SoftReference

Class Overview

Implements a soft reference, which is the least-weak of the three types of references. Once the garbage collector has decided that an object obj is softly-reachable, the following may happen, either immediately or at a later point:

• A set ref of references is determined. ref contains the following elements:
  • All soft references pointing to obj.
  • All soft references pointing to objects from which obj is strongly reachable.
• All references in ref are atomically cleared.
• At the same time or some time in the future, all references in ref will be enqueued with their corresponding reference queues, if any.

The system may decide not to clear and enqueue soft references until a later time, yet all SoftReferences pointing to softly reachable objects are guaranteed to be cleared before the VM will throw an OutOfMemoryError. Soft references are useful for caches that should automatically have their entries removed once they are not referenced any more (from outside), and there is a need for memory. The difference between a SoftReference and a WeakReference is the point of time at which the decision is made to clear and enqueue the reference:

• A SoftReference should be cleared and enqueued as late as possible, that is, in case the VM is in danger of running out of memory.
• A WeakReference may be cleared and enqueued as soon as is known to be weakly-referenced.

Summary

Public Constructors
	SoftReference(T r) Constructs a new soft reference to the given referent.
	SoftReference(T r, ReferenceQueue<? super T> q) Constructs a new soft reference to the given referent.

[Expand] Inherited Methods
From class java.lang.ref.Reference void clear() Makes the referent null. boolean enqueue() Forces the reference object to be enqueued if it has been associated with a queue. T get() Returns the referent of the reference object. boolean isEnqueued() Checks whether the reference object has been enqueued.
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() Is called before the object's memory is being reclaimed by the VM. final Class<? extends Object> getClass() Returns the unique instance of Class which 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 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. final void wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.