Initializing two threads with the same instance of a runnable

Question

Is it bad programming to initialize two threads with the same instance of a runnable? What difference would it make to initialize with separate instances of a runnable, and

Answer 1

Since H doesn't have any instance state, using multiple instances won't matter. You need to take care when the Runnable instances start storing state.

public class Main implements Runnable {
    volatile int i;
        public void run() {
        for (i = 0; i < 100; i++) {
            System.out.println(i);
        }
    }

    public static void main(String[] args) {
        Main a = new Main();
        Thread t1 = new Thread(a);
        Thread t2 = new Thread(a);
        t1.start();
        t2.start();
    }        
}

What gets printed? When you do need to share state between threads, it's a good idea to use the classes in java.util.concurrent. They were written primarily by an expert in multithreading (Doug Lea, author of Concurrent Programming in Java) and tested by many people. Save yourself some heartache. :)