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Added in API level 1

Summary: Ctors | Methods | Inherited Methods | [Expand All]

EnumMap

public class EnumMap
extends AbstractMap<K extends Enum<K>, V> implements Serializable, Cloneable

java.lang.Object
↳	java.util.AbstractMap<K extends java.lang.Enum<K>, V>
	↳	java.util.EnumMap<K extends java.lang.Enum<K>, V>

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 synchronizedMap(Map) 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.

See also:

EnumSet

Summary

Public constructors
`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.

Public methods
`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<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.

Inherited methods

From class


  
    java.util.AbstractMap

`void`	`clear()` Removes all of the mappings from this map (optional operation). This implementation calls `entrySet().clear()`.
`Object`	`clone()` Returns a shallow copy of this `AbstractMap` instance: the keys and values themselves are not cloned.
`boolean`	`containsKey(Object key)` Returns `true` if this map contains a mapping for the specified key. This implementation iterates over `entrySet()` searching for an entry with the specified key.
`boolean`	`containsValue(Object value)` Returns `true` if this map maps one or more keys to the specified value. This implementation iterates over `entrySet()` searching for an entry with the specified value.
`abstract Set<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. This implementation iterates over `entrySet()` searching for an entry with the specified key.
`int`	`hashCode()` Returns the hash code value for this map.
`boolean`	`isEmpty()` Returns `true` if this map contains no key-value mappings. This implementation returns `size() == 0`.
`Set<K>`	`keySet()` Returns a `Set` view of the keys contained in this map. This implementation returns a set that subclasses `AbstractSet`.
`V`	`put(K key, V value)` Associates the specified value with the specified key in this map (optional operation). This implementation always throws an `UnsupportedOperationException`.
`void`	`putAll(Map<? extends K, ? extends V> m)` Copies all of the mappings from the specified map to this map (optional operation). This implementation iterates over the specified map's `entrySet()` collection, and calls this map's `put` operation once for each entry returned by the iteration.
`V`	`remove(Object key)` Removes the mapping for a key from this map if it is present (optional operation). This implementation iterates over `entrySet()` searching for an entry with the specified key.
`int`	`size()` Returns the number of key-value mappings in this map. This implementation returns `entrySet().size()`.
`String`	`toString()` Returns a string representation of this map.
`Collection<V>`	`values()` Returns a `Collection` view of the values contained in this map. This implementation returns a collection that subclasses `AbstractCollection`.

From class


  
    java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long millis, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void`	`wait(long millis)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void`	`wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

From interface


  
    java.util.Map

`abstract void`	`clear()` Removes all of the mappings from this map (optional operation).
`default V`	`compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)` Attempts to compute a mapping for the specified key and its current mapped value (or `null` if there is no current mapping).
`default V`	`computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction)` If the specified key is not already associated with a value (or is mapped to `null`), attempts to compute its value using the given mapping function and enters it into this map unless `null`.
`default V`	`computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)` If the value for the specified key is present and non-null, attempts to compute a new mapping given the key and its current mapped value.
`abstract boolean`	`containsKey(Object key)` Returns `true` if this map contains a mapping for the specified key.
`abstract boolean`	`containsValue(Object value)` Returns `true` if this map maps one or more keys to the specified value.
`abstract Set<Entry<K, V>>`	`entrySet()` Returns a `Set` view of the mappings contained in this map.
`abstract boolean`	`equals(Object o)` Compares the specified object with this map for equality.
`default void`	`forEach(BiConsumer<? super K, ? super V> action)` Performs the given action for each entry in this map until all entries have been processed or the action throws an exception.
`abstract 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.
`default V`	`getOrDefault(Object key, V defaultValue)` Returns the value to which the specified key is mapped, or `defaultValue` if this map contains no mapping for the key.
`abstract int`	`hashCode()` Returns the hash code value for this map.
`abstract boolean`	`isEmpty()` Returns `true` if this map contains no key-value mappings.
`abstract Set<K>`	`keySet()` Returns a `Set` view of the keys contained in this map.
`default V`	`merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction)` If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value.
`abstract V`	`put(K key, V value)` Associates the specified value with the specified key in this map (optional operation).
`abstract void`	`putAll(Map<? extends K, ? extends V> m)` Copies all of the mappings from the specified map to this map (optional operation).
`default V`	`putIfAbsent(K key, V value)` If the specified key is not already associated with a value (or is mapped to `null`) associates it with the given value and returns `null`, else returns the current value.
`default boolean`	`remove(Object key, Object value)` Removes the entry for the specified key only if it is currently mapped to the specified value.
`abstract V`	`remove(Object key)` Removes the mapping for a key from this map if it is present (optional operation).
`default boolean`	`replace(K key, V oldValue, V newValue)` Replaces the entry for the specified key only if currently mapped to the specified value.
`default V`	`replace(K key, V value)` Replaces the entry for the specified key only if it is currently mapped to some value.
`default void`	`replaceAll(BiFunction<? super K, ? super V, ? extends V> function)` Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception.
`abstract int`	`size()` Returns the number of key-value mappings in this map.
`abstract Collection<V>`	`values()` Returns a `Collection` view of the values contained in this map.

Public constructors

EnumMap

Added in API level 1

EnumMap (Class<K> keyType)

Creates an empty enum map with the specified key type.

Parameters
`keyType`	`Class`: the class object of the key type for this enum map

Throws
`NullPointerException`	if `keyType` is null

EnumMap

Added in API level 1

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`	`EnumMap`: the enum map from which to initialize this enum map

Throws
`NullPointerException`	if `m` is null

EnumMap

Added in API level 1

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`	`Map`: 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

Public methods

clear

Added in API level 1

void clear ()

Removes all mappings from this map.

clone

Added in API level 1

EnumMap<K, V> clone ()

Returns a shallow copy of this enum map. (The values themselves are not cloned.

Returns
`EnumMap<K, V>`	a shallow copy of this enum map

containsKey

Added in API level 1

boolean containsKey (Object key)

Returns true if this map contains a mapping for the specified key.

Parameters
`key`	`Object`: the key whose presence in this map is to be tested

Returns
`boolean`	`true` if this map contains a mapping for the specified key

containsValue

Added in API level 1

boolean containsValue (Object value)

Returns true if this map maps one or more keys to the specified value.

Parameters
`value`	`Object`: the value whose presence in this map is to be tested

Returns
`boolean`	`true` if this map maps one or more keys to this value

entrySet

Added in API level 1

Set<Entry<K, V>> entrySet ()

Returns a Set view of the mappings contained in this map. The returned set obeys the general contract outlined in 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).

Returns
`Set<Entry<K, V>>`	a set view of the mappings contained in this enum map

equals

Added in API level 1

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 equals(Object) contract.

Parameters
`o`	`Object`: the object to be compared for equality with this map

Returns
`boolean`	`true` if the specified object is equal to this map

get

Added in API level 1

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.

Parameters
`key`	`Object`: the key whose associated value is to be returned

Returns
`V`	the value to which the specified key is mapped, or `null` if this map contains no mapping for the key

hashCode

Added in API level 1

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.

Returns
`int`	the hash code value for this map

keySet

Added in API level 1

Set<K> keySet ()

Returns a Set view of the keys contained in this map. The returned set obeys the general contract outlined in keySet(). The set's iterator will return the keys in their natural order (the order in which the enum constants are declared).

Returns
`Set<K>`	a set view of the keys contained in this enum map

put

Added in API level 1

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`	`K`: the key with which the specified value is to be associated
`value`	`V`: the value to be associated with the specified key

Returns
`V`	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

putAll

Added in API level 1

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.

Parameters
`m`	`Map`: 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

remove

Added in API level 1

V remove (Object key)

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

Parameters
`key`	`Object`: the key whose mapping is to be removed from the map

Returns
`V`	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.)

size

Added in API level 1

int size ()

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

Returns
`int`	the number of key-value mappings in this map

values

Added in API level 1

Collection<V> values ()

Returns a Collection view of the values contained in this map. The returned collection obeys the general contract outlined in 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).

Returns
`Collection<V>`	a collection view of the values contained in this map

Interfaces

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EnumMap

Summary

Public constructors

Public methods

Inherited methods

Public constructors

EnumMap

EnumMap

EnumMap

Public methods

clear

clone

containsKey

containsValue

entrySet

equals

get

hashCode

keySet

put

putAll

remove

size

values