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

package thread;

public class Pingpong extends Thread {
    static StringBuilder object = new StringBuilder("");
    static int i=1;

    @Override
    public void run() {
        working();
    }
    void working() {
        while (i<=10) {
            synchronized (object) {
                try {
                    System.out.println(Thread.currentThread().getName() +"  "+ i);
                    i++;
                    object.notify();
                    object.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Pingpong();
        Thread t2 = new Pingpong();
        t1.setName("Thread1");
        t2.setName("Thread2");
        t1.start();
        t2.start();
    }
}

Thread1  1
Thread2  2
Thread1  3
Thread2  4
Thread1  5
Thread2  6
Thread1  7
Thread2  8
Thread1  9
Thread2  10

Answer 2

public class Test {

private static int count = 0;

public static void main(String[] args) throws InterruptedException {

    Thread t1 = new Thread(new Runnable() {

        @Override
        public void run() {

            for (int i = 0; i < 25; i++) {
                synchronized (CommonUtil.mLock) {
                    incrementCount();
                    CommonUtil.mLock.notify();
                    try {
                        CommonUtil.mLock.wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }
        }
    });
    Thread t2 = new Thread(new Runnable() {

        @Override
        public void run() {

            for (int i = 0; i < 25; i++) {
                synchronized (CommonUtil.mLock) {
                    incrementCount();
                    CommonUtil.mLock.notify();
                    try {
                        CommonUtil.mLock.wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }
        }
    });
    t1.start();
    Thread.sleep(400);
    t2.start();
    t1.join();
    t2.join();
}

private static void incrementCount() {

    count++;
    System.out.println("Count: " + count + " icnremented by: " +        Thread.currentThread().getName());
}
}
  class CommonUtil {

 static final Object mLock = new Object();
   }