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

java.lang.Object
  com.google.common.collect.ForwardingObject
      com.google.common.collect.ForwardingMap<K,V>

All Implemented Interfaces:

Map<K,V>

Direct Known Subclasses:

EnumBiMap, EnumHashBiMap, ForwardingConcurrentMap, ForwardingSortedMap, HashBiMap, ImmutableClassToInstanceMap, MutableClassToInstanceMap

@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), 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.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.

Since:

2 (imported from Google Collections Library)

Author:

Kevin Bourrillion, Jared Levy, Louis Wasserman

ForwardingMap

protected ForwardingMap()

Constructor for use by subclasses.

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:

• It is reflexive: for any non-null reference value x, x.equals(x) should return true.
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
• It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
• It is consistent: for any non-null reference values 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.
• For any non-null reference value 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.

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:

• Whenever it is invoked on the same object more than once during an execution of a Java application, the 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.
• If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
• It is not required that if two objects are unequal according to the 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 hashtables.

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^TM 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

standardPutAll

@Beta
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.

Since:

7

standardRemove

@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.

Since:

7

standardClear

@Beta
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.

Since:

7

standardKeySet

@Beta
protected Set<K> standardKeySet()

A sensible definition of keySet() in terms of the following methods: clear(), containsKey(java.lang.Object), isEmpty(), remove(java.lang.Object), size(), and the iterator method of entrySet(). In many cases, you may wish to override keySet() to forward to this implementation.

Since:

7

standardContainsKey

@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.

Since:

7

standardValues

@Beta
protected Collection<V> standardValues()

A sensible definition of values() in terms of the following methods: clear(), containsValue(java.lang.Object), isEmpty(), size(), and the iterator method of entrySet(). In many cases, you may wish to override values() to forward to this implementation.

Since:

7

standardContainsValue

@Beta
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.

Since:

7

standardEntrySet

@Beta
protected Set<Map.Entry<K,V>> standardEntrySet(Supplier<Iterator<Map.Entry<K,V>>> entryIteratorSupplier)

A sensible definition of entrySet() in terms of the specified Supplier, which is used to generate iterators over the entry set, and in terms of the following methods: clear(), containsKey(java.lang.Object), get(java.lang.Object), isEmpty(), remove(java.lang.Object), and size(). In many cases, you may wish to override entrySet() to forward to this implementation.

Parameters:

entryIteratorSupplier - A creator for iterators over the entry set. Each call to get must return an iterator that will traverse the entire entry set.

Since:

7

standardIsEmpty

@Beta
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.

Since:

7

standardEquals

@Beta
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.

Since:

7

standardHashCode

@Beta
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.

Since:

7

standardToString

@Beta
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.

Since:

7