import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class MultiThreadedCounter implements Runnable {

    private static volatile int counter = 0;

    @Override
    public void run() {
        counter = counter + 5;
        counter = counter - 5;
    }

    public static void main(String[] args) throws InterruptedException {
        ExecutorService es = Executors.newCachedThreadPool();
        for (int i = 0; i < 20000; i++)
            es.execute(new MultiThreadedCounter());
        es.shutdown();
        es.awaitTermination(10, TimeUnit.MINUTES);
        System.out.println(counter);
    }

}