SoftReference

public class SoftReference extends Reference<T>

Soft reference objects, which are cleared at the discretion of the garbage collector in response to memory demand.

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.

Avoid Soft References for Caching

In practice, soft references are inefficient for caching. The runtime doesn't have enough information on which references to clear and which to keep. Most fatally, it doesn't know what to do when given the choice between clearing a soft reference and growing the heap.

The lack of information on the value to your application of each reference limits the usefulness of soft references. References that are cleared too early cause unnecessary work; those that are cleared too late waste memory.

Most applications should use an android.util.LruCache instead of soft references. LruCache has an effective eviction policy and lets the user tune how much memory is allotted.

Public Constructor Summary

	SoftReference(T referent) Creates a new soft reference that refers to the given object.
	SoftReference(T referent, ReferenceQueue<? super T> q) Creates a new soft reference that refers to the given object and is registered with the given queue.

Inherited Method Summary

From class java.lang.ref.Reference

void	clear() Clears this reference object.
boolean	enqueue() Adds this reference object to the queue with which it is registered, if any.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
T	get() Returns this reference object's referent.
boolean	isEnqueued() Tells whether or not this reference object has been enqueued, either by the program or by the garbage collector.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) 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(long timeout, 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 timeout) 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() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public SoftReference (T referent)

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

Parameters

referent	object the new soft reference will refer to

public SoftReference (T referent, ReferenceQueue<? super T> q)

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

Parameters

referent	object the new soft reference will refer to
q	the queue with which the reference is to be registered, or null if registration is not required