Solid Principles

This is a practical reference for applying SOLID principles during code reviews and refactoring sessions. It gives you concrete Java examples of each principle with before/after code, so you can spot violations like classes doing too much or switch statements that keep growing. The quick reference table and "how to detect" sections make it easy to use when you're actually reviewing pull requests or explaining why a 500-line service class needs to be broken up. The examples are clear enough that you could point a junior developer to specific sections when teaching design patterns. It won't make architectural decisions for you, but it's a solid checklist when you need to justify refactoring work or catch design smells before they ship.

skills.sh installs: 384
GitHub stars: 771
last updated: Feb 8, 2026

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Install

$ npx -y skills add decebals/claude-code-java --skill solid-principles --agent claude-code

Installs into .claude/skills of the current project.

Files

SOLID Principles Skill

Review and apply SOLID principles in Java code.

When to Use

User says "check SOLID" / "SOLID review" / "is this class doing too much?"
Reviewing class design
Refactoring large classes
Code review focusing on design

Quick Reference

Letter	Principle	One-liner
S	Single Responsibility	One class = one reason to change
O	Open/Closed	Open for extension, closed for modification
L	Liskov Substitution	Subtypes must be substitutable for base types
I	Interface Segregation	Many specific interfaces > one general interface
D	Dependency Inversion	Depend on abstractions, not concretions

S - Single Responsibility Principle (SRP)

"A class should have only one reason to change."

Violation

// ❌ BAD: UserService does too much
public class UserService {

    public User createUser(String name, String email) {
        // validation logic
        if (email == null || !email.contains("@")) {
            throw new IllegalArgumentException("Invalid email");
        }

SKILL.md on GitHub