3 Threads Printing numbers in sequence

Question

I am trying to write a simple code to print numbers in sequence. Scenario is like

Thread  Number
T1        1
T2        2
T3        3
T1        4
T2        5
T3          


        

Answer 1

I have tried it below simple way to print in sequence using three threads and it is working well.

public class AppPrint123 {

    static int count = 1;
    static int counter = 1;
    static Object lock = new Object();

    public static void main(String[] args) {

        Thread t1 = new Thread(new Runnable() {

            public void run() {
                while (true) {
                    synchronized (lock) {

                        try {
                            Thread.sleep(100);
                            while (count != 1) {
                                lock.wait();
                            }
                            System.out.println(Thread.currentThread().getName() + ": " + counter);
                            count++;
                            counter++;
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        lock.notifyAll();
                    }
                }

            }

        }, "T1");

        Thread t2 = new Thread(new Runnable() {

            public void run() {
                while (true) {
                    synchronized (lock) {

                        try {
                            Thread.sleep(100);
                            while (count != 2) {
                                lock.wait();
                            }
                            System.out.println(Thread.currentThread().getName() + ": " + counter);
                            counter++;
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        lock.notifyAll();
                    }
                }
            }

        }, "T2");

        Thread t3 = new Thread(new Runnable() {

            public void run() {
                while (true) {
                    synchronized (lock) {
                        try {
                            Thread.sleep(100);
                            while (count != 3) {
                                lock.wait();
                            }
                            System.out.println(Thread.currentThread().getName() + ": " + counter);
                            count = count - 2;
                            counter++;
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        lock.notifyAll();
                    }
                }
            }

        }, "T3");

        t1.start();
        t2.start();
        t3.start();

    }
}

You can print count variable instead if you want to generate output like 123123123 in sequence using three threads.

Answer 2

Well, the problem is that modulo 3 % 3 is 0. Change your threadIds to 0..2 instead of 1..3 and hopefully it should work.