design_patterns.md

Design Patterns

Design Patterns give you a shared vocabulary with other developers:

• shared pattern vocabularies are powerful
• pattern allow you to say more with less
• talking at the pattern level allows you to stay "in the design" longer
• shared vocabularies can turbo charge your development team
• shared vocabularies encourage more junior developers to get up to speed

1. 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
2. the Observer Pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically
3. the Decorator Pattern attaches additional responsibilities to an object dynamically Decorators provide a flexible alternative to sub-classing for extending functionality
4. the Factory Method Pattern defines an interface for creating an object, but lets subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses
5. the Abstract Factory Pattern provides an interface for creating families of related or dependent objects without specifying their concrete classes
6. the Singleton Pattern ensures a class has only one instance, and provides a global point of access to it
7. the Command Pattern encapsulates a request as an object, thereby letting you parameterize other objects with different requests, queue or log requests, and support undo-able operations
8. the Adapter Pattern converts the interface of a class into another interface the clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces
9. the Facade Pattern provides a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use
10. the Template Method Pattern defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure
11. the Iterator Pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation
12. the Composite Pattern allows you to compose objects into three structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
13. the State Pattern allows an object to alter its behavior when its internal state changes. The object will appear to change its class.