程序包 java.util

类 EnumMap<K extends Enum<K>,V>

java.lang.Object

java.util.AbstractMap<K,V>

java.util.EnumMap<K,V>

所有已实现的接口:

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 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.

从以下版本开始:

1.5

另请参阅:

EnumSet, 序列化表格

嵌套类概要

从类继承的嵌套类/接口 java.util.AbstractMap

AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>

从接口继承的嵌套类/接口 java.util.Map

Map.Entry<K,V>

构造器概要

构造器

构造器	说明
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.

方法概要

限定符和类型	方法	说明
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 the specified key is mapped, or null if this map contains no mapping for the key.
int	hashCode()	Returns the hash code value for this map.
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.

从类继承的方法 java.util.AbstractMap

isEmpty, toString

从接口继承的方法 java.util.Map

compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll

从类继承的方法 java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

构造器详细资料

EnumMap

public EnumMap(Class<K> keyType)

Creates an empty enum map with the specified key type.

参数:

keyType - the class object of the key type for this enum map

抛出:

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).

参数:

m - the enum map from which to initialize this enum map

抛出:

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(java.util.EnumMap). Otherwise, the specified map must contain at least one mapping (in order to determine the new enum map's key type).

参数:

m - the map from which to initialize this enum map

抛出:

IllegalArgumentException - if m is not an EnumMap instance and contains no mappings

NullPointerException - if m is null

方法详细资料

size

public int size()

Returns the number of key-value mappings in this map.

指定者:

size 在接口中 Map<K extends Enum<K>,V>

覆盖:

size 在类中 AbstractMap<K extends Enum<K>,V>

返回:

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.

指定者:

containsValue 在接口中 Map<K extends Enum<K>,V>

覆盖:

containsValue 在类中 AbstractMap<K extends Enum<K>,V>

参数:

value - the value whose presence in this map is to be tested

返回:

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.

指定者:

containsKey 在接口中 Map<K extends Enum<K>,V>

覆盖:

containsKey 在类中 AbstractMap<K extends Enum<K>,V>

参数:

key - the key whose presence in this map is to be tested

返回:

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.

指定者:

get 在接口中 Map<K extends Enum<K>,V>

覆盖:

get 在类中 AbstractMap<K extends Enum<K>,V>

参数:

key - the key whose associated value is to be returned

返回:

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.

指定者:

put 在接口中 Map<K extends Enum<K>,V>

覆盖:

put 在类中 AbstractMap<K extends Enum<K>,V>

参数:

key - the key with which the specified value is to be associated

value - the value to be associated with the specified key

返回:

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.)

抛出:

NullPointerException - if the specified key is null

remove

public V remove(Object key)

Removes the mapping for this key from this map if present.

指定者:

remove 在接口中 Map<K extends Enum<K>,V>

覆盖:

remove 在类中 AbstractMap<K extends Enum<K>,V>

参数:

key - the key whose mapping is to be removed from the map

返回:

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.

指定者:

putAll 在接口中 Map<K extends Enum<K>,V>

覆盖:

putAll 在类中 AbstractMap<K extends Enum<K>,V>

参数:

m - the mappings to be stored in this map

抛出:

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.

指定者:

clear 在接口中 Map<K extends Enum<K>,V>

覆盖:

clear 在类中 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).

指定者:

keySet 在接口中 Map<K extends Enum<K>,V>

覆盖:

keySet 在类中 AbstractMap<K extends Enum<K>,V>

返回:

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).

指定者:

values 在接口中 Map<K extends Enum<K>,V>

覆盖:

values 在类中 AbstractMap<K extends Enum<K>,V>

返回:

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).

指定者:

entrySet 在接口中 Map<K extends Enum<K>,V>

指定者:

entrySet 在类中 AbstractMap<K extends Enum<K>,V>

返回:

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.

指定者:

equals 在接口中 Map<K extends Enum<K>,V>

覆盖:

equals 在类中 AbstractMap<K extends Enum<K>,V>

参数:

o - the object to be compared for equality with this map

返回:

true if the specified object is equal to this map

另请参阅:

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.

指定者:

hashCode 在接口中 Map<K extends Enum<K>,V>

覆盖:

hashCode 在类中 AbstractMap<K extends Enum<K>,V>

返回:

the hash code value for this map

另请参阅:

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.

覆盖:

clone 在类中 AbstractMap<K extends Enum<K>,V>

返回:

a shallow copy of this enum map

另请参阅:

Cloneable