/*
 
* 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;

/**
 
* <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(Map.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}.
 
*
 
* <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. The name of this
     
* class, LinkedHashMap.Entry, is confusing in several ways in its
     
* current context, but cannot be changed.
  
Otherwise, even though
     
* it is not exported outside this package, some existing source
     
* code is known to have relied on a symbol resolution corner case
     
* rule in calls to removeEldestEntry that suppressed compilation
     
* errors due to ambiguous usages. So, we keep the name to
     
* preserve unmodified compilability.
     
*
     
* 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 Entry<K,V> extends HashMap.Node<K,V> {
        
Entry<K,V> before, after;
        
Entry(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 LinkedHashMap.Entry<K,V> head;

    
/**
     
* The tail (youngest) of the doubly linked list.
     
*/
    
transient LinkedHashMap.Entry<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(LinkedHashMap.Entry<K,V> p) {
        
LinkedHashMap.Entry<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(LinkedHashMap.Entry<K,V> src,
                               
LinkedHashMap.Entry<K,V> dst) {
        
LinkedHashMap.Entry<K,V> b = dst.before = src.before;
        
LinkedHashMap.Entry<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) {
        
LinkedHashMap.Entry<K,V> p =
            
new LinkedHashMap.Entry<K,V>(hash, key, value, e);
        
linkNodeLast(p);
        
return p;
    
}

    
Node<K,V> replacementNode(Node<K,V> p, Node<K,V> next) {
        
LinkedHashMap.Entry<K,V> q = (LinkedHashMap.Entry<K,V>)p;
        
LinkedHashMap.Entry<K,V> t =
            
new LinkedHashMap.Entry<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) {
        
LinkedHashMap.Entry<K,V> q = (LinkedHashMap.Entry<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
        
LinkedHashMap.Entry<K,V> p =
            
(LinkedHashMap.Entry<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
        
LinkedHashMap.Entry<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
        
LinkedHashMap.Entry<K,V> last;
        
if (accessOrder && (last = tail) != e) {
            
LinkedHashMap.Entry<K,V> p =
                
(LinkedHashMap.Entry<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 (LinkedHashMap.Entry<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
  
accessOrderthe 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 (LinkedHashMap.Entry<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;
    
}

    
/**
     
* 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(Map.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;
            
for (LinkedHashMap.Entry<K,V> e = head; e != null; 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;
            
for (LinkedHashMap.Entry<K,V> e = head; e != null; 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<Map.Entry<K,V>> entrySet() {
        
Set<Map.Entry<K,V>> es;
        
return (es = entrySet) == null ? (entrySet = new LinkedEntrySet()) : es;
    
}

    
final class LinkedEntrySet extends AbstractSet<Map.Entry<K,V>> {
        
public final int size()
                 
{ return size; }
        
public final void clear()
               
{ LinkedHashMap.this.clear(); }
        
public final Iterator<Map.Entry<K,V>> iterator() {
            
return new LinkedEntryIterator();
        
}
        
public final boolean contains(Object o) {
            
if (!(o instanceof Map.Entry))
                
return false;
            
Map.Entry<?,?> e = (Map.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) {
                
Map.Entry<?,?> e = (Map.Entry<?,?>) o;
                
Object key = e.getKey();
                
Object value = e.getValue();
                
return removeNode(hash(key), key, value, true, true) != null;
            
}
            
return false;
        
}
        
public final Spliterator<Map.Entry<K,V>> spliterator() {
            
return Spliterators.spliterator(this, Spliterator.SIZED |
                                            
Spliterator.ORDERED |
                                            
Spliterator.DISTINCT);
        
}
        
public final void forEach(Consumer<? super Map.Entry<K,V>> action) {
            
if (action == null)
                
throw new NullPointerException();
            
int mc = modCount;
            
for (LinkedHashMap.Entry<K,V> e = head; e != null; 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;
        
for (LinkedHashMap.Entry<K,V> e = head; 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;
        
for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
            
e.value = function.apply(e.key, e.value);
        
if (modCount != mc)
            
throw new ConcurrentModificationException();
    
}

    
// Iterators

    
abstract class LinkedHashIterator {
        
LinkedHashMap.Entry<K,V> next;
        
LinkedHashMap.Entry<K,V> current;
        
int expectedModCount;

        
LinkedHashIterator() {
            
next = head;
            
expectedModCount = modCount;
            
current = null;
        
}

        
public final boolean hasNext() {
            
return next != null;
        
}

        
final LinkedHashMap.Entry<K,V> nextNode() {
            
LinkedHashMap.Entry<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<Map.Entry<K,V>> {
        
public final Map.Entry<K,V> next() { return nextNode(); }
    
}


}