My first initial commit with all of mine experimental changes.

Dmitry Kabak (userdima committed 13 years ago

Commit d37b88d1 parent 3f5b46618352 files · +2598093 −-8690Browse files

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	1	+/*
	2	+ * Copyright (c) 1998, 2010, 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.util;
	27	+import java.lang.ref.WeakReference;
	28	+import java.lang.ref.ReferenceQueue;
	29	+
	30	+
	31	+/**
	32	+ * Hash table based implementation of the <tt>Map</tt> interface, with
	33	+ * <em>weak keys</em>.
	34	+ * An entry in a <tt>WeakHashMap</tt> will automatically be removed when
	35	+ * its key is no longer in ordinary use. More precisely, the presence of a
	36	+ * mapping for a given key will not prevent the key from being discarded by the
	37	+ * garbage collector, that is, made finalizable, finalized, and then reclaimed.
	38	+ * When a key has been discarded its entry is effectively removed from the map,
	39	+ * so this class behaves somewhat differently from other <tt>Map</tt>
	40	+ * implementations.
	41	+ *
	42	+ * <p> Both null values and the null key are supported. This class has
	43	+ * performance characteristics similar to those of the <tt>HashMap</tt>
	44	+ * class, and has the same efficiency parameters of <em>initial capacity</em>
	45	+ * and <em>load factor</em>.
	46	+ *
	47	+ * <p> Like most collection classes, this class is not synchronized.
	48	+ * A synchronized <tt>WeakHashMap</tt> may be constructed using the
	49	+ * {@link Collections#synchronizedMap Collections.synchronizedMap}
	50	+ * method.
	51	+ *
	52	+ * <p> This class is intended primarily for use with key objects whose
	53	+ * <tt>equals</tt> methods test for object identity using the
	54	+ * <tt>==</tt> operator. Once such a key is discarded it can never be
	55	+ * recreated, so it is impossible to do a lookup of that key in a
	56	+ * <tt>WeakHashMap</tt> at some later time and be surprised that its entry
	57	+ * has been removed. This class will work perfectly well with key objects
	58	+ * whose <tt>equals</tt> methods are not based upon object identity, such
	59	+ * as <tt>String</tt> instances. With such recreatable key objects,
	60	+ * however, the automatic removal of <tt>WeakHashMap</tt> entries whose
	61	+ * keys have been discarded may prove to be confusing.
	62	+ *
	63	+ * <p> The behavior of the <tt>WeakHashMap</tt> class depends in part upon
	64	+ * the actions of the garbage collector, so several familiar (though not
	65	+ * required) <tt>Map</tt> invariants do not hold for this class. Because
	66	+ * the garbage collector may discard keys at any time, a
	67	+ * <tt>WeakHashMap</tt> may behave as though an unknown thread is silently
	68	+ * removing entries. In particular, even if you synchronize on a
	69	+ * <tt>WeakHashMap</tt> instance and invoke none of its mutator methods, it
	70	+ * is possible for the <tt>size</tt> method to return smaller values over
	71	+ * time, for the <tt>isEmpty</tt> method to return <tt>false</tt> and
	72	+ * then <tt>true</tt>, for the <tt>containsKey</tt> method to return
	73	+ * <tt>true</tt> and later <tt>false</tt> for a given key, for the
	74	+ * <tt>get</tt> method to return a value for a given key but later return
	75	+ * <tt>null</tt>, for the <tt>put</tt> method to return
	76	+ * <tt>null</tt> and the <tt>remove</tt> method to return
	77	+ * <tt>false</tt> for a key that previously appeared to be in the map, and
	78	+ * for successive examinations of the key set, the value collection, and
	79	+ * the entry set to yield successively smaller numbers of elements.
	80	+ *
	81	+ * <p> Each key object in a <tt>WeakHashMap</tt> is stored indirectly as
	82	+ * the referent of a weak reference. Therefore a key will automatically be
	83	+ * removed only after the weak references to it, both inside and outside of the
	84	+ * map, have been cleared by the garbage collector.
	85	+ *
	86	+ * <p> <strong>Implementation note:</strong> The value objects in a
	87	+ * <tt>WeakHashMap</tt> are held by ordinary strong references. Thus care
	88	+ * should be taken to ensure that value objects do not strongly refer to their
	89	+ * own keys, either directly or indirectly, since that will prevent the keys
	90	+ * from being discarded. Note that a value object may refer indirectly to its
	91	+ * key via the <tt>WeakHashMap</tt> itself; that is, a value object may
	92	+ * strongly refer to some other key object whose associated value object, in
	93	+ * turn, strongly refers to the key of the first value object. One way
	94	+ * to deal with this is to wrap values themselves within
	95	+ * <tt>WeakReferences</tt> before
	96	+ * inserting, as in: <tt>m.put(key, new WeakReference(value))</tt>,
	97	+ * and then unwrapping upon each <tt>get</tt>.
	98	+ *
	99	+ * <p>The iterators returned by the <tt>iterator</tt> method of the collections
	100	+ * returned by all of this class's "collection view methods" are
	101	+ * <i>fail-fast</i>: if the map is structurally modified at any time after the
	102	+ * iterator is created, in any way except through the iterator's own
	103	+ * <tt>remove</tt> method, the iterator will throw a {@link
	104	+ * ConcurrentModificationException}. Thus, in the face of concurrent
	105	+ * modification, the iterator fails quickly and cleanly, rather than risking
	106	+ * arbitrary, non-deterministic behavior at an undetermined time in the future.
	107	+ *
	108	+ * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
	109	+ * as it is, generally speaking, impossible to make any hard guarantees in the
	110	+ * presence of unsynchronized concurrent modification. Fail-fast iterators
	111	+ * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
	112	+ * Therefore, it would be wrong to write a program that depended on this
	113	+ * exception for its correctness: <i>the fail-fast behavior of iterators
	114	+ * should be used only to detect bugs.</i>
	115	+ *
	116	+ * <p>This class is a member of the
	117	+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
	118	+ * Java Collections Framework</a>.
	119	+ *
	120	+ * @param <K> the type of keys maintained by this map
	121	+ * @param <V> the type of mapped values
	122	+ *
	123	+ * @author Doug Lea
	124	+ * @author Josh Bloch
	125	+ * @author Mark Reinhold
	126	+ * @since 1.2
	127	+ * @see java.util.HashMap
	128	+ * @see java.lang.ref.WeakReference
	129	+ */
	130	+public class WeakHashMap<K,V>
	131	+ extends AbstractMap<K,V>
	132	+ implements Map<K,V> {
	133	+
	134	+ /**
	135	+ * The default initial capacity -- MUST be a power of two.
	136	+ */
	137	+ private static final int DEFAULT_INITIAL_CAPACITY = 16;
	138	+
	139	+ /**
	140	+ * The maximum capacity, used if a higher value is implicitly specified
	141	+ * by either of the constructors with arguments.
	142	+ * MUST be a power of two <= 1<<30.
	143	+ */
	144	+ private static final int MAXIMUM_CAPACITY = 1 << 30;
	145	+
	146	+ /**
	147	+ * The load factor used when none specified in constructor.
	148	+ */
	149	+ private static final float DEFAULT_LOAD_FACTOR = 0.75f;
	150	+
	151	+ /**
	152	+ * The table, resized as necessary. Length MUST Always be a power of two.
	153	+ */
	154	+ Entry<K,V>[] table;
	155	+
	156	+ /**
	157	+ * The number of key-value mappings contained in this weak hash map.
	158	+ */
	159	+ private int size;
	160	+
	161	+ /**
	162	+ * The next size value at which to resize (capacity * load factor).
	163	+ */
	164	+ private int threshold;
	165	+
	166	+ /**
	167	+ * The load factor for the hash table.
	168	+ */
	169	+ private final float loadFactor;
	170	+
	171	+ /**
	172	+ * Reference queue for cleared WeakEntries
	173	+ */
	174	+ private final ReferenceQueue<Object> queue = new ReferenceQueue<>();
	175	+
	176	+ /**
	177	+ * The number of times this WeakHashMap has been structurally modified.
	178	+ * Structural modifications are those that change the number of
	179	+ * mappings in the map or otherwise modify its internal structure
	180	+ * (e.g., rehash). This field is used to make iterators on
	181	+ * Collection-views of the map fail-fast.
	182	+ *
	183	+ * @see ConcurrentModificationException
	184	+ */
	185	+ int modCount;
	186	+
	187	+ @SuppressWarnings("unchecked")
	188	+ private Entry<K,V>[] newTable(int n) {
	189	+ return (Entry<K,V>[]) new Entry[n];
	190	+ }
	191	+
	192	+ /**
	193	+ * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
	194	+ * capacity and the given load factor.
	195	+ *
	196	+ * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
	197	+ * @param loadFactor The load factor of the <tt>WeakHashMap</tt>
	198	+ * @throws IllegalArgumentException if the initial capacity is negative,
	199	+ * or if the load factor is nonpositive.
	200	+ */
	201	+ public WeakHashMap(int initialCapacity, float loadFactor) {
	202	+ if (initialCapacity < 0)
	203	+ throw new IllegalArgumentException("Illegal Initial Capacity: "+
	204	+ initialCapacity);
	205	+ if (initialCapacity > MAXIMUM_CAPACITY)
	206	+ initialCapacity = MAXIMUM_CAPACITY;
	207	+
	208	+ if (loadFactor <= 0 \|\| Float.isNaN(loadFactor))
	209	+ throw new IllegalArgumentException("Illegal Load factor: "+
	210	+ loadFactor);
	211	+ int capacity = 1;
	212	+ while (capacity < initialCapacity)
	213	+ capacity <<= 1;
	214	+ table = newTable(capacity);
	215	+ this.loadFactor = loadFactor;
	216	+ threshold = (int)(capacity * loadFactor);
	217	+ }
	218	+
	219	+ /**
	220	+ * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
	221	+ * capacity and the default load factor (0.75).
	222	+ *
	223	+ * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
	224	+ * @throws IllegalArgumentException if the initial capacity is negative
	225	+ */
	226	+ public WeakHashMap(int initialCapacity) {
	227	+ this(initialCapacity, DEFAULT_LOAD_FACTOR);
	228	+ }
	229	+
	230	+ /**
	231	+ * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial
	232	+ * capacity (16) and load factor (0.75).
	233	+ */
	234	+ public WeakHashMap() {
	235	+ this.loadFactor = DEFAULT_LOAD_FACTOR;
	236	+ threshold = DEFAULT_INITIAL_CAPACITY;
	237	+ table = newTable(DEFAULT_INITIAL_CAPACITY);
	238	+ }
	239	+
	240	+ /**
	241	+ * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the
	242	+ * specified map. The <tt>WeakHashMap</tt> is created with the default
	243	+ * load factor (0.75) and an initial capacity sufficient to hold the
	244	+ * mappings in the specified map.
	245	+ *
	246	+ * @param m the map whose mappings are to be placed in this map
	247	+ * @throws NullPointerException if the specified map is null
	248	+ * @since 1.3
	249	+ */
	250	+ public WeakHashMap(Map<? extends K, ? extends V> m) {
	251	+ this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, 16),
	252	+ DEFAULT_LOAD_FACTOR);
	253	+ putAll(m);
	254	+ }
	255	+
	256	+ // internal utilities
	257	+
	258	+ /**
	259	+ * Value representing null keys inside tables.
	260	+ */
	261	+ private static final Object NULL_KEY = new Object();
	262	+
	263	+ /**
	264	+ * Use NULL_KEY for key if it is null.
	265	+ */
	266	+ private static Object maskNull(Object key) {
	267	+ return (key == null) ? NULL_KEY : key;
	268	+ }
	269	+
	270	+ /**
	271	+ * Returns internal representation of null key back to caller as null.
	272	+ */
	273	+ static Object unmaskNull(Object key) {
	274	+ return (key == NULL_KEY) ? null : key;
	275	+ }
	276	+
	277	+ /**
	278	+ * Checks for equality of non-null reference x and possibly-null y. By
	279	+ * default uses Object.equals.
	280	+ */
	281	+ private static boolean eq(Object x, Object y) {
	282	+ return x == y \|\| x.equals(y);
	283	+ }
	284	+
	285	+ /**
	286	+ * Returns index for hash code h.
	287	+ */
	288	+ private static int indexFor(int h, int length) {
	289	+ return h & (length-1);
	290	+ }
	291	+
	292	+ /**
	293	+ * Expunges stale entries from the table.
	294	+ */
	295	+ private void expungeStaleEntries() {
	296	+ for (Object x; (x = queue.poll()) != null; ) {
	297	+ synchronized (queue) {
	298	+ @SuppressWarnings("unchecked")
	299	+ Entry<K,V> e = (Entry<K,V>) x;
	300	+ int i = indexFor(e.hash, table.length);
	301	+
	302	+ Entry<K,V> prev = table[i];
	303	+ Entry<K,V> p = prev;
	304	+ while (p != null) {
	305	+ Entry<K,V> next = p.next;
	306	+ if (p == e) {
	307	+ if (prev == e)
	308	+ table[i] = next;
	309	+ else
	310	+ prev.next = next;
	311	+ // Must not null out e.next;
	312	+ // stale entries may be in use by a HashIterator
	313	+ e.value = null; // Help GC
	314	+ size--;
	315	+ break;
	316	+ }
	317	+ prev = p;
	318	+ p = next;
	319	+ }
	320	+ }
	321	+ }
	322	+ }
	323	+
	324	+ /**
	325	+ * Returns the table after first expunging stale entries.
	326	+ */
	327	+ private Entry<K,V>[] getTable() {
	328	+ expungeStaleEntries();
	329	+ return table;
	330	+ }
	331	+
	332	+ /**
	333	+ * Returns the number of key-value mappings in this map.
	334	+ * This result is a snapshot, and may not reflect unprocessed
	335	+ * entries that will be removed before next attempted access
	336	+ * because they are no longer referenced.
	337	+ */
	338	+ public int size() {
	339	+ if (size == 0)
	340	+ return 0;
	341	+ expungeStaleEntries();
	342	+ return size;
	343	+ }
	344	+
	345	+ /**
	346	+ * Returns <tt>true</tt> if this map contains no key-value mappings.
	347	+ * This result is a snapshot, and may not reflect unprocessed
	348	+ * entries that will be removed before next attempted access
	349	+ * because they are no longer referenced.
	350	+ */
	351	+ public boolean isEmpty() {
	352	+ return size() == 0;
	353	+ }
	354	+
	355	+ /**
	356	+ * Returns the value to which the specified key is mapped,
	357	+ * or {@code null} if this map contains no mapping for the key.
	358	+ *
	359	+ * <p>More formally, if this map contains a mapping from a key
	360	+ * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
	361	+ * key.equals(k))}, then this method returns {@code v}; otherwise
	362	+ * it returns {@code null}. (There can be at most one such mapping.)
	363	+ *
	364	+ * <p>A return value of {@code null} does not <i>necessarily</i>
	365	+ * indicate that the map contains no mapping for the key; it's also
	366	+ * possible that the map explicitly maps the key to {@code null}.
	367	+ * The {@link #containsKey containsKey} operation may be used to
	368	+ * distinguish these two cases.
	369	+ *
	370	+ * @see #put(Object, Object)
	371	+ */
	372	+ public V get(Object key) {
	373	+ Object k = maskNull(key);
	374	+ int h = HashMap.hash(k.hashCode());
	375	+ Entry<K,V>[] tab = getTable();
	376	+ int index = indexFor(h, tab.length);
	377	+ Entry<K,V> e = tab[index];
	378	+ while (e != null) {
	379	+ if (e.hash == h && eq(k, e.get()))
	380	+ return e.value;
	381	+ e = e.next;
	382	+ }
	383	+ return null;
	384	+ }
	385	+
	386	+ /**
	387	+ * Returns <tt>true</tt> if this map contains a mapping for the
	388	+ * specified key.
	389	+ *
	390	+ * @param key The key whose presence in this map is to be tested
	391	+ * @return <tt>true</tt> if there is a mapping for <tt>key</tt>;
	392	+ * <tt>false</tt> otherwise
	393	+ */
	394	+ public boolean containsKey(Object key) {
	395	+ return getEntry(key) != null;
	396	+ }
	397	+
	398	+ /**
	399	+ * Returns the entry associated with the specified key in this map.
	400	+ * Returns null if the map contains no mapping for this key.
	401	+ */
	402	+ Entry<K,V> getEntry(Object key) {
	403	+ Object k = maskNull(key);
	404	+ int h = HashMap.hash(k.hashCode());
	405	+ Entry<K,V>[] tab = getTable();
	406	+ int index = indexFor(h, tab.length);
	407	+ Entry<K,V> e = tab[index];
	408	+ while (e != null && !(e.hash == h && eq(k, e.get())))
	409	+ e = e.next;
	410	+ return e;
	411	+ }
	412	+
	413	+ /**
	414	+ * Associates the specified value with the specified key in this map.
	415	+ * If the map previously contained a mapping for this key, the old
	416	+ * value is replaced.
	417	+ *
	418	+ * @param key key with which the specified value is to be associated.
	419	+ * @param value value to be associated with the specified key.
	420	+ * @return the previous value associated with <tt>key</tt>, or
	421	+ * <tt>null</tt> if there was no mapping for <tt>key</tt>.
	422	+ * (A <tt>null</tt> return can also indicate that the map
	423	+ * previously associated <tt>null</tt> with <tt>key</tt>.)
	424	+ */
	425	+ public V put(K key, V value) {
	426	+ Object k = maskNull(key);
	427	+ int h = HashMap.hash(k.hashCode());
	428	+ Entry<K,V>[] tab = getTable();
	429	+ int i = indexFor(h, tab.length);
	430	+
	431	+ for (Entry<K,V> e = tab[i]; e != null; e = e.next) {
	432	+ if (h == e.hash && eq(k, e.get())) {
	433	+ V oldValue = e.value;
	434	+ if (value != oldValue)
	435	+ e.value = value;
	436	+ return oldValue;
	437	+ }
	438	+ }
	439	+
	440	+ modCount++;
	441	+ Entry<K,V> e = tab[i];
	442	+ tab[i] = new Entry<>(k, value, queue, h, e);
	443	+ if (++size >= threshold)
	444	+ resize(tab.length * 2);
	445	+ return null;
	446	+ }
	447	+
	448	+ /**
	449	+ * Rehashes the contents of this map into a new array with a
	450	+ * larger capacity. This method is called automatically when the
	451	+ * number of keys in this map reaches its threshold.
	452	+ *
	453	+ * If current capacity is MAXIMUM_CAPACITY, this method does not
	454	+ * resize the map, but sets threshold to Integer.MAX_VALUE.
	455	+ * This has the effect of preventing future calls.
	456	+ *
	457	+ * @param newCapacity the new capacity, MUST be a power of two;
	458	+ * must be greater than current capacity unless current
	459	+ * capacity is MAXIMUM_CAPACITY (in which case value
	460	+ * is irrelevant).
	461	+ */
	462	+ void resize(int newCapacity) {
	463	+ Entry<K,V>[] oldTable = getTable();
	464	+ int oldCapacity = oldTable.length;
	465	+ if (oldCapacity == MAXIMUM_CAPACITY) {
	466	+ threshold = Integer.MAX_VALUE;
	467	+ return;
	468	+ }
	469	+
	470	+ Entry<K,V>[] newTable = newTable(newCapacity);
	471	+ transfer(oldTable, newTable);
	472	+ table = newTable;
	473	+
	474	+ /*
	475	+ * If ignoring null elements and processing ref queue caused massive
	476	+ * shrinkage, then restore old table. This should be rare, but avoids
	477	+ * unbounded expansion of garbage-filled tables.
	478	+ */
	479	+ if (size >= threshold / 2) {
	480	+ threshold = (int)(newCapacity * loadFactor);
	481	+ } else {
	482	+ expungeStaleEntries();
	483	+ transfer(newTable, oldTable);
	484	+ table = oldTable;
	485	+ }
	486	+ }
	487	+
	488	+ /** Transfers all entries from src to dest tables */
	489	+ private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) {
	490	+ for (int j = 0; j < src.length; ++j) {
	491	+ Entry<K,V> e = src[j];
	492	+ src[j] = null;
	493	+ while (e != null) {
	494	+ Entry<K,V> next = e.next;
	495	+ Object key = e.get();
	496	+ if (key == null) {
	497	+ e.next = null; // Help GC
	498	+ e.value = null; // " "
	499	+ size--;
	500	+ } else {
	501	+ int i = indexFor(e.hash, dest.length);
	502	+ e.next = dest[i];
	503	+ dest[i] = e;
	504	+ }
	505	+ e = next;
	506	+ }
	507	+ }
	508	+ }
	509	+
	510	+ /**
	511	+ * Copies all of the mappings from the specified map to this map.
	512	+ * These mappings will replace any mappings that this map had for any
	513	+ * of the keys currently in the specified map.
	514	+ *
	515	+ * @param m mappings to be stored in this map.
	516	+ * @throws NullPointerException if the specified map is null.
	517	+ */
	518	+ public void putAll(Map<? extends K, ? extends V> m) {
	519	+ int numKeysToBeAdded = m.size();
	520	+ if (numKeysToBeAdded == 0)
	521	+ return;
	522	+
	523	+ /*
	524	+ * Expand the map if the map if the number of mappings to be added
	525	+ * is greater than or equal to threshold. This is conservative; the
	526	+ * obvious condition is (m.size() + size) >= threshold, but this
	527	+ * condition could result in a map with twice the appropriate capacity,
	528	+ * if the keys to be added overlap with the keys already in this map.
	529	+ * By using the conservative calculation, we subject ourself
	530	+ * to at most one extra resize.
	531	+ */
	532	+ if (numKeysToBeAdded > threshold) {
	533	+ int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
	534	+ if (targetCapacity > MAXIMUM_CAPACITY)
	535	+ targetCapacity = MAXIMUM_CAPACITY;
	536	+ int newCapacity = table.length;
	537	+ while (newCapacity < targetCapacity)
	538	+ newCapacity <<= 1;
	539	+ if (newCapacity > table.length)
	540	+ resize(newCapacity);
	541	+ }
	542	+
	543	+ for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
	544	+ put(e.getKey(), e.getValue());
	545	+ }
	546	+
	547	+ /**
	548	+ * Removes the mapping for a key from this weak hash map if it is present.
	549	+ * More formally, if this map contains a mapping from key <tt>k</tt> to
	550	+ * value <tt>v</tt> such that <code>(key==null ? k==null :
	551	+ * key.equals(k))</code>, that mapping is removed. (The map can contain
	552	+ * at most one such mapping.)
	553	+ *
	554	+ * <p>Returns the value to which this map previously associated the key,
	555	+ * or <tt>null</tt> if the map contained no mapping for the key. A
	556	+ * return value of <tt>null</tt> does not <i>necessarily</i> indicate
	557	+ * that the map contained no mapping for the key; it's also possible
	558	+ * that the map explicitly mapped the key to <tt>null</tt>.
	559	+ *
	560	+ * <p>The map will not contain a mapping for the specified key once the
	561	+ * call returns.
	562	+ *
	563	+ * @param key key whose mapping is to be removed from the map
	564	+ * @return the previous value associated with <tt>key</tt>, or
	565	+ * <tt>null</tt> if there was no mapping for <tt>key</tt>
	566	+ */
	567	+ public V remove(Object key) {
	568	+ Object k = maskNull(key);
	569	+ int h = HashMap.hash(k.hashCode());
	570	+ Entry<K,V>[] tab = getTable();
	571	+ int i = indexFor(h, tab.length);
	572	+ Entry<K,V> prev = tab[i];
	573	+ Entry<K,V> e = prev;
	574	+
	575	+ while (e != null) {
	576	+ Entry<K,V> next = e.next;
	577	+ if (h == e.hash && eq(k, e.get())) {
	578	+ modCount++;
	579	+ size--;
	580	+ if (prev == e)
	581	+ tab[i] = next;
	582	+ else
	583	+ prev.next = next;
	584	+ return e.value;
	585	+ }
	586	+ prev = e;
	587	+ e = next;
	588	+ }
	589	+
	590	+ return null;
	591	+ }
	592	+
	593	+ /** Special version of remove needed by Entry set */
	594	+ boolean removeMapping(Object o) {
	595	+ if (!(o instanceof Map.Entry))
	596	+ return false;
	597	+ Entry<K,V>[] tab = getTable();
	598	+ Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
	599	+ Object k = maskNull(entry.getKey());
	600	+ int h = HashMap.hash(k.hashCode());
	601	+ int i = indexFor(h, tab.length);
	602	+ Entry<K,V> prev = tab[i];
	603	+ Entry<K,V> e = prev;
	604	+
	605	+ while (e != null) {
	606	+ Entry<K,V> next = e.next;
	607	+ if (h == e.hash && e.equals(entry)) {
	608	+ modCount++;
	609	+ size--;
	610	+ if (prev == e)
	611	+ tab[i] = next;
	612	+ else
	613	+ prev.next = next;
	614	+ return true;
	615	+ }
	616	+ prev = e;
	617	+ e = next;
	618	+ }
	619	+
	620	+ return false;
	621	+ }
	622	+
	623	+ /**
	624	+ * Removes all of the mappings from this map.
	625	+ * The map will be empty after this call returns.
	626	+ */
	627	+ public void clear() {
	628	+ // clear out ref queue. We don't need to expunge entries
	629	+ // since table is getting cleared.
	630	+ while (queue.poll() != null)
	631	+ ;
	632	+
	633	+ modCount++;
	634	+ Arrays.fill(table, null);
	635	+ size = 0;
	636	+
	637	+ // Allocation of array may have caused GC, which may have caused
	638	+ // additional entries to go stale. Removing these entries from the
	639	+ // reference queue will make them eligible for reclamation.
	640	+ while (queue.poll() != null)
	641	+ ;
	642	+ }
	643	+
	644	+ /**
	645	+ * Returns <tt>true</tt> if this map maps one or more keys to the
	646	+ * specified value.
	647	+ *
	648	+ * @param value value whose presence in this map is to be tested
	649	+ * @return <tt>true</tt> if this map maps one or more keys to the
	650	+ * specified value
	651	+ */
	652	+ public boolean containsValue(Object value) {
	653	+ if (value==null)
	654	+ return containsNullValue();
	655	+
	656	+ Entry<K,V>[] tab = getTable();
	657	+ for (int i = tab.length; i-- > 0;)
	658	+ for (Entry<K,V> e = tab[i]; e != null; e = e.next)
	659	+ if (value.equals(e.value))
	660	+ return true;
	661	+ return false;
	662	+ }
	663	+
	664	+ /**
	665	+ * Special-case code for containsValue with null argument
	666	+ */
	667	+ private boolean containsNullValue() {
	668	+ Entry<K,V>[] tab = getTable();
	669	+ for (int i = tab.length; i-- > 0;)
	670	+ for (Entry<K,V> e = tab[i]; e != null; e = e.next)
	671	+ if (e.value==null)
	672	+ return true;
	673	+ return false;
	674	+ }
	675	+
	676	+ /**
	677	+ * The entries in this hash table extend WeakReference, using its main ref
	678	+ * field as the key.
	679	+ */
	680	+ private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> {
	681	+ V value;
	682	+ final int hash;
	683	+ Entry<K,V> next;
	684	+
	685	+ /**
	686	+ * Creates new entry.
	687	+ */
	688	+ Entry(Object key, V value,
	689	+ ReferenceQueue<Object> queue,
	690	+ int hash, Entry<K,V> next) {
	691	+ super(key, queue);
	692	+ this.value = value;
	693	+ this.hash = hash;
	694	+ this.next = next;
	695	+ }
	696	+
	697	+ @SuppressWarnings("unchecked")
	698	+ public K getKey() {
	699	+ return (K) WeakHashMap.unmaskNull(get());
	700	+ }
	701	+
	702	+ public V getValue() {
	703	+ return value;
	704	+ }
	705	+
	706	+ public V setValue(V newValue) {
	707	+ V oldValue = value;
	708	+ value = newValue;
	709	+ return oldValue;
	710	+ }
	711	+
	712	+ public boolean equals(Object o) {
	713	+ if (!(o instanceof Map.Entry))
	714	+ return false;
	715	+ Map.Entry<?,?> e = (Map.Entry<?,?>)o;
	716	+ K k1 = getKey();
	717	+ Object k2 = e.getKey();
	718	+ if (k1 == k2 \|\| (k1 != null && k1.equals(k2))) {
	719	+ V v1 = getValue();
	720	+ Object v2 = e.getValue();
	721	+ if (v1 == v2 \|\| (v1 != null && v1.equals(v2)))
	722	+ return true;
	723	+ }
	724	+ return false;
	725	+ }
	726	+
	727	+ public int hashCode() {
	728	+ K k = getKey();
	729	+ V v = getValue();
	730	+ return ((k==null ? 0 : k.hashCode()) ^
	731	+ (v==null ? 0 : v.hashCode()));
	732	+ }
	733	+
	734	+ public String toString() {
	735	+ return getKey() + "=" + getValue();
	736	+ }
	737	+ }
	738	+
	739	+ private abstract class HashIterator<T> implements Iterator<T> {
	740	+ private int index;
	741	+ private Entry<K,V> entry = null;
	742	+ private Entry<K,V> lastReturned = null;
	743	+ private int expectedModCount = modCount;
	744	+
	745	+ /**
	746	+ * Strong reference needed to avoid disappearance of key
	747	+ * between hasNext and next
	748	+ */
	749	+ private Object nextKey = null;
	750	+
	751	+ /**
	752	+ * Strong reference needed to avoid disappearance of key
	753	+ * between nextEntry() and any use of the entry
	754	+ */
	755	+ private Object currentKey = null;
	756	+
	757	+ HashIterator() {
	758	+ index = isEmpty() ? 0 : table.length;
	759	+ }
	760	+
	761	+ public boolean hasNext() {
	762	+ Entry<K,V>[] t = table;
	763	+
	764	+ while (nextKey == null) {
	765	+ Entry<K,V> e = entry;
	766	+ int i = index;
	767	+ while (e == null && i > 0)
	768	+ e = t[--i];
	769	+ entry = e;
	770	+ index = i;
	771	+ if (e == null) {
	772	+ currentKey = null;
	773	+ return false;
	774	+ }
	775	+ nextKey = e.get(); // hold on to key in strong ref
	776	+ if (nextKey == null)
	777	+ entry = entry.next;
	778	+ }
	779	+ return true;
	780	+ }
	781	+
	782	+ /** The common parts of next() across different types of iterators */
	783	+ protected Entry<K,V> nextEntry() {
	784	+ if (modCount != expectedModCount)
	785	+ throw new ConcurrentModificationException();
	786	+ if (nextKey == null && !hasNext())
	787	+ throw new NoSuchElementException();
	788	+
	789	+ lastReturned = entry;
	790	+ entry = entry.next;
	791	+ currentKey = nextKey;
	792	+ nextKey = null;
	793	+ return lastReturned;
	794	+ }
	795	+
	796	+ public void remove() {
	797	+ if (lastReturned == null)
	798	+ throw new IllegalStateException();
	799	+ if (modCount != expectedModCount)
	800	+ throw new ConcurrentModificationException();
	801	+
	802	+ WeakHashMap.this.remove(currentKey);
	803	+ expectedModCount = modCount;
	804	+ lastReturned = null;
	805	+ currentKey = null;
	806	+ }
	807	+
	808	+ }
	809	+
	810	+ private class ValueIterator extends HashIterator<V> {
	811	+ public V next() {
	812	+ return nextEntry().value;
	813	+ }
	814	+ }
	815	+
	816	+ private class KeyIterator extends HashIterator<K> {
	817	+ public K next() {
	818	+ return nextEntry().getKey();
	819	+ }
	820	+ }
	821	+
	822	+ private class EntryIterator extends HashIterator<Map.Entry<K,V>> {
	823	+ public Map.Entry<K,V> next() {
	824	+ return nextEntry();
	825	+ }
	826	+ }
	827	+
	828	+ // Views
	829	+
	830	+ private transient Set<Map.Entry<K,V>> entrySet = null;
	831	+
	832	+ /**
	833	+ * Returns a {@link Set} view of the keys contained in this map.
	834	+ * The set is backed by the map, so changes to the map are
	835	+ * reflected in the set, and vice-versa. If the map is modified
	836	+ * while an iteration over the set is in progress (except through
	837	+ * the iterator's own <tt>remove</tt> operation), the results of
	838	+ * the iteration are undefined. The set supports element removal,
	839	+ * which removes the corresponding mapping from the map, via the
	840	+ * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
	841	+ * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
	842	+ * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
	843	+ * operations.
	844	+ */
	845	+ public Set<K> keySet() {
	846	+ Set<K> ks = keySet;
	847	+ return (ks != null ? ks : (keySet = new KeySet()));
	848	+ }
	849	+
	850	+ private class KeySet extends AbstractSet<K> {
	851	+ public Iterator<K> iterator() {
	852	+ return new KeyIterator();
	853	+ }
	854	+
	855	+ public int size() {
	856	+ return WeakHashMap.this.size();
	857	+ }
	858	+
	859	+ public boolean contains(Object o) {
	860	+ return containsKey(o);
	861	+ }
	862	+
	863	+ public boolean remove(Object o) {
	864	+ if (containsKey(o)) {
	865	+ WeakHashMap.this.remove(o);
	866	+ return true;
	867	+ }
	868	+ else
	869	+ return false;
	870	+ }
	871	+
	872	+ public void clear() {
	873	+ WeakHashMap.this.clear();
	874	+ }
	875	+ }
	876	+
	877	+ /**
	878	+ * Returns a {@link Collection} view of the values contained in this map.
	879	+ * The collection is backed by the map, so changes to the map are
	880	+ * reflected in the collection, and vice-versa. If the map is
	881	+ * modified while an iteration over the collection is in progress
	882	+ * (except through the iterator's own <tt>remove</tt> operation),
	883	+ * the results of the iteration are undefined. The collection
	884	+ * supports element removal, which removes the corresponding
	885	+ * mapping from the map, via the <tt>Iterator.remove</tt>,
	886	+ * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
	887	+ * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
	888	+ * support the <tt>add</tt> or <tt>addAll</tt> operations.
	889	+ */
	890	+ public Collection<V> values() {
	891	+ Collection<V> vs = values;
	892	+ return (vs != null) ? vs : (values = new Values());
	893	+ }
	894	+
	895	+ private class Values extends AbstractCollection<V> {
	896	+ public Iterator<V> iterator() {
	897	+ return new ValueIterator();
	898	+ }
	899	+
	900	+ public int size() {
	901	+ return WeakHashMap.this.size();
	902	+ }
	903	+
	904	+ public boolean contains(Object o) {
	905	+ return containsValue(o);
	906	+ }
	907	+
	908	+ public void clear() {
	909	+ WeakHashMap.this.clear();
	910	+ }
	911	+ }
	912	+
	913	+ /**
	914	+ * Returns a {@link Set} view of the mappings contained in this map.
	915	+ * The set is backed by the map, so changes to the map are
	916	+ * reflected in the set, and vice-versa. If the map is modified
	917	+ * while an iteration over the set is in progress (except through
	918	+ * the iterator's own <tt>remove</tt> operation, or through the
	919	+ * <tt>setValue</tt> operation on a map entry returned by the
	920	+ * iterator) the results of the iteration are undefined. The set
	921	+ * supports element removal, which removes the corresponding
	922	+ * mapping from the map, via the <tt>Iterator.remove</tt>,
	923	+ * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
	924	+ * <tt>clear</tt> operations. It does not support the
	925	+ * <tt>add</tt> or <tt>addAll</tt> operations.
	926	+ */
	927	+ public Set<Map.Entry<K,V>> entrySet() {
	928	+ Set<Map.Entry<K,V>> es = entrySet;
	929	+ return es != null ? es : (entrySet = new EntrySet());
	930	+ }
	931	+
	932	+ private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
	933	+ public Iterator<Map.Entry<K,V>> iterator() {
	934	+ return new EntryIterator();
	935	+ }
	936	+
	937	+ public boolean contains(Object o) {
	938	+ if (!(o instanceof Map.Entry))
	939	+ return false;
	940	+ Map.Entry<?,?> e = (Map.Entry<?,?>)o;
	941	+ Entry<K,V> candidate = getEntry(e.getKey());
	942	+ return candidate != null && candidate.equals(e);
	943	+ }
	944	+
	945	+ public boolean remove(Object o) {
	946	+ return removeMapping(o);
	947	+ }
	948	+
	949	+ public int size() {
	950	+ return WeakHashMap.this.size();
	951	+ }
	952	+
	953	+ public void clear() {
	954	+ WeakHashMap.this.clear();
	955	+ }
	956	+
	957	+ private List<Map.Entry<K,V>> deepCopy() {
	958	+ List<Map.Entry<K,V>> list = new ArrayList<>(size());
	959	+ for (Map.Entry<K,V> e : this)
	960	+ list.add(new AbstractMap.SimpleEntry<>(e));
	961	+ return list;
	962	+ }
	963	+
	964	+ public Object[] toArray() {
	965	+ return deepCopy().toArray();
	966	+ }
	967	+
	968	+ public <T> T[] toArray(T[] a) {
	969	+ return deepCopy().toArray(a);
	970	+ }
	971	+ }
	972	+}