ImageButton

Listing 1:

import java.awt.*;

import java.lang.ref.*;

public class ImageButton extends Button {

    private SoftReference imageReference=null;

    public ImageButton() { 

super(); 

    }

    public void paint(Graphics g) {

Image image=null;

if (imageReference != null)  // null first time we paint

    image = (Image)imageReference.get();

if (image == null) {

    image = loadImage("Image name");

    imageReference = new SoftReference(image);

}

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.

.

image = null;

    }

    public Image loadImage(String name) { 

.

.

.

   }

}

}

Listing 2:      

  }

import java.lang.ref.*;

import java.util.Vector;

public class SoftCache {

    Vector vector=null;

    Thread remover;

    ReferenceQueue clearedRefs;

    public SoftCache() {

vector = new Vector();

clearedRefs = new ReferenceQueue();

// start thread to delete cleared references from the cache

remover = new Remover(clearedRefs,vector);

remover.start();

    }

    public void put(Object o) {

synchronized (vector) {

    vector.addElement(new SoftReference(o,clearedRefs));

}

    }

    public Object get() {

synchronized (vector) {

    if (vector.size() > 0) {

SoftReference sr = (SoftReference)vector.elementAt(0);

vector.remove(0);

return sr.get();

    }

}

return null;

    }

    private class Remover extends Thread {

ReferenceQueue refQ;

Vector cache;

public Remover (ReferenceQueue rq, Vector v) {

    super();

    refQ = rq;

    cache = v;

    setDaemon(true);

}

public void run() {

    try {

while (true) {

    Object o = refQ.remove();

    synchronized (cache) {

cache.removeElement(o);

System.out.println("Removing " + o);

    }

}

    } catch (InterruptedException e) { ; }

}

    }

}