thread-join.java

import java.util.concurrent.TimeUnit; 

/** 
  * Simple Java Program to show how to execute threads in a particular order. You
  * can enforce ordering or execution sequence using Thread.join() method in
  * Java. * * @author Javin Paul 
  */ 

public class JoinDemo {

  private static class ParallelTask implements Runnable { 
    private Thread predecessor;
    
    @Override public void run() {
      System.out.println(Thread.currentThread().getName() + " Started"); 

      if (predecessor != null) {
        try {
          predecessor.join(); 
        } catch (InterruptedException e) { 
          e.printStackTrace(); 
        } 
      } 
      System.out.println(Thread.currentThread().getName() + " Finished"); 
    } 

    public void setPredecessor(Thread t) { 
      this.predecessor = t; 
    } 
  } 

  public static void main(String[] args) {
    // we have three threads and we need to run in the 
    // order T1, T2 and T3 i.e. T1 should start first 
    // and T3 should start last. 
    // You can enforce this ordering using join() method 
    // but join method must be called from run() method 
    // because the thread which will execute run() method 
    // will wait for thread on which join is called. 

    ParallelTask task1 = new ParallelTask();
    ParallelTask task2 = new ParallelTask();
    ParallelTask task3 = new ParallelTask(); 

    final Thread t1 = new Thread(task1, "Thread - 1");
    final Thread t2 = new Thread(task2, "Thread - 2");
    final Thread t3 = new Thread(task3, "Thread - 3");
    
    task2.setPredecessor(t1);
    task3.setPredecessor(t2);
    
    // now, let's start all three threads
    t1.start();
    t2.start();
    t3.start();
  }
}

/**
Output
Thread - 1 Started
Thread - 1 Finished
Thread - 2 Started
Thread - 3 Started
Thread - 2 Finished
Thread - 3 Finished


Read more: https://www.java67.com/2015/07/how-to-join-two-threads-in-java-example.html#ixzz6bDWHDPHp
**/