Design Patterns
Someone has already solved your problems
The best way to use patterns is to load your brain with them and then recognize places in your designs and existing applications where you can apply them. Instead of code reuse, with patterns you get experience reuse
The one constant in software development
No matter where you work, what you’re building, or what language you are programming in, what’s the one true constant that will be with you always?
Take the parts that vary and encapsulate them, so that later you can alter or extend the parts that vary without affecting those that don’t
Strive for loosely coupled designs between objects that interact
OO Basics
- Abstraction
- Encapsulation
- Inheritance
- Polimorphism
OO Principles
- Encapsulate what varies
- Favor composition over inheritance
- Program to an interface, not an implementation
Relationships
Is-a extents -|> inheritance Implements ..|> interface Has-a -> extends
Strategy Pattern
The Strategy Pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it
Observer Pattern
The Observer Pattern defines a one-to-many dependency between objects so that when one object changes state, all of its dependents are notified and updated automatically
| Pattern | Usage |
|---|---|
| Abstract Factory | 5 |
| Builder | 2 |
| Factory Method | 5 |
| Prototype | 3 |
| Singleton | 4 |
| Adapter | 4 |
| Bridge | 3 |
| Composite | 4 |
| Decorator | 3 |
| Facade | 5 |
| Flyweight | 1 |
| Proxy | 4 |
| Chain of Responsibility | 2 |
| Command | 4 |
| Interpreter | 1 |
| Iterator | 5 |
| Mediator | 2 |
| Memento | 1 |
| Observer | 5 |
| State | 3 |
| Strategy | 4 |
| Template Method | 3 |
| Visitor | 1 |