Class ConcurrentHashMap.KeySetView<K,V> 
- Type Parameters:
- K- the type of keys
- V- the type of values in the backing map
- All Implemented Interfaces:
- Serializable,- Iterable<K>,- Collection<K>,- Set<K>
- Enclosing class:
- ConcurrentHashMap<K,- V> 
Set of keys, in
 which additions may optionally be enabled by mapping to a
 common value.  This class cannot be directly instantiated.
 See keySet(),
 keySet(V),
 newKeySet(),
 newKeySet(int).- Since:
- 1.8
- See Also:
- 
Method SummaryModifier and TypeMethodDescriptionbooleanAdds the specified key to this set view by mapping the key to the default mapped value in the backing map, if defined.booleanaddAll(Collection<? extends K> c) Adds all of the elements in the specified collection to this set, as if by callingadd(K)on each one.final voidclear()Removes all of the elements from this view, by removing all the mappings from the map backing this view.booleanReturnstrueif this collection contains the specified element.final booleancontainsAll(Collection<?> c) Returnstrueif this collection contains all of the elements in the specified collection.booleanCompares the specified object with this collection for equality.getMap()Returns the map backing this view.Returns the default mapped value for additions, ornullif additions are not supported.inthashCode()Returns the hash code value for this collection.final booleanisEmpty()Returnstrueif this collection contains no elements.iterator()Returns an iterator over the elements in this collection.booleanRemoves the key from this map view, by removing the key (and its corresponding value) from the backing map.booleanremoveAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).final booleanretainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation).final intsize()Returns the number of elements in this collection.final Object[]toArray()Returns an array containing all of the elements in this collection.final <T> T[]toArray(T[] a) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.final StringtoString()Returns a string representation of this collection.Methods declared in class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitMethods declared in interface java.util.CollectionparallelStream, removeIf, stream, toArrayMethods declared in interface java.util.Setclear, containsAll, isEmpty, removeAll, retainAll, size, spliterator, toArray, toArray
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Method Details- 
getMappedValueReturns the default mapped value for additions, ornullif additions are not supported.- Returns:
- the default mapped value for additions, or nullif not supported
 
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containsReturnstrueif this collection contains the specified element. More formally, returnstrueif and only if this collection contains at least one elementesuch thatObjects.equals(o, e).- Specified by:
- containsin interface- Collection<K>
- Specified by:
- containsin interface- Set<K>
- Parameters:
- o- element whose presence in this collection is to be tested
- Returns:
- trueif this collection contains the specified element
- Throws:
- NullPointerException- if the specified key is null
 
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removeRemoves the key from this map view, by removing the key (and its corresponding value) from the backing map. This method does nothing if the key is not in the map.- Specified by:
- removein interface- Collection<K>
- Specified by:
- removein interface- Set<K>
- Parameters:
- o- the key to be removed from the backing map
- Returns:
- trueif the backing map contained the specified key
- Throws:
- NullPointerException- if the specified key is null
 
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iteratorReturns an iterator over the elements in this collection.The returned iterator is weakly consistent. 
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addAdds the specified key to this set view by mapping the key to the default mapped value in the backing map, if defined.- Specified by:
- addin interface- Collection<K>
- Specified by:
- addin interface- Set<K>
- Parameters:
- e- key to be added
- Returns:
- trueif this set changed as a result of the call
- Throws:
- NullPointerException- if the specified key is null
- UnsupportedOperationException- if no default mapped value for additions was provided
 
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addAllAdds all of the elements in the specified collection to this set, as if by callingadd(K)on each one.- Specified by:
- addAllin interface- Collection<K>
- Specified by:
- addAllin interface- Set<K>
- Parameters:
- c- the elements to be inserted into this set
- Returns:
- trueif this set changed as a result of the call
- Throws:
- NullPointerException- if the collection or any of its elements are- null
- UnsupportedOperationException- if no default mapped value for additions was provided
- See Also:
 
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hashCodepublic int hashCode()Description copied from interface:CollectionReturns the hash code value for this collection. While theCollectioninterface adds no stipulations to the general contract for theObject.hashCodemethod, programmers should take note that any class that overrides theObject.equalsmethod must also override theObject.hashCodemethod in order to satisfy the general contract for theObject.hashCodemethod. In particular,c1.equals(c2)implies thatc1.hashCode()==c2.hashCode().
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equalsDescription copied from interface:CollectionCompares the specified object with this collection for equality.While the Collectioninterface adds no stipulations to the general contract for theObject.equals, programmers who implement theCollectioninterface "directly" (in other words, create a class that is aCollectionbut is not aSetor aList) must exercise care if they choose to override theObject.equals. It is not necessary to do so, and the simplest course of action is to rely onObject's implementation, but the implementor may wish to implement a "value comparison" in place of the default "reference comparison." (TheListandSetinterfaces mandate such value comparisons.)The general contract for the Object.equalsmethod states that equals must be symmetric (in other words,a.equals(b)if and only ifb.equals(a)). The contracts forList.equalsandSet.equalsstate that lists are only equal to other lists, and sets to other sets. Thus, a customequalsmethod for a collection class that implements neither theListnorSetinterface must returnfalsewhen this collection is compared to any list or set. (By the same logic, it is not possible to write a class that correctly implements both theSetandListinterfaces.)
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getMapReturns the map backing this view.- Returns:
- the map backing this view
 
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clearpublic final void clear()Removes all of the elements from this view, by removing all the mappings from the map backing this view.- Specified by:
- clearin interface- Collection<K>
 
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sizepublic final int size()Description copied from interface:CollectionReturns the number of elements in this collection. If this collection contains more thanInteger.MAX_VALUEelements, returnsInteger.MAX_VALUE.- Specified by:
- sizein interface- Collection<K>
- Returns:
- the number of elements in this collection
 
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isEmptypublic final boolean isEmpty()Description copied from interface:CollectionReturnstrueif this collection contains no elements.- Specified by:
- isEmptyin interface- Collection<K>
- Returns:
- trueif this collection contains no elements
 
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toArrayDescription copied from interface:CollectionReturns an array containing all of the elements in this collection. If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array's runtime component type isObject.The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array. - Specified by:
- toArrayin interface- Collection<K>
- Returns:
- an array, whose runtime component
 type is Object, containing all of the elements in this collection
 
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toArraypublic final <T> T[] toArray(T[] a) Description copied from interface:CollectionReturns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain anynullelements.)If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. - Specified by:
- toArrayin interface- Collection<K>
- Type Parameters:
- T- the component type of the array to contain the collection
- Parameters:
- a- the array into which the elements of this collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
- Returns:
- an array containing all of the elements in this collection
 
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toStringReturns a string representation of this collection. The string representation consists of the string representations of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters", "(comma and space). Elements are converted to strings as byString.valueOf(Object).
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containsAllDescription copied from interface:CollectionReturnstrueif this collection contains all of the elements in the specified collection.- Specified by:
- containsAllin interface- Collection<K>
- Parameters:
- c- collection to be checked for containment in this collection
- Returns:
- trueif this collection contains all of the elements in the specified collection
- See Also:
 
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removeAllDescription copied from interface:CollectionRemoves all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.- Specified by:
- removeAllin interface- Collection<K>
- Parameters:
- c- collection containing elements to be removed from this collection
- Returns:
- trueif this collection changed as a result of the call
- See Also:
 
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retainAllDescription copied from interface:CollectionRetains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.- Specified by:
- retainAllin interface- Collection<K>
- Parameters:
- c- collection containing elements to be retained in this collection
- Returns:
- trueif this collection changed as a result of the call
- See Also:
 
 
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