content: /*
   * Copyright (c) 1997, 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.util.function.Consumer;
  import java.util.function.BiConsumer;
  import java.util.function.BiFunction;
  import java.io.IOException;
  
  // Android-added: Note about spliterator order b/33945212 in Android N
  
  /**
   * <p>Hash table and linked list implementation of the <tt>Map</tt> interface,
   * with predictable iteration order.  This implementation differs from
   * <tt>HashMap</tt> in that it maintains a doubly-linked list running through
   * all of its entries.  This linked list defines the iteration ordering,
   * which is normally the order in which keys were inserted into the map
   * (<i>insertion-order</i>).  Note that insertion order is not affected
   * if a key is <i>re-inserted</i> into the map.  (A key <tt>k</tt> is
   * reinserted into a map <tt>m</tt> if <tt>m.put(k, v)</tt> is invoked when
   * <tt>m.containsKey(k)</tt> would return <tt>true</tt> immediately prior to
   * the invocation.)
   *
   * <p>This implementation spares its clients from the unspecified, generally
   * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}),
   * without incurring the increased cost associated with {@link TreeMap}.  It
   * can be used to produce a copy of a map that has the same order as the
   * original, regardless of the original map's implementation:
   * <pre>
   *     void foo(Map m) {
   *         Map copy = new LinkedHashMap(m);
   *         ...
   *     }
   * </pre>
   * This technique is particularly useful if a module takes a map on input,
   * copies it, and later returns results whose order is determined by that of
   * the copy.  (Clients generally appreciate having things returned in the same
   * order they were presented.)
   *
   * <p>A special {@link #LinkedHashMap(int,float,boolean) constructor} is
   * provided to create a linked hash map whose order of iteration is the order
   * in which its entries were last accessed, from least-recently accessed to
   * most-recently (<i>access-order</i>).  This kind of map is well-suited to
   * building LRU caches.  Invoking the {@code put}, {@code putIfAbsent},
   * {@code get}, {@code getOrDefault}, {@code compute}, {@code computeIfAbsent},
   * {@code computeIfPresent}, or {@code merge} methods results
   * in an access to the corresponding entry (assuming it exists after the
   * invocation completes). The {@code replace} methods only result in an access
   * of the entry if the value is replaced.  The {@code putAll} method generates one
   * entry access for each mapping in the specified map, in the order that
   * key-value mappings are provided by the specified map's entry set iterator.
   * <i>No other methods generate entry accesses.</i>  In particular, operations
   * on collection-views do <i>not</i> affect the order of iteration of the
   * backing map.
   *
   * <p>The {@link #removeEldestEntry(Entry)} method may be overridden to
   * impose a policy for removing stale mappings automatically when new mappings
   * are added to the map.
   *
   * <p>This class provides all of the optional <tt>Map</tt> operations, and
   * permits null elements.  Like <tt>HashMap</tt>, it provides constant-time
   * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and
   * <tt>remove</tt>), assuming the hash function disperses elements
   * properly among the buckets.  Performance is likely to be just slightly
   * below that of <tt>HashMap</tt>, due to the added expense of maintaining the
   * linked list, with one exception: Iteration over the collection-views
   * of a <tt>LinkedHashMap</tt> requires time proportional to the <i>size</i>
   * of the map, regardless of its capacity.  Iteration over a <tt>HashMap</tt>
   * is likely to be more expensive, requiring time proportional to its
   * <i>capacity</i>.
   *
   * <p>A linked hash map has two parameters that affect its performance:
   * <i>initial capacity</i> and <i>load factor</i>.  They are defined precisely
   * as for <tt>HashMap</tt>.  Note, however, that the penalty for choosing an
   * excessively high value for initial capacity is less severe for this class
   * than for <tt>HashMap</tt>, as iteration times for this class are unaffected
   * by capacity.
   *
   * <p><strong>Note that this implementation is not synchronized.</strong>
   * If multiple threads access a linked hash map concurrently, and at least
   * one of the threads modifies the map structurally, it <em>must</em> be
   * synchronized externally.  This is typically accomplished by
   * synchronizing on some object that naturally encapsulates the map.
   *
   * If no such object exists, the map should be "wrapped" using the
   * {@link Collections#synchronizedMap Collections.synchronizedMap}
   * method.  This is best done at creation time, to prevent accidental
   * unsynchronized access to the map:<pre>
   *   Map m = Collections.synchronizedMap(new LinkedHashMap(...));</pre>
   *
   * A structural modification is any operation that adds or deletes one or more
   * mappings or, in the case of access-ordered linked hash maps, affects
   * iteration order.  In insertion-ordered linked hash maps, merely changing
   * the value associated with a key that is already contained in the map is not
   * a structural modification.  <strong>In access-ordered linked hash maps,
   * merely querying the map with <tt>get</tt> is a structural modification.
   * </strong>)
   *
   * <p>The iterators returned by the <tt>iterator</tt> method of the collections
   * returned by all of this class's collection view methods are
   * <em>fail-fast</em>: 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>The spliterators returned by the spliterator method of the collections
   * returned by all of this class's collection view methods are
   * <em><a href="Spliterator.html#binding">late-binding</a></em>,
   * <em>fail-fast</em>, and additionally report {@link Spliterator#ORDERED}.
   * <em>Note</em>: The implementation of these spliterators in Android Nougat
   * (API levels 24 and 25) uses the wrong order (inconsistent with the
   * iterators, which use the correct order), despite reporting
   * {@link Spliterator#ORDERED}. You may use the following code fragments
   * to obtain a correctly ordered Spliterator on API level 24 and 25:
   * <ul>
   *     <li>For a Collection view {@code c = lhm.keySet()},
   *         {@code c = lhm.entrySet()} or {@code c = lhm.values()}, use
   *         {@code java.util.Spliterators.spliterator(c, c.spliterator().characteristics())}
   *         instead of {@code c.spliterator()}.
   *     <li>Instead of {@code c.stream()} or {@code c.parallelStream()}, use
   *         {@code java.util.stream.StreamSupport.stream(spliterator, false)}
   *         to construct a (nonparallel) {@link java.util.stream.Stream} from
   *         such a {@code Spliterator}.
   * </ul>
   * Note that these workarounds are only suggested where {@code lhm} is a
   * {@code LinkedHashMap}.
   *
   * <p>This class is a member of the
   * <a href="{@docRoot}/../technotes/guides/collections/index.html">
   * Java Collections Framework</a>.
   *
   * @implNote
   * The spliterators returned by the spliterator method of the collections
   * returned by all of this class's collection view methods are created from
   * the iterators of the corresponding collections.
   *
   * @param <K> the type of keys maintained by this map
   * @param <V> the type of mapped values
   *
   * @author  Josh Bloch
   * @see     Object#hashCode()
   * @see     Collection
   * @see     Map
   * @see     HashMap
   * @see     TreeMap
   * @see     Hashtable
   * @since   1.4
   */
  public class LinkedHashMap<K,V>
      extends HashMap<K,V>
      implements Map<K,V>
  {
  
      /*
       * Implementation note.  A previous version of this class was
       * internally structured a little differently. Because superclass
       * HashMap now uses trees for some of its nodes, class
       * LinkedHashMap.Entry is now treated as intermediary node class
       * that can also be converted to tree form.
       *
       // BEGIN Android-changed
       * LinkedHashMapEntry should not be renamed. Specifically, for
       * source compatibility with earlier versions of Android, this
       * nested class must not be named "Entry". Otherwise, it would
       * hide Map.Entry which would break compilation of code like:
       *
       * LinkedHashMap.Entry<K, V> entry = map.entrySet().iterator.next()
       *
       * To compile, that code snippet's "LinkedHashMap.Entry" must
       * mean java.util.Map.Entry which is the compile time type of
       * entrySet()'s elements.
       // END Android-changed
       *
       * The changes in node classes also require using two fields
       * (head, tail) rather than a pointer to a header node to maintain
       * the doubly-linked before/after list. This class also
       * previously used a different style of callback methods upon
       * access, insertion, and removal.
       */
  
      /**
       * HashMap.Node subclass for normal LinkedHashMap entries.
       */
      static class LinkedHashMapEntry<K,V> extends HashMap.Node<K,V> {
          LinkedHashMapEntry<K,V> before, after;
          LinkedHashMapEntry(int hash, K key, V value, Node<K,V> next) {
              super(hash, key, value, next);
          }
      }
  
      private static final long serialVersionUID = 3801124242820219131L;
  
      /**
       * The head (eldest) of the doubly linked list.
       */
      transient LinkedHashMapEntry<K,V> head;
  
      /**
       * The tail (youngest) of the doubly linked list.
       */
      transient LinkedHashMapEntry<K,V> tail;
  
      /**
       * The iteration ordering method for this linked hash map: <tt>true</tt>
       * for access-order, <tt>false</tt> for insertion-order.
       *
       * @serial
       */
      final boolean accessOrder;
  
      // internal utilities
  
      // link at the end of list
      private void linkNodeLast(LinkedHashMapEntry<K,V> p) {
          LinkedHashMapEntry<K,V> last = tail;
          tail = p;
          if (last == null)
              head = p;
          else {
              p.before = last;
              last.after = p;
          }
      }
  
      // apply src's links to dst
      private void transferLinks(LinkedHashMapEntry<K,V> src,
                                 LinkedHashMapEntry<K,V> dst) {
          LinkedHashMapEntry<K,V> b = dst.before = src.before;
          LinkedHashMapEntry<K,V> a = dst.after = src.after;
          if (b == null)
              head = dst;
          else
              b.after = dst;
          if (a == null)
              tail = dst;
          else
              a.before = dst;
      }
  
      // overrides of HashMap hook methods
  
      void reinitialize() {
          super.reinitialize();
          head = tail = null;
      }
  
      Node<K,V> newNode(int hash, K key, V value, Node<K,V> e) {
          LinkedHashMapEntry<K,V> p =
              new LinkedHashMapEntry<K,V>(hash, key, value, e);
          linkNodeLast(p);
          return p;
      }
  
      Node<K,V> replacementNode(Node<K,V> p, Node<K,V> next) {
          LinkedHashMapEntry<K,V> q = (LinkedHashMapEntry<K,V>)p;
          LinkedHashMapEntry<K,V> t =
              new LinkedHashMapEntry<K,V>(q.hash, q.key, q.value, next);
          transferLinks(q, t);
          return t;
      }
  
      TreeNode<K,V> newTreeNode(int hash, K key, V value, Node<K,V> next) {
          TreeNode<K,V> p = new TreeNode<K,V>(hash, key, value, next);
          linkNodeLast(p);
          return p;
      }
  
      TreeNode<K,V> replacementTreeNode(Node<K,V> p, Node<K,V> next) {
          LinkedHashMapEntry<K,V> q = (LinkedHashMapEntry<K,V>)p;
          TreeNode<K,V> t = new TreeNode<K,V>(q.hash, q.key, q.value, next);
          transferLinks(q, t);
          return t;
      }
  
      void afterNodeRemoval(Node<K,V> e) { // unlink
          LinkedHashMapEntry<K,V> p =
              (LinkedHashMapEntry<K,V>)e, b = p.before, a = p.after;
          p.before = p.after = null;
          if (b == null)
              head = a;
          else
              b.after = a;
          if (a == null)
              tail = b;
          else
              a.before = b;
      }
  
      void afterNodeInsertion(boolean evict) { // possibly remove eldest
          LinkedHashMapEntry<K,V> first;
          if (evict && (first = head) != null && removeEldestEntry(first)) {
              K key = first.key;
              removeNode(hash(key), key, null, false, true);
          }
      }
  
      void afterNodeAccess(Node<K,V> e) { // move node to last
          LinkedHashMapEntry<K,V> last;
          if (accessOrder && (last = tail) != e) {
              LinkedHashMapEntry<K,V> p =
                  (LinkedHashMapEntry<K,V>)e, b = p.before, a = p.after;
              p.after = null;
              if (b == null)
                  head = a;
              else
                  b.after = a;
              if (a != null)
                  a.before = b;
              else
                  last = b;
              if (last == null)
                  head = p;
              else {
                  p.before = last;
                  last.after = p;
              }
              tail = p;
              ++modCount;
          }
      }
  
      void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
          for (LinkedHashMapEntry<K,V> e = head; e != null; e = e.after) {
              s.writeObject(e.key);
              s.writeObject(e.value);
          }
      }
  
      /**
       * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
       * with the specified initial capacity and load factor.
       *
       * @param  initialCapacity the initial capacity
       * @param  loadFactor      the load factor
       * @throws IllegalArgumentException if the initial capacity is negative
       *         or the load factor is nonpositive
       */
      public LinkedHashMap(int initialCapacity, float loadFactor) {
          super(initialCapacity, loadFactor);
          accessOrder = false;
      }
  
      /**
       * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
       * with the specified initial capacity and a default load factor (0.75).
       *
       * @param  initialCapacity the initial capacity
       * @throws IllegalArgumentException if the initial capacity is negative
       */
      public LinkedHashMap(int initialCapacity) {
          super(initialCapacity);
          accessOrder = false;
      }
  
      /**
       * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
       * with the default initial capacity (16) and load factor (0.75).
       */
      public LinkedHashMap() {
          super();
          accessOrder = false;
      }
  
      /**
       * Constructs an insertion-ordered <tt>LinkedHashMap</tt> instance with
       * the same mappings as the specified map.  The <tt>LinkedHashMap</tt>
       * instance is created with a 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
       */
      public LinkedHashMap(Map<? extends K, ? extends V> m) {
          super();
          accessOrder = false;
          putMapEntries(m, false);
      }
  
      /**
       * Constructs an empty <tt>LinkedHashMap</tt> instance with the
       * specified initial capacity, load factor and ordering mode.
       *
       * @param  initialCapacity the initial capacity
       * @param  loadFactor      the load factor
       * @param  accessOrder     the ordering mode - <tt>true</tt> for
       *         access-order, <tt>false</tt> for insertion-order
       * @throws IllegalArgumentException if the initial capacity is negative
       *         or the load factor is nonpositive
       */
      public LinkedHashMap(int initialCapacity,
                           float loadFactor,
                           boolean accessOrder) {
          super(initialCapacity, loadFactor);
          this.accessOrder = accessOrder;
      }
  
  
      /**
       * 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) {
          for (LinkedHashMapEntry<K,V> e = head; e != null; e = e.after) {
              V v = e.value;
              if (v == value || (value != null && value.equals(v)))
                  return true;
          }
          return false;
      }
  
      /**
       * 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.
       */
      public V get(Object key) {
          Node<K,V> e;
          if ((e = getNode(hash(key), key)) == null)
              return null;
          if (accessOrder)
              afterNodeAccess(e);
          return e.value;
      }
  
      /**
       * {@inheritDoc}
       */
      public V getOrDefault(Object key, V defaultValue) {
         Node<K,V> e;
         if ((e = getNode(hash(key), key)) == null)
             return defaultValue;
         if (accessOrder)
             afterNodeAccess(e);
         return e.value;
     }
  
      /**
       * {@inheritDoc}
       */
      public void clear() {
          super.clear();
          head = tail = null;
      }
  
      // Android-added: eldest(), for internal use in LRU caches
      /**
       * Returns the eldest entry in the map, or {@code null} if the map is empty.
       * @hide
       */
      public Entry<K, V> eldest() {
          return head;
      }
  
      /**
       * Returns <tt>true</tt> if this map should remove its eldest entry.
       * This method is invoked by <tt>put</tt> and <tt>putAll</tt> after
       * inserting a new entry into the map.  It provides the implementor
       * with the opportunity to remove the eldest entry each time a new one
       * is added.  This is useful if the map represents a cache: it allows
       * the map to reduce memory consumption by deleting stale entries.
       *
       * <p>Sample use: this override will allow the map to grow up to 100
       * entries and then delete the eldest entry each time a new entry is
       * added, maintaining a steady state of 100 entries.
       * <pre>
       *     private static final int MAX_ENTRIES = 100;
       *
       *     protected boolean removeEldestEntry(Map.Entry eldest) {
       *        return size() &gt; MAX_ENTRIES;
       *     }
       * </pre>
       *
       * <p>This method typically does not modify the map in any way,
       * instead allowing the map to modify itself as directed by its
       * return value.  It <i>is</i> permitted for this method to modify
       * the map directly, but if it does so, it <i>must</i> return
       * <tt>false</tt> (indicating that the map should not attempt any
       * further modification).  The effects of returning <tt>true</tt>
       * after modifying the map from within this method are unspecified.
       *
       * <p>This implementation merely returns <tt>false</tt> (so that this
       * map acts like a normal map - the eldest element is never removed).
       *
       * @param    eldest The least recently inserted entry in the map, or if
       *           this is an access-ordered map, the least recently accessed
       *           entry.  This is the entry that will be removed it this
       *           method returns <tt>true</tt>.  If the map was empty prior
       *           to the <tt>put</tt> or <tt>putAll</tt> invocation resulting
       *           in this invocation, this will be the entry that was just
       *           inserted; in other words, if the map contains a single
       *           entry, the eldest entry is also the newest.
       * @return   <tt>true</tt> if the eldest entry should be removed
       *           from the map; <tt>false</tt> if it should be retained.
       */
      protected boolean removeEldestEntry(Entry<K,V> eldest) {
          return false;
      }
  
      /**
       * 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.
       * Its {@link Spliterator} typically provides faster sequential
       * performance but much poorer parallel performance than that of
       * {@code HashMap}.
       *
       * @return a set view of the keys contained in this map
       */
      public Set<K> keySet() {
          Set<K> ks = keySet;
          if (ks == null) {
              ks = new LinkedKeySet();
              keySet = ks;
          }
          return ks;
      }
  
      final class LinkedKeySet extends AbstractSet<K> {
          public final int size()                 { return size; }
          public final void clear()               { LinkedHashMap.this.clear(); }
          public final Iterator<K> iterator() {
              return new LinkedKeyIterator();
          }
          public final boolean contains(Object o) { return containsKey(o); }
          public final boolean remove(Object key) {
              return removeNode(hash(key), key, null, false, true) != null;
          }
          public final Spliterator<K> spliterator()  {
              return Spliterators.spliterator(this, Spliterator.SIZED |
                                              Spliterator.ORDERED |
                                              Spliterator.DISTINCT);
          }
          public final void forEach(Consumer<? super K> action) {
              if (action == null)
                  throw new NullPointerException();
              int mc = modCount;
              // Android-changed: Detect changes to modCount early.
              for (LinkedHashMapEntry<K,V> e = head; (e != null && modCount == mc); e = e.after)
                  action.accept(e.key);
              if (modCount != mc)
                  throw new ConcurrentModificationException();
          }
      }
  
      /**
       * 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.
       * Its {@link Spliterator} typically provides faster sequential
       * performance but much poorer parallel performance than that of
       * {@code HashMap}.
       *
       * @return a view of the values contained in this map
       */
      public Collection<V> values() {
          Collection<V> vs = values;
          if (vs == null) {
              vs = new LinkedValues();
              values = vs;
          }
          return vs;
      }
  
      final class LinkedValues extends AbstractCollection<V> {
          public final int size()                 { return size; }
          public final void clear()               { LinkedHashMap.this.clear(); }
          public final Iterator<V> iterator() {
              return new LinkedValueIterator();
          }
          public final boolean contains(Object o) { return containsValue(o); }
          public final Spliterator<V> spliterator() {
              return Spliterators.spliterator(this, Spliterator.SIZED |
                                              Spliterator.ORDERED);
          }
          public final void forEach(Consumer<? super V> action) {
              if (action == null)
                  throw new NullPointerException();
              int mc = modCount;
              // Android-changed: Detect changes to modCount early.
              for (LinkedHashMapEntry<K,V> e = head; (e != null && modCount == mc); e = e.after)
                  action.accept(e.value);
              if (modCount != mc)
                  throw new ConcurrentModificationException();
          }
      }
  
      /**
       * 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.
       * Its {@link Spliterator} typically provides faster sequential
       * performance but much poorer parallel performance than that of
       * {@code HashMap}.
       *
       * @return a set view of the mappings contained in this map
       */
      public Set<Entry<K,V>> entrySet() {
          Set<Entry<K,V>> es;
          return (es = entrySet) == null ? (entrySet = new LinkedEntrySet()) : es;
      }
  
      final class LinkedEntrySet extends AbstractSet<Entry<K,V>> {
          public final int size()                 { return size; }
          public final void clear()               { LinkedHashMap.this.clear(); }
          public final Iterator<Entry<K,V>> iterator() {
              return new LinkedEntryIterator();
          }
          public final boolean contains(Object o) {
              if (!(o instanceof Map.Entry))
                  return false;
              Entry<?,?> e = (Entry<?,?>) o;
              Object key = e.getKey();
              Node<K,V> candidate = getNode(hash(key), key);
              return candidate != null && candidate.equals(e);
          }
          public final boolean remove(Object o) {
              if (o instanceof Map.Entry) {
                  Entry<?,?> e = (Entry<?,?>) o;
                  Object key = e.getKey();
                  Object value = e.getValue();
                  return removeNode(hash(key), key, value, true, true) != null;
              }
              return false;
          }
          public final Spliterator<Entry<K,V>> spliterator() {
              return Spliterators.spliterator(this, Spliterator.SIZED |
                                              Spliterator.ORDERED |
                                              Spliterator.DISTINCT);
          }
          public final void forEach(Consumer<? super Entry<K,V>> action) {
              if (action == null)
                  throw new NullPointerException();
              int mc = modCount;
              // Android-changed: Detect changes to modCount early.
              for (LinkedHashMapEntry<K,V> e = head; (e != null && mc == modCount); e = e.after)
                  action.accept(e);
              if (modCount != mc)
                  throw new ConcurrentModificationException();
          }
      }
  
      // Map overrides
  
      public void forEach(BiConsumer<? super K, ? super V> action) {
          if (action == null)
              throw new NullPointerException();
          int mc = modCount;
          // Android-changed: Detect changes to modCount early.
          for (LinkedHashMapEntry<K,V> e = head; modCount == mc && e != null; e = e.after)
              action.accept(e.key, e.value);
          if (modCount != mc)
              throw new ConcurrentModificationException();
      }
  
      public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
          if (function == null)
              throw new NullPointerException();
          int mc = modCount;
          // Android-changed: Detect changes to modCount early.
          for (LinkedHashMapEntry<K,V> e = head; modCount == mc && e != null; e = e.after)
              e.value = function.apply(e.key, e.value);
          if (modCount != mc)
              throw new ConcurrentModificationException();
      }
  
      // Iterators
  
      abstract class LinkedHashIterator {
          LinkedHashMapEntry<K,V> next;
          LinkedHashMapEntry<K,V> current;
          int expectedModCount;
  
          LinkedHashIterator() {
              next = head;
              expectedModCount = modCount;
              current = null;
          }
  
          public final boolean hasNext() {
              return next != null;
          }
  
          final LinkedHashMapEntry<K,V> nextNode() {
              LinkedHashMapEntry<K,V> e = next;
              if (modCount != expectedModCount)
                  throw new ConcurrentModificationException();
              if (e == null)
                  throw new NoSuchElementException();
              current = e;
              next = e.after;
              return e;
          }
  
          public final void remove() {
              Node<K,V> p = current;
              if (p == null)
                  throw new IllegalStateException();
              if (modCount != expectedModCount)
                  throw new ConcurrentModificationException();
              current = null;
              K key = p.key;
              removeNode(hash(key), key, null, false, false);
              expectedModCount = modCount;
          }
      }
  
      final class LinkedKeyIterator extends LinkedHashIterator
          implements Iterator<K> {
          public final K next() { return nextNode().getKey(); }
      }
  
      final class LinkedValueIterator extends LinkedHashIterator
          implements Iterator<V> {
          public final V next() { return nextNode().value; }
      }
  
      final class LinkedEntryIterator extends LinkedHashIterator
          implements Iterator<Entry<K,V>> {
          public final Entry<K,V> next() { return nextNode(); }
      }
  
  
  }
  