Thread.sleep()是java提供的函数。在调用该函数的过程中可能会发生InterruptedException异常。
SystemClock.sleep()是android提供的函数。在调用该函数的过程中不会发生InterruptedException异常，中断事件将要被延迟直到下一个中断事件。
SystemClock.sleep(millis) is a utility function very similar to Thread.sleep(millis), but it ignores InterruptedException. Use this function for delays if you do not use Thread.interrupt(), as it will preserve the interrupted state of the thread.
