Thread Part III - Method isAlive and Join

Thread Part III

Method isAlive and Join

Sometime in our program we want our main thread be the last one to stop or finish, after all the child threads finished. For making this happen, firstly we need to check weather the child threads is alive using method isAlive(), then we use method join(), that belong to Thread Class. let’s check how it work first we create thread. As shown below,

public class MyThreadMain implements Runnable {

  private Thread thread;

  private int n;

  MyThreadMain(String name, int n){

   thread = new Thread(this, name);

   this.n = n;

  }

@Override

  public void run() {

  try {

    for (int i = 0; i <n; i++) {

System.out.println("Thread"+ thread.getName() +"second: "+(i+1));

  Thread.sleep(1000);

   }

System.out.println("Thread "+ thread.getName() +" finish.... ");

} catch (Exception e) {

   e.printStackTrace();

   }

}

   public void start(){

     thread.start();

   }

   public Thread getThread(){

     return thread;

   }

}

Now we try to make a few threads running together

public class IsAliveJoinDemo {

public stati cvoid main(String[]args)throws InterruptedException{

   System.out.println("\nMain Thread execute....");

   MyThreadMain t1 = new MyThreadMain("first", 2);

   MyThreadMain t2 = new MyThreadMain("second", 3);

   MyThreadMain t3 = new MyThreadMain("third", 3);

   t1.start();

   t2.start();

   t3.start();

  System.out.println("t1 is alive ? "+ t1.getThread().isAlive());

  System.out.println("t2 is alive ?"+ t2.getThread().isAlive());

  System.out.println("t3 is alive ?"+ t3.getThread().isAlive());

  t1.getThread().join();

  t2.getThread().join();

  t3.getThread().join();

  System.out.println("t1 is alive ? "+ t1.getThread().isAlive());

  System.out.println("t2 is alive ?"+ t2.getThread().isAlive());

  System.out.println("t3 is alive ?"+ t3.getThread().isAlive());

  System.out.println("\nMain Thread is executed..");

  }

}

if we run our code above the console will show below,

Main Thread execute....

t1 is alive ? true

Thread first second : 1

Thread second second : 1

Thread third second : 1

t2 is alive ?true

t3 is alive ?true

Thread third second : 2

Thread second second : 2

Thread first second : 2

Thread second second : 3

Thread third second : 3

Thread first finish....

Thread third finish....

Thread second finish....

t1 is alive ? false

t2 is alive ?false

t3 is alive ?false

Main Thread is executed..

as we saw for the result ,the main thread will be the last to finish after all the child threads is executed.