util.Arrays;

    33 import java.util.Collections;

    34 import java.util.List;

    35 import java.util.Objects;

    36 import java.util.concurrent.ConcurrentMap;

    37 import java.util.concurrent.ConcurrentHashMap;

    38 import sun.invoke.util.BytecodeDescriptor;

    39 import static java.lang.invoke.MethodHandleStatics.*;

    40 import sun.invoke.util.VerifyType;

    41 

    42 /**

    43  * A method type represents the arguments and return type accepted and

    44  * returned by a method handle, or the arguments and return type passed

    45  * and expected  by a method handle caller.  Method types must be properly

    46  * matched between a method handle and all its callers,

    47  * and the JVM's operations enforce this matching at, specifically

    48  * during calls to {@link MethodHandle#invokeExact MethodHandle.invokeExact}

    49  * and {@link MethodHandle#invoke MethodHandle.invoke}, and during execution

    50  * of {@code invokedynamic} instructions.

    51  * <p>

    52  * The structure is a return type accompanied by any number of parameter types.

    53  * The types (primitive, {@code void}, and reference) are represented by {@link Class} objects.

    54  * (For ease of exposition, we treat {@code void} as if it were a type.

    55  * In fact, it denotes the absence of a return type.)

    56  * <p>

    57  * All instances of {@code MethodType} are immutable.

    58  * Two instances are completely interchangeable if they compare equal.

    59  * Equality depends on pairwise correspondence of the return and parameter types and on nothing else.

    60  * <p>

    61  * This type can be created only by factory methods.

    62  * All factory methods may cache values, though caching is not guaranteed.

    63  * Some factory methods are static, while others are virtual methods which

    64  * modify precursor method types, e.g., by changing a selected parameter.

    65  * <p>

    66  * Factory methods which operate on groups of parameter types

    67  * are systematically presented in two versions, so that both Java arrays and

    68  * Java lists can be used to work with groups of parameter types.

    69  * The query methods {@code parameterArray} and {@code parameterList}

    70  * also provide a choice between arrays and lists.

    71  * <p>

    72  * {@code MethodType} objects are sometimes derived from bytecode instructions

    73  * such as {@code invokedynamic}, specifically from the type descriptor strings associated

    74  * with the instructions in a class file's constant pool.

    75  * <p>

    76  * Like classes and strings, method types can also be represented directly

    77  * in a class file's constant pool as constants.

    78  * A method type may be loaded by an {@code ldc} instruction which refers

    79  * to a suitable {@code CONSTANT_MethodType} constant pool entry.

    80  * The entry refers to a {@code CONSTANT_Utf8} spelling for the descriptor string.

    81  * (For full details on method type constants,

    82  * see sections 4.4.8 and 5.4.3.5 of the Java Virtual Machine Specification.)

    83  * <p>

    84  * When the JVM materializes a {@code MethodType} from a descriptor string,

    85  * all classes named in the descriptor must be accessible, and will be loaded.

    86  * (But the classes need not be initialized, as is the case with a {@code CONSTANT_Class}.)

    87  * This loading may occur at any time before the {@code MethodType} object is first derived.

    88  * @author John Rose, JSR 292 EG

    89  */

    90 public final

    91 class MethodType implements java.io.Serializable {

    92     private static final long serialVersionUID = 292L;  // {rtype, {ptype...}}

    93 

    94     // The rtype and ptypes fields define the structural identity of the method type:

    95     private final Class<?>   rtype;

    96     private final Class<?>[] ptypes;

    97 

    98     // The remaining fields are caches of various sorts:

    99     private @Stable MethodTypeForm form; // erased form, plus cached data about primitives

   100     private @Stable MethodType wrapAlt;  // alternative wrapped/unwrapped version

   101     private @Stable Invokers invokers;   // cache of handy higher-order adapters

   102     private @Stable String methodDescriptor;  // cache for toMethodDescriptorString

   103 

   104     /**

   105      * Check the given parameters for validity and store them into the final fields.

   106      */

   107     private MethodType(Class<?> rtype, Class<?>[] ptypes, boolean trusted) {

   108         checkRtype(rtype);

   109         checkPtypes(ptypes);

   110         this.rtype = rtype;

   111         // defensively copy the array passed in by the user

   112         this.ptypes = trusted ? ptypes : Arrays.copyOf(ptypes, ptypes.length);

   113     }

   114 

   115     /**

   116      * Construct a temporary unchecked instance of MethodType for use only as a key to the intern table.

   117      * Does not check the given parameters for validity, and must be discarded after it is used as a searching key.

   118      * The parameters are reversed for this constructor, so that is is not accidentally used.

   119      */

   120     private MethodType(Class<?>[] ptypes, Class<?> rtype) {

   121         this.rtype = rtype;

   122         this.ptypes = ptypes;

   123     }

   124 

   125     /*trusted*/ MethodTypeForm form() { return form; }

   126     /*trusted*/ Class<?> rtype() { return rtype; }

   127     /*trusted*/ Class<?>[] ptypes() { return ptypes; }

   128 

   129     void setForm(MethodTypeForm f) { form = f; }

   130 

   131     /** This number, mandated by the JVM spec as 255,

   132      *  is the maximum number of <em>slots</em>

   133      *  that any Java method can receive in its argument list.

   134      *  It limits both JVM signatures and method type objects.

   135      *  The longest possible invocation will look like

   136      *  {@code staticMethod(arg1, arg2, ..., arg255)} or

   137      *  {@code x.virtualMethod(arg1, arg2, ..., arg254)}.

   138      */

   139     /*non-public*/ static final int MAX_JVM_ARITY = 255;  // this is mandated by the JVM spec.

   140 

   141     /** This number is the maximum arity of a method handle, 254.

   142      *  It is derived from the absolute JVM-imposed arity by subtracting one,

   143      *  which is the slot occupied by the method handle itself at the

   144      *  beginning of the argument list used to invoke the method handle.

   145      *  The longest possible invocation will look like

   146      *  {@code mh.invoke(arg1, arg2, ..., arg254)}.

   147      */

   148     // Issue:  Should we allow MH.invokeWithArguments to go to the full 255?

   149     /*non-public*/ static final int MAX_MH_ARITY = MAX_JVM_ARITY-1;  // deduct one for mh receiver

   150 

   151     /** This number is the maximum arity of a method handle invoker, 253.

   152      *  It is derived from the absolute JVM-imposed arity by subtracting two,

   153      *  which are the slots occupied by invoke method handle, and the

   154      *  target method handle, which are both at the beginning of the argument

   155      *  list used to invoke the target method handle.

   156      *  The longest possible invocation will look like

   157      *  {@code invokermh.invoke(targetmh, arg1, arg2, ..., arg253)}.

   158      */

   159     /*non-public*/ static final int MAX_MH_INVOKER_ARITY = MAX_MH_ARITY-1;  // deduct one more for invoker

   160 

   161     private static void checkRtype(Class<?> rtype) {

   162         Objects.requireNonNull(rtype);

   163     }

   164     private static void checkPtype(Class<?> ptype) {

   165         Objects.requireNonNull(ptype);

   166         if (ptype == void.class)

   167             throw newIllegalArgumentException("parameter type cannot be void");

   168     }

   169     /** Return number of extra slots (count of long/double args). */

   170     private static int checkPtypes(Class<?>[] ptypes) {

   171         int slots = 0;

   172         for (Class<?> ptype : ptypes) {

   173             checkPtype(ptype);

   174             if (ptype == double.class || ptype == long.class) {

   175                 slots++;

   176             }

   177         }

   178         checkSlotCount(ptypes.length + slots);

   179         return slots;

   180     }

   181     static void checkSlotCount(int count) {

   182         assert((MAX_JVM_ARITY & (MAX_JVM_ARITY+1)) == 0);

   183         // MAX_JVM_ARITY must be power of 2 minus 1 for following code trick to work:

   184         if ((count & MAX_JVM_ARITY) != count)

   185             throw newIllegalArgumentException("bad parameter count "+count);

   186     }

   187     private static IndexOutOfBoundsException newIndexOutOfBoundsException(Object num) {

   188         if (num instanceof Integer)  num = "bad index: "+num;

   189         return new IndexOutOfBoundsException(num.toString());

   190     }

   191 

   192     static final ConcurrentWeakInternSet<MethodType> internTable = new ConcurrentWeakInternSet<>();

   193 

   194     static final Class<?>[] NO_PTYPES = {};

   195 

   196     /**

   197      * Finds or creates an instance of the given method type.

   198      * @param rtype  the return type

   199      * @param ptypes the parameter types

   200      * @return a method type with the given components

   201      * @throws NullPointerException if {@code rtype} or {@code ptypes} or any element of {@code ptypes} is null

   202      * @throws IllegalArgumentException if any element of {@code ptypes} is {@code void.class}

   203      */

   204     public static

   205     MethodType methodType(Class<?> rtype, Class<?>[] ptypes) {

   206         return makeImpl(rtype, ptypes, false);

   207     }

   208 

   209     /**

   210      * Finds or creates a method type with the given components.

   211      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   212      * @param rtype  the return type

   213      * @param ptypes the parameter types

   214      * @return a method type with the given components

   215      * @throws NullPointerException if {@code rtype} or {@code ptypes} or any element of {@code ptypes} is null

   216      * @throws IllegalArgumentException if any element of {@code ptypes} is {@code void.class}

   217      */

   218     public static

   219     MethodType methodType(Class<?> rtype, List<Class<?>> ptypes) {

   220         boolean notrust = false;  // random List impl. could return evil ptypes array

   221         return makeImpl(rtype, listToArray(ptypes), notrust);

   222     }

   223 

   224     private static Class<?>[] listToArray(List<Class<?>> ptypes) {

   225         // sanity check the size before the toArray call, since size might be huge

   226         checkSlotCount(ptypes.size());

   227         return ptypes.toArray(NO_PTYPES);

   228     }

   229 

   230     /**

   231      * Finds or creates a method type with the given components.

   232      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   233      * The leading parameter type is prepended to the remaining array.

   234      * @param rtype  the return type

   235      * @param ptype0 the first parameter type

   236      * @param ptypes the remaining parameter types

   237      * @return a method type with the given components

   238      * @throws NullPointerException if {@code rtype} or {@code ptype0} or {@code ptypes} or any element of {@code ptypes} is null

   239      * @throws IllegalArgumentException if {@code ptype0} or {@code ptypes} or any element of {@code ptypes} is {@code void.class}

   240      */

   241     public static

   242     MethodType methodType(Class<?> rtype, Class<?> ptype0, Class<?>... ptypes) {

   243         Class<?>[] ptypes1 = new Class<?>[1+ptypes.length];

   244         ptypes1[0] = ptype0;

   245         System.arraycopy(ptypes, 0, ptypes1, 1, ptypes.length);

   246         return makeImpl(rtype, ptypes1, true);

   247     }

   248 

   249     /**

   250      * Finds or creates a method type with the given components.

   251      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   252      * The resulting method has no parameter types.

   253      * @param rtype  the return type

   254      * @return a method type with the given return value

   255      * @throws NullPointerException if {@code rtype} is null

   256      */

   257     public static

   258     MethodType methodType(Class<?> rtype) {

   259         return makeImpl(rtype, NO_PTYPES, true);

   260     }

   261 

   262     /**

   263      * Finds or creates a method type with the given components.

   264      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   265      * The resulting method has the single given parameter type.

   266      * @param rtype  the return type

   267      * @param ptype0 the parameter type

   268      * @return a method type with the given return value and parameter type

   269      * @throws NullPointerException if {@code rtype} or {@code ptype0} is null

   270      * @throws IllegalArgumentException if {@code ptype0} is {@code void.class}

   271      */

   272     public static

   273     MethodType methodType(Class<?> rtype, Class<?> ptype0) {

   274         return makeImpl(rtype, new Class<?>[]{ ptype0 }, true);

   275     }

   276 

   277     /**

   278      * Finds or creates a method type with the given components.

   279      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   280      * The resulting method has the same parameter types as {@code ptypes},

   281      * and the specified return type.

   282      * @param rtype  the return type

   283      * @param ptypes the method type which supplies the parameter types

   284      * @return a method type with the given components

   285      * @throws NullPointerException if {@code rtype} or {@code ptypes} is null

   286      */

   287     public static

   288     MethodType methodType(Class<?> rtype, MethodType ptypes) {

   289         return makeImpl(rtype, ptypes.ptypes, true);

   290     }

   291 

   292     /**

   293      * Sole factory method to find or create an interned method type.

   294      * @param rtype desired return type

   295      * @param ptypes desired parameter types

   296      * @param trusted whether the ptypes can be used without cloning

   297      * @return the unique method type of the desired structure

   298      */

   299     /*trusted*/ static

   300     MethodType makeImpl(Class<?> rtype, Class<?>[] ptypes, boolean trusted) {

   301         MethodType mt = internTable.get(new MethodType(ptypes, rtype));

   302         if (mt != null)

   303             return mt;

   304         if (ptypes.length == 0) {

   305             ptypes = NO_PTYPES; trusted = true;

   306         }

   307         mt = new MethodType(rtype, ptypes, trusted);

   308         // promote the object to the Real Thing, and reprobe

   309         mt.form = MethodTypeForm.findForm(mt);

   310         return internTable.add(mt);

   311     }

   312     private static final MethodType[] objectOnlyTypes = new MethodType[20];

   313 

   314     /**

   315      * Finds or creates a method type whose components are {@code Object} with an optional trailing {@code Object[]} array.

   316      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   317      * All parameters and the return type will be {@code Object},

   318      * except the final array parameter if any, which will be {@code Object[]}.

   319      * @param objectArgCount number of parameters (excluding the final array parameter if any)

   320      * @param finalArray whether there will be a trailing array parameter, of type {@code Object[]}

   321      * @return a generally applicable method type, for all calls of the given fixed argument count and a collected array of further arguments

   322      * @throws IllegalArgumentException if {@code objectArgCount} is negative or greater than 255 (or 254, if {@code finalArray} is true)

   323      * @see #genericMethodType(int)

   324      */

   325     public static

   326     MethodType genericMethodType(int objectArgCount, boolean finalArray) {

   327         MethodType mt;

   328         checkSlotCount(objectArgCount);

   329         int ivarargs = (!finalArray ? 0 : 1);

   330         int ootIndex = objectArgCount*2 + ivarargs;

   331         if (ootIndex < objectOnlyTypes.length) {

   332             mt = objectOnlyTypes[ootIndex];

   333             if (mt != null)  return mt;

   334         }

   335         Class<?>[] ptypes = new Class<?>[objectArgCount + ivarargs];

   336         Arrays.fill(ptypes, Object.class);

   337         if (ivarargs != 0)  ptypes[objectArgCount] = Object[].class;

   338         mt = makeImpl(Object.class, ptypes, true);

   339         if (ootIndex < objectOnlyTypes.length) {

   340             objectOnlyTypes[ootIndex] = mt;     // cache it here also!

   341         }

   342         return mt;

   343     }

   344 

   345     /**

   346      * Finds or creates a method type whose components are all {@code Object}.

   347      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   348      * All parameters and the return type will be Object.

   349      * @param objectArgCount number of parameters

   350      * @return a generally applicable method type, for all calls of the given argument count

   351      * @throws IllegalArgumentException if {@code objectArgCount} is negative or greater than 255

   352      * @see #genericMethodType(int, boolean)

   353      */

   354     public static

   355     MethodType genericMethodType(int objectArgCount) {

   356         return genericMethodType(objectArgCount, false);

   357     }

   358 

   359     /**

   360      * Finds or creates a method type with a single different parameter type.

   361      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   362      * @param num    the index (zero-based) of the parameter type to change

   363      * @param nptype a new parameter type to replace the old one with

   364      * @return the same type, except with the selected parameter changed

   365      * @throws IndexOutOfBoundsException if {@code num} is not a valid index into {@code parameterArray()}

   366      * @throws IllegalArgumentException if {@code nptype} is {@code void.class}

   367      * @throws NullPointerException if {@code nptype} is null

   368      */

   369     public MethodType changeParameterType(int num, Class<?> nptype) {

   370         if (parameterType(num) == nptype)  return this;

   371         checkPtype(nptype);

   372         Class<?>[] nptypes = ptypes.clone();

   373         nptypes[num] = nptype;

   374         return makeImpl(rtype, nptypes, true);

   375     }

   376 

   377     /**

   378      * Finds or creates a method type with additional parameter types.

   379      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   380      * @param num    the position (zero-based) of the inserted parameter type(s)

   381      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list

   382      * @return the same type, except with the selected parameter(s) inserted

   383      * @throws IndexOutOfBoundsException if {@code num} is negative or greater than {@code parameterCount()}

   384      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}

   385      *                                  or if the resulting method type would have more than 255 parameter slots

   386      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null

   387      */

   388     public MethodType insertParameterTypes(int num, Class<?>... ptypesToInsert) {

   389         int len = ptypes.length;

   390         if (num < 0 || num > len)

   391             throw newIndexOutOfBoundsException(num);

   392         int ins = checkPtypes(ptypesToInsert);

   393         checkSlotCount(parameterSlotCount() + ptypesToInsert.length + ins);

   394         int ilen = ptypesToInsert.length;

   395         if (ilen == 0)  return this;

   396         Class<?>[] nptypes = Arrays.copyOfRange(ptypes, 0, len+ilen);

   397         System.arraycopy(nptypes, num, nptypes, num+ilen, len-num);

   398         System.arraycopy(ptypesToInsert, 0, nptypes, num, ilen);

   399         return makeImpl(rtype, nptypes, true);

   400     }

   401 

   402     /**

   403      * Finds or creates a method type with additional parameter types.

   404      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   405      * @param ptypesToInsert zero or more new parameter types to insert after the end of the parameter list

   406      * @return the same type, except with the selected parameter(s) appended

   407      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}

   408      *                                  or if the resulting method type would have more than 255 parameter slots

   409      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null

   410      */

   411     public MethodType appendParameterTypes(Class<?>... ptypesToInsert) {

   412         return insertParameterTypes(parameterCount(), ptypesToInsert);

   413     }

   414 

   415     /**

   416      * Finds or creates a method type with additional parameter types.

   417      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   418      * @param num    the position (zero-based) of the inserted parameter type(s)

   419      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list

   420      * @return the same type, except with the selected parameter(s) inserted

   421      * @throws IndexOutOfBoundsException if {@code num} is negative or greater than {@code parameterCount()}

   422      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}

   423      *                                  or if the resulting method type would have more than 255 parameter slots

   424      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null

   425      */

   426     public MethodType insertParameterTypes(int num, List<Class<?>> ptypesToInsert) {

   427         return insertParameterTypes(num, listToArray(ptypesToInsert));

   428     }

   429 

   430     /**

   431      * Finds or creates a method type with additional parameter types.

   432      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   433      * @param ptypesToInsert zero or more new parameter types to insert after the end of the parameter list

   434      * @return the same type, except with the selected parameter(s) appended

   435      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}

   436      *                                  or if the resulting method type would have more than 255 parameter slots

   437      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null

   438      */

   439     public MethodType appendParameterTypes(List<Class<?>> ptypesToInsert) {

   440         return insertParameterTypes(parameterCount(), ptypesToInsert);

   441     }

   442 

   443      /**

   444      * Finds or creates a method type with modified parameter types.

   445      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   446      * @param start  the position (zero-based) of the first replaced parameter type(s)

   447      * @param end    the position (zero-based) after the last replaced parameter type(s)

   448      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list

   449      * @return the same type, except with the selected parameter(s) replaced

   450      * @throws IndexOutOfBoundsException if {@code start} is negative or greater than {@code parameterCount()}

   451      *                                  or if {@code end} is negative or greater than {@code parameterCount()}

   452      *                                  or if {@code start} is greater than {@code end}

   453      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}

   454      *                                  or if the resulting method type would have more than 255 parameter slots

   455      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null

   456      */

   457     /*non-public*/ MethodType replaceParameterTypes(int start, int end, Class<?>... ptypesToInsert) {

   458         if (start == end)

   459             return insertParameterTypes(start, ptypesToInsert);

   460         int len = ptypes.length;

   461         if (!(0 <= start && start <= end && end <= len))

   462             throw newIndexOutOfBoundsException("start="+start+" end="+end);

   463         int ilen = ptypesToInsert.length;

   464         if (ilen == 0)

   465             return dropParameterTypes(start, end);

   466         return dropParameterTypes(start, end).insertParameterTypes(start, ptypesToInsert);

   467     }

   468 

   469     /**

   470      * Finds or creates a method type with some parameter types omitted.

   471      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   472      * @param start  the index (zero-based) of the first parameter type to remove

   473      * @param end    the index (greater than {@code start}) of the first parameter type after not to remove

   474      * @return the same type, except with the selected parameter(s) removed

   475      * @throws IndexOutOfBoundsException if {@code start} is negative or greater than {@code parameterCount()}

   476      *                                  or if {@code end} is negative or greater than {@code parameterCount()}

   477      *                                  or if {@code start} is greater than {@code end}

   478      */

   479     public MethodType dropParameterTypes(int start, int end) {

   480         int len = ptypes.length;

   481         if (!(0 <= start && start <= end && end <= len))

   482             throw newIndexOutOfBoundsException("start="+start+" end="+end);

   483         if (start == end)  return this;

   484         Class<?>[] nptypes;

   485         if (start == 0) {

   486             if (end == len) {

   487                 // drop all parameters

   488                 nptypes = NO_PTYPES;

   489             } else {

   490                 // drop initial parameter(s)

   491                 nptypes = Arrays.copyOfRange(ptypes, end, len);

   492             }

   493         } else {

   494             if (end == len) {

   495                 // drop trailing parameter(s)

   496                 nptypes = Arrays.copyOfRange(ptypes, 0, start);

   497             } else {

   498                 int tail = len - end;

   499                 nptypes = Arrays.copyOfRange(ptypes, 0, start + tail);

   500                 System.arraycopy(ptypes, end, nptypes, start, tail);

   501             }

   502         }

   503         return makeImpl(rtype, nptypes, true);

   504     }

   505 

   506     /**

   507      * Finds or creates a method type with a different return type.

   508      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   509      * @param nrtype a return parameter type to replace the old one with

   510      * @return the same type, except with the return type change

   511      * @throws NullPointerException if {@code nrtype} is null

   512      */

   513     public MethodType changeReturnType(Class<?> nrtype) {

   514         if (returnType() == nrtype)  return this;

   515         return makeImpl(nrtype, ptypes, true);

   516     }

   517 

   518     /**

   519      * Reports if this type contains a primitive argument or return value.

   520      * The return type {@code void} counts as a primitive.

   521      * @return true if any of the types are primitives

   522      */

   523     public boolean hasPrimitives() {

   524         return form.hasPrimitives();

   525     }

   526 

   527     /**

   528      * Reports if this type contains a wrapper argument or return value.

   529      * Wrappers are types which box primitive values, such as {@link Integer}.

   530      * The reference type {@code java.lang.Void} counts as a wrapper,

   531      * if it occurs as a return type.

   532      * @return true if any of the types are wrappers

   533      */

   534     public boolean hasWrappers() {

   535         return unwrap() != this;

   536     }

   537 

   538     /**

   539      * Erases all reference types to {@code Object}.

   540      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   541      * All primitive types (including {@code void}) will remain unchanged.

   542      * @return a version of the original type with all reference types replaced

   543      */

   544     public MethodType erase() {

   545         return form.erasedType();

   546     }

   547 

   548     /**

   549      * Erases all reference types to {@code Object}, and all subword types to {@code int}.

   550      * This is the reduced type polymorphism used by private methods

   551      * such as {@link MethodHandle#invokeBasic invokeBasic}.

   552      * @return a version of the original type with all reference and subword types replaced

   553      */

   554     /*non-public*/ MethodType basicType() {

   555         return form.basicType();

   556     }

   557 

   558     /**

   559      * @return a version of the original type with MethodHandle prepended as the first argument

   560      */

   561     /*non-public*/ MethodType invokerType() {

   562         return insertParameterTypes(0, MethodHandle.class);

   563     }

   564 

   565     /**

   566      * Converts all types, both reference and primitive, to {@code Object}.

   567      * Convenience method for {@link #genericMethodType(int) genericMethodType}.

   568      * The expression {@code type.wrap().erase()} produces the same value

   569      * as {@code type.generic()}.

   570      * @return a version of the original type with all types replaced

   571      */

   572     public MethodType generic() {

   573         return genericMethodType(parameterCount());

   574     }

   575 

   576     /**

   577      * Converts all primitive types to their corresponding wrapper types.

   578      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   579      * All reference types (including wrapper types) will remain unchanged.

   580      * A {@code void} return type is changed to the type {@code java.lang.Void}.

   581      * The expression {@code type.wrap().erase()} produces the same value

   582      * as {@code type.generic()}.

   583      * @return a version of the original type with all primitive types replaced

   584      */

   585     public MethodType wrap() {

   586         return hasPrimitives() ? wrapWithPrims(this) : this;

   587     }

   588 

   589     /**

   590      * Converts all wrapper types to their corresponding primitive types.

   591      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   592      * All primitive types (including {@code void}) will remain unchanged.

   593      * A return type of {@code java.lang.Void} is changed to {@code void}.

   594      * @return a version of the original type with all wrapper types replaced

   595      */

   596     public MethodType unwrap() {

   597         MethodType noprims = !hasPrimitives() ? this : wrapWithPrims(this);

   598         return unwrapWithNoPrims(noprims);

   599     }

   600 

   601     private static MethodType wrapWithPrims(MethodType pt) {

   602         assert(pt.hasPrimitives());

   603         MethodType wt = pt.wrapAlt;

   604         if (wt == null) {

   605             // fill in lazily

   606             wt = MethodTypeForm.canonicalize(pt, MethodTypeForm.WRAP, MethodTypeForm.WRAP);

   607             assert(wt != null);

   608             pt.wrapAlt = wt;

   609         }

   610         return wt;

   611     }

   612 

   613     private static MethodType unwrapWithNoPrims(MethodType wt) {

   614         assert(!wt.hasPrimitives());

   615         MethodType uwt = wt.wrapAlt;

   616         if (uwt == null) {

   617             // fill in lazily

   618             uwt = MethodTypeForm.canonicalize(wt, MethodTypeForm.UNWRAP, MethodTypeForm.UNWRAP);

   619             if (uwt == null)

   620                 uwt = wt;    // type has no wrappers or prims at all

   621             wt.wrapAlt = uwt;

   622         }

   623         return uwt;

   624     }

   625 

   626     /**

   627      * Returns the parameter type at the specified index, within this method type.

   628      * @param num the index (zero-based) of the desired parameter type

   629      * @return the selected parameter type

   630      * @throws IndexOutOfBoundsException if {@code num} is not a valid index into {@code parameterArray()}

   631      */

   632     public Class<?> parameterType(int num) {

   633         return ptypes[num];

   634     }

   635     /**

   636      * Returns the number of parameter types in this method type.

   637      * @return the number of parameter types

   638      */

   639     public int parameterCount() {

   640         return ptypes.length;

   641     }

   642     /**

   643      * Returns the return type of this method type.

   644      * @return the return type

   645      */

   646     public Class<?> returnType() {

   647         return rtype;

   648     }

   649 

   650     /**

   651      * Presents the parameter types as a list (a convenience method).

   652      * The list will be immutable.

   653      * @return the parameter types (as an immutable list)

   654      */

   655     public List<Class<?>> parameterList() {

   656         return Collections.unmodifiableList(Arrays.asList(ptypes));

   657     }

   658 

   659     /*non-public*/ Class<?> lastParameterType() {

   660         int len = ptypes.length;

   661         return len == 0 ? void.class : ptypes[len-1];

   662     }

   663 

   664     /**

   665      * Presents the parameter types as an array (a convenience method).

   666      * Changes to the array will not result in changes to the type.

   667      * @return the parameter types (as a fresh copy if necessary)

   668      */

   669     public Class<?>[] parameterArray() {

   670         return ptypes.clone();

   671     }

   672 

   673     /**

   674      * Compares the specified object with this type for equality.

   675      * That is, it returns <tt>true</tt> if and only if the specified object

   676      * is also a method type with exactly the same parameters and return type.

   677      * @param x object to compare

   678      * @see Object#equals(Object)

   679      */

   680     @Override

   681     public boolean equals(Object x) {

   682         return this == x || x instanceof MethodType && equals((MethodType)x);

   683     }

   684 

   685     private boolean equals(MethodType that) {

   686         return this.rtype == that.rtype

   687             && Arrays.equals(this.ptypes, that.ptypes);

   688     }

   689 

   690     /**

   691      * Returns the hash code value for this method type.

   692      * It is defined to be the same as the hashcode of a List

   693      * whose elements are the return type followed by the

   694      * parameter types.

   695      * @return the hash code value for this method type

   696      * @see Object#hashCode()

   697      * @see #equals(Object)

   698      * @see List#hashCode()

   699      */

   700     @Override

   701     public int hashCode() {

   702       int hashCode = 31 + rtype.hashCode();

   703       for (Class<?> ptype : ptypes)

   704           hashCode = 31*hashCode + ptype.hashCode();

   705       return hashCode;

   706     }

   707 

   708     /**

   709      * Returns a string representation of the method type,

   710      * of the form {@code "(PT0,PT1...)RT"}.

   711      * The string representation of a method type is a

   712      * parenthesis enclosed, comma separated list of type names,

   713      * followed immediately by the return type.

   714      * <p>

   715      * Each type is represented by its

   716      * {@link java.lang.Class#getSimpleName simple name}.

   717      */

   718     @Override

   719     public String toString() {

   720         StringBuilder sb = new StringBuilder();

   721         sb.append("(");

   722         for (int i = 0; i < ptypes.length; i++) {

   723             if (i > 0)  sb.append(",");

   724             sb.append(ptypes[i].getSimpleName());

   725         }

   726         sb.append(")");

   727         sb.append(rtype.getSimpleName());

   728         return sb.toString();

   729     }

   730 

   731 

   732     /*non-public*/

   733     boolean isViewableAs(MethodType newType) {

   734         if (!VerifyType.isNullConversion(returnType(), newType.returnType()))

   735             return false;

   736         int argc = parameterCount();

   737         if (argc != newType.parameterCount())

   738             return false;

   739         for (int i = 0; i < argc; i++) {

   740             if (!VerifyType.isNullConversion(newType.parameterType(i), parameterType(i)))

   741                 return false;

   742         }

   743         return true;

   744     }

   745     /*non-public*/

   746     boolean isCastableTo(MethodType newType) {

   747         int argc = parameterCount();

   748         if (argc != newType.parameterCount())

   749             return false;

   750         return true;

   751     }

   752     /*non-public*/

   753     boolean isConvertibleTo(MethodType newType) {

   754         if (!canConvert(returnType(), newType.returnType()))

   755             return false;

   756         int argc = parameterCount();

   757         if (argc != newType.parameterCount())

   758             return false;

   759         for (int i = 0; i < argc; i++) {

   760             if (!canConvert(newType.parameterType(i), parameterType(i)))

   761                 return false;

   762         }

   763         return true;

   764     }

   765     /*non-public*/

   766     static boolean canConvert(Class<?> src, Class<?> dst) {

   767         // short-circuit a few cases:

   768         if (src == dst || dst == Object.class)  return true;

   769         // the remainder of this logic is documented in MethodHandle.asType

   770         if (src.isPrimitive()) {

   771             // can force void to an explicit null, a la reflect.Method.invoke

   772             // can also force void to a primitive zero, by analogy

   773             if (src == void.class)  return true;  //or !dst.isPrimitive()?

   774             Wrapper sw = Wrapper.forPrimitiveType(src);

   775             if (dst.isPrimitive()) {

   776                 // P->P must widen

   777                 return Wrapper.forPrimitiveType(dst).isConvertibleFrom(sw);

   778             } else {

   779                 // P->R must box and widen

   780                 return dst.isAssignableFrom(sw.wrapperType());

   781             }

   782         } else if (dst.isPrimitive()) {

   783             // any value can be dropped

   784             if (dst == void.class)  return true;

   785             Wrapper dw = Wrapper.forPrimitiveType(dst);

   786             // R->P must be able to unbox (from a dynamically chosen type) and widen

   787             // For example:

   788             //   Byte/Number/Comparable/Object -> dw:Byte -> byte.

   789             //   Character/Comparable/Object -> dw:Character -> char

   790             //   Boolean/Comparable/Object -> dw:Boolean -> boolean

   791             // This means that dw must be cast-compatible with src.

   792             if (src.isAssignableFrom(dw.wrapperType())) {

   793                 return true;

   794             }

   795             // The above does not work if the source reference is strongly typed

   796             // to a wrapper whose primitive must be widened.  For example:

   797             //   Byte -> unbox:byte -> short/int/long/float/double

   798             //   Character -> unbox:char -> int/long/float/double

   799             if (Wrapper.isWrapperType(src) &&

   800                 dw.isConvertibleFrom(Wrapper.forWrapperType(src))) {

   801                 // can unbox from src and then widen to dst

   802                 return true;

   803             }

   804             // We have already covered cases which arise due to runtime unboxing

   805             // of a reference type which covers several wrapper types:

   806             //   Object -> cast:Integer -> unbox:int -> long/float/double

   807             //   Serializable -> cast:Byte -> unbox:byte -> byte/short/int/long/float/double

   808             // An marginal case is Number -> dw:Character -> char, which would be OK if there were a

   809             // subclass of Number which wraps a value that can convert to char.

   810             // Since there is none, we don't need an extra check here to cover char or boolean.

   811             return false;

   812         } else {

   813             // R->R always works, since null is always valid dynamically

   814             return true;

   815         }

   816     }

   817 

   818     /// Queries which have to do with the bytecode architecture

   819 

   820     /** Reports the number of JVM stack slots required to invoke a method

   821      * of this type.  Note that (for historical reasons) the JVM requires

   822      * a second stack slot to pass long and double arguments.

   823      * So this method returns {@link #parameterCount() parameterCount} plus the

   824      * number of long and double parameters (if any).

   825      * <p>

   826      * This method is included for the benefit of applications that must

   827      * generate bytecodes that process method handles and invokedynamic.

   828      * @return the number of JVM stack slots for this type's parameters

   829      */

   830     /*non-public*/ int parameterSlotCount() {

   831         return form.parameterSlotCount();

   832     }

   833 

   834     /*non-public*/ Invokers invokers() {

   835         Invokers inv = invokers;

   836         if (inv != null)  return inv;

   837         invokers = inv = new Invokers(this);

   838         return inv;

   839     }

   840 

   841     /** Reports the number of JVM stack slots which carry all parameters including and after

   842      * the given position, which must be in the range of 0 to

   843      * {@code parameterCount} inclusive.  Successive parameters are

   844      * more shallowly stacked, and parameters are indexed in the bytecodes

   845      * according to their trailing edge.  Thus, to obtain the depth

   846      * in the outgoing call stack of parameter {@code N}, obtain

   847      * the {@code parameterSlotDepth} of its trailing edge

   848      * at position {@code N+1}.

   849      * <p>

   850      * Parameters of type {@code long} and {@code double} occupy

   851      * two stack slots (for historical reasons) and all others occupy one.

   852      * Therefore, the number returned is the number of arguments

   853      * <em>including</em> and <em>after</em> the given parameter,

   854      * <em>plus</em> the number of long or double arguments

   855      * at or after after the argument for the given parameter.

   856      * <p>

   857      * This method is included for the benefit of applications that must

   858      * generate bytecodes that process method handles and invokedynamic.

   859      * @param num an index (zero-based, inclusive) within the parameter types

   860      * @return the index of the (shallowest) JVM stack slot transmitting the

   861      *         given parameter

   862      * @throws IllegalArgumentException if {@code num} is negative or greater than {@code parameterCount()}

   863      */

   864     /*non-public*/ int parameterSlotDepth(int num) {

   865         if (num < 0 || num > ptypes.length)

   866             parameterType(num);  // force a range check

   867         return form.parameterToArgSlot(num-1);

   868     }

   869 

   870     /** Reports the number of JVM stack slots required to receive a return value

   871      * from a method of this type.

   872      * If the {@link #returnType() return type} is void, it will be zero,

   873      * else if the return type is long or double, it will be two, else one.

   874      * <p>

   875      * This method is included for the benefit of applications that must

   876      * generate bytecodes that process method handles and invokedynamic.

   877      * @return the number of JVM stack slots (0, 1, or 2) for this type's return value

   878      * Will be removed for PFD.

   879      */

   880     /*non-public*/ int returnSlotCount() {

   881         return form.returnSlotCount();

   882     }

   883 

   884     /**

   885      * Finds or creates an instance of a method type, given the spelling of its bytecode descriptor.

   886      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.

   887      * Any class or interface name embedded in the descriptor string

   888      * will be resolved by calling {@link ClassLoader#loadClass(java.lang.String)}

   889      * on the given loader (or if it is null, on the system class loader).

   890      * <p>

   891      * Note that it is possible to encounter method types which cannot be

   892      * constructed by this method, because their component types are

   893      * not all reachable from a common class loader.

   894      * <p>

   895      * This method is included for the benefit of applications that must

   896      * generate bytecodes that process method handles and {@code invokedynamic}.

   897      * @param descriptor a bytecode-level type descriptor string "(T...)T"

   898      * @param loader the class loader in which to look up the types

   899      * @return a method type matching the bytecode-level type descriptor

   900      * @throws NullPointerException if the string is null

   901      * @throws IllegalArgumentException if the string is not well-formed

   902      * @throws TypeNotPresentException if a named type cannot be found

   903      */

   904     public static MethodType fromMethodDescriptorString(String descriptor, ClassLoader loader)

   905         throws IllegalArgumentException, TypeNotPresentException

   906     {

   907         if (!descriptor.startsWith("(") ||  // also generates NPE if needed

   908             descriptor.indexOf(')') < 0 ||

   909             descriptor.indexOf('.') >= 0)

   910             throw new IllegalArgumentException("not a method descriptor: "+descriptor);

   911         List<Class<?>> types = BytecodeDescriptor.parseMethod(descriptor, loader);

   912         Class<?> rtype = types.remove(types.size() - 1);

   913         checkSlotCount(types.size());

   914         Class<?>[] ptypes = listToArray(types);

   915         return makeImpl(rtype, ptypes, true);

   916     }

   917 

   918     /**

   919      * Produces a bytecode descriptor representation of the method type.

   920      * <p>

   921      * Note that this is not a strict inverse of {@link #fromMethodDescriptorString fromMethodDescriptorString}.

   922      * Two distinct classes which share a common name but have different class loaders

   923      * will appear identical when viewed within descriptor strings.

   924      * <p>

   925      * This method is included for the benefit of applications that must

   926      * generate bytecodes that process method handles and {@code invokedynamic}.

   927      * {@link #fromMethodDescriptorString(java.lang.String, java.lang.ClassLoader) fromMethodDescriptorString},

   928      * because the latter requires a suitable class loader argument.

   929      * @return the bytecode type descriptor representation

   930      */

   931     public String toMethodDescriptorString() {

   932         String desc = methodDescriptor;

   933         if (desc == null) {

   934             desc = BytecodeDescriptor.unparse(this);

   935             methodDescriptor = desc;

   936         }

   937         return desc;

   938     }

   939 

   940     /*non-public*/ static String toFieldDescriptorString(Class<?> cls) {

   941         return BytecodeDescriptor.unparse(cls);

   942     }

   943 

   944     /// Serialization.

   945 

   946     /**

   947      * There are no serializable fields for {@code MethodType}.

   948      */

   949     private static final java.io.ObjectStreamField[] serialPersistentFields = { };

   950 

   951     /**

   952      * Save the {@code MethodType} instance to a stream.

   953      *

   954      * @serialData

   955      * For portability, the serialized format does not refer to named fields.

   956      * Instead, the return type and parameter type arrays are written directly

   957      * from the {@code writeObject} method, using two calls to {@code s.writeObject}

   958      * as follows:

   959      * <blockquote><pre>{@code

   960 s.writeObject(this.returnType());

   961 s.writeObject(this.parameterArray());

   962      * }</pre></blockquote>

   963      * <p>

   964      * The deserialized field values are checked as if they were

   965      * provided to the factory method {@link #methodType(Class,Class[]) methodType}.

   966      * For example, null values, or {@code void} parameter types,

   967      * will lead to exceptions during deserialization.

   968      * @param s the stream to write the object to

   969      * @throws java.io.IOException if there is a problem writing the object

   970      */

   971     private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {

   972         s.defaultWriteObject();  // requires serialPersistentFields to be an empty array

   973         s.writeObject(returnType());

   974         s.writeObject(parameterArray());

   975     }

   976 

   977     /**

   978      * Reconstitute the {@code MethodType} instance from a stream (that is,

   979      * deserialize it).

   980      * This instance is a scratch object with bogus final fields.

   981      * It provides the parameters to the factory method called by

   982      * {@link #readResolve readResolve}.

   983      * After that call it is discarded.

   984      * @param s the stream to read the object from

   985      * @throws java.io.IOException if there is a problem reading the object

   986      * @throws ClassNotFoundException if one of the component classes cannot be resolved

   987      * @see #MethodType()

   988      * @see #readResolve

   989      * @see #writeObject

   990      */

   991     private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {

   992         s.defaultReadObject();  // requires serialPersistentFields to be an empty array

   993 

   994         Class<?>   returnType     = (Class<?>)   s.readObject();

   995         Class<?>[] parameterArray = (Class<?>[]) s.readObject();

   996 

   997         // Probably this object will never escape, but let's check

   998         // the field values now, just to be sure.

   999         checkRtype(returnType);

  1000         checkPtypes(parameterArray);

  1001 

  1002         parameterArray = parameterArray.clone();  // make sure it is unshared

  1003         MethodType_init(returnType, parameterArray);

  1004     }

  1005 

  1006     /**

  1007      * For serialization only.

  1008      * Sets the final fields to null, pending {@code Unsafe.putObject}.

  1009      */

  1010     private MethodType() {

  1011         this.rtype = null;

  1012         this.ptypes = null;

  1013     }

  1014     private void MethodType_init(Class<?> rtype, Class<?>[] ptypes) {

  1015         // In order to communicate these values to readResolve, we must

  1016         // store them into the implementation-specific final fields.

  1017         checkRtype(rtype);

  1018         checkPtypes(ptypes);

  1019         UNSAFE.putObject(this, rtypeOffset, rtype);

  1020         UNSAFE.putObject(this, ptypesOffset, ptypes);

  1021     }

  1022 

  1023     // Support for resetting final fields while deserializing

  1024     private static final long rtypeOffset, ptypesOffset;

  1025     static {

  1026         try {

  1027             rtypeOffset = UNSAFE.objectFieldOffset

  1028                 (MethodType.class.getDeclaredField("rtype"));

  1029             ptypesOffset = UNSAFE.objectFieldOffset

  1030                 (MethodType.class.getDeclaredField("ptypes"));

  1031         } catch (Exception ex) {

  1032             throw new Error(ex);

  1033         }

  1034     }

  1035 

  1036     /**

  1037      * Resolves and initializes a {@code MethodType} object

  1038      * after serialization.

  1039      * @return the fully initialized {@code MethodType} object

  1040      */

  1041     private Object readResolve() {

  1042         // Do not use a trusted path for deserialization:

  1043         //return makeImpl(rtype, ptypes, true);

  1044         // Verify all operands, and make sure ptypes is unshared:

  1045         return methodType(rtype, ptypes);

  1046     }

  1047 

  1048     /**

  1049      * Simple implementation of weak concurrent intern set.

  1050      *

  1051      * @param <T> interned type

  1052      */

  1053     private static class ConcurrentWeakInternSet<T> {

  1054 

  1055         private final ConcurrentMap<WeakEntry<T>, WeakEntry<T>> map;

  1056         private final ReferenceQueue<T> stale;

  1057 

  1058         public ConcurrentWeakInternSet() {

  1059             this.map = new ConcurrentHashMap<>();

  1060             this.stale = new ReferenceQueue<>();

  1061         }

  1062 

  1063         /**

  1064          * Get the existing interned element.

  1065          * This method returns null if no element is interned.

  1066          *

  1067          * @param elem element to look up

  1068          * @return the interned element

  1069          */

  1070         public T get(T elem) {

  1071             if (elem == null) throw new NullPointerException();

  1072             expungeStaleElements();

  1073 

  1074             WeakEntry<T> value = map.get(new WeakEntry<>(elem));

  1075             if (value != null) {

  1076                 T res = value.get();

  1077                 if (res != null) {

  1078                     return res;

  1079                 }

  1080             }

  1081             return null;

  1082         }

  1083 

  1084         /**

  1085          * Interns the element.

  1086          * Always returns non-null element, matching the one in the intern set.

  1087          * Under the race against another add(), it can return <i>different</i>

  1088          * element, if another thread beats us to interning it.

  1089          *

  1090          * @param elem element to add

  1091          * @return element that was actually added

  1092          */

  1093         public T add(T elem) {

  1094             if (elem == null) throw new NullPointerException();

  1095 

  1096             // Playing double race here, and so spinloop is required.

  1097             // First race is with two concurrent updaters.

  1098             // Second race is with GC purging weak ref under our feet.

  1099             // Hopefully, we almost always end up with a single pass.

  1100             T interned;

  1101             WeakEntry<T> e = new WeakEntry<>(elem, stale);

  1102             do {

  1103                 expungeStaleElements();

  1104                 WeakEntry<T> exist = map.putIfAbsent(e, e);

  1105                 interned = (exist == null) ? elem : exist.get();

  1106             } while (interned == null);

  1107             return interned;

  1108         }

  1109 

  1110         private void expungeStaleElements() {

  1111             Reference<? extends T> reference;

  1112             while ((reference = stale.poll()) != null) {

  1113                 map.remove(reference);

  1114             }

  1115         }

  1116 

  1117         private static class WeakEntry<T> extends WeakReference<T> {

  1118 

  1119             public final int hashcode;

  1120 

  1121             public WeakEntry(T key, ReferenceQueue<T> queue) {

  1122                 super(key, queue);

  1123                 hashcode = key.hashCode();

  1124             }

  1125 

  1126             public WeakEntry(T key) {

  1127                 super(key);

  1128                 hashcode = key.hashCode();

  1129             }

  1130 

  1131             @Override

  1132             public boolean equals(Object obj) {

  1133                 if (obj instanceof WeakEntry) {

  1134                     Object that = ((WeakEntry) obj).get();