- Type Parameters:
K
- the enum type of keys maintained by this mapV
- the type of mapped values
- All Implemented Interfaces:
Serializable
,Cloneable
,Map<K,
V>
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<K, V>)
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.
- Since:
- 1.5
- See Also:
-
Nested Class Summary
Nested classes/interfaces declared in class java.util.AbstractMap
AbstractMap.SimpleEntry<K,
V>, AbstractMap.SimpleImmutableEntry<K, V> -
Constructor Summary
ConstructorDescriptionCreates an empty enum map with the specified key type.Creates an enum map with the same key type as the specified enum map, initially containing the same mappings (if any).Creates an enum map initialized from the specified map. -
Method Summary
Modifier and TypeMethodDescriptionvoid
clear()
Removes all mappings from this map.clone()
Returns a shallow copy of this enum map.boolean
containsKey
(Object key) Returnstrue
if this map contains a mapping for the specified key.boolean
containsValue
(Object value) Returnstrue
if this map maps one or more keys to the specified value.entrySet()
Returns aSet
view of the mappings contained in this map.boolean
Compares the specified object with this map for equality.Returns the value to which the specified key is mapped, ornull
if this map contains no mapping for the key.int
hashCode()
Returns the hash code value for this map.keySet()
Returns aSet
view of the keys contained in this map.Associates the specified value with the specified key in this map.void
Copies all of the mappings from the specified map to this map.Removes the mapping for this key from this map if present.int
size()
Returns the number of key-value mappings in this map.values()
Returns aCollection
view of the values contained in this map.Methods declared in class java.util.AbstractMap
isEmpty, toString
Methods declared in interface java.util.Map
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll
-
Constructor Details
-
EnumMap
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
- ifkeyType
is null
-
EnumMap
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
- ifm
is null
-
EnumMap
Creates an enum map initialized from the specified map. If the specified map is anEnumMap
instance, this constructor behaves identically toEnumMap(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
- ifm
is not anEnumMap
instance and contains no mappingsNullPointerException
- ifm
is null
-
-
Method Details
-
size
-
containsValue
Returnstrue
if this map maps one or more keys to the specified value.- Specified by:
containsValue
in interfaceMap<K extends Enum<K>,
V> - Overrides:
containsValue
in classAbstractMap<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
Returnstrue
if this map contains a mapping for the specified key.- Specified by:
containsKey
in interfaceMap<K extends Enum<K>,
V> - Overrides:
containsKey
in classAbstractMap<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
Returns the value to which the specified key is mapped, ornull
if this map contains no mapping for the key.More formally, if this map contains a mapping from a key
k
to a valuev
such that(key == k)
, then this method returnsv
; otherwise it returnsnull
. (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 tonull
. ThecontainsKey
operation may be used to distinguish these two cases. -
put
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 interfaceMap<K extends Enum<K>,
V> - Overrides:
put
in classAbstractMap<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. (Anull
return can also indicate that the map previously associatednull
with the specified key.) - Throws:
NullPointerException
- if the specified key is null
-
remove
Removes the mapping for this key from this map if present.- Specified by:
remove
in interfaceMap<K extends Enum<K>,
V> - Overrides:
remove
in classAbstractMap<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. (Anull
return can also indicate that the map previously associatednull
with the specified key.)
-
putAll
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. -
clear
-
keySet
Returns aSet
view of the keys contained in this map. The returned set obeys the general contract outlined inMap.keySet()
. The set's iterator will return the keys in their natural order (the order in which the enum constants are declared). -
values
Returns aCollection
view of the values contained in this map. The returned collection obeys the general contract outlined inMap.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). -
entrySet
Returns aSet
view of the mappings contained in this map. The returned set obeys the general contract outlined inMap.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). -
equals
Compares the specified object with this map for equality. Returnstrue
if the given object is also a map and the two maps represent the same mappings, as specified in theMap.equals(Object)
contract. -
hashCode
public int hashCode()Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hash codes of each entry in the map. -
clone
-