edu.berkeley.guir.lib.collection
Class ObjectPool

java.lang.Object
  |
  +--edu.berkeley.guir.lib.collection.ObjectPool

Direct Known Subclasses:

SatinConstants.ObjectPoolAffineTransform, SatinConstants.ObjectPoolPoint2D, SatinConstants.ObjectPoolPolygon2D, SatinConstants.ObjectPoolRectangle2D, SatinConstants.ObjectPoolStringBuffer

public abstract class ObjectPool

extends Object

An ObjectPool is a way of reusing objects, in order to avoid garbage collection. Essentially, the ObjectPool gives you an instance of the class you need when requested. When you are done, just notify the ObjectPool that you are no longer using this object, and it will be returned to the ObjectPool.

This implementation is not thread-safe. Use synchronizedObjectPool(ObjectPool) for this purpose. instead.

To use this ObjectPool implementation, you just need to subclass and override the createObject() method to create an empty version of the object you want.

Note: I'm having doubts about the effectiveness of using the ObjectPool in newer versions of JDK. I ran some regression tests with and without ObjectPool, and in most of the cases not using ObjectPool actually won. It may be just this implementation, or it might be that HotSpot really is winning out.

This software is distributed under the Berkeley Software License.

 Revisions:  - GUIRLib-v1.0-1.0.0, Aug 18 1999, JH
               Created class
             - GUIRLib-v1.2-1.0.0, Jun 22 2000, JH
               Touched for GUIRLib release
             - GUIRLib-v1.3-1.0.0, Aug 11 2000, JH
               Touched for GUIRLib release
             - GUIRLib-v1.4-1.0.0, Aug 31 2000, JH
               Touched for GUIRLib release
 

Since:

JDK 1.2

Version:

GUIRLib-v1.4-1.0.0, Aug 31 2000

Author:

(jasonh@cs.berkeley.edu)

Constructor Summary

ObjectPool()
Creates a pool of objects.

ObjectPool(int newCapacity)
Creates a pool of size capacity objects.

Method Summary

static ObjectPool	allocatingObjectPool(ObjectPool p) Get an object pool that isn't really an object pool, but allocates new objects.
protected abstract Object	createObject() Override this method so that it creates the Object you want in the pool.
int	getAvailable() Get the number of available objects.
int	getCapacity() Get the total capacity of the pool.
Object	getObject() Get an object.
boolean	isFree(Object obj) See if an object is free.
boolean	isTaken(Object obj) See if an object is taken.
static void	main(String[] argv)
boolean	ownsObject(Object obj)
void	printDebugStacks() Print what method requested what object from the pool.
void	reinitialize() Clear out all of the objects in the pool and create new ones.
void	releaseObject(Object obj) Mark this object as released.
void	reset() Reset each element in the pool as available.
static ObjectPool	synchronizedObjectPool(ObjectPool p) Get a synchronized object pool.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ObjectPool

public ObjectPool()

Creates a pool of objects.

ObjectPool

public ObjectPool(int newCapacity)

Creates a pool of size capacity objects.

Method Detail

synchronizedObjectPool

public static ObjectPool synchronizedObjectPool(ObjectPool p)

Get a synchronized object pool.

allocatingObjectPool

public static ObjectPool allocatingObjectPool(ObjectPool p)

Get an object pool that isn't really an object pool, but allocates new objects. Useful for debugging purposes.

printDebugStacks

public void printDebugStacks()

Print what method requested what object from the pool. Must compile with debug flag in order for this to work.

createObject

protected abstract Object createObject()

Override this method so that it creates the Object you want in the pool.

getAvailable

public int getAvailable()

Get the number of available objects.

getCapacity

public int getCapacity()

Get the total capacity of the pool.

getObject

public Object getObject()
                 throws EmptyException

Get an object.

Usage Notes:

• It is generally a good idea to override this method and to re-initialize the object before returning it.

Also, be sure not to assign the reference that you get!!! If you do, then you cannot release the object (and will get memory leaks).

Throws:

EmptyException - (a RuntimeException) if empty.

releaseObject

public void releaseObject(Object obj)

Mark this object as released. If this object does not belong to the pool, then ignore.

Override this method to clear out the object's values first, if you want. Be sure to call super correctly. For example, if you have an Object Pool of LinkedList objects, then in your subclass: public void releaseObject(Object obj) { LinkedList list = (LinkedList) obj; list.clear(); super.releaseObject(obj); } // of releaseObject

Parameters:

obj - is the Object to release back into the pool.

Throws:

RuntimeException - if we don't own the object. Useful for detecting errors.

isTaken

public boolean isTaken(Object obj)

See if an object is taken.

Returns:

true if the object is taken, false if not or if it does not belong to this pool.

isFree

public boolean isFree(Object obj)

See if an object is free.

Returns:

true if the object is free, false if not or if it does not belong to this pool.

ownsObject

public boolean ownsObject(Object obj)

reset

public void reset()

Reset each element in the pool as available.

reinitialize

public void reinitialize()

Clear out all of the objects in the pool and create new ones.

toString

public String toString()

Overrides:

toString in class Object

main

public static void main(String[] argv)