Question

Need some help on the following JAVA problem:

Write a program in which the main thread creates two threads named “Display” and “Daemon”. The first thread (Display) executes in an infinite loop and prints out its name and system time every 1 second until it is interrupted by the main thread. The second thread is a daemon thread that executes in an infinite loop and prints out its name. The main thread waits for a specific number of seconds n before interrupting thread Display. The value n should be read in from the keyboard using command-line arguments.

Answer 1

Here is the completed code for this problem. Explanation of the code is given in java comments, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

// Threads.java

import java.util.Calendar;

public class Threads {

    // a flag indicating if the main thread wants to interrup display thread

    static boolean done = false;

    // declaring two Thread objects

    static Thread display = null, daemon = null;

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

         // if no command line arguments provided, displaying usage and quitting

         if (args.length == 0) {

             System.out

                      .println("Specify value for 'n' while running the program");

             System.out.println("Usage: java Threads <n>");

             System.exit(0);

         }

         // otherwise parsing first argument as integer n

         int n = Integer.parseInt(args[0]);

         // initializing display thread

         display = new Thread(new Runnable() {

             @Override

             public void run() {

                 // looping until done is true

                 while (!done) {

                      // displaying thread name and current date and time, if you

                      // prefer to display milliseconds elapsed since epoch, you

                      // may use System.currentTimeMillis() instead.

                      System.out.println(display.getName() + ": "

                               + Calendar.getInstance().getTime());

                      // pausing for 1000 ms or 1 second

                      try {

                          Thread.sleep(1000);

                      } catch (InterruptedException e) {

                      }

                 }

                 // alerting user that display thread is exiting

                 System.out.println("Display thread is exiting.");

             }

         });

         // setting name for display thread

         display.setName("Display");

         // initializing daemon thread

         daemon = new Thread(new Runnable() {

             @Override

             public void run() {

                 // looping indefinitely

                 while (true) {

                      // displaying thread's name

                      System.out.println(daemon.getName());

                      // pausing for 100 ms or 1/10th of a second

                      try {

                          Thread.sleep(100);

                      } catch (InterruptedException e) {

                      }

                 }

             }

         });

         // setting daemon name

         daemon.setName("Daemon");

         // making daemon an actual Daemon thread, which means the thread will

         // run on background independent on other threads, and the system will

         // terminate this thread only if it is the only thread left which is

         // running

         daemon.setDaemon(true);

         // starting both threads

         display.start();

         daemon.start();

         // pausing main thread for n seconds

         Thread.sleep(n * 1000);

         // setting done to true, which will cause the display thread to stop,

         // which make daemon thread the only one left, so the program will

         // finally terminate daemon thread also. if we dont make the second

         // thread a 'daemon', it will loop forever until we manually terminate

         // the program.

         done = true;

    }

}

/*OUTPUT (when n=4 (i.e ran with command: java Threads 4 ))*/

Daemon

Display: Sat Feb 08 10:45:43 IST 2020

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Display: Sat Feb 08 10:45:44 IST 2020

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Display: Sat Feb 08 10:45:45 IST 2020

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Display: Sat Feb 08 10:45:46 IST 2020

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Daemon

Display thread is exiting.