Clears this reference object.

  Clears this reference object. Invoking this method will not cause this object to be enqueued.

This method is invoked only by Java code; when the garbage collector clears references it does so directly, without invoking this method.

  Adds this reference object to the queue with which it is registered, if any.

  Adds this reference object to the queue with which it is registered, if any.

This method is invoked only by Java code; when the garbage collector enqueues references it does so directly, without invoking this method.
Returns: true if this reference object was successfully enqueued; false if it was already enqueued or if it was not registered with a queue when it was created

  Returns this reference object's referent.

  Returns this reference object's referent. If this reference object has
been cleared, either by the program or by the garbage collector, then
this method returns null.
Returns: The object to which this reference refers, or null if this reference object has been cleared

  Tells whether or not this reference object has been enqueued, either by the program or by the garbage collector.

  Tells whether or not this reference object has been enqueued, either by
the program or by the garbage collector. If this reference object was
not registered with a queue when it was created, then this method will
always return false.
Returns: true if and only if this reference object has been enqueued