object without reference and gc()

Consider the following code

class NewThread implements Runnable {

    Thread t;

    NewThread(String name) {
        t = new Thread(this,name);
        System.out.println("New thread : " + t);
        t.start();
    }

    public void run() {
        try {
            for(int i=0; i<5; i++) {
                System.out.println(this + " : " + i);
                Thread.sleep(500);
            }
        }catch(InterruptedException e) {
            System.out.println("Child interrupted");
        }
        System.out.println("Child thread exiting");
    }
}

public class MyThread {

    public static void main(String args[] ) {

        Runtime r = Runtime.getRuntime();
        new NewThread("Ok1");
        new NewThread("Ok2");
        new NewThread("Ok3");

        r.gc();

        try {
            Thread.sleep(1000);
        }catch(InterruptedException e) {
            System.out.println("Main thread interrupted");
        }

        System.out.println("Main thread exiting");
    }

}

In MyThread class, inside main(), I am creating three objects of
NewThread class without storing there references. Hence when I am
calling garbage collector, all these objects should be killed. But in
reality it is not happening. Can anyone help me ???