/*
 
* 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.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.io.Serializable;

/**
 
* An object that maps keys to values.
  
A map cannot contain duplicate keys;
 
* each key can map to at most one value.
 
*
 
* <p>This interface takes the place of the <tt>Dictionary</tt> class, which
 
* was a totally abstract class rather than an interface.
 
*
 
* <p>The <tt>Map</tt> interface provides three <i>collection views</i>, which
 
* allow a map's contents to be viewed as a set of keys, collection of values,
 
* or set of key-value mappings.
  
The <i>order</i> of a map is defined as
 
* the order in which the iterators on the map's collection views return their
 
* elements.
  
Some map implementations, like the <tt>TreeMap</tt> class, make
 
* specific guarantees as to their order; others, like the <tt>HashMap</tt>
 
* class, do not.
 
*
 
* <p>Note: great care must be exercised if mutable objects are used as map
 
* keys.
  
The behavior of a map is not specified if the value of an object is
 
* changed in a manner that affects <tt>equals</tt> comparisons while the
 
* object is a key in the map.
  
A special case of this prohibition is that it
 
* is not permissible for a map to contain itself as a key.
  
While it is
 
* permissible for a map to contain itself as a value, extreme caution is
 
* advised: the <tt>equals</tt> and <tt>hashCode</tt> methods are no longer
 
* well defined on such a map.
 
*
 
* <p>All general-purpose map implementation classes should provide two
 
* "standard" constructors: a void (no arguments) constructor which creates an
 
* empty map, and a constructor with a single argument of type <tt>Map</tt>,
 
* which creates a new map with the same key-value mappings as its argument.
 
* In effect, the latter constructor allows the user to copy any map,
 
* producing an equivalent map of the desired class.
  
There is no way to
 
* enforce this recommendation (as interfaces cannot contain constructors) but
 
* all of the general-purpose map implementations in the JDK comply.
 
*
 
* <p>The "destructive" methods contained in this interface, that is, the
 
* methods that modify the map on which they operate, are specified to throw
 
* <tt>UnsupportedOperationException</tt> if this map does not support the
 
* operation.
  
If this is the case, these methods may, but are not required
 
* to, throw an <tt>UnsupportedOperationException</tt> if the invocation would
 
* have no effect on the map.
  
For example, invoking the {@link #putAll(Map)}
 
* method on an unmodifiable map may, but is not required to, throw the
 
* exception if the map whose mappings are to be "superimposed" is empty.
 
*
 
* <p>Some map implementations have restrictions on the keys and values they
 
* may contain.
  
For example, some implementations prohibit null keys and
 
* values, and some have restrictions on the types of their keys.
  
Attempting
 
* to insert an ineligible key or value throws an unchecked exception,
 
* typically <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.
 
* Attempting to query the presence of an ineligible key or value may throw an
 
* exception, or it may simply return false; some implementations will exhibit
 
* the former behavior and some will exhibit the latter.
  
More generally,
 
* attempting an operation on an ineligible key or value whose completion
 
* would not result in the insertion of an ineligible element into the map may
 
* throw an exception or it may succeed, at the option of the implementation.
 
* Such exceptions are marked as "optional" in the specification for this
 
* interface.
 
*
 
* <p>Many methods in Collections Framework interfaces are defined
 
* in terms of the {@link Object#equals(Object) equals} method.
  
For
 
* example, the specification for the {@link #containsKey(Object)
 
* containsKey(Object key)} method says: "returns <tt>true</tt> if and
 
* only if this map contains a mapping for a key <tt>k</tt> such that
 
* <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should
 
* <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt>
 
* with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to
 
* be invoked for any key <tt>k</tt>.
  
Implementations are free to
 
* implement optimizations whereby the <tt>equals</tt> invocation is avoided,
 
* for example, by first comparing the hash codes of the two keys.
  
(The
 
* {@link Object#hashCode()} specification guarantees that two objects with
 
* unequal hash codes cannot be equal.)
  
More generally, implementations of
 
* the various Collections Framework interfaces are free to take advantage of
 
* the specified behavior of underlying {@link Object} methods wherever the
 
* implementor deems it appropriate.
 
*
 
* <p>Some map operations which perform recursive traversal of the map may fail
 
* with an exception for self-referential instances where the map directly or
 
* indirectly contains itself. This includes the {@code clone()},
 
* {@code equals()}, {@code hashCode()} and {@code toString()} methods.
 
* Implementations may optionally handle the self-referential scenario, however
 
* most current implementations do not do so.
 
*
 
* <p>This interface 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
  
Josh Bloch
 
* @see HashMap
 
* @see TreeMap
 
* @see Hashtable
 
* @see SortedMap
 
* @see Collection
 
* @see Set
 
* @since 1.2
 
*/

public interface Map<K,V> {
    
// Query Operations

    
/**
     
* Returns the number of key-value mappings in this map.
  
If the
     
* map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
     
* <tt>Integer.MAX_VALUE</tt>.
     
*
     
* @return the number of key-value mappings in this map
     
*/

    
int size();

    
/**
     
* Returns <tt>true</tt> if this map contains no key-value mappings.
     
*
     
* @return <tt>true</tt> if this map contains no key-value mappings
     
*/

    
boolean isEmpty();

    
/**
     
* Returns <tt>true</tt> if this map contains a mapping for the specified
     
* key.
  
More formally, returns <tt>true</tt> if and only if
     
* this map contains a mapping for a key <tt>k</tt> such that
     
* <tt>(key==null ? k==null : key.equals(k))</tt>.
  
(There can be
     
* at most one such mapping.)
     
*
     
* @param key key whose presence in this map is to be tested
     
* @return <tt>true</tt> if this map contains a mapping for the specified
     
*
         
key
     
* @throws ClassCastException if the key is of an inappropriate type for
     
*
         
this map
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if the specified key is null and this map
     
*
         
does not permit null keys
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
*/

    
boolean containsKey(Object key);

    
/**
     
* Returns <tt>true</tt> if this map maps one or more keys to the
     
* specified value.
  
More formally, returns <tt>true</tt> if and only if
     
* this map contains at least one mapping to a value <tt>v</tt> such that
     
* <tt>(value==null ? v==null : value.equals(v))</tt>.
  
This operation
     
* will probably require time linear in the map size for most
     
* implementations of the <tt>Map</tt> interface.
     
*
     
* @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
     
* @throws ClassCastException if the value is of an inappropriate type for
     
*
         
this map
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if the specified value is null and this
     
*
         
map does not permit null values
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
*/

    
boolean containsValue(Object value);

    
/**
     
* 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>If this map permits null values, then 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.
     
*
     
* @param key the key whose associated value is to be returned
     
* @return the value to which the specified key is mapped, or
     
*
         
{@code null} if this map contains no mapping for the key
     
* @throws ClassCastException if the key is of an inappropriate type for
     
*
         
this map
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if the specified key is null and this map
     
*
         
does not permit null keys
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
*/

    
V get(Object key);

    
// Modification Operations

    
/**
     
* Associates the specified value with the specified key in this map
     
* (optional operation).
  
If the map previously contained a mapping for
     
* the key, the old value is replaced by the specified value.
  
(A map
     
* <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only
     
* if {@link #containsKey(Object) m.containsKey(k)} would return
     
* <tt>true</tt>.)
     
*
     
* @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>,
     
*
         
if the implementation supports <tt>null</tt> values.)
     
* @throws UnsupportedOperationException if the <tt>put</tt> operation
     
*
         
is not supported by this map
     
* @throws ClassCastException if the class of the specified key or value
     
*
         
prevents it from being stored in this map
     
* @throws NullPointerException if the specified key or value is null
     
*
         
and this map does not permit null keys or values
     
* @throws IllegalArgumentException if some property of the specified key
     
*
         
or value prevents it from being stored in this map
     
*/

    
V put(K key, V value);

    
/**
     
* Removes the mapping for a key from this map if it is present
     
* (optional operation).
   
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.
     
*
     
* <p>If this map permits null values, then 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>.
     
* @throws UnsupportedOperationException if the <tt>remove</tt> operation
     
*
         
is not supported by this map
     
* @throws ClassCastException if the key is of an inappropriate type for
     
*
         
this map
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if the specified key is null and this
     
*
         
map does not permit null keys
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
*/

    
V remove(Object key);


    
// Bulk Operations

    
/**
     
* Copies all of the mappings from the specified map to this map
     
* (optional operation).
  
The effect of this call is equivalent to that
     
* of calling {@link #put(Object,Object) put(k, v)} on this map once
     
* for each mapping from key <tt>k</tt> to value <tt>v</tt> in the
     
* specified map.
  
The behavior of this operation is undefined if the
     
* specified map is modified while the operation is in progress.
     
*
     
* @param m mappings to be stored in this map
     
* @throws UnsupportedOperationException if the <tt>putAll</tt> operation
     
*
         
is not supported by this map
     
* @throws ClassCastException if the class of a key or value in the
     
*
         
specified map prevents it from being stored in this map
     
* @throws NullPointerException if the specified map is null, or if
     
*
         
this map does not permit null keys or values, and the
     
*
         
specified map contains null keys or values
     
* @throws IllegalArgumentException if some property of a key or value in
     
*
         
the specified map prevents it from being stored in this map
     
*/

    
void putAll(Map<? extends K, ? extends V> m);

    
/**
     
* Removes all of the mappings from this map (optional operation).
     
* The map will be empty after this call returns.
     
*
     
* @throws UnsupportedOperationException if the <tt>clear</tt> operation
     
*
         
is not supported by this map
     
*/

    
void clear();


    
// Views

    
/**
     
* 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.
     
*
     
* @return a set view of the keys contained in this map
     
*/

    
Set<K> keySet();

    
/**
     
* 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.
     
*
     
* @return a collection view of the values contained in this map
     
*/

    
Collection<V> values();

    
/**
     
* 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.
     
*
     
* @return a set view of the mappings contained in this map
     
*/

    
Set<Map.Entry<K, V>> entrySet();

    
/**
     
* A map entry (key-value pair).
  
The <tt>Map.entrySet</tt> method returns
     
* a collection-view of the map, whose elements are of this class.
  
The
     
* <i>only</i> way to obtain a reference to a map entry is from the
     
* iterator of this collection-view.
  
These <tt>Map.Entry</tt> objects are
     
* valid <i>only</i> for the duration of the iteration; more formally,
     
* the behavior of a map entry is undefined if the backing map has been
     
* modified after the entry was returned by the iterator, except through
     
* the <tt>setValue</tt> operation on the map entry.
     
*
     
* @see Map#entrySet()
     
* @since 1.2
     
*/

    
interface Entry<K,V> {
        
/**
         
* Returns the key corresponding to this entry.
         
*
         
* @return the key corresponding to this entry
         
* @throws IllegalStateException implementations may, but are not
         
*required to, throw this exception if the entry has been
         
*removed from the backing map.
         
*/

        
K getKey();

        
/**
         
* Returns the value corresponding to this entry.
  
If the mapping
         
* has been removed from the backing map (by the iterator's
         
* <tt>remove</tt> operation), the results of this call are undefined.
         
*
         
* @return the value corresponding to this entry
         
* @throws IllegalStateException implementations may, but are not
         
*required to, throw this exception if the entry has been
         
*removed from the backing map.
         
*/

        
V getValue();

        
/**
         
* Replaces the value corresponding to this entry with the specified
         
* value (optional operation).
  
(Writes through to the map.)The
         
* behavior of this call is undefined if the mapping has already been
         
* removed from the map (by the iterator's <tt>remove</tt> operation).
         
*
         
* @param value new value to be stored in this entry
         
* @return old value corresponding to the entry
         
* @throws UnsupportedOperationException if the <tt>put</tt> operation
         
*is not supported by the backing map
         
* @throws ClassCastException if the class of the specified value
         
*prevents it from being stored in the backing map
         
* @throws NullPointerException if the backing map does not permit
         
*null values, and the specified value is null
         
* @throws IllegalArgumentException if some property of this value
         
*prevents it from being stored in the backing map
         
* @throws IllegalStateException implementations may, but are not
         
*required to, throw this exception if the entry has been
         
*removed from the backing map.
         
*/

        
V setValue(V value);

        
/**
         
* Compares the specified object with this entry for equality.
         
* Returns <tt>true</tt> if the given object is also a map entry and
         
* the two entries represent the same mapping.
  
More formally, two
         
* entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping
         
* if<pre>
         
*
     
(e1.getKey()==null ?
         
*
      
e2.getKey()==null : e1.getKey().equals(e2.getKey()))
  
&amp;&amp;
         
*
     
(e1.getValue()==null ?
         
*
      
e2.getValue()==null : e1.getValue().equals(e2.getValue()))
         
* </pre>
         
* This ensures that the <tt>equals</tt> method works properly across
         
* different implementations of the <tt>Map.Entry</tt> interface.
         
*
         
* @param o object to be compared for equality with this map entry
         
* @return <tt>true</tt> if the specified object is equal to this map
         
*entry
         
*/

        
boolean equals(Object o);

        
/**
         
* Returns the hash code value for this map entry.
  
The hash code
         
* of a map entry <tt>e</tt> is defined to be: <pre>
         
*
     
(e.getKey()==null
   
? 0 : e.getKey().hashCode()) ^
         
*
     
(e.getValue()==null ? 0 : e.getValue().hashCode())
         
* </pre>
         
* This ensures that <tt>e1.equals(e2)</tt> implies that
         
* <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries
         
* <tt>e1</tt> and <tt>e2</tt>, as required by the general
         
* contract of <tt>Object.hashCode</tt>.
         
*
         
* @return the hash code value for this map entry
         
* @see Object#hashCode()
         
* @see Object#equals(Object)
         
* @see #equals(Object)
         
*/

        
int hashCode();

        
/**
         
* Returns a comparator that compares {@link Map.Entry} in natural order on key.
         
*
         
* <p>The returned comparator is serializable and throws {@link
         
* NullPointerException} when comparing an entry with a null key.
         
*
         
* @param
  
<K> the {@link Comparable} type of then map keys
         
* @param
  
<V> the type of the map values
         
* @return a comparator that compares {@link Map.Entry} in natural order on key.
         
* @see Comparable
         
* @since 1.8
         
*/

        
public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> comparingByKey() {
            
return (Comparator<Map.Entry<K, V>> & Serializable)
                
(c1, c2) -> c1.getKey().compareTo(c2.getKey());
        
}

        
/**
         
* Returns a comparator that compares {@link Map.Entry} in natural order on value.
         
*
         
* <p>The returned comparator is serializable and throws {@link
         
* NullPointerException} when comparing an entry with null values.
         
*
         
* @param <K> the type of the map keys
         
* @param <V> the {@link Comparable} type of the map values
         
* @return a comparator that compares {@link Map.Entry} in natural order on value.
         
* @see Comparable
         
* @since 1.8
         
*/

        
public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() {
            
return (Comparator<Map.Entry<K, V>> & Serializable)
                
(c1, c2) -> c1.getValue().compareTo(c2.getValue());
        
}

        
/**
         
* Returns a comparator that compares {@link Map.Entry} by key using the given
         
* {@link Comparator}.
         
*
         
* <p>The returned comparator is serializable if the specified comparator
         
* is also serializable.
         
*
         
* @param
  
<K> the type of the map keys
         
* @param
  
<V> the type of the map values
         
* @param
  
cmp the key {@link Comparator}
         
* @return a comparator that compares {@link Map.Entry} by the key.
         
* @since 1.8
         
*/

        
public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
            
Objects.requireNonNull(cmp);
            
return (Comparator<Map.Entry<K, V>> & Serializable)
                
(c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
        
}

        
/**
         
* Returns a comparator that compares {@link Map.Entry} by value using the given
         
* {@link Comparator}.
         
*
         
* <p>The returned comparator is serializable if the specified comparator
         
* is also serializable.
         
*
         
* @param
  
<K> the type of the map keys
         
* @param
  
<V> the type of the map values
         
* @param
  
cmp the value {@link Comparator}
         
* @return a comparator that compares {@link Map.Entry} by the value.
         
* @since 1.8
         
*/

        
public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
            
Objects.requireNonNull(cmp);
            
return (Comparator<Map.Entry<K, V>> & Serializable)
                
(c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
        
}
    
}

    
// Comparison and hashing

    
/**
     
* Compares the specified object with this map for equality.
  
Returns
     
* <tt>true</tt> if the given object is also a map and the two maps
     
* represent the same mappings.
  
More formally, two maps <tt>m1</tt> and
     
* <tt>m2</tt> represent the same mappings if
     
* <tt>m1.entrySet().equals(m2.entrySet())</tt>.
  
This ensures that the
     
* <tt>equals</tt> method works properly across different implementations
     
* of the <tt>Map</tt> interface.
     
*
     
* @param o object to be compared for equality with this map
     
* @return <tt>true</tt> if the specified object is equal to this map
     
*/

    
boolean equals(Object o);

    
/**
     
* Returns the hash code value for this map.
  
The hash code of a map is
     
* defined to be the sum of the hash codes of each entry in the map's
     
* <tt>entrySet()</tt> view.
  
This ensures that <tt>m1.equals(m2)</tt>
     
* implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
     
* <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
     
* {@link Object#hashCode}.
     
*
     
* @return the hash code value for this map
     
* @see Map.Entry#hashCode()
     
* @see Object#equals(Object)
     
* @see #equals(Object)
     
*/

    
int hashCode();

    
// Defaultable methods

    
/**
     
* Returns the value to which the specified key is mapped, or
     
* {@code defaultValue} if this map contains no mapping for the key.
     
*
     
* @implSpec
     
* The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties.
     
*
     
* @param key the key whose associated value is to be returned
     
* @param defaultValue the default mapping of the key
     
* @return the value to which the specified key is mapped, or
     
* {@code defaultValue} if this map contains no mapping for the key
     
* @throws ClassCastException if the key is of an inappropriate type for
     
* this map
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if the specified key is null and this map
     
* does not permit null keys
     
* (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @since 1.8
     
*/

    
default V getOrDefault(Object key, V defaultValue) {
        
V v;
        
return (((v = get(key)) != null) || containsKey(key))
            
? v
            
: defaultValue;
    
}

    
/**
     
* Performs the given action for each entry in this map until all entries
     
* have been processed or the action throws an exception.
   
Unless
     
* otherwise specified by the implementing class, actions are performed in
     
* the order of entry set iteration (if an iteration order is specified.)
     
* Exceptions thrown by the action are relayed to the caller.
     
*
     
* @implSpec
     
* The default implementation is equivalent to, for this {@code map}:
     
* <pre> {@code
     
* for (Map.Entry<K, V> entry : map.entrySet())
     
*action.accept(entry.getKey(), entry.getValue());
     
* }</pre>
     
*
     
* The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties.
     
*
     
* @param action The action to be performed for each entry
     
* @throws NullPointerException if the specified action is null
     
* @throws ConcurrentModificationException if an entry is found to be
     
* removed during iteration
     
* @since 1.8
     
*/

    
default void forEach(BiConsumer<? super K, ? super V> action) {
        
Objects.requireNonNull(action);
        
for (Map.Entry<K, V> entry : entrySet()) {
            
K k;
            
V v;
            
try {
                
k = entry.getKey();
                
v = entry.getValue();
            
} catch(IllegalStateException ise) {
                
// this usually means the entry is no longer in the map.
                
throw new ConcurrentModificationException(ise);
            
}
            
action.accept(k, v);
        
}
    
}

    
/**
     
* Replaces each entry's value with the result of invoking the given
     
* function on that entry until all entries have been processed or the
     
* function throws an exception.
  
Exceptions thrown by the function are
     
* relayed to the caller.
     
*
     
* @implSpec
     
* <p>The default implementation is equivalent to, for this {@code map}:
     
* <pre> {@code
     
* for (Map.Entry<K, V> entry : map.entrySet())
     
*entry.setValue(function.apply(entry.getKey(), entry.getValue()));
     
* }</pre>
     
*
     
* <p>The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties.
     
*
     
* @param function the function to apply to each entry
     
* @throws UnsupportedOperationException if the {@code set} operation
     
* is not supported by this map's entry set iterator.
     
* @throws ClassCastException if the class of a replacement value
     
* prevents it from being stored in this map
     
* @throws NullPointerException if the specified function is null, or the
     
* specified replacement value is null, and this map does not permit null
     
* values
     
* @throws ClassCastException if a replacement value is of an inappropriate
     
*
         
type for this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if function or a replacement value is null,
     
*
         
and this map does not permit null keys or values
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws IllegalArgumentException if some property of a replacement value
     
*
         
prevents it from being stored in this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws ConcurrentModificationException if an entry is found to be
     
* removed during iteration
     
* @since 1.8
     
*/

    
default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
        
Objects.requireNonNull(function);
        
for (Map.Entry<K, V> entry : entrySet()) {
            
K k;
            
V v;
            
try {
                
k = entry.getKey();
                
v = entry.getValue();
            
} catch(IllegalStateException ise) {
                
// this usually means the entry is no longer in the map.
                
throw new ConcurrentModificationException(ise);
            
}

            
// ise thrown from function is not a cme.
            
v = function.apply(k, v);

            
try {
                
entry.setValue(v);
            
} catch(IllegalStateException ise) {
                
// this usually means the entry is no longer in the map.
                
throw new ConcurrentModificationException(ise);
            
}
        
}
    
}

    
/**
     
* If the specified key is not already associated with a value (or is mapped
     
* to {@code null}) associates it with the given value and returns
     
* {@code null}, else returns the current value.
     
*
     
* @implSpec
     
* The default implementation is equivalent to, for this {@code
     
* map}:
     
*
     
* <pre> {@code
     
* V v = map.get(key);
     
* if (v == null)
     
*v = map.put(key, value);
     
*
     
* return v;
     
* }</pre>
     
*
     
* <p>The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties.
     
*
     
* @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 the specified key, or
     
*
         
{@code null} if there was no mapping for the key.
     
*
         
(A {@code null} return can also indicate that the map
     
*
         
previously associated {@code null} with the key,
     
*
         
if the implementation supports null values.)
     
* @throws UnsupportedOperationException if the {@code put} operation
     
*
         
is not supported by this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws ClassCastException if the key or value is of an inappropriate
     
*
         
type for this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if the specified key or value is null,
     
*
         
and this map does not permit null keys or values
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws IllegalArgumentException if some property of the specified key
     
*
         
or value prevents it from being stored in this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @since 1.8
     
*/

    
default V putIfAbsent(K key, V value) {
        
V v = get(key);
        
if (v == null) {
            
v = put(key, value);
        
}

        
return v;
    
}

    
/**
     
* Removes the entry for the specified key only if it is currently
     
* mapped to the specified value.
     
*
     
* @implSpec
     
* The default implementation is equivalent to, for this {@code map}:
     
*
     
* <pre> {@code
     
* if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
     
*map.remove(key);
     
*return true;
     
* } else
     
*return false;
     
* }</pre>
     
*
     
* <p>The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties.
     
*
     
* @param key key with which the specified value is associated
     
* @param value value expected to be associated with the specified key
     
* @return {@code true} if the value was removed
     
* @throws UnsupportedOperationException if the {@code remove} operation
     
*
         
is not supported by this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws ClassCastException if the key or value is of an inappropriate
     
*
         
type for this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if the specified key or value is null,
     
*
         
and this map does not permit null keys or values
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @since 1.8
     
*/

    
default boolean remove(Object key, Object value) {
        
Object curValue = get(key);
        
if (!Objects.equals(curValue, value) ||
            
(curValue == null && !containsKey(key))) {
            
return false;
        
}
        
remove(key);
        
return true;
    
}

    
/**
     
* Replaces the entry for the specified key only if currently
     
* mapped to the specified value.
     
*
     
* @implSpec
     
* The default implementation is equivalent to, for this {@code map}:
     
*
     
* <pre> {@code
     
* if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
     
*map.put(key, newValue);
     
*return true;
     
* } else
     
*return false;
     
* }</pre>
     
*
     
* The default implementation does not throw NullPointerException
     
* for maps that do not support null values if oldValue is null unless
     
* newValue is also null.
     
*
     
* <p>The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties.
     
*
     
* @param key key with which the specified value is associated
     
* @param oldValue value expected to be associated with the specified key
     
* @param newValue value to be associated with the specified key
     
* @return {@code true} if the value was replaced
     
* @throws UnsupportedOperationException if the {@code put} operation
     
*
         
is not supported by this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws ClassCastException if the class of a specified key or value
     
*
         
prevents it from being stored in this map
     
* @throws NullPointerException if a specified key or newValue is null,
     
*
         
and this map does not permit null keys or values
     
* @throws NullPointerException if oldValue is null and this map does not
     
*
         
permit null values
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws IllegalArgumentException if some property of a specified key
     
*
         
or value prevents it from being stored in this map
     
* @since 1.8
     
*/

    
default boolean replace(K key, V oldValue, V newValue) {
        
Object curValue = get(key);
        
if (!Objects.equals(curValue, oldValue) ||
            
(curValue == null && !containsKey(key))) {
            
return false;
        
}
        
put(key, newValue);
        
return true;
    
}

    
/**
     
* Replaces the entry for the specified key only if it is
     
* currently mapped to some value.
     
*
     
* @implSpec
     
* The default implementation is equivalent to, for this {@code map}:
     
*
     
* <pre> {@code
     
* if (map.containsKey(key)) {
     
*return map.put(key, value);
     
* } else
     
*return null;
     
* }</pre>
     
*
     
* <p>The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties.
      
*
     
* @param key key with which the specified value is associated
     
* @param value value to be associated with the specified key
     
* @return the previous value associated with the specified key, or
     
*
         
{@code null} if there was no mapping for the key.
     
*
         
(A {@code null} return can also indicate that the map
     
*
         
previously associated {@code null} with the key,
     
*
         
if the implementation supports null values.)
     
* @throws UnsupportedOperationException if the {@code put} operation
     
*
         
is not supported by this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws ClassCastException if the class of the specified key or value
     
*
         
prevents it from being stored in this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if the specified key or value is null,
     
*
         
and this map does not permit null keys or values
     
* @throws IllegalArgumentException if some property of the specified key
     
*
         
or value prevents it from being stored in this map
     
* @since 1.8
     
*/

    
default V replace(K key, V value) {
        
V curValue;
        
if (((curValue = get(key)) != null) || containsKey(key)) {
            
curValue = put(key, value);
        
}
        
return curValue;
    
}

    
/**
     
* If the specified key is not already associated with a value (or is mapped
     
* to {@code null}), attempts to compute its value using the given mapping
     
* function and enters it into this map unless {@code null}.
     
*
     
* <p>If the function returns {@code null} no mapping is recorded. If
     
* the function itself throws an (unchecked) exception, the
     
* exception is rethrown, and no mapping is recorded.
  
The most
     
* common usage is to construct a new object serving as an initial
     
* mapped value or memoized result, as in:
     
*
     
* <pre> {@code
     
* map.computeIfAbsent(key, k -> new Value(f(k)));
     
* }</pre>
     
*
     
* <p>Or to implement a multi-value map, {@code Map<K,Collection<V>>},
     
* supporting multiple values per key:
     
*
     
* <pre> {@code
     
* map.computeIfAbsent(key, k -> new HashSet<V>()).add(v);
     
* }</pre>
     
*
     
*
     
* @implSpec
     
* The default implementation is equivalent to the following steps for this
     
* {@code map}, then returning the current value or {@code null} if now
     
* absent:
     
*
     
* <pre> {@code
     
* if (map.get(key) == null) {
     
*V newValue = mappingFunction.apply(key);
     
*if (newValue != null)
     
*
         
map.put(key, newValue);
     
* }
     
* }</pre>
     
*
     
* <p>The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties. In particular, all implementations of
     
* subinterface
 
 
must document
     
* whether the function is applied once atomically only if the value is not
     
* present.
     
*
     
* @param key key with which the specified value is to be associated
     
* @param mappingFunction the function to compute a value
     
* @return the current (existing or computed) value associated with
     
*
         
the specified key, or null if the computed value is null
     
* @throws NullPointerException if the specified key is null and
     
*
         
this map does not support null keys, or the mappingFunction
     
*
         
is null
     
* @throws UnsupportedOperationException if the {@code put} operation
     
*
         
is not supported by this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws ClassCastException if the class of the specified key or value
     
*
         
prevents it from being stored in this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @since 1.8
     
*/

    
default V computeIfAbsent(K key,
            
Function<? super K, ? extends V> mappingFunction) {
        
Objects.requireNonNull(mappingFunction);
        
V v;
        
if ((v = get(key)) == null) {
            
V newValue;
            
if ((newValue = mappingFunction.apply(key)) != null) {
                
put(key, newValue);
                
return newValue;
            
}
        
}

        
return v;
    
}

    
/**
     
* If the value for the specified key is present and non-null, attempts to
     
* compute a new mapping given the key and its current mapped value.
     
*
     
* <p>If the function returns {@code null}, the mapping is removed.
  
If the
     
* function itself throws an (unchecked) exception, the exception is
     
* rethrown, and the current mapping is left unchanged.
    
*
     
* @implSpec
     
* The default implementation is equivalent to performing the following
     
* steps for this {@code map}, then returning the current value or
     
* {@code null} if now absent:
     
*
     
* <pre> {@code
     
* if (map.get(key) != null) {
     
*V oldValue = map.get(key);
     
*V newValue = remappingFunction.apply(key, oldValue);
     
*if (newValue != null)
     
*
         
map.put(key, newValue);
     
*else
     
*
         
map.remove(key);
     
* }
     
* }</pre>
     
*
     
* <p>The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties. In particular, all implementations of
     
* subinterface
 
 
must document
     
* whether the function is applied once atomically only if the value is not
     
* present.
     
*
     
* @param key key with which the specified value is to be associated
     
* @param remappingFunction the function to compute a value
     
* @return the new value associated with the specified key, or null if none
     
* @throws NullPointerException if the specified key is null and
     
*
         
this map does not support null keys, or the
     
*
         
remappingFunction is null
     
* @throws UnsupportedOperationException if the {@code put} operation
     
*
         
is not supported by this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws ClassCastException if the class of the specified key or value
     
*
         
prevents it from being stored in this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @since 1.8
     
*/

    
default V computeIfPresent(K key,
            
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        
Objects.requireNonNull(remappingFunction);
        
V oldValue;
        
if ((oldValue = get(key)) != null) {
            
V newValue = remappingFunction.apply(key, oldValue);
            
if (newValue != null) {
                
put(key, newValue);
                
return newValue;
            
} else {
                
remove(key);
                
return null;
            
}
        
} else {
            
return null;
        
}
    
}

    
/**
     
* Attempts to compute a mapping for the specified key and its current
     
* mapped value (or {@code null} if there is no current mapping). For
     
* example, to either create or append a {@code String} msg to a value
     
* mapping:
     
*
     
* <pre> {@code
     
* map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre>
     
* (Method {@link #merge merge()} is often simpler to use for such purposes.)
     
*
     
* <p>If the function returns {@code null}, the mapping is removed (or
     
* remains absent if initially absent).
  
If the function itself throws an
     
* (unchecked) exception, the exception is rethrown, and the current mapping
     
* is left unchanged.
     
*
     
* @implSpec
     
* The default implementation is equivalent to performing the following
     
* steps for this {@code map}, then returning the current value or
     
* {@code null} if absent:
     
*
     
* <pre> {@code
     
* V oldValue = map.get(key);
     
* V newValue = remappingFunction.apply(key, oldValue);
     
* if (oldValue != null ) {
     
*
    
if (newValue != null)
     
*
       
map.put(key, newValue);
     
*
    
else
     
*
       
map.remove(key);
     
* } else {
     
*
    
if (newValue != null)
     
*
       
map.put(key, newValue);
     
*
    
else
     
*
       
return null;
     
* }
     
* }</pre>
     
*
     
* <p>The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties. In particular, all implementations of
     
* subinterface
 
 
must document
     
* whether the function is applied once atomically only if the value is not
     
* present.
     
*
     
* @param key key with which the specified value is to be associated
     
* @param remappingFunction the function to compute a value
     
* @return the new value associated with the specified key, or null if none
     
* @throws NullPointerException if the specified key is null and
     
*
         
this map does not support null keys, or the
     
*
         
remappingFunction is null
     
* @throws UnsupportedOperationException if the {@code put} operation
     
*
         
is not supported by this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws ClassCastException if the class of the specified key or value
     
*
         
prevents it from being stored in this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @since 1.8
     
*/

    
default V compute(K key,
            
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        
Objects.requireNonNull(remappingFunction);
        
V oldValue = get(key);

        
V newValue = remappingFunction.apply(key, oldValue);
        
if (newValue == null) {
            
// delete mapping
            
if (oldValue != null || containsKey(key)) {
                
// something to remove
                
remove(key);
                
return null;
            
} else {
                
// nothing to do. Leave things as they were.
                
return null;
            
}
        
} else {
            
// add or replace old mapping
            
put(key, newValue);
            
return newValue;
        
}
    
}

    
/**
     
* If the specified key is not already associated with a value or is
     
* associated with null, associates it with the given non-null value.
     
* Otherwise, replaces the associated value with the results of the given
     
* remapping function, or removes if the result is {@code null}. This
     
* method may be of use when combining multiple mapped values for a key.
     
* For example, to either create or append a {@code String msg} to a
     
* value mapping:
     
*
     
* <pre> {@code
     
* map.merge(key, msg, String::concat)
     
* }</pre>
     
*
     
* <p>If the function returns {@code null} the mapping is removed.
  
If the
     
* function itself throws an (unchecked) exception, the exception is
     
* rethrown, and the current mapping is left unchanged.
     
*
     
* @implSpec
     
* The default implementation is equivalent to performing the following
     
* steps for this {@code map}, then returning the current value or
     
* {@code null} if absent:
     
*
     
* <pre> {@code
     
* V oldValue = map.get(key);
     
* V newValue = (oldValue == null) ? value :
     
*
              
remappingFunction.apply(oldValue, value);
     
* if (newValue == null)
     
*map.remove(key);
     
* else
     
*map.put(key, newValue);
     
* }</pre>
     
*
     
* <p>The default implementation makes no guarantees about synchronization
     
* or atomicity properties of this method. Any implementation providing
     
* atomicity guarantees must override this method and document its
     
* concurrency properties. In particular, all implementations of
     
* subinterface
 
 
must document
     
* whether the function is applied once atomically only if the value is not
     
* present.
     
*
     
* @param key key with which the resulting value is to be associated
     
* @param value the non-null value to be merged with the existing value
     
*
        
associated with the key or, if no existing value or a null value
     
*
        
is associated with the key, to be associated with the key
     
* @param remappingFunction the function to recompute a value if present
     
* @return the new value associated with the specified key, or null if no
     
*
         
value is associated with the key
     
* @throws UnsupportedOperationException if the {@code put} operation
     
*
         
is not supported by this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws ClassCastException if the class of the specified key or value
     
*
         
prevents it from being stored in this map
     
*
         
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
     
* @throws NullPointerException if the specified key is null and this map
     
*
         
does not support null keys or the value or remappingFunction is
     
*
         
null
     
* @since 1.8
     
*/

    
default V merge(K key, V value,
            
BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
        
Objects.requireNonNull(remappingFunction);
        
Objects.requireNonNull(value);
        
V oldValue = get(key);
        
V newValue = (oldValue == null) ? value :
                   
remappingFunction.apply(oldValue, value);
        
if(newValue == null) {
            
remove(key);
        
} else {
            
put(key, newValue);
        
}
        
return newValue;
    
}
}