SOLID Principles Explained with Java & Ruby Examples

Learn the five SOLID principles with practical Java and Ruby examples. Improve software design, write maintainable code, and prepare for technical interviews.

By Anderson Alvarez Vásquez · 2026-07-01

• technology
• programming
• ruby
• tutorials
• Java

SOLID Principles Every Developer Should Know With Java & Ruby Examples Writing code that works is only the first step. Writing code that is easy to maintain, extend, and test is what separates good software from code that becomes difficult to evolve. The SOLID principles are five design principles introduced by Robert C. Martin "Uncle Bob" that help developers build maintainable object-oriented software. In this article, we'll explore each principle with practical examples in Java and Ruby . What Is SOLID? SOLID stands for: - Single Responsibility Principle - Open/Closed Principle - Liskov Substitution Principle - Interface Segregation Principle - Dependency Inversion Principle 1. Single Responsibility Principle SRP A class should have only one reason to change. Bad Example Java java public class Invoice { public void calculateTotal {} public void save {} public void sendEmail {} } Better java public class Invoice { public void calculateTotal {} } public class InvoiceRepository { public void save Invoice invoice {} } public class EmailService { public void send Invoice invoice {} } Ruby ruby class Invoice def calculate; end end class InvoiceRepository def save invoice ; end end class EmailService def send invoice ; end end 2. Open/Closed Principle OCP Extend behavior without modifying existing code. java public interface DiscountPolicy { double discount ; } ruby class PremiumDiscount def discount 0.20 end end 3. Liskov Substitution Principle LSP Subclasses should be replaceable by their parent types. java interface Bird {} interface FlyingBird extends Bird { void fly ; } ruby module Bird; end module Flying def fly; end end 4. Interface Segregation Principle ISP Don't force clients to implement methods they don't need. java interface Workable { void work ; } ruby...