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Java Platform 1.2
Beta 4

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Class java.lang.ref.SoftReference

java.lang.Object
  |
  +--java.lang.ref.Reference
        |
        +--java.lang.ref.SoftReference

public class SoftReference

extends Reference

Soft reference objects, which are cleared at the discretion of the garbage collector in order to release memory for reclamation.

If the garbage collector determines at a certain point in time that an object is no longer strongly reachable, then at that time it may choose to clear all soft references to the object in order to release the memory that it occupies for reuse. If a soft reference is registered with a reference queue, then it will be enqueued some time after it is cleared.

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 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.

Since:

JDK1.2

See Also:

Reference

Constructor Summary

SoftReference(Object referent, ReferenceQueue q)
Create a new soft reference that refers to the given object and is registered with the given queue.

SoftReference(Object referent)
Create a new soft reference that refers to the given object.

Method Summary

Object

get() Return the object to which this reference object refers.

Methods inherited from class java.lang.ref.Reference

clear , enqueue , isEnqueued

Methods inherited from class java.lang.Object

clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait

Constructor Detail

SoftReference

public SoftReference(Object referent)

Create a new soft reference that refers to the given object. The new reference is not registered with any queue.

SoftReference

public SoftReference(Object referent,
                     ReferenceQueue q)

Create a new soft reference that refers to the given object and is registered with the given queue.

Throws:

NullPointerException - If the queue argument is null

Method Detail

get

public Object get()

Return the object to which this reference object refers. If this reference has been cleared, either by the program or by the garbage collector, then return null.

Overrides:

get in class Reference