Java Concurrency – Thread join example with Runnable interface a

What thread’s join method?

  • The join method allows one thread to wait for the completion of another thread.
    • Suppose we have couple of threads like thread1 & thread2.
    • If in thread1, we have put thread2.join.
      • Then, thread1 will wait for execution of thread2.
      • Once thread2 finishes its execution then thread1 will resume its execution.
  • There overload methods of join methods, which allow to specify a waiting period.
  • The join method responds to an interrupt by exiting with an InterruptedException.

Join methods of thread class in java:

Method Name Description
void join() Waits for this thread to die.
void join(long millis) Waits at most millis milliseconds for this thread to die.
void join(long millis, int nanos) Waits at most millis milliseconds plus nanos nanoseconds for this thread to die.

Algorithm: Demo of Join methods in multi-thread application

  • Create a task by implementing Runnable interface.
  • We will demonstrate join method and its impact on execution on multiple threads.
  • We will write couple of methods
    1. demoThreadJoin: Method will create multiple threads ( four threads from 1 to 4).
      • Output of a method will demonstrates the execution of join method.
      • Threads will execute one after another (i.e. thread-1 to thread-4).
    2. demoWithoutThreadJoin: Method will demonstrate the execution of multiple threads without join method.
      • Threads will execute randomly, there will be no sequence of thread execution.

Program – thread join example with Runnable interface in java

package org.learn;


class MyTask implements Runnable {
    @Override
    public void run() {
        String name = Thread.currentThread().getName();
        try {
            System.out.printf("Start of %s\n",name);
            Thread.sleep(1500);
            System.out.printf("End of %s\n",name);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class ThreadJoinExample {
    public static void main(String[] args) throws InterruptedException {
        MyTask task = new MyTask();
        System.out.println("1. Working with multiple threads using thread join:");
        demoThreadJoin(task);
        System.out.println("2. Working with multiple threads WITHOUT thread join:");
        demoWithoutThreadJoin(task);

    }

    private static void demoWithoutThreadJoin(MyTask task) throws InterruptedException {
        Thread thread1 = new Thread(task, "Thread-1 without join");
        Thread thread2 = new Thread(task, "Thread-2 without join");
        Thread thread3 = new Thread(task, "Thread-3 without join");
        Thread thread4 = new Thread(task, "Thread-4 without join");

        //Start thread 1
        thread1.start();

        //Start thread 2
        thread2.start();

        //Start thread 3
        thread3.start();

        //Start thread 4
        thread4.start();
    }

    private static void demoThreadJoin(MyTask task) throws InterruptedException {
        Thread thread1 = new Thread(task, "Thread-1 using join");
        Thread thread2 = new Thread(task, "Thread-2 using join");
        Thread thread3 = new Thread(task, "Thread-3 using join");
        Thread thread4 = new Thread(task, "Thread-4 using join");

        //Start thread 1
        thread1.start();
        thread1.join();

        //start thread 2
        thread2.start();
        thread2.join();

        //Start thread 3
        thread3.start();
        thread3.join();

        //start thread 4
        thread4.start();
        thread4.join();
    }
}

Output – thread join example with Runnable interface in java

1. Working with multiple threads using thread join:
Start of Thread-1 using join
End of Thread-1 using join
Start of Thread-2 using join
End of Thread-2 using join
Start of Thread-3 using join
End of Thread-3 using join
Start of Thread-4 using join
End of Thread-4 using join
2. Working with multiple threads WITHOUT thread join:
Start of Thread-1 without join
Start of Thread-2 without join
Start of Thread-4 without join
Start of Thread-3 without join
End of Thread-1 without join
End of Thread-2 without join
End of Thread-4 without join
End of Thread-3 without join
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