Java Thread join() Method

Description

The Java Thread join(long millis, int nanos) method waits at most millis milliseconds plus nanos nanoseconds for this thread to die.

Declaration

Following is the declaration for java.lang.Thread.join() method

public final void join(long millis, int nanos) throws InterruptedException

Parameters

• millis − This is the time to wait in milliseconds.

• nanos − This is 999999 additional nanoseconds to wait.

Return Value

This method does not return any value.

Exception

• IllegalArgumentException − if the value of millis is negative the value of nanos is not in the range 0-999999.

• InterruptedException − if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

Example: Making a thread to wait

The following example shows the usage of Java Thread join() method. In this program, we've created a thread class ThreadDemo by implementing Runnable interface. In constructor, current thread is retrieved using currentThread() method. Its name is printed and using isAlive(), its status is checked whether thread is live or not.

In main method, We've created a Thread using ThreadDemo and using start() method, thread is started. Now using join(), thread is set to wait for given period and then thread name is printed and again using isAlive(), its status being alive is printed.

package com.tutorialspoint;

public class ThreadDemo implements Runnable {

   public void run() {

      Thread t = Thread.currentThread();
      System.out.print(t.getName());
      
      //checks if this thread is alive
      System.out.println(", status = " + t.isAlive());
   }

   public static void main(String args[]) throws Exception {

      Thread t = new Thread(new ThreadDemo());
      
      // this will call run() function
      t.start();
      /* waits at most 2000 milliseconds plus 500 nanoseconds for
         this thread to die */
      t.join(2000, 500);
      System.out.println("after waiting for 2000 milliseconds plus 500 nanoseconds ...");
      System.out.print(t.getName());
      
      //checks if this thread is alive
      System.out.println(", status = " + t.isAlive());
   }
} 

Output

Let us compile and run the above program, this will produce the following result −

Thread-0, status = true
after waiting for 2000 milliseconds plus 500 nanoseconds ...
Thread-0, status = false