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## org.apache.commons.collections.map
Class SingletonMap

    java.lang.Object
      |
      +--org.apache.commons.collections.map.SingletonMap

All Implemented Interfaces:
  BoundedMap, Cloneable, IterableMap, KeyValue, Map, OrderedMap, Serializable

public class SingletonMap
extends Object
implements OrderedMap, BoundedMap, KeyValue, Serializable, Cloneable

A `Map` implementation that holds a single item and is fixed size.

The single key/value pair is specified at creation. The map is fixed size so any action that would change the size is disallowed. However, the `put` or `setValue` methods can change the value associated with the key.

If trying to remove or clear the map, an UnsupportedOperationException is thrown. If trying to put a new mapping into the map, an IllegalArgumentException is thrown. The put method will only suceed if the key specified is the same as the singleton key.

The key and value can be obtained by:

- normal Map methods and views
- the `MapIterator`, see `mapIterator()`
- the `KeyValue` interface (just cast - no object creation)

Since:
  Commons Collections 3.1
Version:
  $Revision: 1.1 $ $Date: 2004/04/09 14:46:35 $
Author:
  Stephen Colebourne
See Also:
  Serialized Form

Constructor Summary
`SingletonMap()` Constructor that creates a map of `null` to `null`.
`SingletonMap(KeyValue keyValue)` Constructor specifying the key and value as a `KeyValue`.
`SingletonMap(Map.Entry entry)` Constructor specifying the key and value as a `MapEntry`.
`SingletonMap(Map map)` Constructor copying elements from another map.
`SingletonMap(Object key, Object value)` Constructor specifying the key and value.

Method Summary
`void` | `clear()` Unsupported operation.
`Object` | `clone()` Clones the map without cloning the key or value.
`boolean` | `containsKey(Object key)` Checks whether the map contains the specified key.
`boolean` | `containsValue(Object value)` Checks whether the map contains the specified value.
`Set` | `entrySet()` Gets the entrySet view of the map.
`boolean` | `equals(Object obj)` Compares this map with another.
`Object` | `firstKey()` Gets the first (and only) key in the map.
`Object` | `get(Object key)` Gets the value mapped to the key specified.
`Object` | `getKey()` Gets the key.
`Object` | `getValue()` Gets the value.
`int` | `hashCode()` Gets the standard Map hashCode.
`boolean` | `isEmpty()` Checks whether the map is currently empty, which it never is.
`protected boolean` | `isEqualKey(Object key)` Compares the specified key to the stored key.
`protected boolean` | `isEqualValue(Object value)` Compares the specified value to the stored value.
`boolean` | `isFull()` Is the map currently full, always true.
`Set` | `keySet()` Gets the unmodifiable keySet view of the map.
`Object` | `lastKey()` Gets the last (and only) key in the map.
`MapIterator` | `mapIterator()` Gets an iterator over the map.
`int` | `maxSize()` Gets the maximum size of the map, always 1.
`Object` | `nextKey(Object key)` Gets the next key after the key specified, always null.
`OrderedMapIterator` | `orderedMapIterator()` Obtains an `OrderedMapIterator` over the map.
`Object` | `previousKey(Object key)` Gets the previous key before the key specified, always null.
`Object` | `put(Object key, Object value)` Puts a key-value mapping into this map where the key must match the existing key.
`void` | `putAll(Map map)` Puts the values from the specified map into this map.
`Object` | `remove(Object key)` Unsupported operation.
`Object` | `setValue(Object value)` Sets the value.
`int` | `size()` Gets the size of the map, always 1.
`String` | `toString()` Gets the map as a String.
`Collection` | `values()` Gets the unmodifiable values view of the map.

Methods inherited from class java.lang.Object
`finalize, getClass, notify, notifyAll, wait, wait, wait`

Constructor Detail

### SingletonMap

    public SingletonMap()

  Constructor that creates a map of `null` to `null`.

### SingletonMap

    public SingletonMap(Object key,
                        Object value)

  Constructor specifying the key and value.

Parameters:
  `key` - the key to use
  `value` - the value to use

### SingletonMap

    public SingletonMap(KeyValue keyValue)

  Constructor specifying the key and value as a `KeyValue`.

Parameters:
  `keyValue` - the key value pair to use

### SingletonMap

    public SingletonMap(Map.Entry entry)

  Constructor specifying the key and value as a `MapEntry`.

### SingletonMap

    public SingletonMap(Map map)

  Constructor copying elements from another map.

Parameters:
  `map` - the map to copy, must be size 1
Throws:
  `NullPointerException` - if the map is null
  `IllegalArgumentException` - if the size is not 1

Method Detail

### getKey

    public Object getKey()

  Gets the key.

  Specified by:
    `getKey` in interface `KeyValue`
  Returns:
    the key

### getValue

    public Object getValue()

  Gets the value.

  Specified by:
    `getValue` in interface `KeyValue`
  Returns:
    the value

### setValue

    public Object setValue(Object value)

  Sets the value.

  Parameters:
    `value` - the new value to set
  Returns:
    the old value

### isFull

    public boolean isFull()

  Is the map currently full, always true.

  Specified by:
    `isFull` in interface `BoundedMap`
  Returns:
    true always

### maxSize

    public int maxSize()

  Gets the maximum size of the map, always 1.

  Specified by:
    `maxSize` in interface `BoundedMap`
  Returns:
    1 always

### get

    public Object get(Object key)

  Gets the value mapped to the key specified.

  Specified by:
    `get` in interface `Map`
  Parameters:
    `key` - the key
  Returns:
    the mapped value, null if no match

### size

    public int size()

  Gets the size of the map, always 1.

  Specified by:
    `size` in interface `Map`
  Returns:
    the size of 1

### isEmpty

    public boolean isEmpty()

  Checks whether the map is currently empty, which it never is.

  Specified by:
    `isEmpty` in interface `Map`
  Returns:
    false always

### containsKey

    public boolean containsKey(Object key)

  Checks whether the map contains the specified key.

  Specified by:
    `containsKey` in interface `Map`
  Parameters:
    `key` - the key to search for
  Returns:
    true if the map contains the key

### containsValue

    public boolean containsValue(Object value)

  Checks whether the map contains the specified value.

  Specified by:
    `containsValue` in interface `Map`
  Parameters:
    `value` - the value to search for
  Returns:
    true if the map contains the key

### put

    public Object put(Object key,
                      Object value)

  Puts a key-value mapping into this map where the key must match the existing key.

  An IllegalArgumentException is thrown if the key does not match as the map is fixed size.

  Specified by:
    `put` in interface `Map`
  Parameters:
    `key` - the key to set, must be the key of the map
    `value` - the value to set
  Returns:
    the value previously mapped to this key, null if none
  Throws:
    `IllegalArgumentException` - if the key does not match

### putAll

    public void putAll(Map map)

  Puts the values from the specified map into this map.

  The map must be of size 0 or size 1. If it is size 1, the key must match the key of this map otherwise an IllegalArgumentException is thrown.

  Specified by:
    `putAll` in interface `Map`
  Parameters:
    `map` - the map to add, must be size 0 or 1, and the key must match
  Throws:
    `NullPointerException` - if the map is null
    `IllegalArgumentException` - if the key does not match

### remove

    public Object remove(Object key)

  Unsupported operation.

  Specified by:
    `remove` in interface `Map`
  Parameters:
    `key` - the mapping to remove
  Returns:
    the value mapped to the removed key, null if key not in map
  Throws:
    `UnsupportedOperationException` - always

### clear

    public void clear()

  Unsupported operation.

  Specified by:
    `clear` in interface `Map`

### entrySet

    public Set entrySet()

  Gets the entrySet view of the map. Changes made via `setValue` affect this map. To simply iterate through the entries, use `mapIterator()`.

  Specified by:
    `entrySet` in interface `Map`
  Returns:
    the entrySet view

### keySet

    public Set keySet()

  Gets the unmodifiable keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, use `mapIterator()`.

  Specified by:
    `keySet` in interface `Map`
  Returns:
    the keySet view

### values

    public Collection values()

  Gets the unmodifiable values view of the map. Changes made to the view affect this map. To simply iterate through the values, use `mapIterator()`.

  Specified by:
    `values` in interface `Map`
  Returns:
    the values view

### mapIterator

    public MapIterator mapIterator()

  Gets an iterator over the map. Changes made to the iterator using `setValue` affect this map. The `remove` method is unsupported.

  A MapIterator returns the keys in the map. It also provides convenient methods to get the key and value, and set the value. It avoids the need to create an entrySet/keySet/values object. It also avoids creating the Map Entry object.

  Specified by:
    `mapIterator` in interface `IterableMap`
  Returns:
    the map iterator

### orderedMapIterator

    public OrderedMapIterator orderedMapIterator()

  Obtains an `OrderedMapIterator` over the map.

  A ordered map iterator is an efficient way of iterating over maps in both directions.

  Specified by:
    `orderedMapIterator` in interface `OrderedMap`
  Returns:
    an ordered map iterator

### firstKey

    public Object firstKey()

  Gets the first (and only) key in the map.

  Specified by:
    `firstKey` in interface `OrderedMap`
  Returns:
    the key

### lastKey

    public Object lastKey()

  Gets the last (and only) key in the map.

  Specified by:
    `lastKey` in interface `OrderedMap`
  Returns:
    the key

### nextKey

    public Object nextKey(Object key)

  Gets the next key after the key specified, always null.

  Specified by:
    `nextKey` in interface `OrderedMap`
  Parameters:
    `key` - the next key
  Returns:
    null always

### previousKey

    public Object previousKey(Object key)

  Gets the previous key before the key specified, always null.

  Specified by:
    `previousKey` in interface `OrderedMap`
  Parameters:
    `key` - the next key
  Returns:
    null always

### isEqualKey

    protected boolean isEqualKey(Object key)

  Compares the specified key to the stored key.

  Parameters:
    `key` - the key to compare
  Returns:
    true if equal

### isEqualValue

    protected boolean isEqualValue(Object value)

  Compares the specified value to the stored value.

  Parameters:
    `value` - the value to compare
  Returns:
    true if equal

### clone

    public Object clone()

  Clones the map without cloning the key or value.

  Overrides:
    `clone` in class `Object`
  Returns:
    a shallow clone

### equals

    public boolean equals(Object obj)

  Compares this map with another.

  Specified by:
    `equals` in interface `Map`
  Overrides:
    `equals` in class `Object`
  Parameters:
    `obj` - the object to compare to
  Returns:
    true if equal

### hashCode

    public int hashCode()

  Gets the standard Map hashCode.

  Specified by:
    `hashCode` in interface `Map`
  Overrides:
    `hashCode` in class `Object`
  Returns:
    the hash code defined in the Map interface

### toString

    public String toString()

  Gets the map as a String.

  Overrides:
    `toString` in class `Object`
  Returns:
    a string version of the map

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