public class EnumMap<K extends Enum<K>,V> extends AbstractMap<K,V> implements Serializable, Cloneable
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(java.util.Map<K, V>)
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.
EnumSet,
Serialized Form AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>| Constructor | Description |
|---|---|
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.
|
| Modifier and Type | Method | Description |
|---|---|---|
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. |
isEmpty, toString finalize, getClass, notify, notifyAll, wait, wait, wait compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll public EnumMap(Class<K> keyType)
keyType - the class object of the key type for this enum mapNullPointerException - if keyType is nullpublic EnumMap(EnumMap<K,? extends V> m)
m - the enum map from which to initialize this enum mapNullPointerException - if m is nullpublic EnumMap(Map<K,? extends V> m)
EnumMap(EnumMap). Otherwise, the specified map
must contain at least one mapping (in order to determine the new
enum map's key type).m - the map from which to initialize this enum mapIllegalArgumentException - if m is not an
EnumMap instance and contains no mappingsNullPointerException - if m is nullpublic int size()
public boolean containsValue(Object value)
containsValue in interface Map<K extends Enum<K>,V>containsValue in class AbstractMap<K extends Enum<K>,V>value - the value whose presence in this map is to be testedpublic boolean containsKey(Object key)
containsKey in interface Map<K extends Enum<K>,V>containsKey in class AbstractMap<K extends Enum<K>,V>key - the key whose presence in this map is to be testedpublic V get(Object key)
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.
public V put(K key, V value)
put in interface Map<K extends Enum<K>,V>put in class AbstractMap<K extends Enum<K>,V>key - the key with which the specified value is to be associatedvalue - the value to be associated with the specified keyNullPointerException - if the specified key is nullpublic V remove(Object key)
remove in interface Map<K extends Enum<K>,V>remove in class AbstractMap<K extends Enum<K>,V>key - the key whose mapping is to be removed from the mappublic void putAll(Map<? extends K,? extends V> m)
public void clear()
public Set<K> keySet()
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).public Collection<V> values()
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).public Set<Map.Entry<K,V>> entrySet()
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).public boolean equals(Object o)
Map.equals(Object) contract.public int hashCode()
hashCode in interface Map<K extends Enum<K>,V>hashCode in class AbstractMap<K extends Enum<K>,V>Map.Entry.hashCode(),
Object.equals(Object),
Set.equals(Object) Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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