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 CachingIn 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
Creates a new soft reference that refers to the given object.
Inherited Method Summary
Clears this reference object.
Adds this reference object to the queue with which it is registered, if any.
Invoked when the garbage collector has detected that this instance is no longer reachable.
Returns this reference object's referent.
Tells whether or