Classifications

The design patterns are split into 3 general classifications. Creational, Structural and Behavioural. This section gives a brief overview to each of these classifications.

Creational

The GOF book advocates working only through interfaces (ie the abstract classes). However at some point, the concrete objects must still be created. The idea behind creational patterns is to abstract away the creation process. Instead of having the client application create concrete objects all over your application, the creation of patterns is centralized in one place. While these patterns instantiate concrete objects, they hide their creation process and even specific objects. Instead they return only their abstract types.

Structural

Structural patterns are used to compose objects into more complicated structures.

Behavioural

GOF describes behavioural patterns as dealing with algorithms and responsibilities of objects. "Behavioral patterns describe not just patterns of objects or classes but also the patterns of communication between them. "