@GwtCompatible public abstract class ForwardingMap<K,V> extends ForwardingObject implements Map<K,V>
A map which forwards all its method calls to another map. Subclasses should override one or more methods to modify the behavior of the backing map as desired per the decorator pattern.
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.
Each of the standard methods, where appropriate, use Objects.equals(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() |
boolean |
containsKey(Object key) |
boolean |
containsValue(Object value) |
protected abstract Map<K,V> |
delegate()
Returns the backing delegate instance that methods are forwarded to.
|
Set<Map.Entry<K,V>> |
entrySet() |
boolean |
equals(Object object) |
V |
get(Object key) |
int |
hashCode() |
boolean |
isEmpty() |
Set<K> |
keySet() |
V |
put(K key,
V value) |
void |
putAll(Map<? extends K,? extends V> map) |
V |
remove(Object object) |
int |
size() |
protected void |
standardClear()
|
protected boolean |
standardContainsKey(Object key)
A sensible, albeit inefficient, definition of
containsKey(java.lang.Object) in terms of the iterator method of entrySet(). |
protected boolean |
standardContainsValue(Object value)
A sensible definition of
containsValue(java.lang.Object) in terms of the iterator method of entrySet(). |
protected boolean |
standardEquals(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(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() |
toStringclone, finalize, getClass, notify, notifyAll, wait, wait, waitcompute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAllprotected abstract Map<K,V> delegate()
ForwardingObjectReturns the backing delegate instance that methods are forwarded to. Abstract subclasses generally override this method with an abstract method that has a more specific return type, such as ForwardingSet.delegate(). Concrete subclasses override this method to supply the instance being decorated.
delegate in class ForwardingObjectpublic boolean containsKey(@Nullable Object key)
containsKey in interface Map<K,V>public boolean containsValue(@Nullable Object value)
containsValue in interface Map<K,V>public int hashCode()
protected void standardPutAll(Map<? extends K,? extends V> map)
A sensible definition of 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)
A sensible, albeit inefficient, definition of 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()
A sensible definition of 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)
A sensible, albeit inefficient, definition of 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)
A sensible definition of 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()
A sensible definition of 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)
A sensible definition of 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()
A sensible definition of 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()
A sensible definition of 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.