ReentrantLock

    private int i = 1;

    @Test
    public void reentrantLock(){
        // 可重入 默认非公平锁
        ReentrantLock lock = new ReentrantLock();

        for (int j = 0; j < 1000; j++) {
            new Thread(() -> {
                lock.lock();

                try {
                    i++;
                    System.out.println("i:" + i);
                } finally {
                    lock.unlock();
                }
            }).start();
        }
    }