Added in API level 1

CopyOnWriteArraySet

open class CopyOnWriteArraySet<E : Any!> : AbstractSet<E>, Serializable
kotlin.Any
   ↳ java.util.AbstractCollection<E>
   ↳ java.util.AbstractSet<E>
   ↳ java.util.concurrent.CopyOnWriteArraySet

A Set that uses an internal CopyOnWriteArrayList for all of its operations. Thus, it shares the same basic properties:

  • It is best suited for applications in which set sizes generally stay small, read-only operations vastly outnumber mutative operations, and you need to prevent interference among threads during traversal.
  • It is thread-safe.
  • Mutative operations (add, set, remove, etc.) are expensive since they usually entail copying the entire underlying array.
  • Iterators do not support the mutative remove operation.
  • Traversal via iterators is fast and cannot encounter interference from other threads. Iterators rely on unchanging snapshots of the array at the time the iterators were constructed.

Sample Usage. The following code sketch uses a copy-on-write set to maintain a set of Handler objects that perform some action upon state updates.

<code>class Handler { void handle() { ... } }
 
  class X {
    private final CopyOnWriteArraySet&lt;Handler&gt; handlers
      = new CopyOnWriteArraySet&lt;&gt;();
    public void addHandler(Handler h) { handlers.add(h); }
 
    private long internalState;
    private synchronized void changeState() { internalState = ...; }
 
    public void update() {
      changeState();
      for (Handler handler : handlers)
        handler.handle();
    }
  }</code>

This class is a member of the Java Collections Framework.

Summary

Public constructors

Creates an empty set.

Creates a set containing all of the elements of the specified collection.

Public methods
open Boolean
add(element: E)

Adds the specified element to this set if it is not already present.

open Boolean
addAll(elements: Collection<E>)

Adds all of the elements in the specified collection to this set if they're not already present.

open Unit

Removes all of the elements from this set.

open Boolean
contains(element: E?)

Returns true if this set contains the specified element.

open Boolean
containsAll(elements: Collection<E>)

Returns true if this set contains all of the elements of the specified collection.

open Boolean
equals(other: Any?)

Compares the specified object with this set for equality.

open Unit
forEach(action: Consumer<in E>)

open Boolean

Returns true if this set contains no elements.

open MutableIterator<E>

Returns an iterator over the elements contained in this set in the order in which these elements were added.

open Boolean
remove(element: E?)

Removes the specified element from this set if it is present.

open Boolean
removeAll(elements: Collection<E>)

Removes from this set all of its elements that are contained in the specified collection.

open Boolean
removeIf(filter: Predicate<in E>)

open Boolean
retainAll(elements: Collection<E>)

Retains only the elements in this set that are contained in the specified collection.

open Spliterator<E>

Returns a Spliterator over the elements in this set in the order in which these elements were added.

open Array<Any!>

Returns an array containing all of the elements in this set.

open Array<T>
toArray(a: Array<T>)

Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array.

Inherited functions
Properties
open Int

Returns the number of elements in this set.

Inherited properties

Public constructors

CopyOnWriteArraySet

Added in API level 1
CopyOnWriteArraySet()

Creates an empty set.

CopyOnWriteArraySet

Added in API level 1
CopyOnWriteArraySet(c: MutableCollection<out E>!)

Creates a set containing all of the elements of the specified collection.

Parameters
c MutableCollection<out E>!: the collection of elements to initially contain
Exceptions
java.lang.NullPointerException if the specified collection is null

Public methods

add

Added in API level 1
open fun add(element: E): Boolean

Adds the specified element to this set if it is not already present. More formally, adds the specified element e to this set if the set contains no element e2 such that Objects.equals(e, e2). If this set already contains the element, the call leaves the set unchanged and returns false.

Parameters
e element to be added to this set
Return
Boolean true if this set did not already contain the specified element
Exceptions
java.lang.UnsupportedOperationException if the add operation is not supported by this set
java.lang.ClassCastException if the class of the specified element prevents it from being added to this set
java.lang.NullPointerException if the specified element is null and this set does not permit null elements
java.lang.IllegalArgumentException if some property of the specified element prevents it from being added to this set
java.lang.IllegalStateException if the element cannot be added at this time due to insertion restrictions

addAll

Added in API level 1
open fun addAll(elements: Collection<E>): Boolean

Adds all of the elements in the specified collection to this set if they're not already present. If the specified collection is also a set, the addAll operation effectively modifies this set so that its value is the union of the two sets. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Parameters
c collection containing elements to be added to this set
Return
Boolean true if this set changed as a result of the call
Exceptions
java.lang.UnsupportedOperationException if the addAll operation is not supported by this set
java.lang.ClassCastException if the class of an element of the specified collection prevents it from being added to this set
java.lang.NullPointerException if the specified collection is null
java.lang.IllegalArgumentException if some property of an element of the specified collection prevents it from being added to this set
java.lang.IllegalStateException if not all the elements can be added at this time due to insertion restrictions

See Also

    clear

    Added in API level 1
    open fun clear(): Unit

    Removes all of the elements from this set. The set will be empty after this call returns.

    Exceptions
    java.lang.UnsupportedOperationException if the clear method is not supported by this set

    contains

    Added in API level 1
    open fun contains(element: E?): Boolean

    Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that Objects.equals(o, e).

    Parameters
    o element whose presence in this set is to be tested
    Return
    Boolean true if this set contains the specified element
    Exceptions
    java.lang.ClassCastException if the type of the specified element is incompatible with this set (optional)
    java.lang.NullPointerException if the specified element is null and this set does not permit null elements (optional)

    containsAll

    Added in API level 1
    open fun containsAll(elements: Collection<E>): Boolean

    Returns true if this set contains all of the elements of the specified collection. If the specified collection is also a set, this method returns true if it is a subset of this set.

    Parameters
    c collection to be checked for containment in this set
    Return
    Boolean true if this set contains all of the elements of the specified collection
    Exceptions
    java.lang.ClassCastException if the types of one or more elements in the specified collection are incompatible with this set (optional)
    java.lang.NullPointerException if the specified collection is null

    See Also

      equals

      Added in API level 1
      open fun equals(other: Any?): Boolean

      Compares the specified object with this set for equality. Returns true if the specified object is the same object as this object, or if it is also a Set and the elements returned by an java.util.Set#iterator() over the specified set are the same as the elements returned by an iterator over this set. More formally, the two iterators are considered to return the same elements if they return the same number of elements and for every element e1 returned by the iterator over the specified set, there is an element e2 returned by the iterator over this set such that Objects.equals(e1, e2).

      Parameters
      obj the reference object with which to compare.
      o object to be compared for equality with this set
      Return
      Boolean true if the specified object is equal to this set

      forEach

      Added in API level 24
      open fun forEach(action: Consumer<in E>): Unit
      Parameters
      action Consumer<in E>: The action to be performed for each element
      Exceptions
      java.lang.NullPointerException if the specified action is null

      isEmpty

      Added in API level 1
      open fun isEmpty(): Boolean

      Returns true if this set contains no elements.

      Return
      Boolean true if this set contains no elements

      iterator

      Added in API level 1
      open fun iterator(): MutableIterator<E>

      Returns an iterator over the elements contained in this set in the order in which these elements were added.

      The returned iterator provides a snapshot of the state of the set when the iterator was constructed. No synchronization is needed while traversing the iterator. The iterator does NOT support the remove method.

      Return
      MutableIterator<E> an iterator over the elements in this set

      remove

      Added in API level 1
      open fun remove(element: E?): Boolean

      Removes the specified element from this set if it is present. More formally, removes an element e such that Objects.equals(o, e), if this set contains such an element. Returns true if this set contained the element (or equivalently, if this set changed as a result of the call). (This set will not contain the element once the call returns.)

      Parameters
      o object to be removed from this set, if present
      Return
      Boolean true if this set contained the specified element
      Exceptions
      java.lang.ClassCastException if the type of the specified element is incompatible with this set (optional)
      java.lang.NullPointerException if the specified element is null and this set does not permit null elements (optional)
      java.lang.UnsupportedOperationException if the remove operation is not supported by this set

      removeAll

      Added in API level 1
      open fun removeAll(elements: Collection<E>): Boolean

      Removes from this set all of its elements that are contained in the specified collection. If the specified collection is also a set, this operation effectively modifies this set so that its value is the asymmetric set difference of the two sets.

      Parameters
      c collection containing elements to be removed from this set
      Return
      Boolean true if this set changed as a result of the call
      Exceptions
      java.lang.UnsupportedOperationException if the removeAll operation is not supported by this set
      java.lang.ClassCastException if the class of an element of this set is incompatible with the specified collection (optional)
      java.lang.NullPointerException if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null

      See Also

        removeIf

        Added in API level 24
        open fun removeIf(filter: Predicate<in E>): Boolean
        Parameters
        filter Predicate<in E>: a predicate which returns true for elements to be removed
        Return
        Boolean true if any elements were removed
        Exceptions
        java.lang.NullPointerException if the specified filter is null
        java.lang.UnsupportedOperationException if elements cannot be removed from this collection. Implementations may throw this exception if a matching element cannot be removed or if, in general, removal is not supported.

        retainAll

        Added in API level 1
        open fun retainAll(elements: Collection<E>): Boolean

        Retains only the elements in this set that are contained in the specified collection. In other words, removes from this set all of its elements that are not contained in the specified collection. If the specified collection is also a set, this operation effectively modifies this set so that its value is the intersection of the two sets.

        Parameters
        c collection containing elements to be retained in this set
        Return
        Boolean true if this set changed as a result of the call
        Exceptions
        java.lang.UnsupportedOperationException if the retainAll operation is not supported by this set
        java.lang.ClassCastException if the class of an element of this set is incompatible with the specified collection (optional)
        java.lang.NullPointerException if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null

        See Also

          spliterator

          Added in API level 24
          open fun spliterator(): Spliterator<E>

          Returns a Spliterator over the elements in this set in the order in which these elements were added.

          The Spliterator reports Spliterator#IMMUTABLE, Spliterator#DISTINCT, Spliterator#SIZED, and Spliterator#SUBSIZED.

          The spliterator provides a snapshot of the state of the set when the spliterator was constructed. No synchronization is needed while operating on the spliterator.

          Return
          Spliterator<E> a Spliterator over the elements in this set

          toArray

          Added in API level 1
          open fun toArray(): Array<Any!>

          Returns an array containing all of the elements in this set. If this set 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 set. (In other words, this method must allocate a new array even if this set 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.

          Return
          Array<Any!> an array containing all the elements in this set

          toArray

          Added in API level 1
          open fun <T : Any!> toArray(a: Array<T>): Array<T>

          Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array. If the set 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 set.

          If this set fits in the specified array with room to spare (i.e., the array has more elements than this set), the element in the array immediately following the end of the set is set to null. (This is useful in determining the length of this set only if the caller knows that this set does not contain any null elements.)

          If this set 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 #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 set known to contain only strings. The following code can be used to dump the set into a newly allocated array of String:

          <code>String[] y = x.toArray(new String[0]);</code>
          Note that toArray(new Object[0]) is identical in function to toArray().
          Parameters
          <T> the component type of the array to contain the collection
          a Array<T>: the array into which the elements of this set are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
          Return
          Array<T> an array containing all the elements in this set
          Exceptions
          java.lang.ArrayStoreException if the runtime type of the specified array is not a supertype of the runtime type of every element in this set
          java.lang.NullPointerException if the specified array is null

          Properties

          size

          Added in API level 1
          open val size: Int

          Returns the number of elements in this set.

          Return
          Int the number of elements in this set