Introduction

Design patterns are reusable solutions to recurring software design problems, codified by the Gang of Four (Gamma, Helm, Johnson, Vlissides, 1994).

Core Concepts

What: Templates for solving common object-oriented design problems Why: Proven solutions, shared vocabulary, maintainable code When: Complex systems requiring flexibility and clear structure When Not: Simple problems, performance-critical code, unnecessary abstraction

Categories

Creational - Object creation mechanisms Behavioral - Object interaction and responsibility distribution Structural - Object composition and relationships