Module java.base
Package java.util.concurrent

Class ConcurrentHashMap.KeySetView<K,​V>

java.lang.Object
java.util.concurrent.ConcurrentHashMap.KeySetView<K,​V>
All Implemented Interfaces:
Serializable, Iterable<K>, Collection<K>, Set<K>
Enclosing class:
ConcurrentHashMap<K,​V>
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).
Since:
1.8
See Also:
Serialized Form

  • Method Summary

    Modifier and Type
    Method
    Description
    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.
    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.
    void
    clear()
    Removes all of the elements from this view, by removing all the mappings from the map backing this view.
    boolean
    contains​(Object o)
    Returns true if this collection contains the specified element.
    boolean
    containsAll​(Collection<?> c)
    Returns true if this collection contains all of the elements in the specified collection.
    boolean
    equals​(Object o)
    Indicates whether some other object is "equal to" this one.
    ConcurrentHashMap<K,​V>
    getMap()
    Returns the map backing this view.
    V
    getMappedValue()
    Returns the default mapped value for additions, or null if additions are not supported.
    int
    hashCode()
    Returns a hash code value for the object.
    boolean
    isEmpty()
    Returns true if this collection contains no elements.
    Iterator<K>
    iterator()
    Returns an iterator over the elements in this collection.
    boolean
    remove​(Object o)
    Removes the key from this map view, by removing the key (and its corresponding value) from the backing map.
    boolean
    removeAll​(Collection<?> c)
    Removes all of this collection's elements that are also contained in the specified collection (optional operation).
    boolean
    retainAll​(Collection<?> c)
    Retains only the elements in this collection that are contained in the specified collection (optional operation).
    int
    size()
    Returns the number of elements in this collection.
    Object[]
    toArray()
    Returns an array containing all of the elements in this collection.
    <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.
    String
    toString()
    Returns a string representation of this collection.

    Methods declared in class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

    Methods declared in interface java.util.Collection

    parallelStream, removeIf, stream, toArray

    Methods declared in interface java.lang.Iterable

    forEach

    Methods declared in interface java.util.Set

    clear, containsAll, isEmpty, removeAll, retainAll, size, spliterator, toArray, toArray

  • Method Details

    • getMappedValue

      public V getMappedValue()
      Returns the default mapped value for additions, or null if additions are not supported.
      Returns:
      the default mapped value for additions, or null if not supported

    • contains

      public 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 Objects.equals(o, e).
      Specified by:
      contains in interface Collection<K>
      Specified by:
      contains in interface Set<K>
      Parameters:
      o - element whose presence in this collection is to be tested
      Returns:
      true if this collection contains the specified element
      Throws:
      NullPointerException - if the specified key is null

    • remove

      public 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.
      Specified by:
      remove in interface Collection<K>
      Specified by:
      remove in interface Set<K>
      Parameters:
      o - the key to be removed from the backing map
      Returns:
      true if the backing map contained the specified key
      Throws:
      NullPointerException - if the specified key is null

    • iterator

      public Iterator<K> iterator()
      Returns an iterator over the elements in this collection.

      The returned iterator is weakly consistent.

      Specified by:
      iterator in interface Collection<K>
      Specified by:
      iterator in interface Iterable<K>
      Specified by:
      iterator in interface Set<K>
      Returns:
      an iterator over the keys of the backing map

    • add

      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.
      Specified by:
      add in interface Collection<K>
      Specified by:
      add in interface Set<K>
      Parameters:
      e - key to be added
      Returns:
      true if 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

    • addAll

      public 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.
      Specified by:
      addAll in interface Collection<K>
      Specified by:
      addAll in interface Set<K>
      Parameters:
      c - the elements to be inserted into this set
      Returns:
      true if 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:
      Set.add(Object)

    • hashCode

      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:

      • Whenever it is invoked on the same object more than once during an execution of a Java application, the 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.
      • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
      • It is not required that if two objects are unequal according to the 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.
      Specified by:
      hashCode in interface Collection<K>
      Specified by:
      hashCode in interface Set<K>
      Overrides:
      hashCode in class Object
      Returns:
      a hash code value for this object.
      See Also:
      Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

    • equals

      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:

      • It is reflexive: for any non-null reference value x, x.equals(x) should return true.
      • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
      • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
      • It is consistent: for any non-null reference values 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.
      • For any non-null reference value 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.

      Specified by:
      equals in interface Collection<K>
      Specified by:
      equals in interface Set<K>
      Overrides:
      equals in class Object
      Parameters:
      o - the reference object with which to compare.
      Returns:
      true if this object is the same as the obj argument; false otherwise.
      See Also:
      Object.hashCode(), HashMap

    • getMap

      public ConcurrentHashMap<K,​V> getMap()
      Returns the map backing this view.
      Returns:
      the map backing this view

    • clear

      public final void clear()
      Removes all of the elements from this view, by removing all the mappings from the map backing this view.
      Specified by:
      clear in interface Collection<K>

    • size

      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.
      Specified by:
      size in interface Collection<K>
      Returns:
      the number of elements in this collection

    • isEmpty

      public final boolean isEmpty()
      Description copied from interface: Collection
      Returns true if this collection contains no elements.
      Specified by:
      isEmpty in interface Collection<K>
      Returns:
      true if this collection contains no elements

    • toArray

      public 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's runtime component type is Object.

      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:
      toArray in interface Collection<K>
      Returns:
      an array, whose runtime component type is Object, containing all of the elements in this collection

    • toArray

      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.

      Specified by:
      toArray in 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

    • toString

      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).
      Overrides:
      toString in class Object
      Returns:
      a string representation of this collection

    • containsAll

      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.
      Specified by:
      containsAll in interface Collection<K>
      Parameters:
      c - collection to be checked for containment in this collection
      Returns:
      true if this collection contains all of the elements in the specified collection
      See Also:
      Collection.contains(Object)

    • removeAll

      public 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.
      Specified by:
      removeAll in interface Collection<K>
      Parameters:
      c - collection containing elements to be removed from this collection
      Returns:
      true if this collection changed as a result of the call
      See Also:
      Collection.remove(Object), Collection.contains(Object)

    • retainAll

      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.
      Specified by:
      retainAll in interface Collection<K>
      Parameters:
      c - collection containing elements to be retained in this collection
      Returns:
      true if this collection changed as a result of the call
      See Also:
      Collection.remove(Object), Collection.contains(Object)