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<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:
-
EnumSet
, Serialized Form
Nested Class Summary
Nested classes/interfaces declared in class java.util.AbstractMap
AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>
Nested classes/interfaces declared in interface java.util.Map
Map.Entry<K,V>
Constructor Summary
Constructor | Description |
---|---|
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
Modifier and Type | Method | Description |
---|---|---|
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 |
boolean | containsValue(Object value) | Returns |
Set<Map.Entry<K,V>> | entrySet() | Returns a |
boolean | equals(Object o) | Compares the specified object with this map for equality. |
V | get(Object key) | Returns the value to which the specified key is mapped, or |
int | hashCode() | Returns the hash code value for this map. |
Set<K> | keySet() | Returns a |
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 |
Methods declared in class java.util.AbstractMap
isEmpty, toString
Methods declared in class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Map
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll
Constructor Detail
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
- ifkeyType
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
- ifm
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
- ifm
is not anEnumMap
instance and contains no mappings -
NullPointerException
- ifm
is null
Method Detail
size
public int size()
Returns the number of key-value mappings in this map.
- Specified by:
-
size
in interfaceMap<K extends Enum<K>,V>
- Overrides:
-
size
in classAbstractMap<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 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
public boolean containsKey(Object key)
Returns true
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
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
. (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 interfaceMap<K extends Enum<K>,V>
- Overrides:
-
get
in classAbstractMap<K extends Enum<K>,V>
- Parameters:
-
key
- the key whose associated value is to be returned - Returns:
- the value to which the specified key is mapped, or
null
if this map contains no mapping for the key
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 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 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. (Anull
return can also indicate that the map previously associatednull
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 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
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 interfaceMap<K extends Enum<K>,V>
- Overrides:
-
putAll
in classAbstractMap<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 interfaceMap<K extends Enum<K>,V>
- Overrides:
-
clear
in classAbstractMap<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 interfaceMap<K extends Enum<K>,V>
- Overrides:
-
keySet
in classAbstractMap<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 interfaceMap<K extends Enum<K>,V>
- Overrides:
-
values
in classAbstractMap<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 interfaceMap<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 interfaceMap<K extends Enum<K>,V>
- Overrides:
-
equals
in classAbstractMap<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()
,HashMap
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.
- Specified by:
-
hashCode
in interfaceMap<K extends Enum<K>,V>
- Overrides:
-
hashCode
in classAbstractMap<K extends Enum<K>,V>
- Returns:
- the hash code value for this map
- See Also:
-
Map.Entry.hashCode()
,Object.equals(Object)
,Set.equals(Object)
clone
public EnumMap<K,V> clone()
Returns a shallow copy of this enum map. The values themselves are not cloned.