An experiment in breaking certain "easy" CS questions about whether an expression can evaluate to "true". (Note that you can get "a != a" to be true without messing with threads (Java Puzzlers, Puzzle 29; left as an exercise for the reader), but this method is far more general; you can get things like "a < 0 && a > 0" to be true, but only someti…

troll.java

public class Troll {
	static volatile int a;
	public static void main(String[] args) {
		new Thread(new Runnable(){
			public void run(){
				while (true){ a = -42; a = 1337; }
			}
		}).start();
		for (int i = 0; i < 1000000; i++){
			if (a != a) {
				System.out.println("!");
				System.exit(1);
			}
		}
		System.exit(0);
	}
}