| java.util.EnumMap
| EnumMap | | public class EnumMap extends AbstractMap implements java.io.Serializable,Cloneable(Code) | | 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 (
EnumMap.keySet() ,
EnumMap.entrySet() , and
EnumMap.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 method. This is best done at creation time, to prevent accidental
unsynchronized access:
Map<EnumKey, V> m
= Collections.synchronizedMap(new EnumMap<EnumKey, V>(...));
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.
author:
Josh Bloch
version:
1.22, 05/05/07
See Also: EnumSet
since:
1.5 |
| Constructor Summary | |
| public | EnumMap(Class<K> keyType)
Creates an empty enum map with the specified key type. | | 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). | | public | EnumMap(Map<K, ? extends V> m)
Creates an enum map initialized from the specified map. |
| Method Summary | |
| public void | clear()
Removes all mappings from this map. | | public EnumMap<K, V> | clone()
Returns a shallow copy of this enum map. | | public boolean | containsKey(Object key)
Returns true if this map contains a mapping for the specified
key. | | public boolean | containsValue(Object value)
Returns true if this map maps one or more keys to the
specified value. | | 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 . | | public boolean | equals(Object o)
Compares the specified object with this map for equality. | | public 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.
More formally, if this map contains a mapping from a key
k to a value
v such that
(key == k) ,
then this method returns
v ; otherwise it returns
null . | | 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 . | | 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.
Parameters:
key - the key with which the specified value is to be associated
Parameters:
value - the value to be associated with the specified key the previous value associated with specified key, ornull if there was no mapping for key. | | public void | putAll(Map<? extends K, ? extends V> m)
Copies all of the mappings from the specified map to this map. | | public V | remove(Object key)
Removes the mapping for this key from this map if present.
Parameters:
key - the key whose mapping is to be removed from the map the previous value associated with specified key, ornull if there was no entry for key. | | public int | size()
Returns the number of key-value mappings in this map. | | 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 . |
| EnumMap | | public EnumMap(Class<K> keyType)(Code) | | 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)(Code) | | 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)(Code) | | Creates an enum map initialized from the specified map. If the
specified map is an EnumMap instance, this constructor behaves
identically to
EnumMap.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 anEnumMap instance and contains no mappings
throws:
NullPointerException - if m is null |
| clear | | public void clear()(Code) | | Removes all mappings from this map.
|
| clone | | public EnumMap<K, V> clone()(Code) | | Returns a shallow copy of this enum map. (The values themselves
are not cloned.
a shallow copy of this enum map |
| containsKey | | public boolean containsKey(Object key)(Code) | | Returns true if this map contains a mapping for the specified
key.
Parameters:
key - the key whose presence in this map is to be tested true if this map contains a mapping for the specifiedkey |
| containsValue | | public boolean containsValue(Object value)(Code) | | Returns true if this map maps one or more keys to the
specified value.
Parameters:
value - the value whose presence in this map is to be tested true if this map maps one or more keys to this value |
| entrySet | | public Set<Map.Entry<K, V>> entrySet()(Code) | | 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).
a set view of the mappings contained in this enum map |
| equals | | public boolean equals(Object o)(Code) | | 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.
Parameters:
o - the object to be compared for equality with this map true if the specified object is equal to this map |
| get | | public V get(Object key)(Code) | | 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 == k) ,
then this method returns
v ; otherwise it returns
null . (There can be at most one such mapping.)
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
EnumMap.containsKey containsKey operation may be used to
distinguish these two cases.
|
| keySet | | public Set<K> keySet()(Code) | | 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).
a set view of the keys contained in this enum map |
| put | | public V put(K key, V value)(Code) | | 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.
Parameters:
key - the key with which the specified value is to be associated
Parameters:
value - the value to be associated with the specified key the previous value associated with specified key, ornull if there was no mapping for key. (A nullreturn can also indicate that the map previously associatednull with the specified key.)
throws:
NullPointerException - if the specified key is null |
| putAll | | public void putAll(Map<? extends K, ? extends V> m)(Code) | | 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.
Parameters:
m - the mappings to be stored in this map
throws:
NullPointerException - the specified map is null, or ifone or more keys in the specified map are null |
| remove | | public V remove(Object key)(Code) | | Removes the mapping for this key from this map if present.
Parameters:
key - the key whose mapping is to be removed from the map the previous value associated with specified key, ornull if there was no entry for key. (A nullreturn can also indicate that the map previously associatednull with the specified key.) |
| size | | public int size()(Code) | | Returns the number of key-value mappings in this map.
the number of key-value mappings in this map |
| values | | public Collection<V> values()(Code) | | 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).
a collection view of the values contained in this map |
|
|