Java Weak - Soft - Phantom References (Confused Coders)

References.java

import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;



class SomeClass{
	

	/** toString() is called every time we print the object. **/
	public String toString(){
		return "I am an Object, Still in Heap";
	}

	
	/** finalize() would be called just before the object dies **/
	public void finalize(){
		System.out.println("The GC just shot me..I am dying ..");
	}
}

public class References {
	
	public static void main(String[] args) throws InterruptedException{
		
	ReferenceQueue refQueue = null;		
	
	
	System.out.println("\n--- Strong Ref -------------------");
	SomeClass strongRef = new SomeClass();
	System.gc();Thread.sleep(2000);
	System.out.println("Post GC: "+strongRef);
		
		
	System.out.println("\n--- Weak Ref ---------------------");
	refQueue = new ReferenceQueue();      
	WeakReference weakRef 
			= new WeakReference(new SomeClass(),refQueue); 
	System.out.println("Pre GC, weakRef.get(): "+weakRef.get());
	System.out.println("Pre GC, refQueue.poll(): "+refQueue.poll());
	System.gc(); Thread.sleep(2000);
	System.out.println("Post GC, weakRef.get(): "+weakRef.get());
	System.out.println("Post GC, refQueue.poll(): "+refQueue.poll());
		
		
	System.out.println("\n--- Soft Ref ---------------------");
	refQueue = new ReferenceQueue(); 
	SoftReference softRef 
			= new SoftReference(new SomeClass(), refQueue);
	System.out.println("Pre GC, softRef.get():"+softRef.get());
	System.out.println("Pre GC, refQueue.poll():"+refQueue.poll());
	System.gc();Thread.sleep(2000);
	System.out.println("Post GC, softRef.get():"+softRef.get());
	System.out.println("Post GC, refQueue.poll():"+refQueue.poll());
		
		
	System.out.println("\n--- Phantom Ref ------------------");
	refQueue = new ReferenceQueue(); 
	PhantomReference phantomRef 
			= new PhantomReference(new SomeClass(), refQueue);
	System.out.println("Pre GC, phantomRef.get():"+phantomRef.get());
	System.out.println("Pre GC, refQueue.poll():"+refQueue.poll());
	System.gc();Thread.sleep(2000);
	System.out.println("Post GC, phantomRef.get():"+phantomRef.get());
	System.out.println("Post GC, refQueue.poll():"+refQueue.poll());		
	
	}
}