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
- Compile project before OOD changes
Run ./mvnw compile or mvn compile and stop immediately if compilation fails.
- Read OOD reference and assess code
Read references/121-java-object-oriented-design.md and identify applicable SOLID/OOP/code-smell improvements.
- Apply focused refactorings
Implement the selected object-oriented design improvements while preserving behavior.
- 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.
1---2name: 121-java-object-oriented-design3description: 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 project4license: Apache-2.05---6# Java Object-Oriented Design Guidelines
7
8Review and improve Java code using comprehensive object-oriented design guidelines and refactoring practices.
9
10**What is covered in this Skill?**
11
12- Fundamental design principles (SOLID, DRY, YAGNI)
13- Class and interface design: composition over inheritance, immutability, accessibility minimization, accessor methods
14- Core OOP concepts: encapsulation, inheritance, polymorphism
15- Object creation patterns: static factory methods, Builder, Singleton, dependency injection, avoiding unnecessary objects
16- OOD code smells: God Class, Feature Envy, Inappropriate Intimacy, Refused Bequest, Shotgun Surgery, Data Clumps
17- Method design: parameter validation, defensive copies, careful signatures, empty collections over nulls, Optional usage
18- Exception handling: checked vs. runtime exceptions, standard exceptions, failure-capture messages, no silent ignoring
19
20**Scope:** The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.
21
22## Constraints
23
24Before applying any OOD changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification.
25
26- **MANDATORY**: Run `./mvnw compile` or `mvn compile` before applying any change
27- **SAFETY**: If compilation fails, stop immediately and do not proceed — compilation failure is a blocking condition
28- **VERIFY**: Run `./mvnw clean verify` or `mvn clean verify` after applying improvements
29- **BEFORE APPLYING**: Read the reference for detailed examples, good/bad patterns, and constraints
30- **EDGE CASE**: If request scope is ambiguous, stop and ask a clarifying question before applying changes
31- **EDGE CASE**: If required inputs, files, or tooling are missing, report what is missing and ask whether to proceed with setup guidance
32
33## When to use this skill
34
35- Review Java code for object-oriented design
36- Refactor Java code for object-oriented design
37- Improve Java code for object-oriented design
38- Fix OOP concept misuse in Java code
39- Identify and resolve code smells in Java code
40- Improve object creation patterns in Java code
41- Improve method design in Java code
42- Improve exception handling in Java code
43
44## Workflow
45
461. **Compile project before OOD changes**
47
48Run `./mvnw compile` or `mvn compile` and stop immediately if compilation fails.
49
502. **Read OOD reference and assess code**
51
52Read `references/121-java-object-oriented-design.md` and identify applicable SOLID/OOP/code-smell improvements.
53
543. **Apply focused refactorings**
55
56Implement the selected object-oriented design improvements while preserving behavior.
57
584. **Verify with full build**
59
60Run `./mvnw clean verify` or `mvn clean verify` after applying improvements.
61
62## Reference
63
64For detailed guidance, examples, and constraints, see [references/121-java-object-oriented-design.md](references/121-java-object-oriented-design.md).
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