Design Patterns Tutorial

Design patterns are reusable solutions to common software design problems that help developers build cleaner and more maintainable systems. They provide templates for solving issues in object creation, structure, and behaviour. They improve code flexibility and scalability.

• Provide standard, proven solutions to recurring design problems.
• Improve code readability, reusability, and maintainability.
• Help developers follow best practices in software architecture.
• Reduce development time by avoiding reinventing solutions.

Design Pattern Basics

Design patterns provide reusable solutions to common software design problems. They help developers write cleaner, maintainable, and scalable applications.

• Introduction
• Types of Design Patterns
• Gang of Four (GoF) Overview

Creational Design Patterns

These Creational Design Patterns deal with object creation in a flexible and efficient manner. They help you control how and when objects are instantiated.

• Singleton Pattern
• Factory Method Pattern
• Abstract Factory Pattern
• Builder Pattern
• Prototype Pattern
• Object Pool Pattern
• Lazy Initialization

Structural Design Patterns

Structural patterns explain how classes and objects are combined to form larger structures. They improve code flexibility by simplifying relationships between components.

• Adapter Pattern
• Decorator Pattern
• Facade Pattern
• Composite Pattern
• Proxy Pattern
• Bridge Pattern
• Flyweight Pattern

Behavioral Design Patterns

Behavioral patterns define how objects communicate and distribute responsibilities. They help manage workflows, interactions, and decision-making within a system

• Observer Pattern
• Strategy Pattern
• Command Pattern
• Chain of Responsibility Pattern
• Template Method Pattern
• Iterator Pattern
• State Pattern
• Mediator Pattern
• Memento Pattern
• Visitor Pattern

Advanced Design Pattern

Advanced topics cover architectural principles and deeper system-design concepts. They help you build enterprise-level, scalable, and robust software systems

• SOLID Principles
• Dependency Injection Pattern
• Composition Vs Inheritance
• Event-Driven Architecture & Patterns
• CQRS Design Pattern
• Event Sourcing Patterns
• CQRS Vs Event Sourcing Patterns
• Repository Pattern

MVC separates an application into Model, View, and Controller for clean architecture. It improves scalability, maintainability, and parallel development in large systems

• MVC Design Pattern

Design Pattern Interview Questions

This section prepares you for common interview questions on design patterns. It strengthens conceptual clarity and helps you explain patterns confidently.

• Interview Questions on Software Design Patterns

Applications of Design Patterns

• Help solve common software design problems using proven solutions.
• Improve code reusability, readability, and maintainability.
• Enable loose coupling between components in large applications.
• Simplify object creation, communication, and structure.
• Enhance scalability and support clean system growth.
• Provide a shared vocabulary for developers to discuss architecture.
• Used heavily in frameworks, libraries, and enterprise-level projects.
• Reduce bugs by following well-tested best practices.

Why Learn Design Patterns?

There are multiple reasons to learn design patterns:

• Code that is simpler to comprehend, update, and expand is produced with the help of design patterns.
• They offer solutions that have been tried and tested as well as best practices.
• Learning this enables them to quickly and effectively address similar challenges in various projects.
• Developers can produce reusable components that can be utilized in a variety of applications by implementing design patterns.
• This reduces redundancy and saves development time.

Approach to Learn Design Patterns

• In Week 1, you'll learn the foundations needed for design patterns, including classes, objects, abstraction, inheritance, polymorphism, and encapsulation. You will also study SOLID principles, which help you write clean, maintainable, and loosely coupled code — essential before learning design patterns.
• Week 2 focuses on Creational Patterns such as Singleton, Factory Method, Abstract Factory, Builder, and Prototype. You'll understand how these patterns manage object creation, reduce code complexity, and improve flexibility.
• In Week 3, you’ll explore Adapter, Decorator, Facade, Composite, Proxy, Bridge, and Flyweight patterns. These patterns teach you how to structure classes and objects efficiently, simplifying complex systems.
• Week 4 dives into Strategy, Observer, Command, Chain of Responsibility, Iterator, Mediator, State, Template Method, and more. You’ll learn how objects communicate, coordinate actions, and share responsibilities in real systems.
• In Week 5, you'll study system-level patterns like MVC, MVVM, Dependency Injection, Repository Pattern, and Service Layer Pattern. These patterns are widely used in backend systems, frameworks, and enterprise applications.
• Week 6 helps you apply patterns to real situations: Logger (Singleton), Notification System (Observer), Payment Gateway (Strategy), Undo/Redo (Command), and API Facade (Facade Pattern). This week focuses fully on hands-on implementation.
• Week 7 covers low-level design problems where design patterns are essential. You’ll practice Parking Lot System, In-Memory File System, BookMyShow LLD, and securing Singleton from Reflection, Cloning, and Serialization.
• In Week 8, you'll build real-world projects using multiple design patterns combined. You’ll also revise interview questions, pattern comparisons, and architecture-based solutions to strengthen your problem-solving skills.

Important Links

• Design a Parking lot using Object Oriented Principles
• Design data structures and algorithms for in-memory file system
• How to prevent Singleton Pattern from Reflection, Serialization and Cloning?