设计模式是解决特定类型问题（例如迭代器或观察器）的常用方法。设计模式的概念在 Gamma，Helm，Johnson 和 Vlissides 的《设计模式：可重用的面向对象软件的元素》一书中得到了普及，现在设计模式已广泛用于面向对象的软件开发中。
设计模式代表了设计的替代方法：与其从头设计新的机制，不如应用一种众所周知的设计模式。在大多数情况下，这是件好事：出现设计模式是因为它们解决了常见的问题，并且因为它们被普遍同意提供干净的解决方案。如果设计模式在特定情况下运作良好，那么您可能很难想出另一种更好的方法。
设计模式的最大风险是过度使用。使用现有的设计模式并不能完全解决所有问题。当自定义方法更加简洁时，请勿尝试将问题强加到设计模式中。使用设计模式并不能自动改善软件系统。只有在设计模式合适的情况下才这样做。与软件设计中的许多想法一样，设计模式良好的概念并不一定意味着更多的设计模式会更好。
A design pattern is a commonly used approach for solving a particular kind of problem, such as an iterator or an observer. The notion of design patterns was popularized by the book Design Patterns: Elements of Reusable Object-Oriented Software by Gamma, Helm, Johnson, and Vlissides, and design patterns are now widely used in object-oriented software development.
Design patterns represent an alternative to design: rather than designing a new mechanism from scratch, just apply a well-known design pattern. For the most part, this is good: design patterns arose because they solve common problems, and because they are generally agreed to provide clean solutions. If a design pattern works well in a particular situation, it will probably be hard for you to come up with a different approach that is better.
The greatest risk with design patterns is over-application. Not every problem can be solved cleanly with an existing design pattern; don’t try to force a problem into a design pattern when a custom approach will be cleaner. Using design patterns doesn’t automatically improve a software system; it only does so if the design patterns fit. As with many ideas in software design, the notion that design patterns are good doesn’t necessarily mean that more design patterns are better.