What Is a Design Pattern

What Is a Design Pattern

A design pattern names, abstracts, and identifies the key aspects of a common design structure. 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.

A pattern has four essential elements:

1. Pattern name — a handle we can use to describe a design problem
2. Problem — describes when to apply the pattern
3. Solution — describes the elements that make up the design
4. Consequences — the results and trade-offs of applying the pattern

Design Patterns in Smalltalk MVC

The Model/View/Controller triad of classes is used to build user interfaces in Smalltalk-80. MVC consists of three kinds of objects: the Model is the application object, the View is its screen presentation, and the Controller defines the way the user interface reacts to user input.

MVC decouples views and models by establishing a subscribe/notify protocol between them — a pattern known as Observer.