E - the type of elements held in this collectionpublic 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:
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.
CopyOnWriteArrayList,
Serialized Form| Constructor and Description |
|---|
CopyOnWriteArraySet()
Creates an empty set.
|
CopyOnWriteArraySet(Collection<? extends E> c)
Creates a set containing all of the elements of the specified
collection.
|
| Modifier and Type | Method and Description |
|---|---|
boolean |
add(E e)
Adds the specified element to this set if it is not already present.
|
boolean |
addAll(Collection<? extends E> c)
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(Object o)
Returns true if this set contains the specified element.
|
boolean |
containsAll(Collection<?> c)
Returns true if this set contains all of the elements of the
specified collection.
|
boolean |
equals(Object o)
Compares the specified object with this set for equality.
|
boolean |
isEmpty()
Returns true if this set contains no elements.
|
Iterator<E> |
iterator()
Returns an iterator over the elements contained in this set
in the order in which these elements were added.
|
boolean |
remove(Object o)
Removes the specified element from this set if it is present.
|
boolean |
removeAll(Collection<?> c)
Removes from this set all of its elements that are contained in the
specified collection.
|
boolean |
retainAll(Collection<?> c)
Retains only the elements in this set that are contained in the
specified collection.
|
int |
size()
Returns the number of elements in this set.
|
Object[] |
toArray()
Returns an array containing all of the elements in this set.
|
<T> T[] |
toArray(T[] 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.
|
hashCodetoStringpublic CopyOnWriteArraySet()
public CopyOnWriteArraySet(Collection<? extends E> c)
c - the collection of elements to initially containNullPointerException - if the specified collection is nullpublic int size()
size in interface Collection<E>size in interface Set<E>size in class AbstractCollection<E>public boolean isEmpty()
isEmpty in interface Collection<E>isEmpty in interface Set<E>isEmpty in class AbstractCollection<E>public boolean contains(Object o)
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 testedpublic 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>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.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)
remove in interface Collection<E>remove in interface Set<E>remove in class AbstractCollection<E>o - object to be removed from this set, if presentpublic boolean add(E e)
add in interface Collection<E>add in interface Set<E>add in class AbstractCollection<E>e - element to be added to this setpublic boolean containsAll(Collection<?> c)
containsAll in interface Collection<E>containsAll in interface Set<E>containsAll in class AbstractCollection<E>c - collection to be checked for containment in this setNullPointerException - if the specified collection is nullcontains(Object)public boolean addAll(Collection<? extends E> c)
addAll in interface Collection<E>addAll in interface Set<E>addAll in class AbstractCollection<E>c - collection containing elements to be added to this setNullPointerException - if the specified collection is nulladd(Object)public 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 setClassCastException - 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 nullremove(Object)public 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 setClassCastException - 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 nullremove(Object)public 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
(e1==null ? e2==null : e1.equals(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 setObject.hashCode(),
HashMap