Typical usage of Object.wait() and Object.notify()

JavaWaitAndNotify

package test;

public class Main {

    private final Object MONITOR = new Object();

    private class PrintNum extends Thread {

        volatile int num = 1;

        @Override
        public void run() {
            while (true) {
                synchronized (MONITOR) {
                    for (int i = 0; i < 2; i++) {
                        System.out.print(num++);
                    }
                    MONITOR.notifyAll();
                    if (num > 52) {
                        return;
                    }
                    try {
                        MONITOR.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }

    private class PrintWord extends Thread {

        volatile char word = 'A';

        @Override
        public void run() {
            while (true) {
                synchronized (MONITOR) {
                    System.out.println(word++);
                    MONITOR.notifyAll();
                    if (word > 'Z') {
                        return;
                    }
                    try {
                        MONITOR.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }

    public void test() throws InterruptedException {
        PrintNum printNum = new PrintNum();
        PrintWord printWord = new PrintWord();
        printNum.start();
        Thread.sleep(100);
        printWord.start();
    }

    public static void main(String[] args) throws InterruptedException {
        new Main().test();
    }
}