Question

I am looking at an example which code is:

class SimpleThread extends Thread {
    public SimpleThread(String str) {
        super(str);
}

public void run() {
    for (int i = 0; i < 10; i++) {
        System.out.println(i + " " + getName());
            try {
        sleep((int)(Math.random() * 1000));
        } catch (InterruptedException e) {}
    }
    System.out.println("DONE! " + getName());
    }
}

and

class TwoThreadsTest {
    public static void main (String args[]) {
        new SimpleThread("Jamaica").start();
        new SimpleThread("Fiji").start();
    }
}

My question is: is there a way each thread does its own code? For example, one thread increments a variable, while the other thread increments other variable.
Thanks.

P.S. Example’s link is: http://www.cs.nccu.edu.tw/~linw/javadoc/tutorial/java/threads/simple.html

Answer 1

Each instance of SimpleThread has it’s own local class storage. As long as you aren’t using fields marked as static, then each thread will “do its own code”. It is much harder to synchronize values between threads.

For example:

class SimpleThread extends Thread {

    // this is local to an _instance_ of SimpleThread
    private long sleepTotal;

    public SimpleThread(String str) {
        super(str);
    }

    public void run() {
        for (int i = 0; i < 10; i++) {
            System.out.println(i + " " + getName());
            try {
                long toSleep = Math.random() * 1000;
                // add it to our per-thread local total
                sleepTotal += toSleep;
                sleep(toSleep);
            } catch (InterruptedException e) {}
        }
        System.out.println("DONE!  " + getName());
    }
}