What are design patterns?

Every experienced developer has a set of informal strategies that shape how they design and write applications. These strategies are shaped by their past experiences and the obstacles that they have had to overcome in previous projects. While these developers might swear by their own strategies, it does not mean that their strategies have been fully vetted. The use of these strategies can also introduce inconsistent implementations between different projects and developers.

While the concept of design patterns dates back to the mid 80s, they did not gain popularity until the Gang of Four released their Design Patterns: Elements of Reusable Object-Oriented Software book, published in 1994. The book's authors, Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (also known as the Gang of Four), discuss the pitfalls of object-oriented programming and describe 23 classic software design patterns. These 23 patterns are broken up into three categories:...