import java.util.HashMap;

import java.lang.ref.SoftReference;

class SoftCache<K, V>{

private HashMap<K, SoftReference<V>> map;

public SoftCache(){

map = new HashMap<K, SoftReference<V>>();

}

public V get(K key){

SoftReference<V> softRef = map.get(key);

if(softRef == null){

return null;

}else{

return softRef.get();

}

}

public V put(K key, V value){

SoftReference<V> previousSoftRef = map.put(key, new SoftReference<V>(value));

if(previousSoftRef == null){

return null;

}else{

V oldValue = previousSoftRef.get();

previousSoftRef.clear(); // Make the old referent null.

return oldValue;

}

}

public V remove(K key){

SoftReference<V> softRef = map.remove(key);

if(softRef == null){

return null;

}else{

V oldValue = softRef.get();

softRef.clear();

return oldValue;

}

}

}

class Image{

private byte[] image;

private Image(String name){

image = new byte[1024*1024*100];

}

static Image getImage(String name){

return new Image(name);

}

}

public class SoftCacheDemo{

public static void main(String[] args){

SoftCache<Integer, Image> sc = new SoftCache<Integer, Image>();

int i = 0;

while(true){

System.out.printf("Putting large image %d into soft cache%n", i);

sc.put(i, Image.getImage("large.png" + i));

i++;

int x = (int)(Math.random()*i); // less than i

System.out.printf("Acquiring image %d from cache.%n", x);

Image img = sc.get(x);

if(img == null){

System.out.printf("Image %d no longer in cache. Re-caching.%n", x);

sc.put(x, img = Image.getImage("large.png" + x));

}

System.out.printf("Drawing image %d%n", x);

img = null; // Remove strong reference to image.

}

}

}