Class demonstrating the lack of happens-before link

HappensBefore.java

package concurrency;

public class HappensBefore {

    private static class Value {
        private int index;

        void increment() {
            index++;
        }

        void print() {
            if (index == 0)
                System.out.println("got zero");
        }
    }

    public static void main(String... args) throws InterruptedException {

        for (int i = 0; i < 10_000; i++) {
            Value value = new Value();

            Runnable r1 = () -> value.increment();
            Runnable r2 = () -> value.print();

            Thread t1 = new Thread(r1);
            Thread t2 = new Thread(r2);

            t1.start();
            t2.start();

            t1.join();
            t2.join();
        }
    }
}