5.2 Information leakage 信息泄漏

The opposite of information hiding is information leakage. Information leakage occurs when a design decision is reflected in multiple modules. This creates a dependency between the modules: any change to that design decision will require changes to all of the involved modules. If a piece of information is reflected in the interface for a module, then by definition it has been leaked; thus, simpler interfaces tend to correlate with better information hiding. However, information can be leaked even if it doesn’t appear in a module’s interface. Suppose two classes both have knowledge of a particular file format (perhaps one class reads files in that format and the other class writes them). Even if neither class exposes that information in its interface, they both depend on the file format: if the format changes, both classes will need to be modified. Back-door leakage like this is more pernicious than leakage through an interface, because it isn’t obvious.

信息隐藏的反面是信息泄漏。当一个设计决策反映在多个模块中时，就会发生信息泄漏。这在模块之间创建了依赖关系：对该设计决策的任何更改都将要求对所有涉及的模块进行更改。如果一条信息反映在模块的界面中，则根据定义，该信息已经泄漏；因此，更简单的界面往往与更好的信息隐藏相关。但是，即使信息未出现在模块的界面中，也可能会泄漏信息。假设两个类都具有特定文件格式的知识（也许一个类读取该格式的文件，而另一个类写入它们）。即使两个类都不在其接口中公开该信息，它们都取决于文件格式：如果格式更改，则两个类都将需要修改。

Information leakage is one of the most important red flags in software design. One of the best skills you can learn as a software designer is a high level of sensitivity to information leakage. If you encounter information leakage between classes, ask yourself “How can I reorganize these classes so that this particular piece of knowledge only affects a single class?” If the affected classes are relatively small and closely tied to the leaked information, it may make sense to merge them into a single class. Another possible approach is to pull the information out of all of the affected classes and create a new class that encapsulates just that information. However, this approach will be effective only if you can find a simple interface that abstracts away from the details; if the new class exposes most of the knowledge through its interface, then it won’t provide much value (you’ve simply replaced back-door leakage with leakage through an interface).

信息泄漏是软件设计中最重要的危险信号之一。作为一个软件设计师，你能学到的最好的技能之一就是对信息泄露的高度敏感性。如果您在类之间遇到信息泄漏，请自问“我如何才能重新组织这些类，使这些特定的知识只影响一个类?”如果受影响的类相对较小，并且与泄漏的信息紧密相关，那么将它们合并到一个类中是有意义的。另一种可能的方法是从所有受影响的类中提取信息，并创建一个只封装这些信息的新类。但是，这种方法只有在您能够找到一个从细节中抽象出来的简单接口时才有效;如果新类通过其接口公开了大部分知识，那么它就不会提供太多的价值(您只是用通过接口的泄漏替换了后门泄漏)。

img Red Flag: Information Leakage img

Information leakage occurs when the same knowledge is used in multiple places, such as two different classes that both understand the format of a particular type of file.

当在多个地方使用相同的知识时，例如两个都理解特定类型文件格式的不同类，就会发生信息泄漏。