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This file contains all the changes in documentation in the packagejava.lang.ref
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Phantom reference objects which are enqueued after the collector determines that their referents may otherwise be reclaimed. Phantom references are most often used for scheduling pre-mortem cleanup actions in a more flexible way than is possible with the Java finalization mechanism.Class PhantomReference, constructor PhantomReference(Object, ReferenceQueue)If the garbage collector determines at a certain point in time that the referent of a phantom reference is phantom reachable then at that time or at some later time it will enqueue the reference.
In order to ensure that a reclaimable object remains so the referent of a phantom reference may not be retrieved: The
get
method of a phantom reference always returnsnull
.Unlike soft and weak references phantom references are not automatically cleared by the garbage collector as they are enqueued. An object that is reachable via phantom references will remain so until all such references are cleared or themselves become unreachable. @version 1.
12 0214 12/0203/0001 @author Mark Reinhold @since 1.2
Creates a new phantom reference that refers to the given object and is registered with the given queue. @param referent the object the new phantom reference will refer to @param q queue the phantom reference is registered with @throws NullPointerException If thequeue
argument isnull
Abstract base class for reference objects. This class defines the operations common to all reference objects. Because reference objects are implemented in close cooperation with the garbage collector this class may not be subclassed directly. @version 1.29 0231 12/0203/0001 @author Mark Reinhold @since 1.2
Reference queues to which registered reference objects are appended by the garbage collector after the appropriate reachability changes are detected. @version 1.Class ReferenceQueue, Reference poll()14 0219 12/0203/0001 @author Mark Reinhold @since 1.2
Polls this queue to see if a reference object is available.Class ReferenceQueue, Reference remove()returningIf oneimmediatelyisifavailableso.withoutIffurther delay then it is removed from the queueisand returned.emptyOtherwise this method immediately returns null. @return A reference object if one was immediately available otherwisenull
Removes the next reference object in this queue blocking until one becomes available. @return A reference object blocking until one becomes available @throws InterruptedException If the wait is interruptedClass ReferenceQueue, Reference remove(long)
Removes the next reference object in this queue blocking until either one becomes available or the given timeout period expires.This method does not offer real-time guarantees: It schedules the timeout as if by invoking the Object#wait(long) method. @param timeout If positive block for up
timeout
milliseconds while waiting for a reference to be added to this queue. If zero block indefinitely. @return A reference object if one was available within the specified timeout period otherwisenull
@throws IllegalArgumentException If the value of the timeout argument is negative @throws InterruptedException If the timeout wait is interrupted
Soft reference objects which are cleared at the discretion of the garbage collector in response to memory demand. Soft references are most often used to implement memory-sensitive caches.Class SoftReference, constructor SoftReference(Object)Suppose that the garbage collector determines at a certain point in time that an object is softly reachable. At that time it may choose to clear atomically all soft references to that object and all soft references to any other softly-reachable objects from which that object is reachable through a chain of strong references. At the same time or at some later time it will enqueue those newly-cleared soft references that are registered with reference queues.
All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an
OutOfMemoryError
. Otherwise no constraints are placed upon the time at which a soft reference will be cleared or the order in which a set of such references to different objects will be cleared. Virtual machine implementations are however encouraged to bias against clearing recently-created or recently-used soft references.Direct instances of this class may be used to implement simple caches; this class or derived subclasses may also be used in larger data structures to implement more sophisticated caches. As long as the referent of a soft reference is strongly reachable that is is actually in use the soft reference will not be cleared. Thus a sophisticated cache can for example prevent its most recently used entries from being discarded by keeping strong referents to those entries leaving the remaining entries to be discarded at the discretion of the garbage collector. @version 1.
27 0229 12/0203/0001 @author Mark Reinhold @since 1.2
Creates a new soft reference that refers to the given object. The new reference is not registered with any queue. @param referent object the new soft reference will refer toClass SoftReference, constructor SoftReference(Object, ReferenceQueue)
Creates a new soft reference that refers to the given object and is registered with the given queue. @param referent object the new soft reference will refer to @param q queue the soft reference is registered with @throws NullPointerException If thequeue
argument isnull
Weak reference objects which do not prevent their referents from being made finalizable finalized and then reclaimed. Weak references are most often used to implement canonicalizing mappings.Class WeakReference, constructor WeakReference(Object)Suppose that the garbage collector determines at a certain point in time that an object is weakly reachable. At that time it will atomically clear all weak references to that object and all weak references to any other weakly-reachable objects from which that object is reachable through a chain of strong and soft references. At the same time it will declare all of the formerly weakly-reachable objects to be finalizable. At the same time or at some later time it will enqueue those newly-cleared weak references that are registered with reference queues. @version 1.
11 0213 12/0203/0001 @author Mark Reinhold @since 1.2
Creates a new weak reference that refers to the given object. The new reference is not registered with any queue. @param referent object the new weak reference will refer toClass WeakReference, constructor WeakReference(Object, ReferenceQueue)
Creates a new weak reference that refers to the given object and is registered with the given queue. @param referent object the new weak reference will refer to @param q queue the weak reference is registered with @throws NullPointerException If thequeue
argument isnull