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jdk.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.

class Handler { void handle(); ... }

class X { private final CopyOnWriteArraySet<Handler> handlers = new CopyOnWriteArraySet<Handler>(); 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(); } }

This class is a member of the

Java Collections Framework.

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.



class Handler { void handle(); ... }

class X {
  private final CopyOnWriteArraySet<Handler> handlers
    = new CopyOnWriteArraySet<Handler>();
  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();
  }
}

This class is a member of the

Java Collections Framework.
raw docstring

->copy-on-write-array-setclj

(->copy-on-write-array-set)
(->copy-on-write-array-set c)

Constructor.

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

c - the collection of elements to initially contain - java.util.Collection

throws: java.lang.NullPointerException - if the specified collection is null

Constructor.

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

c - the collection of elements to initially contain - `java.util.Collection`

throws: java.lang.NullPointerException - if the specified collection is null
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addclj

(add this e)

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 (e==null ? e2==null : e.equals(e2)). If this set already contains the element, the call leaves the set unchanged and returns false.

e - element to be added to this set - E

returns: true if this set did not already contain the specified element - 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
 (e==null ? e2==null : e.equals(e2)).
 If this set already contains the element, the call leaves the set
 unchanged and returns false.

e - element to be added to this set - `E`

returns: true if this set did not already contain the specified
         element - `boolean`
raw docstring

add-allclj

(add-all this c)

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.

c - collection containing elements to be added to this set - java.util.Collection

returns: true if this set changed as a result of the call - boolean

throws: java.lang.NullPointerException - if the specified collection is null

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.

c - collection containing elements to be added to this set - `java.util.Collection`

returns: true if this set changed as a result of the call - `boolean`

throws: java.lang.NullPointerException - if the specified collection is null
raw docstring

clearclj

(clear this)

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

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

(contains this o)

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 (o==null ? e==null : o.equals(e)).

o - element whose presence in this set is to be tested - java.lang.Object

returns: true if this set contains the specified element - 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
 (o==null ? e==null : o.equals(e)).

o - element whose presence in this set is to be tested - `java.lang.Object`

returns: true if this set contains the specified element - `boolean`
raw docstring

contains-allclj

(contains-all this c)

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.

c - collection to be checked for containment in this set - java.util.Collection

returns: true if this set contains all of the elements of the specified collection - boolean

throws: java.lang.NullPointerException - if the specified collection is null

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.

c - collection to be checked for containment in this set - `java.util.Collection`

returns: true if this set contains all of the elements of the
         specified collection - `boolean`

throws: java.lang.NullPointerException - if the specified collection is null
raw docstring

empty?clj

(empty? this)

Returns true if this set contains no elements.

returns: true if this set contains no elements - boolean

Returns true if this set contains no elements.

returns: true if this set contains no elements - `boolean`
raw docstring

equalsclj

(equals this o)

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 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 (e1==null ? e2==null : e1.equals(e2)).

o - object to be compared for equality with this set - java.lang.Object

returns: true if the specified object is equal to this set - 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 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
 (e1==null ? e2==null : e1.equals(e2)).

o - object to be compared for equality with this set - `java.lang.Object`

returns: true if the specified object is equal to this set - `boolean`
raw docstring

for-eachclj

(for-each this action)

Description copied from interface: Iterable

action - The action to be performed for each element - java.util.function.Consumer

Description copied from interface: Iterable

action - The action to be performed for each element - `java.util.function.Consumer`
raw docstring

iteratorclj

(iterator this)

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.

returns: an iterator over the elements in this set - java.util.Iterator<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.

returns: an iterator over the elements in this set - `java.util.Iterator<E>`
raw docstring

removeclj

(remove this o)

Removes the specified element from this set if it is present. More formally, removes an element e such that (o==null ? e==null : o.equals(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.)

o - object to be removed from this set, if present - java.lang.Object

returns: true if this set contained the specified element - boolean

Removes the specified element from this set if it is present.
 More formally, removes an element e such that
 (o==null ? e==null : o.equals(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.)

o - object to be removed from this set, if present - `java.lang.Object`

returns: true if this set contained the specified element - `boolean`
raw docstring

remove-allclj

(remove-all this c)

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.

c - collection containing elements to be removed from this set - java.util.Collection

returns: true if this set changed as a result of the call - boolean

throws: java.lang.ClassCastException - if the class of an element of this set is incompatible with the specified collection (optional)

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.

c - collection containing elements to be removed from this set - `java.util.Collection`

returns: true if this set changed as a result of the call - `boolean`

throws: java.lang.ClassCastException - if the class of an element of this set is incompatible with the specified collection (optional)
raw docstring

remove-ifclj

(remove-if this filter)

Description copied from interface: Collection

filter - a predicate which returns true for elements to be removed - java.util.function.Predicate

returns: true if any elements were removed - boolean

Description copied from interface: Collection

filter - a predicate which returns true for elements to be removed - `java.util.function.Predicate`

returns: true if any elements were removed - `boolean`
raw docstring

retain-allclj

(retain-all this c)

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.

c - collection containing elements to be retained in this set - java.util.Collection

returns: true if this set changed as a result of the call - boolean

throws: java.lang.ClassCastException - if the class of an element of this set is incompatible with the specified collection (optional)

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.

c - collection containing elements to be retained in this set - `java.util.Collection`

returns: true if this set changed as a result of the call - `boolean`

throws: java.lang.ClassCastException - if the class of an element of this set is incompatible with the specified collection (optional)
raw docstring

sizeclj

(size this)

Returns the number of elements in this set.

returns: the number of elements in this set - int

Returns the number of elements in this set.

returns: the number of elements in this set - `int`
raw docstring

spliteratorclj

(spliterator this)

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.

returns: a Spliterator over the elements in this set - java.util.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.

returns: a Spliterator over the elements in this set - `java.util.Spliterator<E>`
raw docstring

to-arrayclj

(to-array this)
(to-array this a)

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:

String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function to toArray().

a - 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. - T[]

returns: an array containing all the elements in this set - <T> T[]

throws: 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

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:



  String[] y = x.toArray(new String[0]);

 Note that toArray(new Object[0]) is identical in function to
 toArray().

a - 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. - `T[]`

returns: an array containing all the elements in this set - `<T> T[]`

throws: 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
raw docstring

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