Reference

Class Overview

Provides an abstract class which describes behavior common to all reference objects. It is not possible to create immediate subclasses of Reference in addition to the ones provided by this package. It is also not desirable to do so, since references require very close cooperation with the system's garbage collector. The existing, specialized reference classes should be used instead.

Three different type of references exist, each being weaker than the preceding one: SoftReference , WeakReference , and PhantomReference . "Weakness" here means that less restrictions are being imposed on the garbage collector as to when it is allowed to actually garbage-collect the referenced object.

In order to use reference objects properly it is important to understand the different types of reachability that trigger their clearing and enqueueing. The following table lists these, from strongest to weakest. For each row, an object is said to have the reachability on the left side if (and only if) it fulfills all of the requirements on the right side. In all rows, consider the root set to be a set of references that are "resistant" to garbage collection (that is, running threads, method parameters, local variables, static fields and the like).

Summary

[Expand] Inherited Methods

From class java.lang.Object Object clone () Creates and returns a copy of this Object . boolean equals ( Object o) Compares this instance with the specified object and indicates if they are equal. void finalize () Invoked when the garbage collector has detected that this instance is no longer reachable. final Class <?> getClass () Returns the unique instance of Class that represents this object's class. int hashCode () Returns an integer hash code for this object. final void notify () Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll () Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString () Returns a string containing a concise, human-readable description of this object. final void wait () Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object. final void wait (long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait (long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.