面向对象程序设计
The value of entry and exit actions is that they provide means for "guaranteed initialization and cleanup", very much like class constructors and destructors in Object-oriented programming. For example, consider the "door_open" state from Figure 5, which corresponds to the toaster oven behavior while the door is open. This state has a very important safety-critical requirement: Always disable the heater when the door is open. Additionally, while the door is open, the internal lamp illuminating the oven should light up.