Software Engineering basics - Design Pattern

A Design Pattern is a reusable solution to a common problem that occurs in software design. Each pattern provides a general template for solving a particular design issue — not actual code, but a blueprint for how to structure your solution.

Every design pattern is typically described using four essential elements:

1. Pattern Name

  • The identifier used to describe the pattern.

  • Provides a common vocabulary for designers and developers.

  • Makes it easier to discuss and communicate design ideas.

Example:

  • Singleton, Observer, Factory Method, Adapter, etc.

Explanation:
If a developer says “let’s use the Singleton pattern,” everyone understands that it refers to ensuring a class has only one instance and provides a global point of access.

2. Problem

  • Describes when to apply the pattern.

  • Explains the context, conditions, and design challenges the pattern addresses.

  • May include a list of symptoms that indicate the problem exists.

Example:

  • In the Observer pattern, the problem is how to automatically update dependent objects when one object changes its state.

Explanation:
The problem section helps you recognize a situation where the pattern can be applied effectively.

3. Solution

  • Describes how the pattern solves the problem — the elements involved, their relationships, responsibilities, and collaborations.

  • It provides an abstract description, not a concrete implementation.

  • Often illustrated using UML diagrams or class relationships.

Example:

  • In the Factory Method pattern, the solution is to create an interface for object creation but let subclasses decide which class to instantiate.

Explanation:
The solution section gives a structural outline of how components interact, without tying it to a specific programming language.

4. Consequences

  • Describes the results, trade-offs, and impacts of applying the pattern.

  • Includes aspects like performance, scalability, flexibility, and complexity.

  • Helps developers understand the costs and benefits of using the pattern.

Example:

  • The Singleton pattern ensures a single instance but can make unit testing difficult and reduce code flexibility.

Explanation:
This section helps decide whether the benefits of applying the pattern outweigh its drawbacks.

In Summary

Element Description
Pattern Name Identifies and communicates the design pattern clearly.
Problem Explains when and why to use the pattern.
Solution Describes the general design structure and how it solves the problem.
Consequences Lists the results, pros, and cons of applying the pattern.