Design Patterns Types Overview

A design pattern is a reusable solution to a common problem in software design. Think of it like a recipe — you do not cook the dish itself, but you follow a proven set of steps to get a great result every time. Design patterns help developers write code that is easier to understand, extend, and maintain.

Every design pattern belongs to one of three main categories: Creational, Structural, and Behavioral. Each category solves a different kind of problem.

The Three Categories at a Glance

┌─────────────────────────────────────────────────────────────────┐
│                     DESIGN PATTERN TYPES                        │
├───────────────────┬──────────────────────┬──────────────────────┤
│   CREATIONAL      │     STRUCTURAL       │    BEHAVIORAL        │
│  (How to create)  │  (How to assemble)   │  (How to interact)   │
├───────────────────┼──────────────────────┼──────────────────────┤
│ • Singleton       │ • Adapter            │ • Observer           │
│ • Factory Method  │ • Decorator          │ • Strategy           │
│ • Abstract Factory│ • Facade             │ • Command            │
│ • Builder         │ • Composite          │ • Iterator           │
│ • Prototype       │                      │                      │
└───────────────────┴──────────────────────┴──────────────────────┘

Creational Patterns

Creational patterns deal with object creation. They control how objects are created so your code does not depend on hard-coded class names. Imagine a toy factory — instead of building each toy by hand every time, you have a machine that produces them on demand.

Real-Life Analogy

You walk into a coffee shop and say "Give me a large latte." You do not tell the barista which coffee machine to use, how to steam milk, or where the cups are stored. The shop handles all that internally. Creational patterns work the same way — they hide the messy details of object creation from the rest of your code.

Patterns in This Category

• Singleton — Ensures only one instance of a class exists (like a single configuration file for your whole app).
• Factory Method — Lets a class decide which object to create based on input.
• Abstract Factory — Creates families of related objects without specifying their exact classes.
• Builder — Builds a complex object step by step (like assembling a custom burger).
• Prototype — Copies an existing object instead of creating a new one from scratch.

Structural Patterns

Structural patterns deal with how objects and classes are assembled into larger structures. They help you combine simple parts into a working whole without breaking each part's independence.

Real-Life Analogy

Think of a power adapter you use when travelling abroad. Your laptop plug does not fit the foreign wall socket, so you use an adapter in between. The Adapter pattern in code works exactly like that — it makes two incompatible parts work together without changing either one.

Patterns in This Category

• Adapter — Bridges two incompatible interfaces so they can work together.
• Decorator — Adds new behaviour to an object dynamically, like adding toppings to a pizza.
• Facade — Provides a simple front door to a complex system (like a hotel concierge).
• Composite — Treats individual objects and groups of objects the same way (like a folder containing files and other folders).

Behavioral Patterns

Behavioral patterns deal with how objects communicate and share responsibilities. They define clear lines of communication between objects so code stays organised and flexible.

Real-Life Analogy

Picture a newspaper subscription. You subscribe once, and every time a new edition is published, it arrives at your door automatically. The Observer pattern works the same way — objects subscribe to events and get notified when something changes, without constantly checking for updates.

Patterns in This Category

• Observer — Notifies many objects when one object changes its state.
• Strategy — Swaps one algorithm for another at runtime without changing the surrounding code.
• Command — Wraps a request as an object so you can queue, log, or undo it.
• Iterator — Steps through a collection of items without exposing its internal structure.

Why Patterns Are Organised This Way

PROBLEM YOU FACE          → PATTERN CATEGORY TO USE

"I need to control how    → CREATIONAL
 objects are created"

"I need to combine or     → STRUCTURAL
 connect objects cleanly"

"I need objects to        → BEHAVIORAL
 communicate better"

Knowing which category a pattern belongs to helps you find the right tool faster. When you face a problem related to object creation, you scan the Creational list. When two systems do not speak to each other, you look at Structural patterns. When communication between objects is tangled, Behavioral patterns offer the solution.

How Patterns Fit Together in a Real Project

  [ User clicks "Order" button ]
         │
         ▼
  Command Pattern  ◄─── wraps the order as an object
         │
         ▼
  Factory Method   ◄─── creates the right order type
         │
         ▼
  Builder Pattern  ◄─── assembles the order step by step
         │
         ▼
  Observer Pattern ◄─── notifies kitchen, stock system, user

A single real-world feature often uses patterns from all three categories working together. Creational patterns build the objects, structural patterns connect them, and behavioral patterns make them communicate.

Key Takeaways

• Design patterns are proven, reusable solutions — not finished code.
• The three categories are Creational (creation), Structural (assembly), and Behavioral (communication).
• Patterns reduce repetition, improve readability, and make code easier to change.
• Most real projects combine patterns from all three categories.