Writing a program with 2 threads which prints alternatively

Question

I got asked this question recently in an interview.

Write a program with two threads (A and B), where A prints 1 , B prints 2 and so on until 50 is r

Answer 1

public class Testing implements Runnable {
private static int counter = 1;
private static final Object lock = new Object();

public static void main(String[] args)  {

    Thread t1 = new Thread(new Testing(), "1");
    t1.start();
    Thread t2 = new Thread(new Testing(), "2");
    t2.start();

}

@Override
public void run() {
    while (counter<=100) {
        synchronized (lock) {
            if (counter % 2 == 0) {
                System.out.println(counter +" Written By Thread-"+ Thread.currentThread().getName());
                counter++;
                try {
                    lock.notifyAll();
                    lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

            } else if (counter % 2 == 1) {
                System.out.println(counter +" Written By Thread-"+ Thread.currentThread().getName());
                counter++;

                try {
                    lock.notifyAll();
                    lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

            }
        }
    }
  }
}