Skills Sh Jabrena Cursor Rules Java 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. This should trigger for requests such as 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. Part of cursor-rules-java project
license: Apache-2.0
metadata:
  author: Juan Antonio Breña Moral
  version: 0.15.0
---
# 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
- **EDGE CASE**: If request scope is ambiguous, stop and ask a clarifying question before applying changes
- **EDGE CASE**: If required inputs, files, or tooling are missing, report what is missing and ask whether to proceed with setup guidance

## 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](references/121-java-object-oriented-design.md).