E - the type of elements held in this setSerializable, Iterable<E>, Collection<E>, Set<E>
public class CopyOnWriteArraySet<E> extends AbstractSet<E> implements Serializable
Set that uses an internal CopyOnWriteArrayList for all of its operations. Thus, it shares the same basic properties: add, set, remove, etc.) are expensive since they usually entail copying the entire underlying array. remove operation. 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<>();
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.
| Constructor | Description |
|---|---|
CopyOnWriteArraySet() |
Creates an empty set. |
CopyOnWriteArraySet |
Creates a set containing all of the elements of the specified collection. |
| Modifier and Type | Method | Description |
|---|---|---|
boolean |
add |
Adds the specified element to this set if it is not already present. |
boolean |
addAll |
Adds all of the elements in the specified collection to this set if they're not already present. |
void |
clear() |
Removes all of the elements from this set. |
boolean |
contains |
Returns true if this set contains the specified element. |
boolean |
containsAll |
Returns true if this set contains all of the elements of the specified collection. |
boolean |
equals |
Compares the specified object with this set for equality. |
void |
forEach |
Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. |
boolean |
isEmpty() |
Returns true if this set contains no elements. |
Iterator |
iterator() |
Returns an iterator over the elements contained in this set in the order in which these elements were added. |
boolean |
remove |
Removes the specified element from this set if it is present. |
boolean |
removeAll |
Removes from this set all of its elements that are contained in the specified collection. |
boolean |
removeIf |
Removes all of the elements of this collection that satisfy the given predicate. |
boolean |
retainAll |
Retains only the elements in this set that are contained in the specified collection. |
int |
size() |
Returns the number of elements in this set. |
Spliterator |
spliterator() |
Returns a Spliterator over the elements in this set in the order in which these elements were added. |
Object[] |
toArray() |
Returns an array containing all of the elements in this set. |
<T> T[] |
toArray |
Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array. |
hashCode
toString
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
parallelStream, stream, toArray
public CopyOnWriteArraySet()
public CopyOnWriteArraySet(Collection<? extends E> c)
c - the collection of elements to initially containNullPointerException - if the specified collection is nullpublic int size()
public boolean isEmpty()
true if this set contains no elements.isEmpty in interface Collection<E>
isEmpty in interface Set<E>
isEmpty in class AbstractCollection<E>
true if this set contains no elementspublic boolean contains(Object o)
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).contains in interface Collection<E>
contains in interface Set<E>
contains in class AbstractCollection<E>
o - element whose presence in this set is to be testedtrue if this set contains the specified elementpublic Object[] toArray()
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.
toArray in interface Collection<E>
toArray in interface Set<E>
toArray in class AbstractCollection<E>
public <T> T[] toArray(T[] a)
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().toArray in interface Collection<E>
toArray in interface Set<E>
toArray in class AbstractCollection<E>
T - the component type of the array to contain the collectiona - 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.ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this setNullPointerException - if the specified array is nullpublic void clear()
clear in interface Collection<E>
clear in interface Set<E>
clear in class AbstractCollection<E>
public boolean remove(Object o)
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.)remove in interface Collection<E>
remove in interface Set<E>
remove in class AbstractCollection<E>
o - object to be removed from this set, if presenttrue if this set contained the specified elementpublic boolean add(E e)
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.add in interface Collection<E>
add in interface Set<E>
add in class AbstractCollection<E>
e - element to be added to this settrue if this set did not already contain the specified elementpublic boolean containsAll(Collection<?> c)
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.containsAll in interface Collection<E>
containsAll in interface Set<E>
containsAll in class AbstractCollection<E>
c - collection to be checked for containment in this settrue if this set contains all of the elements of the specified collectionNullPointerException - if the specified collection is nullpublic boolean addAll(Collection<? extends E> c)
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.addAll in interface Collection<E>
addAll in interface Set<E>
addAll in class AbstractCollection<E>
c - collection containing elements to be added to this settrue if this set changed as a result of the callNullPointerException - if the specified collection is nullpublic boolean removeAll(Collection<?> c)
removeAll in interface Collection<E>
removeAll in interface Set<E>
removeAll in class AbstractSet<E>
c - collection containing elements to be removed from this settrue if this set changed as a result of the callClassCastException - if the class of an element of this set is incompatible with the specified collection (optional)NullPointerException - if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is nullpublic boolean retainAll(Collection<?> c)
retainAll in interface Collection<E>
retainAll in interface Set<E>
retainAll in class AbstractCollection<E>
c - collection containing elements to be retained in this settrue if this set changed as a result of the callClassCastException - if the class of an element of this set is incompatible with the specified collection (optional)NullPointerException - if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is nullpublic Iterator<E> iterator()
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.
public boolean equals(Object o)
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 Objects.equals(e1, e2).equals in interface Collection<E>
equals in interface Set<E>
equals in class AbstractSet<E>
o - object to be compared for equality with this settrue if the specified object is equal to this setpublic boolean removeIf(Predicate<? super E> filter)
CollectionremoveIf in interface Collection<E>
filter - a predicate which returns true for elements to be removedtrue if any elements were removedNullPointerException - if the specified filter is nullpublic void forEach(Consumer<? super E> action)
IterableIterable until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller. The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
forEach in interface Iterable<E>
action - The action to be performed for each elementNullPointerException - if the specified action is nullpublic Spliterator<E> spliterator()
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.
spliterator in interface Collection<E>
spliterator in interface Iterable<E>
spliterator in interface Set<E>
Spliterator over the elements in this set
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/CopyOnWriteArraySet.html