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## 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

    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:

  - 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 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`

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