计数器AtomicInteger

private static final int THREADS_CONUT = 20;
public static AtomicInteger count = new AtomicInteger(0);

public static void increase() {
    count.incrementAndGet();
}

public static void main(String[] args) {
    Thread[] threads = new Thread[THREADS_CONUT];
    for (int i = 0; i < THREADS_CONUT; i++) {
        threads[i] = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    increase();
                }
            }
        });
        threads[i].start();
    }

    while (Thread.activeCount() > 1) {
        Thread.yield();
    }
    System.out.println(count.get());
}