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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<EnumKey, V>(...));
![](../../diffpics/oold.gif)
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
Returns the value to which
this map maps
the specified
key is mapped,
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 is mapped,
key,
or null if this map contains no mapping for the
specified
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
containsKey
operation may be used to distinguish these two cases.
-
-
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 is mapped,
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 associated
-
value - 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