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copied!<p>Bob Martin wrote a series of articles on class design, which he refers to as the SOLID principles:</p> <p><a href="http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod" rel="noreferrer">http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod</a></p> <p>The principles are:</p> <ol> <li>The Single Responsibility Principle: <em>A class should have one, and only one, reason to change.</em></li> <li>The Open-Closed Principle: <em>You should be able to extend a classes behavior, without modifying it.</em></li> <li>The Liskov Substitution Principle: <em>Derived classes must be substitutable for their base classes.</em></li> <li>The Interface Segregation Principle: <em>Make fine grained interfaces that are client specific.</em></li> <li>The Dependency Inversion Principle: <em>Depend on abstractions, not on concretions.</em></li> </ol> <p>So in light of those, let's look at some of the statements:</p> <blockquote> <p>So over time the YadaYadaFile starts growing. Several overloads to save in different formats, including XML etc, and the file starts pushing towards 800 lines or so</p> </blockquote> <p>This is a first Big Red Flag: YadaYadaFile starts out with two responsibilities: 1) maintaining a section/key/value data structure, and 2) knowing how to read and write an INI-like file. So there's the first problem. Adding more file formats compounds the issue: YadaYadaFile changes when 1) the data structure changes, or 2) a file format changes, or 3) a new file format is added.</p> <p>Similarly, having a single validator for all three of those responsibilities puts too much responsibility on that single class.</p> <p>A large class is a "code smell": it's not bad in and of itself, but it very often results from something that really is bad--in this case, a class that tries to be too many things.</p>

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