Java Multithreading Challenge

Question

Can someone please explain or give an example on how to create multiple threads with different functionalities in Java?

This is the code... I am trying to create a thread that does what public void rnd_list() is supposed to do ( a list of 30 random numbers) which is a different task than the one define in public void run() which is the method that by default when thread.start() its executed. I want to know how to create a thread within the same class Apple with a different functionality in this case the one in public void rnd_list().

import java.util.Random;

public class Apple implements Runnable{

 String name;
 int time, number, first, last, maximum;
 Random r = new Random();
 Random n = new Random();
 int[] array = new int[10]; 


 public Apple(String s, int f, int l){
  name = s;
  first = f;
  last = l;
  maximum = array[0];
 }

// public void rnd_list()
// {
//   for(int j = 0; j < 30; j++)
//  {
//   number = n.nextInt(100);
//   array[j] = number;
//   System.out.println("thread" + name + "array [" + j + "] =" + array[j]);
//  }
// }

 public void run(){
  try{

   for(int i = first; i < last; i++ )
   {

    if(maximum < array[i])
    {
     maximum = array[i];
    }
   }

   System.out.println("maximum = " + maximum);
  }catch(Exception e){}
  }



 public static void main(String[] args){

  Thread t1 = new Thread(new Apple("one ", 0, 2));
  Thread t2 = new Thread(new Apple("two ", 3, 5 ));
  Thread t3 = new Thread(new Apple("three ", 6, 9));

  try{
   t1.start();
               t2.start();
               t3.start();


   }catch(Exception e){}

 }
}

Answer 1

A good place to start would be sun's website

Answer 2

When a Thread is created with a Runnable, the Runnable.run() method will be run when Thread.start() is called. If you want the rnd_list() method to be run, you have two options.

1. Create a new class which implements Runnable and have the run() method in that class call rnd_list()
2. Change the implementation of Apple.run() to check some state belonging to Apple and optionally execute rnd_list().

Answer 3

Just to clarify: you want to run rnd_list() in a separate thread, and use run() for some other task?

It's not terribly good practice, but you could start a new thread on this specific method by adding this method to your Apple class

   Thread startRndList()
   {
      Thread t = new Thread(new Runnable() {
              public void run()
              {
                  rnd_list();
              }
        });
      t.start();
      return t;
   }

But rather than directly instantiating threads, you're better off using concurrency utils ExecutorService class.

Answer 4

I think you could use anonymous classes or nested classes that implement Runnable, but it would be nasty and you might have concurrency issues...