Design Principles: Building Robust, Maintainable Systems
Overview
Design principles provide essential guidelines for writing high-quality, maintainable, and scalable software, ensuring your code is robust, modular, and intuitive.
This section’s 18 lessons cover critical principles like SOLID, DRY, KISS, YAGNI, Law of Demeter, Composition over Inheritance, Programming to an Interface, Favor Immutability, and more — equipping you to design elegant Java systems.
By mastering these principles, you’ll create reliable software and explain your decisions clearly in interviews. This hub is inspired by Clean Code, Effective Java, and Head First Design Patterns, with a strong focus on practical Java applications.
Learning Objectives
- Master SOLID principles for modular, extensible code.
- Learn DRY, KISS, and YAGNI for simplicity and efficiency.
- Apply Law of Demeter, Separation of Concerns, Information Hiding, and High Cohesion/Low Coupling for decoupled design.
- Understand modern guidelines like Composition over Inheritance, Favor Immutability, and Principle of Least Privilege.
- Connect principles to clean code and design patterns in later sections.
Lessons
Introduction to Design Principles
Why principles matter, and how they differ from design patterns.
Start Lesson →Single Responsibility Principle (SRP)
One class, one job.
Start Lesson →Open-Closed Principle (OCP)
Open for extension, closed for modification.
Start Lesson →Liskov Substitution Principle (LSP)
Subtypes must be substitutable for base types.
Start Lesson →Interface Segregation Principle (ISP)
Small, specific interfaces for flexibility.
Start Lesson →Dependency Inversion Principle (DIP)
Depend on abstractions, not concretions.
Start Lesson →Programming to an Interface, not an Implementation
Design against contracts, not concrete classes.
Start Lesson →Composition over Inheritance
Favor object composition to reduce rigidity.
Start Lesson →DRY: Don’t Repeat Yourself
Eliminate duplication with reusable abstractions.
Start Lesson →KISS: Keep It Simple, Stupid
Strive for simplicity in code and design.
Start Lesson →YAGNI: You Aren’t Gonna Need It
Don’t build features until you actually need them.
Start Lesson →Law of Demeter (Principle of Least Knowledge)
Minimize coupling by limiting object interactions.
Start Lesson →Separation of Concerns
Modularize functionality into distinct layers or modules.
Start Lesson →Information Hiding
Hide internal details, expose only necessary APIs.
Start Lesson →High Cohesion & Low Coupling
Group related responsibilities; minimize dependencies.
Start Lesson →Favor Immutability
Prefer immutable designs for safety and clarity.
Start Lesson →Principle of Least Privilege / Least Authority
Grant only the minimum rights necessary.
Start Lesson →POLA and GRASP Principles
Principle of Least Astonishment + General Responsibility Assignment Software Patterns.
Start Lesson →
Start Your Journey
Begin with Introduction to Design Principles, or explore other interview topics to strengthen your engineering and interview prep journey.