public static class ConcurrentHashMap.KeySetView<K,V> extends Object implements Set<K>, Serializable
A view of a ConcurrentHashMap as a 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).
public V getMappedValue()
Returns the default mapped value for additions, or null if additions are not supported.
null if not supportedpublic boolean contains(Object o)
Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that (o==null ? e==null : o.equals(e)).
contains in interface Collection<K>
contains in interface Set<K>
o - element whose presence in this collection is to be testedtrue if this collection contains the specified elementNullPointerException - if the specified key is nullpublic boolean remove(Object o)
Removes 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.
remove in interface Collection<K>
remove in interface Set<K>
o - the key to be removed from the backing maptrue if the backing map contained the specified keyNullPointerException - if the specified key is nullpublic Iterator<K> iterator()
Returns an iterator over the elements in this collection.
The returned iterator is weakly consistent.
iterator in interface Iterable<K>
iterator in interface Collection<K>
iterator in interface Set<K>
public boolean add(K e)
Adds the specified key to this set view by mapping the key to the default mapped value in the backing map, if defined.
add in interface Collection<K>
add in interface Set<K>
e - key to be addedtrue if this set changed as a result of the callNullPointerException - if the specified key is nullUnsupportedOperationException - if no default mapped value for additions was providedpublic boolean addAll(Collection<? extends K> c)
Adds all of the elements in the specified collection to this set, as if by calling add(K) on each one.
addAll in interface Collection<K>
addAll in interface Set<K>
c - the elements to be inserted into this settrue if this set changed as a result of the callNullPointerException - if the collection or any of its elements are null
UnsupportedOperationException - if no default mapped value for additions was providedSet.add(Object)public int hashCode()
Description copied from class: Object
Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.
The general contract of hashCode is:
hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application. equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result. Object.equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables. As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the Java™ programming language.)
hashCode in interface Collection<K>
hashCode in interface Set<K>
hashCode in class Object
Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)
public boolean equals(Object o)
Description copied from class: Object
Indicates whether some other object is "equal to" this one.
The equals method implements an equivalence relation on non-null object references:
x, x.equals(x) should return true. x and y, x.equals(y) should return true if and only if y.equals(x) returns true. x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true. x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified. x, x.equals(null) should return false. The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).
Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.
equals in interface Collection<K>
equals in interface Set<K>
equals in class Object
o - the reference object with which to compare.true if this object is the same as the obj argument; false otherwise.Object.hashCode(), HashMap
public Spliterator<K> spliterator()
Description copied from interface: Set
Creates a Spliterator over the elements in this set.
The Spliterator reports Spliterator.DISTINCT. Implementations should document the reporting of additional characteristic values.
spliterator in interface Iterable<K>
spliterator in interface Collection<K>
spliterator in interface Set<K>
Spliterator over the elements in this setpublic void forEach(Consumer<? super K> action)
Description copied from interface: Iterable
Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. Unless otherwise specified by the implementing class, actions are performed in the order of iteration (if an iteration order is specified). Exceptions thrown by the action are relayed to the caller.
forEach in interface Iterable<K>
action - The action to be performed for each elementpublic ConcurrentHashMap<K,V> getMap()
Returns the map backing this view.
public final void clear()
Removes all of the elements from this view, by removing all the mappings from the map backing this view.
clear in interface Collection<E>
public final int size()
Description copied from interface: Collection
Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
size in interface Collection<E>
public final boolean isEmpty()
Description copied from interface: Collection
Returns true if this collection contains no elements.
isEmpty in interface Collection<E>
true if this collection contains no elementspublic final Object[] toArray()
Description copied from interface: Collection
Returns 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 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.
This method acts as bridge between array-based and collection-based APIs.
toArray in interface Collection<E>
public final <T> T[] toArray(T[] a)
Description copied from interface: Collection
Returns 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 any null elements.)
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.
Like the Collection.toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.
Suppose x is a collection known to contain only strings. The following code can be used to dump the collection into a newly allocated array of String:
String[] y = x.toArray(new String[0]);Note that
toArray(new Object[0]) is identical in function to toArray().toArray in interface Collection<E>
T - the runtime type of the array to contain the collectiona - 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.public final String toString()
Returns 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 by String.valueOf(Object).
public final boolean containsAll(Collection<?> c)
Description copied from interface: Collection
Returns true if this collection contains all of the elements in the specified collection.
containsAll in interface Collection<E>
c - collection to be checked for containment in this collectiontrue if this collection contains all of the elements in the specified collectionCollection.contains(Object)public final boolean removeAll(Collection<?> c)
Description copied from interface: Collection
Removes 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.
removeAll in interface Collection<E>
c - collection containing elements to be removed from this collectiontrue if this collection changed as a result of the callCollection.remove(Object), Collection.contains(Object)
public final boolean retainAll(Collection<?> c)
Description copied from interface: Collection
Retains 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.
retainAll in interface Collection<E>
c - collection containing elements to be retained in this collectiontrue if this collection changed as a result of the callCollection.remove(Object), Collection.contains(Object)
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