com.google.common.collect
Class ForwardingMap<K,V>

java.lang.Object
  extended by com.google.common.collect.ForwardingObject
      extended by com.google.common.collect.ForwardingMap<K,V>
All Implemented Interfaces:
Map<K,V>
Direct Known Subclasses:
EnumBiMap, EnumHashBiMap, ForwardingConcurrentMap, ForwardingSortedMap, HashBiMap, ImmutableClassToInstanceMap, MutableClassToInstanceMap

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.

Author:
Kevin Bourrillion, Jared Levy
See Also:
ForwardingObject

Nested Class Summary
 
Nested classes/interfaces inherited from interface java.util.Map
Map.Entry<K,V>
 
Constructor Summary
ForwardingMap()
           
 
Method Summary
 void clear()
          Removes all of the mappings from this map (optional operation).
 boolean containsKey(Object key)
          Returns true if this map contains a mapping for the specified key.
 boolean containsValue(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(Object object)
          Indicates whether some other object is "equal to" this one.
 V get(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.
 Collection<V> values()
          Returns a Collection view of the values contained in this map.
 
Methods inherited from class com.google.common.collect.ForwardingObject
toString
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

ForwardingMap

public ForwardingMap()
Method Detail

delegate

protected abstract Map<K,V> delegate()
Description copied from class: ForwardingObject
Returns 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.

Specified by:
delegate in class ForwardingObject

size

public int size()
Description copied from interface: java.util.Map
Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Specified by:
size in interface Map<K,V>
Returns:
the number of key-value mappings in this map

isEmpty

public boolean isEmpty()
Description copied from interface: java.util.Map
Returns true if this map contains no key-value mappings.

Specified by:
isEmpty in interface Map<K,V>
Returns:
true if this map contains no key-value mappings

remove

public V remove(Object object)
Description copied from interface: java.util.Map
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 k to value v such that (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.

Specified by:
remove in interface Map<K,V>
Parameters:
object - key whose mapping is to be removed from the map
Returns:
the previous value associated with key, or null if there was no mapping for key.

clear

public void clear()
Description copied from interface: java.util.Map
Removes all of the mappings from this map (optional operation). The map will be empty after this call returns.

Specified by:
clear in interface Map<K,V>

containsKey

public boolean containsKey(Object key)
Description copied from interface: java.util.Map
Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains a mapping for a key k such that (key==null ? k==null : key.equals(k)). (There can be at most one such mapping.)

Specified by:
containsKey in interface Map<K,V>
Parameters:
key - key whose presence in this map is to be tested
Returns:
true if this map contains a mapping for the specified key

containsValue

public boolean containsValue(Object value)
Description copied from interface: java.util.Map
Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations of the Map interface.

Specified by:
containsValue in interface Map<K,V>
Parameters:
value - value whose presence in this map is to be tested
Returns:
true if this map maps one or more keys to the specified value

get

public V get(Object key)
Description copied from interface: java.util.Map
Returns the value to which the specified key is mapped, or 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.

Specified by:
get in interface Map<K,V>
Parameters:
key - the key whose associated value is to be returned
Returns:
the value to which the specified key is mapped, or null if this map contains no mapping for the key

put

public V put(K key,
             V value)
Description copied from interface: java.util.Map
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 m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.)

Specified by:
put in interface Map<K,V>
Parameters:
key - key with which the specified value is to be associated
value - value to be associated with the specified key
Returns:
the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key, if the implementation supports null values.)

putAll

public void putAll(Map<? extends K,? extends V> map)
Description copied from interface: java.util.Map
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 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.

Specified by:
putAll in interface Map<K,V>
Parameters:
map - mappings to be stored in this map

keySet

public Set<K> keySet()
Description copied from interface: java.util.Map
Returns a 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.

Specified by:
keySet in interface Map<K,V>
Returns:
a set view of the keys contained in this map

values

public Collection<V> values()
Description copied from interface: java.util.Map
Returns a 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.

Specified by:
values in interface Map<K,V>
Returns:
a collection view of the values contained in this map

entrySet

public Set<Map.Entry<K,V>> entrySet()
Description copied from interface: java.util.Map
Returns a 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.

Specified by:
entrySet in interface Map<K,V>
Returns:
a set view of the mappings contained in this map

equals

public boolean equals(@Nullable
                      Object object)
Description copied from class: java.lang.Object
Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

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.

Specified by:
equals in interface Map<K,V>
Overrides:
equals in class Object
Parameters:
object - the reference object with which to compare.
Returns:
true if this object is the same as the obj argument; false otherwise.
See Also:
Object.hashCode(), Hashtable

hashCode

public int hashCode()
Description copied from class: java.lang.Object
Returns a hash code value for the object. This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable.

The general contract of hashCode is:

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 JavaTM programming language.)

Specified by:
hashCode in interface Map<K,V>
Overrides:
hashCode in class Object
Returns:
a hash code value for this object.
See Also:
Object.equals(java.lang.Object), Hashtable