本章中的示例着重于信息隐藏，因为它与类的外部可见 API 有关，但是信息隐藏也可以应用于系统中的其他级别，例如类内。尝试在一个类中设计私有方法，以便每个方法都封装一些信息或功能，并将其隐藏在类的其余部分中。此外，请尽量减少使用每个实例变量的位置数量。有些变量可能需要在整个类中广泛使用，但是其他变量可能只需要在少数地方使用；如果可以减少使用变量的位置的数量，则将消除类内的依赖关系并降低其复杂性。
仅当在其模块外部不需要隐藏信息时，隐藏信息才有意义。如果模块外部需要该信息，则不得隐藏它。假设模块的性能受某些配置参数的影响，并且模块的不同用途将需要对参数进行不同的设置。在这种情况下，将参数暴露在模块的界面中很重要，以便可以对其进行适当的旋转。作为软件设计师，您的目标应该是最大程度地减少模块外部所需的信息量。例如，如果模块可以自动调整其配置，那将比公开配置参数更好。但是，重要的是要识别模块外部需要哪些信息，并确保将其公开。
The examples in this chapter focused on information hiding as it relates to the externally visible APIs for classes, but information hiding can also be applied at other levels in the system, such as within a class. Try to design the private methods within a class so that each method encapsulates some information or capability and hides it from the rest of the class. In addition, try to minimize the number of places where each instance variable is used. Some variables may need to be accessed widely across the class, but others may be needed in only a few places; if you can reduce the number of places where a variable is used, you will eliminate dependencies within the class and reduce its complexity.
Information hiding only makes sense when the information being hidden is not needed outside its module. If the information is needed outside the module, then you must not hide it. Suppose that the performance of a module is affected by certain configuration parameters, and that different uses of the module will require different settings of the parameters. In this case it is important that the parameters are exposed in the interface of the module, so that they can be turned appropriately. As a software designer, your goal should be to minimize the amount of information needed outside a module; for example, if a module can automatically adjust its configuration, that is better than exposing configuration parameters. But, it’s important to recognize which information is needed outside a module and make sure it is exposed.