This project has an educational purpose.
I decided to, after almost 10 years, review all design patterns and create a material that could help people who want quick access to refresh their minds about it. Through these years, I worked with many of these design patterns and they helped me to create solutions:
- easier to maintain;
- reusable;
- reliable;
- flexible;
- and adaptable.
To do these review, I'm reading again the design patterns bible written by Gang of Four. In addition, I will also use other references that will be cited at the end of these notes.
Happy studies :)
“Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice”, Christopher Alexander.
Even though Alexander was talking about patterns in buildings and towns, what he says is true about object-oriented design patterns. Our solutions are expressed in terms of objects and interfaces instead of walls and doors, but at the core of both kinds of patterns is a solution to a problem in a context. Gamma, Erich. (pp. 27-28).
Each pattern has:
- name: it will increase your vocabulary when discussing solutions.
- problem: a description of when you should use it.
- solution
- consequences: trade-offs of applying the pattern. This is importanttt!! There is no silver bullet.
Design Principles, such as SOLID, are high-level guidelines to design reusable software applications. They are pure abstraction, because they can be applied in any programming languages.
Design Patterns are low-level solutions of frequent object-oriented programing related problems. They are concrete implementations and state-of-the-art problem specific solutions.
Some design principles can be implemented by design patterns.
"The key to maximizing reuse lies in anticipating new requirements and changes to existing requirements, and in designing your systems so that they can evolve accordingly." (p. 62). Kindle Edition
These patterns are designed for class instantiation (class and object creational patterns).
"In software engineering creational patterns provide various object creation mechanisms which increase flexibility and reuse of existing code"
- Abstract Factory
- Builder
- Singleton
- Factory Method
- Prototype