一个电梯的模拟程序，并且能够设置了一个特殊的按钮，可以取消某一层的请求。 在实现中用了两个定时器，实现了多线程的操作。-A lift simulation procedures, and can set up a special button, you can cancel the request of a particular floor. Used in the realization of two timers, a multi-threaded operation.