Question

Question 1 8 pts Write all the different possible outputs of the following Java multi-threaded program: class MultithreadingDemo extends Thread public void runot try{ System.out.println (--Multithread.countDown): catch (Exception e) w public class Multithread{ public static int countDown = 10; public static void main(String[] args) { for (int i = 0; i < 3; i++) { MultithreadingDemo object = new MultithreadingDemol); object.start(); } میه

Answer 1

Please find the following output for the given program.

Explanation:

1. Its a multithreading program in java which creates three threads and all the three threads share the variable countDown.

2. Here all the three threads will be running concurrently and its very hard to determine the order of thread execution.

3. In this program we can judge only the possible outcomes/display in the program when the program is executed.

4. Only the values 9.8.7 will be the output but the order in which thread executed will change the display.

5. For example, if the thread 1, first runs, its value is 9 and if the thread 0 might have decremented the countDown value to 8 and the thread 2 would have got time slice to executed which will decrement again and print 7 before 8.

Possible Outputs:

9

8

7

and

9

7

8

Modified program to understand which thread runs in which order and its value:

import java.util.Random;

class MultithreadingDemo extends Thread{
public void run(){
try{
//added the following line to understand how thread runs, instead of line#8
System.out.println("Name: " + getName() +" and countDown values is " + --MultiThread.countDown);
//System.out.println(--MultiThread.countDown);
}
catch(Exception e){
  
}
}
}
public class MultiThread
{

//countDown is shared between the 3 threads
public static int countDown=10;
public static void main(String[] args) {
   for (int i=0; i<3;i++){
   MultithreadingDemo object = new MultithreadingDemo();
   object.start();
   }
   }
}

Following different executions shows different order of thread execution.

Output 1:

Name: Thread-0 and countDown values is 9
Name: Thread-2 and countDown values is 7
Name: Thread-1 and countDown values is 8

Output 2:

Name: Thread-1 and countDown values is 9
Name: Thread-0 and countDown values is 8
Name: Thread-2 and countDown values is 7

Output 3:

Name: Thread-0 and countDown values is 9
Name: Thread-1 and countDown values is 8
Name: Thread-2 and countDown values is 7

Note: for example assume any of 3 threads started its first execution and decremented the countDown value to 9 but it didnt print to console, mean while if anyother 2 threads started execution and decremented the value to 8 and prints immediately to console, then there is chance that 8 prints to console before 9. then the following output is possible.

8

9

7.

In multithreading environment we cant ensure the order of outputs but the possible outputs could always be there.

As i mentioned in "Note" following are the possible outputs of the given program based on thread execution.

9 8 7

9 7 8

7 9 8

7 8 9

8 9 7

8 7 9

Screen shot:

} بہا 3 4. class MultithreadingDemo extends Thread{ 5. public void run() { 6 try{ 7 //added the following line to understand how thread runs, instead of line# 8 System.out.println("Name: " + getName()+" and countDown values is " + -MultiThread.countDown); 9 //System.out.println(--MultiThread.countDown); 10 11 catch(Exception e) { 12 13 14 15 } 16 public class MultiThread 17-{ 18 public static int countDown=10; 19 public static void main(String[] args) { 20 for (int i=0; i<3;i++){ 21 MultithreadingDemo object = new MultithreadingDemo(); 22 object.start(); 23 24 25 } 26 بہا } بہا