Weak Referencies

class TheStrong {
	public Object link;
 
	public Object getLink(){ return link; }
 
	public void print(Object newlink){
		link = newlink;
		System.out.println("TheStrong: my link =" + getLink());
	}
}
 
class TheWeak {
	public WeakReference<Object> link;
 
	public Object getLink(){ return link.get();	}
 
	public void print(Object newlink){
		link =  new WeakReference<>( newlink );
		System.out.println("TheWeak:   my link =" + getLink());
	}
}
 
public class Test {
	public static void main(String[] args) throws IOException {
		TheStrong thestrong = new TheStrong();
		thestrong.print(Arrays.asList(4,5,6));
 
		TheWeak theweak = new TheWeak();
		theweak.print(Arrays.asList(1,2,3));
 
		Runtime r = Runtime.getRuntime();
		r.gc();
 
		System.out.println("TheWeak:   its link=" + theweak.getLink());
		System.out.println("TheStrong: its link=" + thestrong.getLink());
	}
}

Result:

TheWeak:   my link =[1, 2, 3]
TheStrong: my link =[4, 5, 6]
TheWeak:   its link=null
TheStrong: its link=[4, 5, 6]