Low-Level Design: Concepts, Code Examples, and Design Examples

This repository serves as a comprehensive guide to Low-Level Design (LLD), aimed at helping developers understand and implement essential design concepts in software development. It contains a collection of:

• Core Concepts: Key principles and techniques in LLD such as SOLID principles, object-oriented design, and common design patterns.

• Code Examples: Practical Java code implementations showcasing various design techniques, including dependency injection, design pattern usage, and object modeling.

• Design Examples: Step-by-step breakdowns of real-world design problems, with detailed explanations of how to design and architect scalable, maintainable software systems.

• Whether you're preparing for interviews, aiming to improve your design skills, or looking to see best practices in action, this repository provides a solid foundation for mastering Low-Level Design.

Concepts

• Basic OOP
  • Classes in Java
  • Scope
  • UML
  • Main OOP Concepts in Java
    • Encapsulation
    • Abstraction
    • Inheritance
    • Polymorphism
  • Composition
  • Collections
  • Generics
  • Concurrency
  • Java Glossary
• Springboot
  • Dependency Inversion - IOC

SOLID Principles

SOLID is an acronym for five fundamental principles of object-oriented programming and design that help create more maintainable, flexible, and robust software.

• S - Single Responsibility Principle
• O - Open Closed Principle
• L - Liskov Substitution Principle
• I - Interface Segmented Principle
• D - Dependency Inversion Principle

Design Patterns

• Design patterns are reusable solutions to commonly occurring problems in software design.
• They represent best practices and proven approaches that experienced developers have identified and documented over time.
• Categories of design patterns include Creational, Structural, and Behavioral patterns.
  • Creational Patterns: Deal with object creation mechanisms (Singleton, Factory, Builder)
  • Structural Patterns: Deal with object composition and relationships (Adapter, Decorator, Facade)
  • Behavioral Patterns: Deal with communication between objects and assignment of responsibilities (Observer, strategy.Strategy, Command)

Creational Patterns	Structural Patterns	Behavioral Patterns
Singleton	Adapter	Chain of Responsibility
Factory Method	Bridge	Command
Abstract Factory	Composite	Iterator
Builder	Decorator	Mediator
Prototype	Facade	Memento
	Flyweight	Observer
	Proxy	State
		Strategy
		Template Method
		Visitor
		Null Object

Common Confusing Patterns

• Builder vs Decorator
• Facade vs Proxy
• Facade vs Adapter

Design Examples

Easy Problems

• Design a Parking Lot
• Design a weather PubSub System
• Design a Bank Account System
• Design Linkedin Verdict
• Design a Coffee Vending Machine
• Design a Traffic Signal Control System
• Design a Vending Machine

Medium Problems

• Design a LRU Cache
• Design a PubSub Model
• Design a Tic Tac Toe Game
• Design a Library Management System

Hard Problems

• Design an Elevator System
• Design a Conference Room Booking System
• Design Splitwise
• Design a Movie Ticket Booking System
• Design Music Streaming Service

Notations

• Is-A (Inheritance)
• Has-A (Composition/Aggregation)

Syntax	Symbol	Meaning	Usage	Line Style
`<	--`	Solid	Class inheritance	Concrete or abstract classes	Solid line
`<	..`	Dotted	Interface implementation	Class implements interface	Dotted line

Relationships

Terminology

• DAO (Data Access Object): A design pattern that provides an abstract interface to a database or other persistence mechanism.

Resources

• Design Patterns with Refactoring Guru

NOTE: This repository was created during my learning journey in Low-Level Design. If you notice any improvements or corrections, feel free to reach out.