How do I use join method to wait for threads to finish in Java?

If you want a thread to work until another thread dies, you can join the thread onto the end of the another thread using the join() method. For example, you want thread B only work until thread Acompletes its work, then you want thread B to join thread A.

public class ThreadJoin implements Runnable {
    private int numberOfLoop;

    public ThreadJoin(int numberOfLoop) {
        this.numberOfLoop = numberOfLoop;
    }

    public void run() {
        System.out.println("[" +
                Thread.currentThread().getName() + "] - Running.");

        for (int i = 0; i < this.numberOfLoop; i++) {
            System.out.println("[" +
                    Thread.currentThread().getName() + "] " + i);
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        System.out.println("[" +
                Thread.currentThread().getName() + "] - Done.");
    }

    public static void main(String[] args) {
        Thread t1 = new Thread(new ThreadJoin(10), "FirstThread");
        Thread t2 = new Thread(new ThreadJoin(20), "SecondThread");

        try {
            //
            // start t1 and waits for this thread to die before
            // starting the t2 thread.
            //
            t1.start();
            t1.join();

            // start t2
            t2.start();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}