Sometimes we need to wait for other threads to finish it’s execution before we can proceed. We can achieve this using Thread join, learn how it works and when we should use it.

ThreadJoin.java

import java.util.logging.Logger;

/**
 * Thread join
 * <a href="http://www.journaldev.com/1024/java-thread-join-example">Java Thread Join</a>
 */
class ThreadJoin {

    static Logger logger = Logger.getLogger(App.class.getSimpleName());

    public static void main(String[] args) {
        System.setProperty("java.util.logging.SimpleFormatter.format",
                "%1$tF %1$tT %4$s %2$s %5$s%6$s%n");
        logger.info("Starting");

        Thread t1 = new Thread(new MyRunnable(), "t1");
        Thread t2 = new Thread(new MyRunnable(), "t2");
        Thread t3 = new Thread(new MyRunnable(), "t3");

        t1.start();

        //start second thread after waiting for 2 seconds or if it's dead
        try {
            t1.join(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        t2.start();

        //start third thread only when first thread is dead
        try {
            t1.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        t3.start();

        //let all threads finish execution before finishing main thread
        try {
            t1.join();
            t2.join();
            t3.join();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        logger.info("All threads are dead, exiting main thread");
    }

}

class MyRunnable implements Runnable {

    @Override
    public void run() {
        App.logger.info("Thread started:::" + Thread.currentThread().getName());
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        App.logger.info("Thread ended:::" + Thread.currentThread().getName());
    }

}