可重入锁是什么和demo

new Thread(new Runnable() {
    @Override
    public void run() {
        synchronized (this) {
            System.out.println("第1次获取锁，这个锁是：" + this);
            int index = 1;
            while (true) {
                synchronized (this) {
                    System.out.println("第" + (++index) + "次获取锁，这个锁是：" + this);
                }
                if (index == 10) {
                    break;
                }
            }
        }
    }
}).start();