Print 1 to 100 using 3 Threads

• Thread-1 prints: 1, 4, 7, 10, …
• Thread-2 prints: 2, 5, 8, 11, …
• Thread-3 prints: 3, 6, 9, 12, …

Output becomes:

T1 -> 1
T2 -> 2
T3 -> 3
T1 -> 4
T2 -> 5
T3 -> 6
...
T1 -> 100

One way is using wait() / notifyAll() and a shared counter.

package exercise.threads;

public class Print1To100 {

    private int number = 1;
    private final int MAX = 100;
    private int nextTurn = 1;

    private synchronized void print(int threadId){

        while (number <= MAX) {

            while (nextTurn != threadId && number <= MAX){
                try {
                    wait();
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            }
            if(number > MAX)
            {
                notifyAll();
                return;
            }
            System.out.println(Thread.currentThread().getName() + "--> " + number);
            number++;

            nextTurn = (nextTurn % 3) + 1;
            notifyAll();
        }

    }


    public static void main(String[] args) {

        Print1To100 printer = new Print1To100();

        Thread t1 = new Thread(() -> printer.print(1),"Thread-1");
        Thread t2 = new Thread(() -> printer.print(2),"Thread-2");
        Thread t3 = new Thread(() -> printer.print(3),"Thread-3");

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

    }
}