121-java-object-oriented-design

name	121-java-object-oriented-design
description	Use when you need to review, improve, or refactor Java code for object-oriented design quality — including applying SOLID, DRY, and YAGNI principles, improving class and interface design, fixing OOP concept misuse (encapsulation, inheritance, polymorphism), identifying and resolving code smells (God Class, Feature Envy, Data Clumps), or improving object creation patterns, method design, and exception handling. Part of the skills-for-java project
license	Apache-2.0
metadata	{"author":"Juan Antonio Breña Moral","version":"0.15.0-SNAPSHOT"}

Java Object-Oriented Design Guidelines

Review and improve Java code using comprehensive object-oriented design guidelines and refactoring practices.

What is covered in this Skill?

• Fundamental design principles (SOLID, DRY, YAGNI)
• Class and interface design: composition over inheritance, immutability, accessibility minimization, accessor methods
• Core OOP concepts: encapsulation, inheritance, polymorphism
• Object creation patterns: static factory methods, Builder, Singleton, dependency injection, avoiding unnecessary objects
• OOD code smells: God Class, Feature Envy, Inappropriate Intimacy, Refused Bequest, Shotgun Surgery, Data Clumps
• Method design: parameter validation, defensive copies, careful signatures, empty collections over nulls, Optional usage
• Exception handling: checked vs. runtime exceptions, standard exceptions, failure-capture messages, no silent ignoring

Scope: The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.

Constraints

Before applying any OOD changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification.

• MANDATORY: Run ./mvnw compile or mvn compile before applying any change
• SAFETY: If compilation fails, stop immediately and do not proceed — compilation failure is a blocking condition
• VERIFY: Run ./mvnw clean verify or mvn clean verify after applying improvements
• BEFORE APPLYING: Read the reference for detailed examples, good/bad patterns, and constraints

When to use this skill

• Review Java code for object-oriented design
• Refactor Java code for object-oriented design
• Improve Java code for object-oriented design
• Fix OOP concept misuse in Java code
• Identify and resolve code smells in Java code
• Improve object creation patterns in Java code
• Improve method design in Java code
• Improve exception handling in Java code

Workflow

1. Compile project before OOD changes

Run ./mvnw compile or mvn compile and stop immediately if compilation fails.

2. Read OOD reference and assess code

Read references/121-java-object-oriented-design.md and identify applicable SOLID/OOP/code-smell improvements.

3. Apply focused refactorings

Implement the selected object-oriented design improvements while preserving behavior.

4. Verify with full build

Run ./mvnw clean verify or mvn clean verify after applying improvements.

Reference

For detailed guidance, examples, and constraints, see references/121-java-object-oriented-design.md.