Measuring time through for loop - Threads Java

Question

I have a task to create a race in Java using Threads with 10 different participants who will run distance of 100 m and the winner is, of course, who gets first to the 100m.

However, the race should end when all participants finish the race and after the race program should also display the time that was needed for every participant to finish the race.

My question is how to add time in program, since I tried using 2D for loop, but didn't succeed.

This is my so far code

P.S My Syso should like smthing like:

Distance covered by Kazim was 100m and 40 seconds

Distance covered by Lloran was 100m and 36 seconds.

I haven't implemented time at all

public class Race implements Runnable

    {
       public static String winner;

       public void race()
       {
          for (int distance = 1; distance <= 100; distance++)
          {
             System.out.println("Distance covered is by" + " "
                   + Thread.currentThread().getName() + " is" + " " + distance);
             boolean isRaceFinished = this.isRaceFinished(distance);
             if (isRaceFinished)
             {
                break;
             }

          }

       }

       private boolean isRaceFinished(int distance)
       {
          boolean isRaceFinished = false;

          if (winner == null && distance == 100)
          {
             String winnerName = Thread.currentThread().getName();
             winner = winnerName;
             System.out.println("The winner is" + " " + winner);

          }
          else if (winner == null)
          {
             isRaceFinished = false;
          }
          else if (winner != null)
          {
             isRaceFinished = true;
          }
          return isRaceFinished;
       }

       @Override
       public void run()
       {
          this.race();

       }
    }
    public class Main
{

   public static void main(String[] args)
   {
      Race race = new Race();
      Thread t1 = new Thread(race, "Dean");
      Thread t2 = new Thread(race, "Lloran");
      Thread t3 = new Thread(race, "Vinsel");
      Thread t4 = new Thread(race, "Jimmy");
      Thread t5 = new Thread(race, "Khan");
      Thread t6 = new Thread(race, "Kazim");
      Thread t7 = new Thread(race, "Richards");
      Thread t8 = new Thread(race, "Malvo");
      Thread t9 = new Thread(race, "Leddan");
      Thread t10 = new Thread(race, "Joseph");

      t1.start();
      t2.start();
      t3.start();
      t4.start();
      t5.start();
      t6.start();
      t7.start();
      t8.start();
      t9.start();
      t10.start();

   }

}

One problem you've got here is that the earlier-started threads could start doing work before the later-started threads - the earlier ones will almost certainly win (if not always t1). You should use something like a CountdownLatch to block the threads until all are ready. — Andy Turner
– Andy Turner, Commented Mar 14, 2016 at 12:51
Another is that you need to synchronize read/write access to winner, otherwise it is not guaranteed that all threads will see that a winner has been set. Or use an AtomicReference<String>, of course. — Andy Turner
– Andy Turner, Commented Mar 14, 2016 at 12:52

Jack · Accepted Answer · 2016-03-14 12:51:38Z

1

Take a look at System.currentTimeMillis(). If you store the current time at the start of your race thread and the check it again at the end, the difference will give you the number of milliseconds for that thread.

answered Mar 14, 2016 at 12:51

Jack

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Pavel Krizhanovskiy · Accepted Answer · 2016-03-14 13:04:26Z

1

Add field in class:

public class Race implements Runnable
    {
       public long timeStart, timeFinish;
       public static String winner;

In run():

public void run()
       {
          this.time = System.currentTimeMillis();
          this.race();
       }

In isRaceFinished():

if (winner == null && distance == 100)
          {
             String winnerName = Thread.currentThread().getName();
             winner = winnerName;
             this.timeFinish = System.currentTimeMillis();

Then calculate time interval for each thread.

edited Mar 14, 2016 at 13:04

answered Mar 14, 2016 at 12:53

Pavel Krizhanovskiy

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1 Comment

Seinfeld Over a year ago

I just realize that my program is much more wrong than the time only. Thanks for the help guys anyway, I'll have this in mind.

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