Model experience/understanding

1. Command mode: In short: Waiter-command-cook barbecue

2. Facade mode: the client can obtain many underlying class functions by dealing with only one class, for example, a class in the service can call some functions of many Dao classes in the DaO package. If the client wants to use these functions of these classes in the DaO package, you only need to deal with the service class.

3. Bridge Mode: allows the service package to have different classes with different functions, and also allows Dao to have different classes with different functions. To get different products, then assemble these different classes. For example, add a class in the service package to the parent class of some classes in the DaO package, then we can inject different Dao classes into this class of the service package to implement the Assembly principle.

4. Observer mode: The Observer pays attention to the target and puts the target in his mind. The target may take effect for a series of people who observe the target. Therefore, the observer list is saved. Once the target appears, the target allows the observer to update the observer's own status.