Use of volatile

Question

public class MyClass {
     public static void main(String[] a) throws InterruptedException {
          new Thread(new A(),"thread1 ").start();
          Thread.sleep(500);
          new Thread(new A(),"thread2 ").start();
class A implements Runnable {
     volatile int value = 0;
     public void run() {
          value++;
          System.out.println(Thread.currentThread().getName() + value);
}Hi, I tried running this code with value being both volatile and not, but I get the same answer each time. Both threads turn value to 1. Shouldn't volatile make it 1 then 2?
I tried the same thing but making value static, in which case it works as I thought it would have worked with volatile. I'm not too sure what volatile does anymore, could somebody please help clarify all this for me?
Thanks.

Answer 1

public class MyClass implements Runnable {
     Other o = new Other();
     public static void main(String[] a) throws InterruptedException {
          MyClass m = new MyClass();
          new Thread(m,"thread1 ").start();
          Thread.sleep(500);
          new Thread(m,"thread2 ").start();
     public void run() {
          o.value++;
          System.out.println(Thread.currentThread().getName() + o.value);
class Other {
     volatile int value;
}I looked at this one a bit longer, and I came up with this new example. Is this case more likely to need the volatile keyword as a precaution (as the variable in question is in an indepedent class)?
Any help on this topic would be really appreciated. I looked up several websites on volatile, but none really clarified the use of volatile (actually, I don't recall whether any mentioned that the caching problem doesn't always happen!).
Thanks.