Write a Java program to demonstrate the Thread.join() method

The Java code demonstrates how to use the join() method to wait for multiple threads to complete their execution before proceeding with the main thread. In the ThreadJoin class, the main method creates three threads: thread1, thread2, and thread3, each associated with an instance of the MyRunnable class. Then, it starts the execution of all three threads using the start() method.

The MyRunnable class implements the Runnable interface and defines the behavior of the threads. Inside the run() method, each thread prints a message indicating that it is running, then sleeps for 2 seconds using Thread.sleep(2000), and finally prints a completion message before exiting.

After starting the threads, the main thread uses the join() method to wait for each thread to complete before proceeding. The join() method blocks the calling thread (in this case, the main thread) until the target thread (the thread on which join() is called) completes its execution. Therefore, the main thread will wait for thread1, thread2, and thread3 to complete in order, as they are joined in that order. Once all three threads have completed their execution, the main thread prints "All threads have Completed" and the program terminates.

Source Code

public class ThreadJoin
{
 
	public static void main(String[] args)
	{
		Thread thread1 = new Thread(new MyRunnable(), "Thread 1");
		Thread thread2 = new Thread(new MyRunnable(), "Thread 2");
		Thread thread3 = new Thread(new MyRunnable(), "Thread 3");
 
		thread1.start();
		thread2.start();
		thread3.start();
 
		try {
			thread1.join(); // Wait for thread1 to complete
			System.out.println(thread1.getName() + " has Completed");
 
			thread2.join(); // Wait for thread2 to complete
			System.out.println(thread2.getName() + " has Completed");
 
			thread3.join(); // Wait for thread3 to complete
			System.out.println(thread3.getName() + " has Completed");
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
 
		System.out.println("All threads have Completed");
	}
 
	static class MyRunnable implements Runnable
	{
		public void run()
		{
			System.out.println(Thread.currentThread().getName() + " is running.");
			try {
				Thread.sleep(2000); // Sleep for 2 seconds
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			System.out.println(Thread.currentThread().getName() + " has Completed");
		}
	}
}

Output

Thread 1 is running.
Thread 2 is running.
Thread 3 is running.
Thread 2 has Completed
Thread 3 has Completed
Thread 1 has Completed
Thread 1 has Completed
Thread 2 has Completed
Thread 3 has Completed
All threads have Completed