| /* |
| * Copyright (C) 2014 The Android Open Source Project |
| * Copyright (c) 1998, 2010, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package java.util; |
| import java.lang.ref.WeakReference; |
| import java.lang.ref.ReferenceQueue; |
| import java.util.function.BiConsumer; |
| import java.util.function.Consumer; |
| |
| |
| /** |
| * Hash table based implementation of the <tt>Map</tt> interface, with |
| * <em>weak keys</em>. |
| * An entry in a <tt>WeakHashMap</tt> will automatically be removed when |
| * its key is no longer in ordinary use. More precisely, the presence of a |
| * mapping for a given key will not prevent the key from being discarded by the |
| * garbage collector, that is, made finalizable, finalized, and then reclaimed. |
| * When a key has been discarded its entry is effectively removed from the map, |
| * so this class behaves somewhat differently from other <tt>Map</tt> |
| * implementations. |
| * |
| * <p> Both null values and the null key are supported. This class has |
| * performance characteristics similar to those of the <tt>HashMap</tt> |
| * class, and has the same efficiency parameters of <em>initial capacity</em> |
| * and <em>load factor</em>. |
| * |
| * <p> Like most collection classes, this class is not synchronized. |
| * A synchronized <tt>WeakHashMap</tt> may be constructed using the |
| * {@link Collections#synchronizedMap Collections.synchronizedMap} |
| * method. |
| * |
| * <p> This class is intended primarily for use with key objects whose |
| * <tt>equals</tt> methods test for object identity using the |
| * <tt>==</tt> operator. Once such a key is discarded it can never be |
| * recreated, so it is impossible to do a lookup of that key in a |
| * <tt>WeakHashMap</tt> at some later time and be surprised that its entry |
| * has been removed. This class will work perfectly well with key objects |
| * whose <tt>equals</tt> methods are not based upon object identity, such |
| * as <tt>String</tt> instances. With such recreatable key objects, |
| * however, the automatic removal of <tt>WeakHashMap</tt> entries whose |
| * keys have been discarded may prove to be confusing. |
| * |
| * <p> The behavior of the <tt>WeakHashMap</tt> class depends in part upon |
| * the actions of the garbage collector, so several familiar (though not |
| * required) <tt>Map</tt> invariants do not hold for this class. Because |
| * the garbage collector may discard keys at any time, a |
| * <tt>WeakHashMap</tt> may behave as though an unknown thread is silently |
| * removing entries. In particular, even if you synchronize on a |
| * <tt>WeakHashMap</tt> instance and invoke none of its mutator methods, it |
| * is possible for the <tt>size</tt> method to return smaller values over |
| * time, for the <tt>isEmpty</tt> method to return <tt>false</tt> and |
| * then <tt>true</tt>, for the <tt>containsKey</tt> method to return |
| * <tt>true</tt> and later <tt>false</tt> for a given key, for the |
| * <tt>get</tt> method to return a value for a given key but later return |
| * <tt>null</tt>, for the <tt>put</tt> method to return |
| * <tt>null</tt> and the <tt>remove</tt> method to return |
| * <tt>false</tt> for a key that previously appeared to be in the map, and |
| * for successive examinations of the key set, the value collection, and |
| * the entry set to yield successively smaller numbers of elements. |
| * |
| * <p> Each key object in a <tt>WeakHashMap</tt> is stored indirectly as |
| * the referent of a weak reference. Therefore a key will automatically be |
| * removed only after the weak references to it, both inside and outside of the |
| * map, have been cleared by the garbage collector. |
| * |
| * <p> <strong>Implementation note:</strong> The value objects in a |
| * <tt>WeakHashMap</tt> are held by ordinary strong references. Thus care |
| * should be taken to ensure that value objects do not strongly refer to their |
| * own keys, either directly or indirectly, since that will prevent the keys |
| * from being discarded. Note that a value object may refer indirectly to its |
| * key via the <tt>WeakHashMap</tt> itself; that is, a value object may |
| * strongly refer to some other key object whose associated value object, in |
| * turn, strongly refers to the key of the first value object. If the values |
| * in the map do not rely on the map holding strong references to them, one way |
| * to deal with this is to wrap values themselves within |
| * <tt>WeakReferences</tt> before |
| * inserting, as in: <tt>m.put(key, new WeakReference(value))</tt>, |
| * and then unwrapping upon each <tt>get</tt>. |
| * |
| * <p>The iterators returned by the <tt>iterator</tt> method of the collections |
| * returned by all of this class's "collection view methods" are |
| * <i>fail-fast</i>: if the map is structurally modified at any time after the |
| * iterator is created, in any way except through the iterator's own |
| * <tt>remove</tt> method, the iterator will throw a {@link |
| * ConcurrentModificationException}. Thus, in the face of concurrent |
| * modification, the iterator fails quickly and cleanly, rather than risking |
| * arbitrary, non-deterministic behavior at an undetermined time in the future. |
| * |
| * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
| * as it is, generally speaking, impossible to make any hard guarantees in the |
| * presence of unsynchronized concurrent modification. Fail-fast iterators |
| * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. |
| * Therefore, it would be wrong to write a program that depended on this |
| * exception for its correctness: <i>the fail-fast behavior of iterators |
| * should be used only to detect bugs.</i> |
| * |
| * <p>This class is a member of the |
| * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| * Java Collections Framework</a>. |
| * |
| * @param <K> the type of keys maintained by this map |
| * @param <V> the type of mapped values |
| * |
| * @author Doug Lea |
| * @author Josh Bloch |
| * @author Mark Reinhold |
| * @since 1.2 |
| * @see java.util.HashMap |
| * @see java.lang.ref.WeakReference |
| */ |
| public class WeakHashMap<K,V> |
| extends AbstractMap<K,V> |
| implements Map<K,V> { |
| |
| /** |
| * The default initial capacity -- MUST be a power of two. |
| */ |
| private static final int DEFAULT_INITIAL_CAPACITY = 16; |
| |
| /** |
| * The maximum capacity, used if a higher value is implicitly specified |
| * by either of the constructors with arguments. |
| * MUST be a power of two <= 1<<30. |
| */ |
| private static final int MAXIMUM_CAPACITY = 1 << 30; |
| |
| /** |
| * The load factor used when none specified in constructor. |
| */ |
| private static final float DEFAULT_LOAD_FACTOR = 0.75f; |
| |
| /** |
| * The table, resized as necessary. Length MUST Always be a power of two. |
| */ |
| Entry<K,V>[] table; |
| |
| /** |
| * The number of key-value mappings contained in this weak hash map. |
| */ |
| private int size; |
| |
| /** |
| * The next size value at which to resize (capacity * load factor). |
| */ |
| private int threshold; |
| |
| /** |
| * The load factor for the hash table. |
| */ |
| private final float loadFactor; |
| |
| /** |
| * Reference queue for cleared WeakEntries |
| */ |
| private final ReferenceQueue<Object> queue = new ReferenceQueue<>(); |
| |
| /** |
| * The number of times this WeakHashMap has been structurally modified. |
| * Structural modifications are those that change the number of |
| * mappings in the map or otherwise modify its internal structure |
| * (e.g., rehash). This field is used to make iterators on |
| * Collection-views of the map fail-fast. |
| * |
| * @see ConcurrentModificationException |
| */ |
| int modCount; |
| |
| /** |
| * The default threshold of map capacity above which alternative hashing is |
| * used for String keys. Alternative hashing reduces the incidence of |
| * collisions due to weak hash code calculation for String keys. |
| * <p/> |
| * This value may be overridden by defining the system property |
| * {@code jdk.map.althashing.threshold}. A property value of {@code 1} |
| * forces alternative hashing to be used at all times whereas |
| * {@code -1} value ensures that alternative hashing is never used. |
| */ |
| static final int ALTERNATIVE_HASHING_THRESHOLD_DEFAULT = Integer.MAX_VALUE; |
| |
| /** |
| * holds values which can't be initialized until after VM is booted. |
| */ |
| private static class Holder { |
| |
| /** |
| * Table capacity above which to switch to use alternative hashing. |
| */ |
| static final int ALTERNATIVE_HASHING_THRESHOLD; |
| |
| static { |
| String altThreshold = java.security.AccessController.doPrivileged( |
| new sun.security.action.GetPropertyAction( |
| "jdk.map.althashing.threshold")); |
| |
| int threshold; |
| try { |
| threshold = (null != altThreshold) |
| ? Integer.parseInt(altThreshold) |
| : ALTERNATIVE_HASHING_THRESHOLD_DEFAULT; |
| |
| // disable alternative hashing if -1 |
| if (threshold == -1) { |
| threshold = Integer.MAX_VALUE; |
| } |
| |
| if (threshold < 0) { |
| throw new IllegalArgumentException("value must be positive integer."); |
| } |
| } catch(IllegalArgumentException failed) { |
| throw new Error("Illegal value for 'jdk.map.althashing.threshold'", failed); |
| } |
| ALTERNATIVE_HASHING_THRESHOLD = threshold; |
| } |
| } |
| |
| /** |
| * If {@code true} then perform alternate hashing to reduce the incidence of |
| * collisions due to weak hash code calculation. |
| */ |
| transient boolean useAltHashing; |
| |
| /** |
| * A randomizing value associated with this instance that is applied to |
| * hash code of keys to make hash collisions harder to find. |
| * |
| * This hash seed is only used if {@code useAltHashing} is true. |
| */ |
| transient int hashSeed; |
| |
| @SuppressWarnings("unchecked") |
| private Entry<K,V>[] newTable(int n) { |
| return (Entry<K,V>[]) new Entry[n]; |
| } |
| |
| /** |
| * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial |
| * capacity and the given load factor. |
| * |
| * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt> |
| * @param loadFactor The load factor of the <tt>WeakHashMap</tt> |
| * @throws IllegalArgumentException if the initial capacity is negative, |
| * or if the load factor is nonpositive. |
| */ |
| public WeakHashMap(int initialCapacity, float loadFactor) { |
| if (initialCapacity < 0) |
| throw new IllegalArgumentException("Illegal Initial Capacity: "+ |
| initialCapacity); |
| if (initialCapacity > MAXIMUM_CAPACITY) |
| initialCapacity = MAXIMUM_CAPACITY; |
| |
| if (loadFactor <= 0 || Float.isNaN(loadFactor)) |
| throw new IllegalArgumentException("Illegal Load factor: "+ |
| loadFactor); |
| int capacity = 1; |
| while (capacity < initialCapacity) |
| capacity <<= 1; |
| table = newTable(capacity); |
| this.loadFactor = loadFactor; |
| threshold = (int)(capacity * loadFactor); |
| useAltHashing = sun.misc.VM.isBooted() && |
| (capacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD); |
| if (useAltHashing) { |
| hashSeed = sun.misc.Hashing.randomHashSeed(this); |
| } else { |
| hashSeed = 0; |
| } |
| } |
| |
| /** |
| * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial |
| * capacity and the default load factor (0.75). |
| * |
| * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt> |
| * @throws IllegalArgumentException if the initial capacity is negative |
| */ |
| public WeakHashMap(int initialCapacity) { |
| this(initialCapacity, DEFAULT_LOAD_FACTOR); |
| } |
| |
| /** |
| * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial |
| * capacity (16) and load factor (0.75). |
| */ |
| public WeakHashMap() { |
| this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); |
| } |
| |
| /** |
| * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the |
| * specified map. The <tt>WeakHashMap</tt> is created with the default |
| * load factor (0.75) and an initial capacity sufficient to hold the |
| * mappings in the specified map. |
| * |
| * @param m the map whose mappings are to be placed in this map |
| * @throws NullPointerException if the specified map is null |
| * @since 1.3 |
| */ |
| public WeakHashMap(Map<? extends K, ? extends V> m) { |
| this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, |
| DEFAULT_INITIAL_CAPACITY), |
| DEFAULT_LOAD_FACTOR); |
| putAll(m); |
| } |
| |
| // internal utilities |
| |
| /** |
| * Value representing null keys inside tables. |
| */ |
| private static final Object NULL_KEY = new Object(); |
| |
| /** |
| * Use NULL_KEY for key if it is null. |
| */ |
| private static Object maskNull(Object key) { |
| return (key == null) ? NULL_KEY : key; |
| } |
| |
| /** |
| * Returns internal representation of null key back to caller as null. |
| */ |
| static Object unmaskNull(Object key) { |
| return (key == NULL_KEY) ? null : key; |
| } |
| |
| /** |
| * Checks for equality of non-null reference x and possibly-null y. By |
| * default uses Object.equals. |
| */ |
| private static boolean eq(Object x, Object y) { |
| return x == y || x.equals(y); |
| } |
| |
| /** |
| * Retrieve object hash code and applies a supplemental hash function to the |
| * result hash, which defends against poor quality hash functions. This is |
| * critical because HashMap uses power-of-two length hash tables, that |
| * otherwise encounter collisions for hashCodes that do not differ |
| * in lower bits. |
| */ |
| int hash(Object k) { |
| |
| int h; |
| if (useAltHashing) { |
| h = hashSeed; |
| if (k instanceof String) { |
| return sun.misc.Hashing.stringHash32((String) k); |
| } else { |
| h ^= k.hashCode(); |
| } |
| } else { |
| h = k.hashCode(); |
| } |
| |
| // This function ensures that hashCodes that differ only by |
| // constant multiples at each bit position have a bounded |
| // number of collisions (approximately 8 at default load factor). |
| h ^= (h >>> 20) ^ (h >>> 12); |
| return h ^ (h >>> 7) ^ (h >>> 4); |
| } |
| |
| /** |
| * Returns index for hash code h. |
| */ |
| private static int indexFor(int h, int length) { |
| return h & (length-1); |
| } |
| |
| /** |
| * Expunges stale entries from the table. |
| */ |
| private void expungeStaleEntries() { |
| for (Object x; (x = queue.poll()) != null; ) { |
| synchronized (queue) { |
| @SuppressWarnings("unchecked") |
| Entry<K,V> e = (Entry<K,V>) x; |
| int i = indexFor(e.hash, table.length); |
| |
| Entry<K,V> prev = table[i]; |
| Entry<K,V> p = prev; |
| while (p != null) { |
| Entry<K,V> next = p.next; |
| if (p == e) { |
| if (prev == e) |
| table[i] = next; |
| else |
| prev.next = next; |
| // Must not null out e.next; |
| // stale entries may be in use by a HashIterator |
| e.value = null; // Help GC |
| size--; |
| break; |
| } |
| prev = p; |
| p = next; |
| } |
| } |
| } |
| } |
| |
| /** |
| * Returns the table after first expunging stale entries. |
| */ |
| private Entry<K,V>[] getTable() { |
| expungeStaleEntries(); |
| return table; |
| } |
| |
| /** |
| * Returns the number of key-value mappings in this map. |
| * This result is a snapshot, and may not reflect unprocessed |
| * entries that will be removed before next attempted access |
| * because they are no longer referenced. |
| */ |
| public int size() { |
| if (size == 0) |
| return 0; |
| expungeStaleEntries(); |
| return size; |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this map contains no key-value mappings. |
| * This result is a snapshot, and may not reflect unprocessed |
| * entries that will be removed before next attempted access |
| * because they are no longer referenced. |
| */ |
| public boolean isEmpty() { |
| return size() == 0; |
| } |
| |
| /** |
| * Returns the value to which the specified key is mapped, |
| * or {@code null} if this map contains no mapping for the key. |
| * |
| * <p>More formally, if this map contains a mapping from a key |
| * {@code k} to a value {@code v} such that {@code (key==null ? k==null : |
| * key.equals(k))}, then this method returns {@code v}; otherwise |
| * it returns {@code null}. (There can be at most one such mapping.) |
| * |
| * <p>A return value of {@code null} does not <i>necessarily</i> |
| * indicate that the map contains no mapping for the key; it's also |
| * possible that the map explicitly maps the key to {@code null}. |
| * The {@link #containsKey containsKey} operation may be used to |
| * distinguish these two cases. |
| * |
| * @see #put(Object, Object) |
| */ |
| public V get(Object key) { |
| Object k = maskNull(key); |
| int h = hash(k); |
| Entry<K,V>[] tab = getTable(); |
| int index = indexFor(h, tab.length); |
| Entry<K,V> e = tab[index]; |
| while (e != null) { |
| if (e.hash == h && eq(k, e.get())) |
| return e.value; |
| e = e.next; |
| } |
| return null; |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this map contains a mapping for the |
| * specified key. |
| * |
| * @param key The key whose presence in this map is to be tested |
| * @return <tt>true</tt> if there is a mapping for <tt>key</tt>; |
| * <tt>false</tt> otherwise |
| */ |
| public boolean containsKey(Object key) { |
| return getEntry(key) != null; |
| } |
| |
| /** |
| * Returns the entry associated with the specified key in this map. |
| * Returns null if the map contains no mapping for this key. |
| */ |
| Entry<K,V> getEntry(Object key) { |
| Object k = maskNull(key); |
| int h = hash(k); |
| Entry<K,V>[] tab = getTable(); |
| int index = indexFor(h, tab.length); |
| Entry<K,V> e = tab[index]; |
| while (e != null && !(e.hash == h && eq(k, e.get()))) |
| e = e.next; |
| return e; |
| } |
| |
| /** |
| * Associates the specified value with the specified key in this map. |
| * If the map previously contained a mapping for this key, the old |
| * value is replaced. |
| * |
| * @param key key with which the specified value is to be associated. |
| * @param value value to be associated with the specified key. |
| * @return the previous value associated with <tt>key</tt>, or |
| * <tt>null</tt> if there was no mapping for <tt>key</tt>. |
| * (A <tt>null</tt> return can also indicate that the map |
| * previously associated <tt>null</tt> with <tt>key</tt>.) |
| */ |
| public V put(K key, V value) { |
| Object k = maskNull(key); |
| int h = hash(k); |
| Entry<K,V>[] tab = getTable(); |
| int i = indexFor(h, tab.length); |
| |
| for (Entry<K,V> e = tab[i]; e != null; e = e.next) { |
| if (h == e.hash && eq(k, e.get())) { |
| V oldValue = e.value; |
| if (value != oldValue) |
| e.value = value; |
| return oldValue; |
| } |
| } |
| |
| modCount++; |
| Entry<K,V> e = tab[i]; |
| tab[i] = new Entry<>(k, value, queue, h, e); |
| if (++size >= threshold) |
| resize(tab.length * 2); |
| return null; |
| } |
| |
| /** |
| * Rehashes the contents of this map into a new array with a |
| * larger capacity. This method is called automatically when the |
| * number of keys in this map reaches its threshold. |
| * |
| * If current capacity is MAXIMUM_CAPACITY, this method does not |
| * resize the map, but sets threshold to Integer.MAX_VALUE. |
| * This has the effect of preventing future calls. |
| * |
| * @param newCapacity the new capacity, MUST be a power of two; |
| * must be greater than current capacity unless current |
| * capacity is MAXIMUM_CAPACITY (in which case value |
| * is irrelevant). |
| */ |
| void resize(int newCapacity) { |
| Entry<K,V>[] oldTable = getTable(); |
| int oldCapacity = oldTable.length; |
| if (oldCapacity == MAXIMUM_CAPACITY) { |
| threshold = Integer.MAX_VALUE; |
| return; |
| } |
| |
| Entry<K,V>[] newTable = newTable(newCapacity); |
| boolean oldAltHashing = useAltHashing; |
| useAltHashing |= sun.misc.VM.isBooted() && |
| (newCapacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD); |
| boolean rehash = oldAltHashing ^ useAltHashing; |
| if (rehash) { |
| hashSeed = sun.misc.Hashing.randomHashSeed(this); |
| } |
| transfer(oldTable, newTable, rehash); |
| table = newTable; |
| |
| /* |
| * If ignoring null elements and processing ref queue caused massive |
| * shrinkage, then restore old table. This should be rare, but avoids |
| * unbounded expansion of garbage-filled tables. |
| */ |
| if (size >= threshold / 2) { |
| threshold = (int)(newCapacity * loadFactor); |
| } else { |
| expungeStaleEntries(); |
| transfer(newTable, oldTable, false); |
| table = oldTable; |
| } |
| } |
| |
| /** Transfers all entries from src to dest tables */ |
| private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest, boolean rehash) { |
| for (int j = 0; j < src.length; ++j) { |
| Entry<K,V> e = src[j]; |
| src[j] = null; |
| while (e != null) { |
| Entry<K,V> next = e.next; |
| Object key = e.get(); |
| if (key == null) { |
| e.next = null; // Help GC |
| e.value = null; // " " |
| size--; |
| } else { |
| if (rehash) { |
| e.hash = hash(key); |
| } |
| int i = indexFor(e.hash, dest.length); |
| e.next = dest[i]; |
| dest[i] = e; |
| } |
| e = next; |
| } |
| } |
| } |
| |
| /** |
| * Copies all of the mappings from the specified map to this map. |
| * These mappings will replace any mappings that this map had for any |
| * of the keys currently in the specified map. |
| * |
| * @param m mappings to be stored in this map. |
| * @throws NullPointerException if the specified map is null. |
| */ |
| public void putAll(Map<? extends K, ? extends V> m) { |
| int numKeysToBeAdded = m.size(); |
| if (numKeysToBeAdded == 0) |
| return; |
| |
| /* |
| * Expand the map if the map if the number of mappings to be added |
| * is greater than or equal to threshold. This is conservative; the |
| * obvious condition is (m.size() + size) >= threshold, but this |
| * condition could result in a map with twice the appropriate capacity, |
| * if the keys to be added overlap with the keys already in this map. |
| * By using the conservative calculation, we subject ourself |
| * to at most one extra resize. |
| */ |
| if (numKeysToBeAdded > threshold) { |
| int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1); |
| if (targetCapacity > MAXIMUM_CAPACITY) |
| targetCapacity = MAXIMUM_CAPACITY; |
| int newCapacity = table.length; |
| while (newCapacity < targetCapacity) |
| newCapacity <<= 1; |
| if (newCapacity > table.length) |
| resize(newCapacity); |
| } |
| |
| for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) |
| put(e.getKey(), e.getValue()); |
| } |
| |
| /** |
| * Removes the mapping for a key from this weak hash map if it is present. |
| * More formally, if this map contains a mapping from key <tt>k</tt> to |
| * value <tt>v</tt> such that <code>(key==null ? k==null : |
| * key.equals(k))</code>, that mapping is removed. (The map can contain |
| * at most one such mapping.) |
| * |
| * <p>Returns the value to which this map previously associated the key, |
| * or <tt>null</tt> if the map contained no mapping for the key. A |
| * return value of <tt>null</tt> does not <i>necessarily</i> indicate |
| * that the map contained no mapping for the key; it's also possible |
| * that the map explicitly mapped the key to <tt>null</tt>. |
| * |
| * <p>The map will not contain a mapping for the specified key once the |
| * call returns. |
| * |
| * @param key key whose mapping is to be removed from the map |
| * @return the previous value associated with <tt>key</tt>, or |
| * <tt>null</tt> if there was no mapping for <tt>key</tt> |
| */ |
| public V remove(Object key) { |
| Object k = maskNull(key); |
| int h = hash(k); |
| Entry<K,V>[] tab = getTable(); |
| int i = indexFor(h, tab.length); |
| Entry<K,V> prev = tab[i]; |
| Entry<K,V> e = prev; |
| |
| while (e != null) { |
| Entry<K,V> next = e.next; |
| if (h == e.hash && eq(k, e.get())) { |
| modCount++; |
| size--; |
| if (prev == e) |
| tab[i] = next; |
| else |
| prev.next = next; |
| return e.value; |
| } |
| prev = e; |
| e = next; |
| } |
| |
| return null; |
| } |
| |
| /** Special version of remove needed by Entry set */ |
| boolean removeMapping(Object o) { |
| if (!(o instanceof Map.Entry)) |
| return false; |
| Entry<K,V>[] tab = getTable(); |
| Map.Entry<?,?> entry = (Map.Entry<?,?>)o; |
| Object k = maskNull(entry.getKey()); |
| int h = hash(k); |
| int i = indexFor(h, tab.length); |
| Entry<K,V> prev = tab[i]; |
| Entry<K,V> e = prev; |
| |
| while (e != null) { |
| Entry<K,V> next = e.next; |
| if (h == e.hash && e.equals(entry)) { |
| modCount++; |
| size--; |
| if (prev == e) |
| tab[i] = next; |
| else |
| prev.next = next; |
| return true; |
| } |
| prev = e; |
| e = next; |
| } |
| |
| return false; |
| } |
| |
| /** |
| * Removes all of the mappings from this map. |
| * The map will be empty after this call returns. |
| */ |
| public void clear() { |
| // clear out ref queue. We don't need to expunge entries |
| // since table is getting cleared. |
| while (queue.poll() != null) |
| ; |
| |
| modCount++; |
| Arrays.fill(table, null); |
| size = 0; |
| |
| // Allocation of array may have caused GC, which may have caused |
| // additional entries to go stale. Removing these entries from the |
| // reference queue will make them eligible for reclamation. |
| while (queue.poll() != null) |
| ; |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this map maps one or more keys to the |
| * specified value. |
| * |
| * @param value value whose presence in this map is to be tested |
| * @return <tt>true</tt> if this map maps one or more keys to the |
| * specified value |
| */ |
| public boolean containsValue(Object value) { |
| if (value==null) |
| return containsNullValue(); |
| |
| Entry<K,V>[] tab = getTable(); |
| for (int i = tab.length; i-- > 0;) |
| for (Entry<K,V> e = tab[i]; e != null; e = e.next) |
| if (value.equals(e.value)) |
| return true; |
| return false; |
| } |
| |
| /** |
| * Special-case code for containsValue with null argument |
| */ |
| private boolean containsNullValue() { |
| Entry<K,V>[] tab = getTable(); |
| for (int i = tab.length; i-- > 0;) |
| for (Entry<K,V> e = tab[i]; e != null; e = e.next) |
| if (e.value==null) |
| return true; |
| return false; |
| } |
| |
| /** |
| * The entries in this hash table extend WeakReference, using its main ref |
| * field as the key. |
| */ |
| private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> { |
| V value; |
| int hash; |
| Entry<K,V> next; |
| |
| /** |
| * Creates new entry. |
| */ |
| Entry(Object key, V value, |
| ReferenceQueue<Object> queue, |
| int hash, Entry<K,V> next) { |
| super(key, queue); |
| this.value = value; |
| this.hash = hash; |
| this.next = next; |
| } |
| |
| @SuppressWarnings("unchecked") |
| public K getKey() { |
| return (K) WeakHashMap.unmaskNull(get()); |
| } |
| |
| public V getValue() { |
| return value; |
| } |
| |
| public V setValue(V newValue) { |
| V oldValue = value; |
| value = newValue; |
| return oldValue; |
| } |
| |
| public boolean equals(Object o) { |
| if (!(o instanceof Map.Entry)) |
| return false; |
| Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
| K k1 = getKey(); |
| Object k2 = e.getKey(); |
| if (k1 == k2 || (k1 != null && k1.equals(k2))) { |
| V v1 = getValue(); |
| Object v2 = e.getValue(); |
| if (v1 == v2 || (v1 != null && v1.equals(v2))) |
| return true; |
| } |
| return false; |
| } |
| |
| public int hashCode() { |
| K k = getKey(); |
| V v = getValue(); |
| return ((k==null ? 0 : k.hashCode()) ^ |
| (v==null ? 0 : v.hashCode())); |
| } |
| |
| public String toString() { |
| return getKey() + "=" + getValue(); |
| } |
| } |
| |
| private abstract class HashIterator<T> implements Iterator<T> { |
| private int index; |
| private Entry<K,V> entry = null; |
| private Entry<K,V> lastReturned = null; |
| private int expectedModCount = modCount; |
| |
| /** |
| * Strong reference needed to avoid disappearance of key |
| * between hasNext and next |
| */ |
| private Object nextKey = null; |
| |
| /** |
| * Strong reference needed to avoid disappearance of key |
| * between nextEntry() and any use of the entry |
| */ |
| private Object currentKey = null; |
| |
| HashIterator() { |
| index = isEmpty() ? 0 : table.length; |
| } |
| |
| public boolean hasNext() { |
| Entry<K,V>[] t = table; |
| |
| while (nextKey == null) { |
| Entry<K,V> e = entry; |
| int i = index; |
| while (e == null && i > 0) |
| e = t[--i]; |
| entry = e; |
| index = i; |
| if (e == null) { |
| currentKey = null; |
| return false; |
| } |
| nextKey = e.get(); // hold on to key in strong ref |
| if (nextKey == null) |
| entry = entry.next; |
| } |
| return true; |
| } |
| |
| /** The common parts of next() across different types of iterators */ |
| protected Entry<K,V> nextEntry() { |
| if (modCount != expectedModCount) |
| throw new ConcurrentModificationException(); |
| if (nextKey == null && !hasNext()) |
| throw new NoSuchElementException(); |
| |
| lastReturned = entry; |
| entry = entry.next; |
| currentKey = nextKey; |
| nextKey = null; |
| return lastReturned; |
| } |
| |
| public void remove() { |
| if (lastReturned == null) |
| throw new IllegalStateException(); |
| if (modCount != expectedModCount) |
| throw new ConcurrentModificationException(); |
| |
| WeakHashMap.this.remove(currentKey); |
| expectedModCount = modCount; |
| lastReturned = null; |
| currentKey = null; |
| } |
| |
| } |
| |
| private class ValueIterator extends HashIterator<V> { |
| public V next() { |
| return nextEntry().value; |
| } |
| } |
| |
| private class KeyIterator extends HashIterator<K> { |
| public K next() { |
| return nextEntry().getKey(); |
| } |
| } |
| |
| private class EntryIterator extends HashIterator<Map.Entry<K,V>> { |
| public Map.Entry<K,V> next() { |
| return nextEntry(); |
| } |
| } |
| |
| // Views |
| |
| private transient Set<Map.Entry<K,V>> entrySet = null; |
| |
| /** |
| * Returns a {@link Set} view of the keys contained in this map. |
| * The set is backed by the map, so changes to the map are |
| * reflected in the set, and vice-versa. If the map is modified |
| * while an iteration over the set is in progress (except through |
| * the iterator's own <tt>remove</tt> operation), the results of |
| * the iteration are undefined. The set supports element removal, |
| * which removes the corresponding mapping from the map, via the |
| * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
| * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
| * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> |
| * operations. |
| */ |
| public Set<K> keySet() { |
| Set<K> ks = keySet; |
| return (ks != null ? ks : (keySet = new KeySet())); |
| } |
| |
| private class KeySet extends AbstractSet<K> { |
| public Iterator<K> iterator() { |
| return new KeyIterator(); |
| } |
| |
| public int size() { |
| return WeakHashMap.this.size(); |
| } |
| |
| public boolean contains(Object o) { |
| return containsKey(o); |
| } |
| |
| public boolean remove(Object o) { |
| if (containsKey(o)) { |
| WeakHashMap.this.remove(o); |
| return true; |
| } |
| else |
| return false; |
| } |
| |
| public void clear() { |
| WeakHashMap.this.clear(); |
| } |
| } |
| |
| /** |
| * Returns a {@link Collection} view of the values contained in this map. |
| * The collection is backed by the map, so changes to the map are |
| * reflected in the collection, and vice-versa. If the map is |
| * modified while an iteration over the collection is in progress |
| * (except through the iterator's own <tt>remove</tt> operation), |
| * the results of the iteration are undefined. The collection |
| * supports element removal, which removes the corresponding |
| * mapping from the map, via the <tt>Iterator.remove</tt>, |
| * <tt>Collection.remove</tt>, <tt>removeAll</tt>, |
| * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not |
| * support the <tt>add</tt> or <tt>addAll</tt> operations. |
| */ |
| public Collection<V> values() { |
| Collection<V> vs = values; |
| return (vs != null) ? vs : (values = new Values()); |
| } |
| |
| private class Values extends AbstractCollection<V> { |
| public Iterator<V> iterator() { |
| return new ValueIterator(); |
| } |
| |
| public int size() { |
| return WeakHashMap.this.size(); |
| } |
| |
| public boolean contains(Object o) { |
| return containsValue(o); |
| } |
| |
| public void clear() { |
| WeakHashMap.this.clear(); |
| } |
| } |
| |
| /** |
| * Returns a {@link Set} view of the mappings contained in this map. |
| * The set is backed by the map, so changes to the map are |
| * reflected in the set, and vice-versa. If the map is modified |
| * while an iteration over the set is in progress (except through |
| * the iterator's own <tt>remove</tt> operation, or through the |
| * <tt>setValue</tt> operation on a map entry returned by the |
| * iterator) the results of the iteration are undefined. The set |
| * supports element removal, which removes the corresponding |
| * mapping from the map, via the <tt>Iterator.remove</tt>, |
| * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and |
| * <tt>clear</tt> operations. It does not support the |
| * <tt>add</tt> or <tt>addAll</tt> operations. |
| */ |
| public Set<Map.Entry<K,V>> entrySet() { |
| Set<Map.Entry<K,V>> es = entrySet; |
| return es != null ? es : (entrySet = new EntrySet()); |
| } |
| |
| private class EntrySet extends AbstractSet<Map.Entry<K,V>> { |
| public Iterator<Map.Entry<K,V>> iterator() { |
| return new EntryIterator(); |
| } |
| |
| public boolean contains(Object o) { |
| if (!(o instanceof Map.Entry)) |
| return false; |
| Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
| Entry<K,V> candidate = getEntry(e.getKey()); |
| return candidate != null && candidate.equals(e); |
| } |
| |
| public boolean remove(Object o) { |
| return removeMapping(o); |
| } |
| |
| public int size() { |
| return WeakHashMap.this.size(); |
| } |
| |
| public void clear() { |
| WeakHashMap.this.clear(); |
| } |
| |
| private List<Map.Entry<K,V>> deepCopy() { |
| List<Map.Entry<K,V>> list = new ArrayList<>(size()); |
| for (Map.Entry<K,V> e : this) |
| list.add(new AbstractMap.SimpleEntry<>(e)); |
| return list; |
| } |
| |
| public Object[] toArray() { |
| return deepCopy().toArray(); |
| } |
| |
| public <T> T[] toArray(T[] a) { |
| return deepCopy().toArray(a); |
| } |
| } |
| |
| @SuppressWarnings("unchecked") |
| @Override |
| public void forEach(BiConsumer<? super K, ? super V> action) { |
| Objects.requireNonNull(action); |
| int expectedModCount = modCount; |
| |
| Entry<K, V>[] tab = getTable(); |
| for (Entry<K, V> entry : tab) { |
| while (entry != null) { |
| Object key = entry.get(); |
| if (key != null) { |
| action.accept((K)WeakHashMap.unmaskNull(key), entry.value); |
| } |
| entry = entry.next; |
| |
| if (expectedModCount != modCount) { |
| throw new ConcurrentModificationException(); |
| } |
| } |
| } |
| } |
| } |