content: /*
   * Copyright (c) 1998, 2013, 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.concurrent.ThreadLocalRandom;
  import java.util.function.BiConsumer;
  import java.util.function.BiFunction;
  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         HashMap
   * @see         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;
  
      @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);
      }
  
      /**
       * 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.
       */
      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.
       */
      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);
          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>
       */
      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;
          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;
          if (ks == null) {
              ks = new KeySet();
              keySet = ks;
          }
          return ks;
      }
  
      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;
          if (vs == null) {
              vs = new Values();
              values = vs;
          }
          return vs;
      }
  
      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 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;
          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;
              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)) {
                  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();
              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;
              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)) {
                  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();
              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;
              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)) {
                  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 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();
              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 SimpleImmutableEntry<K,V>(k, v));
                              if (map.modCount != expectedModCount)
                                  throw new ConcurrentModificationException();
                              return true;
                          }
                      }
                  }
              }
              return false;
          }
  
          public int characteristics() {
              return Spliterator.DISTINCT;
          }
      }
  
  }
  