- java.lang.Object
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- java.util.AbstractMap<K,V>
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- java.util.EnumMap<K,V>
 
 
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- All Implemented Interfaces:
- Serializable,- Cloneable,- Map<K,V>
 
 public class EnumMap<K extends Enum<K>,V> extends AbstractMap<K,V> implements Serializable, Cloneable A specializedMapimplementation 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(), andvalues()).Iterators returned by the collection views are weakly consistent: they will never throw ConcurrentModificationExceptionand 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 EnumMapis 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 theCollections.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 HashMapcounterparts.This class is a member of the Java Collections Framework. - Since:
- 1.5
- See Also:
- EnumSet, Serialized Form
 
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Nested Class Summary- 
Nested classes/interfaces declared in class java.util.AbstractMapAbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>
 
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Constructor SummaryConstructors 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.
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Method SummaryAll Methods Instance Methods Concrete Methods Modifier and Type Method Description voidclear()Removes all mappings from this map.EnumMap<K,V>clone()Returns a shallow copy of this enum map.booleancontainsKey(Object key)Returnstrueif this map contains a mapping for the specified key.booleancontainsValue(Object value)Returnstrueif this map maps one or more keys to the specified value.Set<Map.Entry<K,V>>entrySet()Returns aSetview of the mappings contained in this map.booleanequals(Object o)Compares the specified object with this map for equality.Vget(Object key)Returns the value to which the specified key is mapped, ornullif this map contains no mapping for the key.inthashCode()Returns the hash code value for this map.Set<K>keySet()Returns aSetview of the keys contained in this map.Vput(K key, V value)Associates the specified value with the specified key in this map.voidputAll(Map<? extends K,? extends V> m)Copies all of the mappings from the specified map to this map.Vremove(Object key)Removes the mapping for this key from this map if present.intsize()Returns the number of key-value mappings in this map.Collection<V>values()Returns aCollectionview of the values contained in this map.- 
Methods declared in class java.util.AbstractMapisEmpty, toString
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Methods declared in interface java.util.Mapcompute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll
 
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Constructor Detail- 
EnumMappublic EnumMap(Class<K> 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- keyTypeis null
 
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EnumMappublic 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- the enum map from which to initialize this enum map
- Throws:
- NullPointerException- if- mis null
 
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EnumMappublic EnumMap(Map<K,? extends V> m) Creates an enum map initialized from the specified map. If the specified map is anEnumMapinstance, this constructor behaves identically toEnumMap(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- mis not an- EnumMapinstance and contains no mappings
- NullPointerException- if- mis null
 
 
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Method Detail- 
sizepublic int size() Returns the number of key-value mappings in this map.
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containsValuepublic boolean containsValue(Object value) Returnstrueif this map maps one or more keys to the specified value.- Specified by:
- containsValuein interface- Map<K extends Enum<K>,V>
- Overrides:
- containsValuein class- AbstractMap<K extends Enum<K>,V>
- Parameters:
- value- the value whose presence in this map is to be tested
- Returns:
- trueif this map maps one or more keys to this value
 
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containsKeypublic boolean containsKey(Object key) Returnstrueif this map contains a mapping for the specified key.- Specified by:
- containsKeyin interface- Map<K extends Enum<K>,V>
- Overrides:
- containsKeyin class- AbstractMap<K extends Enum<K>,V>
- Parameters:
- key- the key whose presence in this map is to be tested
- Returns:
- trueif this map contains a mapping for the specified key
 
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getpublic V get(Object key) Returns the value to which the specified key is mapped, ornullif this map contains no mapping for the key.More formally, if this map contains a mapping from a key kto a valuevsuch that(key == k), then this method returnsv; otherwise it returnsnull. (There can be at most one such mapping.)A return value of nulldoes not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key tonull. ThecontainsKeyoperation may be used to distinguish these two cases.
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putpublic 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:
- putin interface- Map<K extends Enum<K>,V>
- Overrides:
- putin class- AbstractMap<K extends Enum<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
     nullif there was no mapping for key. (Anullreturn can also indicate that the map previously associatednullwith the specified key.)
- Throws:
- NullPointerException- if the specified key is null
 
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removepublic V remove(Object key) Removes the mapping for this key from this map if present.- Specified by:
- removein interface- Map<K extends Enum<K>,V>
- Overrides:
- removein class- AbstractMap<K extends Enum<K>,V>
- Parameters:
- key- the key whose mapping is to be removed from the map
- Returns:
- the previous value associated with specified key, or
     nullif there was no entry for key. (Anullreturn can also indicate that the map previously associatednullwith the specified key.)
 
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putAllpublic 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.
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clearpublic void clear() Removes all mappings from this map.
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keySetpublic Set<K> keySet() Returns aSetview of the keys contained in this map. The returned set obeys the general contract outlined inMap.keySet(). The set's iterator will return the keys in their natural order (the order in which the enum constants are declared).
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valuespublic Collection<V> values() Returns aCollectionview of the values contained in this map. The returned collection obeys the general contract outlined inMap.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).
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entrySetpublic Set<Map.Entry<K,V>> entrySet() Returns aSetview of the mappings contained in this map. The returned set obeys the general contract outlined inMap.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).
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equalspublic boolean equals(Object o) Compares the specified object with this map for equality. Returnstrueif the given object is also a map and the two maps represent the same mappings, as specified in theMap.equals(Object)contract.
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hashCodepublic 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.- Specified by:
- hashCodein interface- Map<K extends Enum<K>,V>
- Overrides:
- hashCodein class- AbstractMap<K extends Enum<K>,V>
- Returns:
- the hash code value for this map
- See Also:
- Map.Entry.hashCode(),- Object.equals(Object),- Set.equals(Object)
 
 
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