import java.lang.ref.ReferenceQueue;

import java.lang.ref.PhantomReference;

public class PhantomReferenceDemo{

public static void main(String[] args){

ReferenceQueue<LargeObject> refQueue = new ReferenceQueue<LargeObject>();

PhantomReference<LargeObject> phantomRef = new PhantomReference<LargeObject>(new LargeObject(), refQueue);

while(refQueue.poll() == null){ // GC did not detect phantom reference type yet.

System.out.println("Waiting for first large object to be finalized...");

new LargeObject(); // Create another unreferenced object.

}

System.out.println("First LargeObject is finalized. Created LargeObject " + LargeObject.objectCounter + " totally.");

System.out.println("phantomRef.get() returns : " + phantomRef.get());

}

}

class LargeObject{

volatile static int objectCounter = 0;

private byte[] largeData = new byte[1024*1024*250]; // 250 megabytes

LargeObject(){

System.out.println("A new LargeObject is being constrcted.");

objectCounter++;

}

}