java.util
Class EnumMap

public class EnumMap
extends java.util.AbstractMap
implements java.io.Serializable, java.lang.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 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 Java Collections Framework.

Version:
1.5, 12/19/03
Author:
Josh Bloch
Since:
1.5
See Also:
EnumSet
Field Detail

keyType

private final java.lang.Class keyType
The class of all the keys of this map.

keyUniverse

private transient K[] keyUniverse
All of the values comprising K. (Cached for performance.)

vals

private transient java.lang.Object[] vals
Array representation of this map. The ith element is the value to which universe[i] is currently mapped, or null if it isn't mapped to anything, or NULL if it's mapped to null.

size

private transient int size
The number of mappings in this map.

NULL

private static final java.lang.Object NULL
Distinguished non-null value for representing null values.

entrySet

private transient java.util.Set entrySet
This field is initialized to contain an instance of the entry set view the first time this view is requested. The view is stateless, so there's no reason to create more than one.

Constructor Detail

EnumMap

public EnumMap(java.lang.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

EnumMap

public EnumMap(java.util.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(java.util.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 Detail

size

public int size()
Returns the number of key-value mappings in this map.
Returns:
the number of key-value mappings in this map

containsValue

public boolean containsValue(java.lang.Object value)
Returns true if this map maps one or more keys to the specified value.
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(java.lang.Object key)
Returns true if this map contains a mapping for the specified key.
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(java.lang.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.
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

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.
Parameters:
the - key key with which the specified value is to be associated
the - value 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

remove

public V remove(java.lang.Object key)
Removes the mapping for this key from this map if present.
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.)

isValidKey

private boolean isValidKey(java.lang.Object key)
Returns true if key is of the proper type to bey a key in this enum map.

putAll

public void putAll(java.util.Map 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:
t - 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.

keySet

public java.util.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).
Returns:
a set view of the keys contained in this enum map

values

public java.util.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).
Returns:
a collection view of the values contained in this map

entrySet

public java.util.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).
Returns:
a set view of the mappings contained in this enum map

equals

public boolean equals(java.lang.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.
Parameters:
o - the object to be compared for equality with this map
Returns:
true if the specified object is equal to this map

clone

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

writeObject

private void writeObject(java.io.ObjectOutputStream s)
Save the state of the EnumMap instance to a stream (i.e., serialize it).

readObject

private void readObject(java.io.ObjectInputStream s)
Reconstitute the EnumMap instance from a stream (i.e., deserialize it).