No client should be forced to depend on methods it does not use. ISP keeps interfaces focused, prevents unnecessary recompilation, and — at the architectural level — prevents importing modules that drag in unwanted dependencies.
High-level policy should not depend on low-level details. Both should depend on abstractions. DIP is the mechanism that makes Clean Architecture possible — and the most architecturally consequential of all SOLID principles.
The most misunderstood SOLID principle. SRP is NOT "every class does one thing" — it means a module should have only one reason to change, i.e., it serves only one actor. Learn the two symptoms of SRP violation and how to solve them.
A software artifact should be open for extension but closed for modification. OCP is the architectural goal that drives Clean Architecture: protect high-level policy from changes in low-level details by controlling the direction of dependencies.
If S is a subtype of T, objects of type S must be substitutable for objects of type T without altering the correctness of the program. LSP governs not just inheritance but any interface contract — and its violation breaks architectural boundaries.
Don't let your important business logic classes depend directly on concrete implementations (like a specific database driver, a specific email provider, etc.).
Keep your interfaces **small and focused**. Don't create a "fat" interface that bundles unrelated methods together, forcing classes to implement things they.
Welcome! This guide will walk you through the **SOLID principles** — five essential design principles that help you write Java code that is **clean, scalable.
Comprehensive answers to Java Software Design Patterns and Garbage Collection interview questions.
If class `B` extends class `A`, then anywhere you use `A`, you should be able to swap in `B` without anything breaking.
Guide to object-oriented programming in Java, covering encapsulation, inheritance, polymorphism, abstraction, and SOLID principles.
Your class should be: - **Open for extension** → You can add new behavior - **Closed for modification** → You don't change existing, working code
Every class should do **exactly one thing** and do it well. If a class is handling multiple unrelated responsibilities, then it has multiple reasons to change.
Congratulations! You've learned all 5 SOLID principles. Here's everything at a glance.