JavaTM 2 Platform Std. Ed. v1.5.0
java.util
Class EnumMap<K extends Enum<K>,V>
java.lang.Object
java.util.AbstractMap<K,V>
java.util.EnumMap<K,V>
- All Implemented Interfaces:
- Serializable, Cloneable, Map<K,V>
public class EnumMap<K extends Enum<K>,V> - extends AbstractMap<K,V>
- implements Serializable, Cloneable
A specialized Map implementation for use with enum type keys. All
of the keys in an enum map must come from a single enum type that is
specified, explicitly or implicitly, when the map is created. Enum maps
are represented internally as arrays. This representation is extremely
compact and efficient.
Enum maps are maintained in the natural order of their keys
(the order in which the enum constants are declared). This is reflected
in the iterators returned by the collections views (keySet() ,
entrySet() , and values() ).
Iterators returned by the collection views are weakly consistent:
they will never throw ConcurrentModificationException and they may
or may not show the effects of any modifications to the map that occur while
the iteration is in progress.
Null keys are not permitted. Attempts to insert a null key will
throw NullPointerException . Attempts to test for the
presence of a null key or to remove one will, however, function properly.
Null values are permitted.
Like most collection implementations EnumMap is not
synchronized. If multiple threads access an enum map concurrently, and at
least one of the threads modifies the map, it should be synchronized
externally. This is typically accomplished by synchronizing on some
object that naturally encapsulates the enum map. If no such object exists,
the map should be "wrapped" using the Collections.synchronizedMap(java.util.Map)
method. This is best done at creation time, to prevent accidental
unsynchronized access:
Map<EnumKey, V> m = Collections.synchronizedMap(new EnumMap(...));
Implementation note: All basic operations execute in constant time.
They are likely (though not guaranteed) to be faster than their
HashMap counterparts.
This class is a member of the
Java Collections Framework.
- Since:
- 1.5
- See Also:
EnumSet ,
Serialized Form
Nested classes/interfaces inherited from interface java.util.Map |
Map.Entry<K,V> |
Constructor Summary |
EnumMap(Class<K> keyType)
Creates an empty enum map with the specified key type. |
EnumMap(EnumMap<K,? extends V> m)
Creates an enum map with the same key type as the specified enum
map, initially containing the same mappings (if any). |
EnumMap(Map<K,? extends V> m)
Creates an enum map initialized from the specified map. |
Method Summary |
void |
clear()
Removes all mappings from this map. |
EnumMap<K,V> |
clone()
Returns a shallow copy of this enum map. |
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. |
Set<Map.Entry<K,V>> |
entrySet()
Returns a Set view of the mappings contained in this map. |
boolean |
equals(Object o)
Compares the specified object with this map for equality. |
V |
get(Object key)
Returns the value to which this map maps the specified key, or null
if this map contains no mapping for the specified key. |
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. |
void |
putAll(Map<? extends K,? extends V> m)
Copies all of the mappings from the specified map to this map. |
V |
remove(Object key)
Removes the mapping for this key from this map if present. |
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. |
EnumMap
public EnumMap(Class<K> keyType)
- Creates an empty enum map with the specified key type.
- Parameters:
keyType - the class object of the key type for this enum map
- Throws:
NullPointerException - if keyType is null
EnumMap
public EnumMap(EnumMap<K,? extends V> m)
- Creates an enum map with the same key type as the specified enum
map, initially containing the same mappings (if any).
- Parameters:
m - the enum map from which to initialize this enum map
- Throws:
NullPointerException - if m is null
EnumMap
public EnumMap(Map<K,? extends V> m)
- Creates an enum map initialized from the specified map. If the
specified map is an EnumMap instance, this constructor behaves
identically to
EnumMap(EnumMap) . Otherwise, the specified map
must contain at least one mapping (in order to determine the new
enum map's key type).
- Parameters:
m - the map from which to initialize this enum map
- Throws:
IllegalArgumentException - if m is not an
EnumMap instance and contains no mappings
NullPointerException - if m is null
size
public int size()
- Returns the number of key-value mappings in this map.
- Specified by:
size in interface Map<K extends Enum<K>,V> - Overrides:
size in class AbstractMap<K extends Enum<K>,V>
- Returns:
- the number of key-value mappings in this map
containsValue
public boolean containsValue(Object value)
- Returns true if this map maps one or more keys to the
specified value.
- Specified by:
containsValue in interface Map<K extends Enum<K>,V> - Overrides:
containsValue in class AbstractMap<K extends Enum<K>,V>
- Parameters:
value - the value whose presence in this map is to be tested
- Returns:
- true if this map maps one or more keys to this value
containsKey
public boolean containsKey(Object key)
- Returns true if this map contains a mapping for the specified
key.
- Specified by:
containsKey in interface Map<K extends Enum<K>,V> - Overrides:
containsKey in class AbstractMap<K extends Enum<K>,V>
- Parameters:
key - the key whose presence in this map is to be tested
- Returns:
- true if this map contains a mapping for the specified
key
get
public V get(Object key)
- Returns the value to which this map maps the specified key, or null
if this map contains no mapping for the specified key.
- Specified by:
get in interface Map<K extends Enum<K>,V> - Overrides:
get in class AbstractMap<K extends Enum<K>,V>
- Parameters:
key - the key whose associated value is to be returned
- Returns:
- the value to which this map maps the specified key, or null
if this map contains no mapping for the specified key
- See Also:
AbstractMap.containsKey(Object)
put
public V put(K key,
V value)
- Associates the specified value with the specified key in this map.
If the map previously contained a mapping for this key, the old
value is replaced.
- Specified by:
put in interface Map<K extends Enum<K>,V> - Overrides:
put in class AbstractMap<K extends Enum<K>,V>
- Parameters:
key - the key with which the specified value is to be associatedvalue - the value to be associated with the specified key
- Returns:
- the previous value associated with specified key, or
null if there was no mapping for key. (A null
return can also indicate that the map previously associated
null with the specified key.)
- Throws:
NullPointerException - if the specified key is null
remove
public V remove(Object key)
- Removes the mapping for this key from this map if present.
- Specified by:
remove in interface Map<K extends Enum<K>,V> - Overrides:
remove in class AbstractMap<K extends Enum<K>,V>
- Parameters:
key - the key whose mapping is to be removed from the map
- Returns:
- the previous value associated with specified key, or
null if there was no entry for key. (A null
return can also indicate that the map previously associated
null with the specified key.)
putAll
public void putAll(Map<? extends K,? extends V> m)
- Copies all of the mappings from the specified map to this map.
These mappings will replace any mappings that this map had for
any of the keys currently in the specified map.
- Specified by:
putAll in interface Map<K extends Enum<K>,V> - Overrides:
putAll in class AbstractMap<K extends Enum<K>,V>
- Parameters:
m - the mappings to be stored in this map
- Throws:
NullPointerException - the specified map is null, or if
one or more keys in the specified map are null
clear
public void clear()
- Removes all mappings from this map.
- Specified by:
clear in interface Map<K extends Enum<K>,V> - Overrides:
clear in class AbstractMap<K extends Enum<K>,V>
keySet
public Set<K> keySet()
- Returns a
Set view of the keys contained in this map.
The returned set obeys the general contract outlined in
Map.keySet() . The set's iterator will return the keys
in their natural order (the order in which the enum constants
are declared).
- Specified by:
keySet in interface Map<K extends Enum<K>,V> - Overrides:
keySet in class AbstractMap<K extends Enum<K>,V>
- Returns:
- a set view of the keys contained in this enum map
values
public Collection<V> values()
- Returns a
Collection view of the values contained in this map.
The returned collection obeys the general contract outlined in
Map.values() . The collection's iterator will return the
values in the order their corresponding keys appear in map,
which is their natural order (the order in which the enum constants
are declared).
- Specified by:
values in interface Map<K extends Enum<K>,V> - Overrides:
values in class AbstractMap<K extends Enum<K>,V>
- Returns:
- a collection view of the values contained in this map
entrySet
public Set<Map.Entry<K,V>> entrySet()
- Returns a
Set view of the mappings contained in this map.
The returned set obeys the general contract outlined in
Map.keySet() . The set's iterator will return the
mappings in the order their keys appear in map, which is their
natural order (the order in which the enum constants are declared).
- Specified by:
entrySet in interface Map<K extends Enum<K>,V> - Specified by:
entrySet in class AbstractMap<K extends Enum<K>,V>
- Returns:
- a set view of the mappings contained in this enum map
equals
public boolean equals(Object o)
- Compares the specified object with this map for equality. Returns
true if the given object is also a map and the two maps
represent the same mappings, as specified in the
Map.equals(Object) contract.
- Specified by:
equals in interface Map<K extends Enum<K>,V> - Overrides:
equals in class AbstractMap<K extends Enum<K>,V>
- Parameters:
o - the object to be compared for equality with this map
- Returns:
- true if the specified object is equal to this map
- See Also:
Object.hashCode() ,
Hashtable
clone
public EnumMap<K,V> clone()
- Returns a shallow copy of this enum map. (The values themselves
are not cloned.
- Overrides:
clone in class AbstractMap<K extends Enum<K>,V>
- Returns:
- a shallow copy of this enum map
- See Also:
Cloneable
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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