E - the type of elements in the set.public class WeakHashSet<E> extends AbstractSet<E> implements CheckedContainer<E>
WeakHashSet will automatically
be removed when it is no longer in ordinary use. More precisely, the presence of an entry will
not prevent the entry from being discarded by the garbage collector, that is, made finalizable,
finalized, and then reclaimed. When an entry has been discarded it is effectively removed from
the set, so this class behaves somewhat differently than other Set implementations.
If the elements stored in this set are arrays like int[], float[] or
Object[], then the hash code computations and the comparisons are performed using
the static hashCode(a) and equals(a1, a2) methods defined in the Arrays
class.
WeakHashSet class has a get(Object) method that is not part of the
Set interface. This get method retrieves an entry from this set
that is equals to the supplied object. The unique(Object) method combines a
get followed by a add operation if the specified object was not in the set.
This is similar in spirit to the String.intern() method. The following example shows
a convenient way to use WeakHashSet as an internal pool of immutable objects:
private final WeakHashSet<Foo> pool = new WeakHashSet<Foo>(Foo.class);
public Foo create(String definition) {
Foo created = new Foo(definition);
return pool.unique(created);
}
Thus, WeakHashSet can be used inside a factory to prevent creating duplicate immutable objects.
WeakHashSet instance can be safely used by many threads without synchronization on the part of
the caller. But if a sequence of two or more method calls need to appear atomic from other threads perspective,
then the caller can synchronize on this.WeakHashMapDefined in the sis-utility module
| Constructor and Description |
|---|
WeakHashSet(Class<E> type)
Creates a
WeakHashSet for elements of the specified type. |
| Modifier and Type | Method and Description |
|---|---|
boolean |
add(E element)
Adds the specified element to this set if it is not already present.
|
void |
clear()
Removes all of the elements from this set.
|
boolean |
contains(Object element)
Returns
true if this set contains the specified element. |
E |
get(Object element)
Returns an object equals to the specified object, if present.
|
Class<E> |
getElementType()
Returns the type of elements in this set.
|
Iterator<E> |
iterator()
Returns an iterator over the elements contained in this collection.
|
boolean |
remove(Object element)
Removes a single instance of the specified element from this set, if it is present
Null values are considered never present.
|
int |
size()
Returns the count of element in this set.
|
E[] |
toArray()
Returns a view of this set as an array.
|
<T extends E> |
unique(T element)
Returns an object equals to
element if such an object already exist in this
WeakHashSet. |
equals, hashCode, removeAlladdAll, containsAll, isEmpty, retainAll, toArray, toStringclone, finalize, getClass, notify, notifyAll, wait, wait, waitaddAll, containsAll, isEmpty, retainAll, spliterator, toArrayparallelStream, removeIf, streampublic Class<E> getElementType()
getElementType in interface CheckedContainer<E>public int size()
size in interface Collection<E>size in interface Set<E>size in class AbstractCollection<E>public boolean add(E element) throws NullArgumentException
false.add in interface Collection<E>add in interface Set<E>add in class AbstractCollection<E>element - element to be added to this set.true if this set did not already contain the specified element.NullArgumentException - if the given object is null.public boolean remove(Object element)
remove in interface Collection<E>remove in interface Set<E>remove in class AbstractCollection<E>element - element to be removed from this set, if present. Can be null.true if the set contained the specified element.public E get(Object element)
element, then this method returns null.
Null values are considered never present.element - the element to get.null otherwise.unique(Object)public boolean contains(Object element)
true if this set contains the specified element.
Null values are considered never present.contains in interface Collection<E>contains in interface Set<E>contains in class AbstractCollection<E>element - object to be checked for containment in this set. Can be null.true if this set contains the specified element.public <T extends E> T unique(T element)
element if such an object already exist in this
WeakHashSet. Otherwise, adds element to this WeakHashSet.
This method is functionally equivalents to the following code:
if (element != null) {
T current = get(element);
if (current != null) {
return current;
} else {
add(element);
}
}
return element;T - the type of the element to get. Can be null.element - the element to get or to add in the set if not already presents,
or null if the given element was null.object otherwise.public void clear()
clear in interface Collection<E>clear in interface Set<E>clear in class AbstractCollection<E>public E[] toArray()
toArray in interface Collection<E>toArray in interface Set<E>toArray in class AbstractCollection<E>Copyright © 2010–2017 The Apache Software Foundation. All rights reserved.