Question

I saw the following example on the internet:

public class TwoThreads {
public static class Thread1 extends Thread {
    public void run() {
        System.out.println("A");
        System.out.println("B");
    }
}
public static class Thread2 extends Thread {
    public void run() {
        System.out.println("1");
        System.out.println("2");
    }
}
public static void main(String[] args) {
    new Thread1().start();
    new Thread2().start();
}

}

My question is :

1. It is guarantee that “A” will be printed Before “B” and “1” will be printed before “2”, but is it possible that “1” will be printed twice successively by another thread?.In this piece of code we have at least 3 threads(1 main and 2 created). can we imagine the scheduler runs 1 thread: new Thread1().start(); then gave up immediately after System.out.println(“1”); then again run another threat in Thread1().start(); that prints “1” again ?

2. I am using NetBeans IDE, it seems running such a program always lead to the same first result, so it seems there something with caching. From my understanding you deal with that with declaring volatile variables, can it be done here,how ? if not then what is the solution for caching ?

3. In today’s Computer’s processor, we mostly have 2 processors,and still we find many multi-threading programs on the net uses more than 2 threads! isn’t this process becomes heavy and slow regarding compiling ?

Answer 1

Answer to your 1/2 question:
Though threads run parallel code inside run method of thread is always executed sequentially.

Answer to your 3 question you can best tune your. Application if number of processors = number of threads but this is not a complete truth since if thread is waiting for some blocking operation then it will lead to un optimized performance since during that time another thread could run.