ReferenceQueue

AI-generated Key Takeaways

• ReferenceQueue is used by the garbage collector to hold registered reference objects after their reachability changes.

• It provides methods like poll, remove to retrieve these reference objects from the queue.

• poll is non-blocking and returns immediately with a reference object if available or null otherwise.

• remove is blocking and waits for a reference object to become available, optionally with a timeout.

• Using ReferenceQueue, you can be notified about objects becoming eligible for garbage collection and perform cleanup tasks.

public class ReferenceQueue extends Object

Reference queues, to which registered reference objects are appended by the garbage collector after the appropriate reachability changes are detected.

Public Constructor Summary

ReferenceQueue() Constructs a new reference-object queue.

Public Method Summary

Reference<? extends T>	poll() Polls this queue to see if a reference object is available.
Reference<? extends T>	remove(long timeout) Removes the next reference object in this queue, blocking until either one becomes available or the given timeout period expires.
Reference<? extends T>	remove() Removes the next reference object in this queue, blocking until one becomes available.

Inherited Method Summary

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 ReferenceQueue ()

Constructs a new reference-object queue.

Public Methods

public Reference<? extends T> poll ()

Polls this queue to see if a reference object is available. If one is available without further delay then it is removed from the queue and returned. Otherwise this method immediately returns null.

Returns

• A reference object, if one was immediately available, otherwise null

public Reference<? extends T> remove (long timeout)

Removes the next reference object in this queue, blocking until either one becomes available or the given timeout period expires.

This method does not offer real-time guarantees: It schedules the timeout as if by invoking the Object.wait(long) method.

Parameters

timeout	If positive, block for up to timeout milliseconds while waiting for a reference to be added to this queue. If zero, block indefinitely.

Returns

• A reference object, if one was available within the specified timeout period, otherwise null

Throws

IllegalArgumentException	If the value of the timeout argument is negative
InterruptedException	If the timeout wait is interrupted

public Reference<? extends T> remove ()

Removes the next reference object in this queue, blocking until one becomes available.

Returns

• A reference object, blocking until one becomes available

Throws

InterruptedException	If the wait is interrupted