为什么线程停止执行以及为什么sleep（）会影响它？

Question

当我跑步时：

class ThreadOne extends Thread {

    ThreadOne(String name) {
        super(name);
        start();
    }

    public void run() {
        try {
            sleep(1);
        } catch (InterruptedException ie) {
        }
    }

    public static void main(String args[]) throws InterruptedException {
        ThreadOne n1 = new ThreadOne("Thread 1");
        int counter = 0;
        while (true) {
            if (n1.isAlive() == true) {
                counter++;
                System.out.println("Thread 1 still running. Counter: " + counter);

            } else {
                System.out.println("Thread 1 executed");
                break;
            }
        }
    }
}

我得到的结果如下：

Thread 1 still running. Counter: 1
Thread 1 still running. Counter: 2
...
Thread 1 still running. Counter: 40
Thread 1 still running. Counter: 41
Thread 1 executed

但是当我在sleep（）中更改参数时，计数器会急剧增加。这是我放睡眠的例子（5）：

Thread 1 still running. Counter: 1
Thread 1 still running. Counter: 2
...
Thread 1 still running. Counter: 154
Thread 1 still running. Counter: 155
Thread 1 executed

是什么让这个线程停止执行，为什么sleep()会影响计数器？