Java in a Nutshell, 5th Edition

Name

WeakReference<T>

Synopsis

This class refers to an object in a way that does not prevent that referent object from being finalized and reclaimed by the garbage collector. When the garbage collector determines that there are no more hard (direct) references to the object, and that there are no SoftReference objects that refer to the object, it clears the WeakReference and marks the referent object for finalization. At some point after this, it also enqueues the WeakReference on its associated ReferenceQueue, if there is one, in order to provide notification that the referent has been reclaimed.

WeakReference is used by java.util.WeakHashMap to implement a hashtable that does not prevent the hashtable key object from being garbage-collected. WeakHashMap is useful when you want to associate auxiliary information with an object but do not want to prevent the object from being reclaimed.

Figure 10-90. java.lang.ref.WeakReference<T>

public class WeakReference<T> extends Reference<T> {
// Public Constructors
     public WeakReference(T referent);  
     public WeakReference(T referent, ReferenceQueue<? super T> q);  

}