@GwtCompatible public abstract class ForwardingMap<K,V> extends ForwardingObject implements Map<K,V>
Warning: The methods of ForwardingMap
forward indiscriminately to the
methods of the delegate. For example, overriding put(K, V)
alone will not change the
behavior of putAll(java.util.Map<? extends K, ? extends V>)
, which can lead to unexpected behavior. In this case, you should
override putAll
as well, either providing your own implementation, or delegating to the
provided standardPutAll
method.
default
method warning: This class does not forward calls to default
methods. Instead, it inherits their default implementations. When those implementations
invoke methods, they invoke methods on the ForwardingMap
.
Each of the standard
methods, where appropriate, use Objects.equal(java.lang.Object, java.lang.Object)
to test
equality for both keys and values. This may not be the desired behavior for map implementations
that use non-standard notions of key equality, such as a SortedMap
whose comparator is
not consistent with equals
.
The standard
methods and the collection views they return are not guaranteed to be
thread-safe, even when all of the methods that they depend on are thread-safe.
Modifier and Type | Class and Description |
---|---|
protected class |
ForwardingMap.StandardEntrySet
A sensible implementation of
Map.entrySet() in terms of the following methods: clear() , containsKey(java.lang.Object) , get(java.lang.Object) , isEmpty() , remove(java.lang.Object) , and size() . |
protected class |
ForwardingMap.StandardKeySet
A sensible implementation of
Map.keySet() in terms of the following methods: clear() , containsKey(java.lang.Object) , isEmpty() , remove(java.lang.Object) , size() , and the Set.iterator() method of
entrySet() . |
protected class |
ForwardingMap.StandardValues
A sensible implementation of
Map.values() in terms of the following methods: clear() , containsValue(java.lang.Object) , isEmpty() ,
size() , and the Set.iterator() method of entrySet() . |
Modifier | Constructor and Description |
---|---|
protected |
ForwardingMap()
Constructor for use by subclasses.
|
Modifier and Type | Method and Description |
---|---|
void |
clear()
Removes all of the mappings from this map (optional operation).
|
boolean |
containsKey(@Nullable Object key)
Returns true if this map contains a mapping for the specified
key.
|
boolean |
containsValue(@Nullable Object value)
Returns true if this map maps one or more keys to the
specified value.
|
protected abstract Map<K,V> |
delegate()
Returns the backing delegate instance that methods are forwarded to.
|
Set<Map.Entry<K,V>> |
entrySet()
Returns a
Set view of the mappings contained in this map. |
boolean |
equals(@Nullable Object object)
Indicates whether some other object is "equal to" this one.
|
V |
get(@Nullable Object key)
Returns the value to which the specified key is mapped,
or
null if this map contains no mapping for the key. |
int |
hashCode()
Returns a hash code value for the object.
|
boolean |
isEmpty()
Returns true if this map contains no key-value mappings.
|
Set<K> |
keySet()
Returns a
Set view of the keys contained in this map. |
V |
put(K key,
V value)
Associates the specified value with the specified key in this map
(optional operation).
|
void |
putAll(Map<? extends K,? extends V> map)
Copies all of the mappings from the specified map to this map
(optional operation).
|
V |
remove(Object object)
Removes the mapping for a key from this map if it is present
(optional operation).
|
int |
size()
Returns the number of key-value mappings in this map.
|
protected void |
standardClear()
|
protected boolean |
standardContainsKey(@Nullable Object key)
A sensible, albeit inefficient, definition of
containsKey(java.lang.Object) in terms of the iterator method of entrySet() . |
protected boolean |
standardContainsValue(@Nullable Object value)
A sensible definition of
containsValue(java.lang.Object) in terms of the iterator method of
entrySet() . |
protected boolean |
standardEquals(@Nullable Object object)
|
protected int |
standardHashCode()
|
protected boolean |
standardIsEmpty()
|
protected void |
standardPutAll(Map<? extends K,? extends V> map)
A sensible definition of
putAll(Map) in terms of put(Object, Object) . |
protected V |
standardRemove(@Nullable Object key)
A sensible, albeit inefficient, definition of
remove(java.lang.Object) in terms of the iterator
method of entrySet() . |
protected String |
standardToString()
|
Collection<V> |
values()
Returns a
Collection view of the values contained in this map. |
toString
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll
protected ForwardingMap()
protected abstract Map<K,V> delegate()
ForwardingObject
ForwardingSet.delegate()
. Concrete subclasses override this method to supply the
instance being decorated.delegate
in class ForwardingObject
public int size()
java.util.Map
public boolean isEmpty()
java.util.Map
@CanIgnoreReturnValue public V remove(Object object)
java.util.Map
(key==null ? k==null : key.equals(k))
, that mapping
is removed. (The map can contain at most one such mapping.)
Returns the value to which this map previously associated the key, or null if the map contained no mapping for the key.
If this map permits null values, then a return value of null does not necessarily indicate that the map contained no mapping for the key; it's also possible that the map explicitly mapped the key to null.
The map will not contain a mapping for the specified key once the call returns.
public void clear()
java.util.Map
public boolean containsKey(@Nullable Object key)
java.util.Map
containsKey
in interface Map<K,V>
key
- key whose presence in this map is to be testedpublic boolean containsValue(@Nullable Object value)
java.util.Map
containsValue
in interface Map<K,V>
value
- value whose presence in this map is to be testedpublic V get(@Nullable Object key)
java.util.Map
null
if this map contains no mapping for the key.
More formally, if this map contains a mapping from a key
k
to a value v
such that (key==null ? k==null :
key.equals(k))
, then this method returns v
; otherwise
it returns null
. (There can be at most one such mapping.)
If this map permits null values, then a return value of
null
does not necessarily indicate that the map
contains no mapping for the key; it's also possible that the map
explicitly maps the key to null
. The containsKey
operation may be used to distinguish these two cases.
@CanIgnoreReturnValue public V put(K key, V value)
java.util.Map
m.containsKey(k)
would return
true.)put
in interface Map<K,V>
key
- key with which the specified value is to be associatedvalue
- value to be associated with the specified keypublic void putAll(Map<? extends K,? extends V> map)
java.util.Map
put(k, v)
on this map once
for each mapping from key k to value v in the
specified map. The behavior of this operation is undefined if the
specified map is modified while the operation is in progress.public Set<K> keySet()
java.util.Map
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 remove operation), the results of
the iteration are undefined. The set supports element removal,
which removes the corresponding mapping from the map, via the
Iterator.remove, Set.remove,
removeAll, retainAll, and clear
operations. It does not support the add or addAll
operations.public Collection<V> values()
java.util.Map
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 remove operation),
the results of the iteration are undefined. The collection
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove,
Collection.remove, removeAll,
retainAll and clear operations. It does not
support the add or addAll operations.public Set<Map.Entry<K,V>> entrySet()
java.util.Map
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 remove operation, or through the
setValue 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 Iterator.remove,
Set.remove, removeAll, retainAll and
clear operations. It does not support the
add or addAll operations.public boolean equals(@Nullable Object object)
java.lang.Object
The equals
method implements an equivalence relation
on non-null object references:
x
, x.equals(x)
should return
true
.
x
and y
, x.equals(y)
should return true
if and only if
y.equals(x)
returns true
.
x
, y
, and z
, if
x.equals(y)
returns true
and
y.equals(z)
returns true
, then
x.equals(z)
should return true
.
x
and y
, multiple invocations of
x.equals(y)
consistently return true
or consistently return false
, provided no
information used in equals
comparisons on the
objects is modified.
x
,
x.equals(null)
should return false
.
The equals
method for class Object
implements
the most discriminating possible equivalence relation on objects;
that is, for any non-null reference values x
and
y
, this method returns true
if and only
if x
and y
refer to the same object
(x == y
has the value true
).
Note that it is generally necessary to override the hashCode
method whenever this method is overridden, so as to maintain the
general contract for the hashCode
method, which states
that equal objects must have equal hash codes.
public int hashCode()
java.lang.Object
HashMap
.
The general contract of hashCode
is:
hashCode
method
must consistently return the same integer, provided no information
used in equals
comparisons on the object is modified.
This integer need not remain consistent from one execution of an
application to another execution of the same application.
equals(Object)
method, then calling the hashCode
method on each of
the two objects must produce the same integer result.
Object.equals(java.lang.Object)
method, then calling the hashCode
method on each of the
two objects must produce distinct integer results. However, the
programmer should be aware that producing distinct integer results
for unequal objects may improve the performance of hash tables.
As much as is reasonably practical, the hashCode method defined by
class Object
does return distinct integers for distinct
objects. (This is typically implemented by converting the internal
address of the object into an integer, but this implementation
technique is not required by the
Java™ programming language.)
hashCode
in interface Map<K,V>
hashCode
in class Object
Object.equals(java.lang.Object)
,
System.identityHashCode(java.lang.Object)
protected void standardPutAll(Map<? extends K,? extends V> map)
putAll(Map)
in terms of put(Object, Object)
. If you
override put(Object, Object)
, you may wish to override putAll(Map)
to forward
to this implementation.@Beta protected V standardRemove(@Nullable Object key)
remove(java.lang.Object)
in terms of the iterator
method of entrySet()
. If you override entrySet()
, you may wish to override remove(java.lang.Object)
to forward to this implementation.
Alternately, you may wish to override remove(java.lang.Object)
with keySet().remove
, assuming
that approach would not lead to an infinite loop.
protected void standardClear()
clear()
in terms of the iterator
method of entrySet()
. In many cases, you may wish to override clear()
to forward to this
implementation.@Beta protected boolean standardContainsKey(@Nullable Object key)
containsKey(java.lang.Object)
in terms of the iterator
method of entrySet()
. If you override entrySet()
, you may wish to
override containsKey(java.lang.Object)
to forward to this implementation.protected boolean standardContainsValue(@Nullable Object value)
containsValue(java.lang.Object)
in terms of the iterator
method of
entrySet()
. If you override entrySet()
, you may wish to override containsValue(java.lang.Object)
to forward to this implementation.protected boolean standardIsEmpty()
isEmpty()
in terms of the iterator
method of entrySet()
. If you override entrySet()
, you may wish to override isEmpty()
to
forward to this implementation.protected boolean standardEquals(@Nullable Object object)
equals(java.lang.Object)
in terms of the equals
method of entrySet()
. If you override entrySet()
, you may wish to override equals(java.lang.Object)
to
forward to this implementation.protected int standardHashCode()
hashCode()
in terms of the iterator
method of entrySet()
. If you override entrySet()
, you may wish to override hashCode()
to
forward to this implementation.protected String standardToString()
ForwardingObject.toString()
in terms of the iterator
method of entrySet()
. If you override entrySet()
, you may wish to override ForwardingObject.toString()
to
forward to this implementation.Copyright © 2010–2019. All rights reserved.