java.util

Class EnumMap<K,extends,Enum,K,V>

Implemented Interfaces:
Cloneable, Map<K,V>, Serializable

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 method. This is best done at creation time, to prevent accidental unsynchronized access:

     Map<EnumKey, V> m = Collections.synchronizedMap(new EnumMap(...));
 

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 ../../../guide/collections/index.html"> Java Collections Framework.

Since:
1.5
See Also:
EnumSet, Serialized Form

Constructor Summary

EnumMap(Class keyType)
Creates an empty enum map with the specified key type.
EnumMap(EnumMap m)
Creates an enum map with the same key type as the specified enum map, initially containing the same mappings (if any).
EnumMap(Map m)
Creates an enum map initialized from the specified map.

Method Summary

EnumMap
V> clone()
Returns a shallow copy of this enum map.
void
clear()
Removes all mappings from this 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>
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 this map maps the specified key, or null if this map contains no mapping for the specified key.
Set
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(extends K, 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
values()
Returns a Collection view of the values contained in this map.

Methods inherited from class java.util.AbstractMap<K,V>

clear, clone, containsKey, containsValue, entrySet, equals, get, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

EnumMap

public EnumMap(Class 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 - if keyType is null
Usages and Demos :

View More Examples of EnumMap(Class keyType)
   1:         try {
   2:             new EnumMap(String.class);
   3:             fail();
   4:         ...
   5:             m.put("a", "b");
   6:             new EnumMap(m);
   7:             fail();
   8:         ...
   9:         assertEquals(3, map.size());
  10:         EnumMap strings = new EnumMap(ElementType.class);
  11:         map.putAll(strings);

View Full Code Here

EnumMap

public EnumMap(EnumMap 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 - if m is null

EnumMap

public EnumMap(Map 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 - if m is not an EnumMap instance and contains no mappings
NullPointerException - if m is null

Method Details

V> clone

public EnumMapV> clone()
Returns a shallow copy of this enum map. (The values themselves are not cloned.
Returns:
a shallow copy of this enum map

clear

public void clear()
Removes all mappings from this map.
Specified by:
clear in interface Map<K,V>
Overrides:
clear in interface AbstractMap<K,V>

containsKey

public boolean containsKey(Object key)
Returns true if this map contains a mapping for the specified key.
Specified by:
containsKey in interface Map<K,V>
Overrides:
containsKey in interface AbstractMap<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

containsValue

public boolean containsValue(Object value)
Returns true if this map maps one or more keys to the specified value.
Specified by:
containsValue in interface Map<K,V>
Overrides:
containsValue in interface AbstractMap<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

entrySet

public Set> 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).
Overrides:
entrySet in interface AbstractMap<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 interface Map<K,V>
Overrides:
equals in interface AbstractMap<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

get

public V get(Object key)
Returns the value to which this map maps the specified key, or null if this map contains no mapping for the specified key.
Specified by:
get in interface Map<K,V>
Overrides:
get in interface AbstractMap<K,V>
Parameters:
key - the key whose associated value is to be returned
Returns:
the value to which this map maps the specified key, or null if this map contains no mapping for the specified key

keySet

public Set 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 interface Map<K,V>
Overrides:
keySet in interface AbstractMap<K,V>
Returns:
a set view of the keys contained in this enum map

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 interface Map<K,V>
Overrides:
put in interface AbstractMap<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. (A null return can also indicate that the map previously associated null with the specified key.)
Throws:
NullPointerException - if the specified key is null
Usages and Demos :

View More Examples of put(K key,V value)
   1: 
   2: import java.util.EnumMap;
   3: 
   4:         ...
   5:         xstream.alias("simple", SimpleEnum.class);
   6:         EnumMap map = new EnumMap<SimpleEnum,String>(SimpleEnum.class);
   7:         ...
   8:         map.put(SimpleEnum.BLUE, "sky");
   9:         ...
  10:         map.put(SimpleEnum.GREEN, "grass");

View Full Code Here
   1:     public void testClear() {
   2:         EnumMap<Day, String> map = getSampleMap();
   3:         assertFalse(map.isEmpty());
   4:         ...
   5:     public void testClone() {
   6:         EnumMap<Day, String> clone = getSampleMap().clone();
   7:         assertTrue(clone.equals(getSampleMap()));
   8:         ...
   9:     public void testConstructors() {
  10:         EnumMap<Day, String> map = getSampleMap();
  11:         assertEquals(3, new EnumMap<Day, String>(map).size());
  12:         ...
  13:             HashMap m = new HashMap();
  14:             m.put("a", "b");

View Full Code Here

putAll

public void putAll(extends K,
                   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 interface Map<K,V>
Overrides:
putAll in interface AbstractMap<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

remove

public V remove(Object key)
Removes the mapping for this key from this map if present.
Specified by:
remove in interface Map<K,V>
Overrides:
remove in interface AbstractMap<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. (A null return can also indicate that the map previously associated null with the specified key.)

size

public int size()
Returns the number of key-value mappings in this map.
Specified by:
size in interface Map<K,V>
Overrides:
size in interface AbstractMap<K,V>
Returns:
the number of key-value mappings in this map

values

public Collection 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 interface Map<K,V>
Overrides:
values in interface AbstractMap<K,V>
Returns:
a collection view of the values contained in this map