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.

Nested classes/interfaces inherited from class java.util.AbstractMap

AbstractMap.SimpleEntry, AbstractMap.SimpleImmutableEntry

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry

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

Methods inherited from class java.util.AbstractMap

hashCode, isEmpty, toString

Methods inherited from class java.lang.Object

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