java.lang.ref

Class Reference<T>

public abstract class Reference<T> extends Object

This is the base class of all references. A reference allows refering to an object without preventing the garbage collector to collect it. The only way to get the referred object is via the get()-method. This method will return null if the object was collected.
A reference may be registered with a queue. When a referred element gets collected the reference will be put on the queue, so that you will be notified.
There are currently three types of references: soft reference, weak reference and phantom reference.
Soft references will be cleared if the garbage collector is told to free some memory and there are no unreferenced or weakly referenced objects. It is useful for caches.
Weak references will be cleared as soon as the garbage collector determines that the refered object is only weakly reachable. They are useful as keys in hashtables (see WeakHashtable) as you get notified when nobody has the key anymore. Phantom references don't prevent finalization. If an object is only phantom reachable, it will be finalized, and the reference will be enqueued, but not cleared. Since you mustn't access an finalized object, the get method of a phantom reference will never work. It is useful to keep track, when an object is finalized.

See Also: WeakHashMap

Method Summary
voidclear()
Clears the reference, so that it doesn't refer to its object anymore.
booleanenqueue()
Enqueue an object on a reference queue.
Tget()
Returns the object, this reference refers to.
booleanisEnqueued()
Tells if the object is enqueued on a reference queue.

Method Detail

clear

public void clear()
Clears the reference, so that it doesn't refer to its object anymore. For soft and weak references this is called by the garbage collector. For phantom references you should call this when enqueuing the reference.

enqueue

public boolean enqueue()
Enqueue an object on a reference queue. This is normally executed by the garbage collector.

get

public T get()
Returns the object, this reference refers to.

Returns: the object, this reference refers to, or null if the reference was cleared.

isEnqueued

public boolean isEnqueued()
Tells if the object is enqueued on a reference queue.

Returns: true if it is enqueued, false otherwise.