{"id":"106c76eb-ee51-40a9-ac2e-4f7caa96eb6d","shortId":"4Nhvdf","kind":"skill","title":"121-java-object-oriented-design","tagline":"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 resolv","description":"# Java Object-Oriented Design Guidelines\n\nReview and improve Java code using comprehensive object-oriented design guidelines and refactoring practices.\n\n**What is covered in this Skill?**\n\n- Fundamental design principles (SOLID, DRY, YAGNI)\n- Class and interface design: composition over inheritance, immutability, accessibility minimization, accessor methods\n- Core OOP concepts: encapsulation, inheritance, polymorphism\n- Object creation patterns: static factory methods, Builder, Singleton, dependency injection, avoiding unnecessary objects\n- OOD code smells: God Class, Feature Envy, Inappropriate Intimacy, Refused Bequest, Shotgun Surgery, Data Clumps\n- Method design: parameter validation, defensive copies, careful signatures, empty collections over nulls, Optional usage\n- Exception handling: checked vs. runtime exceptions, standard exceptions, failure-capture messages, no silent ignoring\n\n**Scope:** The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.\n\n## Constraints\n\nBefore applying any OOD changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification.\n\n- **MANDATORY**: Run `./mvnw compile` or `mvn compile` before applying any change\n- **SAFETY**: If compilation fails, stop immediately and do not proceed — compilation failure is a blocking condition\n- **VERIFY**: Run `./mvnw clean verify` or `mvn clean verify` after applying improvements\n- **BEFORE APPLYING**: Read the reference for detailed examples, good/bad patterns, and constraints\n- **EDGE CASE**: If request scope is ambiguous, stop and ask a clarifying question before applying changes\n- **EDGE CASE**: If required inputs, files, or tooling are missing, report what is missing and ask whether to proceed with setup guidance\n\n## When to use this skill\n\n- Review Java code for object-oriented design\n- Refactor Java code for object-oriented design\n- Improve Java code for object-oriented design\n- Fix OOP concept misuse in Java code\n- Identify and resolve code smells in Java code\n- Improve object creation patterns in Java code\n- Improve method design in Java code\n- Improve exception handling in Java code\n\n## Workflow\n\n1. **Compile project before OOD changes**\n\nRun `./mvnw compile` or `mvn compile` and stop immediately if compilation fails.\n\n2. **Read OOD reference and assess code**\n\nRead `references/121-java-object-oriented-design.md` and identify applicable SOLID/OOP/code-smell improvements.\n\n3. **Apply focused refactorings**\n\nImplement the selected object-oriented design improvements while preserving behavior.\n\n4. **Verify with full build**\n\nRun `./mvnw clean verify` or `mvn clean verify` after applying improvements.\n\n## Reference\n\nFor detailed guidance, examples, and constraints, see 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