Java集合之WeakHashMap[通俗易懂]

void                   clear()
Object                 clone()
boolean                containsKey(Object key)
boolean                containsValue(Object value)
Set<Entry<K, V>>       entrySet()
V                      get(Object key)
boolean                isEmpty()
Set<K>                 keySet()
V                      put(K key, V value)
void                   putAll(Map<? extends K, ? extends V> map)
V                      remove(Object key)
int                    size()
Collection<V>          values()

WeakHashMap的遍历方式

Integer integ = null;
Iterator iter = map.entrySet().iterator();
while(iter.hasNext()) 
{    
    Map.Entry entry = (Map.Entry)iter.next();
// 获取key
key = (String)entry.getKey();
// 获取value
integ = (Integer)entry.getValue();
}

（2）遍历WeakHashMap的键：首先通过keySet()获取WeakHashMap的键的set集合，通过Iterator迭代器遍历集合来获得键值。

String key = null;
Integer integ = null;
Iterator iter = map.keySet().iterator();
while (iter.hasNext()) {
  
  
    // 获取key
    key = (String)iter.next();                            
    // 根据key，获取value
    integ = (Integer)map.get(key);
}

（3）遍历WeakHashMap的值：首先通过values()获取WeakHashMap的value集合，然后对集合进行迭代获得数据。

Integer value = null;
Collection c = map.values();
Iterator iter= c.iterator();
while (iter.hasNext()) 
{
  
  
    value = (Integer)iter.next();
}

WeakHashMap示例程序：

public class Hello {

    public static void main(String[] args) throws Exception {
        testWeakHashMapAPIs();
    }

    private static void testWeakHashMapAPIs()
    {
        // 初始化3个“弱键”
        String w1 = new String("one");
        String w2 = new String("two");
        String w3 = new String("three");
        // 新建WeakHashMap
        Map wmap = new WeakHashMap();
        // 添加键值对
        wmap.put(w1, "w1");
        wmap.put(w2, "w2");
        wmap.put(w3, "w3");

        // 打印出wmap
        System.out.printf("\nwmap:%s\n",wmap );

        // containsKey(Object key) :是否包含键key
        System.out.printf("contains key two : %s\n",wmap.containsKey("two"));
        System.out.printf("contains key five : %s\n",wmap.containsKey("five"));
        // containsValue(Object value) :是否包含值value
        System.out.printf("contains value 0 : %s\n",wmap.containsValue(new Integer(0)));
        // remove(Object key) ： 删除键key对应的键值对
        wmap.remove("three");
        System.out.printf("wmap: %s\n",wmap );
        // ---- 测试 WeakHashMap 的自动回收特性 ----
        // 将w1设置null。
        // 这意味着“弱键”w1再没有被其它对象引用，调用gc时会回收WeakHashMap中与“w1”对应的键值对
        w1 = null;
        // 内存回收。这里，会回收WeakHashMap中与“w1”对应的键值对
        System.gc();
        // 遍历WeakHashMap
        Iterator iter = wmap.entrySet().iterator();
        while (iter.hasNext())
        {
            Map.Entry en = (Map.Entry)iter.next();
            System.out.printf("next : %s - %s\n",en.getKey(),en.getValue());
        }
        // 打印WeakHashMap的实际大小
        System.out.printf(" after gc WeakHashMap size:%s\n", wmap.size());
    }

}

public class WeakHashMap<K,V> extends AbstractMap<K,V> implements Map<K,V> { private static final int DEFAULT_INITIAL_CAPACITY = 16;//默认初始大小，必须是2的次幂  private static final int MAXIMUM_CAPACITY = 1 << 30;//最大值2的30次方  private static final float DEFAULT_LOAD_FACTOR = 0.75f;//加载因子  Entry<K,V>[] table;  private int size;//数目  private int threshold;//阈值  private final float loadFactor;//加载因子  private final ReferenceQueue<Object> queue = new ReferenceQueue<>();//引用队列  int modCount;//fail-fast  @SuppressWarnings("unchecked") private Entry<K,V>[] newTable(int n) { return (Entry<K,V>[]) new Entry<?,?>[n];  } //构造函数  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);  } //初始值的构造函数  public WeakHashMap(int initialCapacity) { this(initialCapacity, DEFAULT_LOAD_FACTOR);  } //构造函数  public WeakHashMap() { this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);  } 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.  */  //计算k的hash  final int hash(Object k) { int 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.  */  //返回数目  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.  */  //判断是否为空  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)  */  //通过key获得value  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  */  //判断是否包含某个key  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.  */  //通过key获得entry  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>.)  */  //插入key和value  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).  */  //跳转大小  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);  transfer(oldTable, newTable);  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);  table = oldTable;  } } /** Transfers all entries from src to dest tables */  private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) { 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 { 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>  */  //根据key删除  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.  */  //清空  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  */  //判断是否包含某个值  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  */  //判断是否有空值  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.  */  //entry继承了虚引用  private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> { V value;  final 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 Objects.hashCode(k) ^ Objects.hashCode(v);  } public String toString() { return getKey() + "=" + getValue();  } } private abstract class HashIterator<T> implements Iterator<T> { private int index;  private Entry<K,V> entry;  private Entry<K,V> lastReturned;  private int expectedModCount = modCount;   /**  * Strong reference needed to avoid disappearance of key  * between hasNext and next  */  private Object nextKey;   /**  * Strong reference needed to avoid disappearance of key  * between nextEntry() and any use of the entry  */  private Object currentKey;   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;   /**  * 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();  } public Spliterator<K> spliterator() { return new KeySpliterator<>(WeakHashMap.this, 0, -1, 0, 0);  } } /**  * 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();  } public Spliterator<V> spliterator() { return new ValueSpliterator<>(WeakHashMap.this, 0, -1, 0, 0);  } } /**  * 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);  } public Spliterator<Map.Entry<K,V>> spliterator() { return new EntrySpliterator<>(WeakHashMap.this, 0, -1, 0, 0);  } } @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();  } } } } @SuppressWarnings("unchecked") @Override  public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { Objects.requireNonNull(function);  int expectedModCount = modCount;   Entry<K, V>[] tab = getTable();;  for (Entry<K, V> entry : tab) { while (entry != null) { Object key = entry.get();  if (key != null) { entry.value = function.apply((K)WeakHashMap.unmaskNull(key), entry.value);  } entry = entry.next;   if (expectedModCount != modCount) { throw new ConcurrentModificationException();  } } } } /**  * Similar form as other hash Spliterators, but skips dead  * elements.  */  static class WeakHashMapSpliterator<K,V> { final WeakHashMap<K,V> map;  WeakHashMap.Entry<K,V> current; // current node  int index; // current index, modified on advance/split  int fence; // -1 until first use; then one past last index  int est; // size estimate  int expectedModCount; // for comodification checks   WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin,  int fence, int est,  int expectedModCount) { this.map = m;  this.index = origin;  this.fence = fence;  this.est = est;  this.expectedModCount = expectedModCount;  } final int getFence() { // initialize fence and size on first use  int hi;  if ((hi = fence) < 0) { WeakHashMap<K,V> m = map;  est = m.size();  expectedModCount = m.modCount;  hi = fence = m.table.length;  } return hi;  } public final long estimateSize() { getFence(); // force init  return (long) est;  } } static final class KeySpliterator<K,V> extends WeakHashMapSpliterator<K,V> implements Spliterator<K> { KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est,  int expectedModCount) { super(m, origin, fence, est, expectedModCount);  } public KeySpliterator<K,V> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;  return (lo >= mid) ? null : new KeySpliterator<K,V>(map, lo, index = mid, est >>>= 1,  expectedModCount);  } public void forEachRemaining(Consumer<? super K> action) { int i, hi, mc;  if (action == null) throw new NullPointerException();  WeakHashMap<K,V> m = map;  WeakHashMap.Entry<K,V>[] tab = m.table;  if ((hi = fence) < 0) { mc = expectedModCount = m.modCount;  hi = fence = tab.length;  } else  mc = expectedModCount;  if (tab.length >= hi && (i = index) >= 0 && (i < (index = hi) || current != null)) { WeakHashMap.Entry<K,V> p = current;  current = null; // exhaust  do { if (p == null) p = tab[i++];  else { Object x = p.get();  p = p.next;  if (x != null) { @SuppressWarnings("unchecked") K k = (K) WeakHashMap.unmaskNull(x);  action.accept(k);  } } } while (p != null || i < hi);  } if (m.modCount != mc) throw new ConcurrentModificationException();  } public boolean tryAdvance(Consumer<? super K> action) { int hi;  if (action == null) throw new NullPointerException();  WeakHashMap.Entry<K,V>[] tab = map.table;  if (tab.length >= (hi = getFence()) && index >= 0) { while (current != null || index < hi) { if (current == null) current = tab[index++];  else { Object x = current.get();  current = current.next;  if (x != null) { @SuppressWarnings("unchecked") K k = (K) WeakHashMap.unmaskNull(x);  action.accept(k);  if (map.modCount != expectedModCount) throw new ConcurrentModificationException();  return true;  } } } } return false;  } public int characteristics() { return Spliterator.DISTINCT;  } } static final class ValueSpliterator<K,V> extends WeakHashMapSpliterator<K,V> implements Spliterator<V> { ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est,  int expectedModCount) { super(m, origin, fence, est, expectedModCount);  } public ValueSpliterator<K,V> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;  return (lo >= mid) ? null : new ValueSpliterator<K,V>(map, lo, index = mid, est >>>= 1,  expectedModCount);  } public void forEachRemaining(Consumer<? super V> action) { int i, hi, mc;  if (action == null) throw new NullPointerException();  WeakHashMap<K,V> m = map;  WeakHashMap.Entry<K,V>[] tab = m.table;  if ((hi = fence) < 0) { mc = expectedModCount = m.modCount;  hi = fence = tab.length;  } else  mc = expectedModCount;  if (tab.length >= hi && (i = index) >= 0 && (i < (index = hi) || current != null)) { WeakHashMap.Entry<K,V> p = current;  current = null; // exhaust  do { if (p == null) p = tab[i++];  else { Object x = p.get();  V v = p.value;  p = p.next;  if (x != null) action.accept(v);  } } while (p != null || i < hi);  } if (m.modCount != mc) throw new ConcurrentModificationException();  } public boolean tryAdvance(Consumer<? super V> action) { int hi;  if (action == null) throw new NullPointerException();  WeakHashMap.Entry<K,V>[] tab = map.table;  if (tab.length >= (hi = getFence()) && index >= 0) { while (current != null || index < hi) { if (current == null) current = tab[index++];  else { Object x = current.get();  V v = current.value;  current = current.next;  if (x != null) { action.accept(v);  if (map.modCount != expectedModCount) throw new ConcurrentModificationException();  return true;  } } } } return false;  } public int characteristics() { return 0;  } } static final class EntrySpliterator<K,V> extends WeakHashMapSpliterator<K,V> implements Spliterator<Map.Entry<K,V>> { EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est,  int expectedModCount) { super(m, origin, fence, est, expectedModCount);  } public EntrySpliterator<K,V> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;  return (lo >= mid) ? null : new EntrySpliterator<K,V>(map, lo, index = mid, est >>>= 1,  expectedModCount);  } public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { int i, hi, mc;  if (action == null) throw new NullPointerException();  WeakHashMap<K,V> m = map;  WeakHashMap.Entry<K,V>[] tab = m.table;  if ((hi = fence) < 0) { mc = expectedModCount = m.modCount;  hi = fence = tab.length;  } else  mc = expectedModCount;  if (tab.length >= hi && (i = index) >= 0 && (i < (index = hi) || current != null)) { WeakHashMap.Entry<K,V> p = current;  current = null; // exhaust  do { if (p == null) p = tab[i++];  else { Object x = p.get();  V v = p.value;  p = p.next;  if (x != null) { @SuppressWarnings("unchecked") K k = (K) WeakHashMap.unmaskNull(x);  action.accept (new AbstractMap.SimpleImmutableEntry<K,V>(k, v));  } } } while (p != null || i < hi);  } if (m.modCount != mc) throw new ConcurrentModificationException();  } public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) { int hi;  if (action == null) throw new NullPointerException();  WeakHashMap.Entry<K,V>[] tab = map.table;  if (tab.length >= (hi = getFence()) && index >= 0) { while (current != null || index < hi) { if (current == null) current = tab[index++];  else { Object x = current.get();  V v = current.value;  current = current.next;  if (x != null) { @SuppressWarnings("unchecked") K k = (K) WeakHashMap.unmaskNull(x);  action.accept (new AbstractMap.SimpleImmutableEntry<K,V>(k, v));  if (map.modCount != expectedModCount) throw new ConcurrentModificationException();  return true;  } } } } return false;  } public int characteristics() { return Spliterator.DISTINCT;  } } }