144-java-data-oriented-programming

# Java Data-Oriented Programming Best Practices Apply data-oriented programming in Java: separate data from behavior with records, use immutable data structures, pure functions for transformations, flat denormalized structures with ID references, generic-to-specific type conversion when needed, pure validation functions, and flexible generic data access layers. All transformations should be explicit, traceable, and composed of clear pure functional steps. **What is covered in this Skill?** - Separation of concerns: data structures (records, POJOs) vs behavior (utility classes, services) - Immutability: records, final fields, transformations produce new instances - Pure data transformations: functions depending only on inputs, no side effects - Flat and denormalized data: ID references instead of deep nesting - Generic until specific: Map<String,Object> for dynamic data, convert to records when processing - Data integrity: pure validation functions returning validation results - Flexible generic data access: generic CRUD interfaces, interchangeable implementations **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 data-oriented programming recommendations, ensure the project compiles. Compilation failure is a blocking condition. After applying improvements, run full verification. - **MANDATORY**: Run `./mvnw compile` or `mvn compile` before applying any change - **SAFETY**: If compilation fails, stop immediately — do not proceed until resolved - **VERIFY**: Run `./mvnw clean verify` or `mvn clean verify` after applying improvements - **BEFORE APPLYING**: Read the reference for detailed good/bad examples, constraints, and safeguards for each data-oriented programming pattern ## When to use this skill - Improve the code with Data-Oriented Programming - Apply Data-Oriented Programming - Refactor the code with Data-Oriented Programming - Apply Data-Oriented Programming - Refactor the code with Data-Oriented Programming - Apply Data-Oriented Programming ## Workflow 1. **Compile project before data-oriented changes** Run `./mvnw compile` or `mvn compile` and stop immediately if compilation fails. 2. **Read data-oriented reference and assess model design** Read `references/144-java-data-oriented-programming.md` and identify candidates for data/behavior separation and immutable transformations. 3. **Apply data-oriented refactorings** Implement selected improvements using records, pure transformation functions, flat structures, and explicit validation. 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/144-java-data-oriented-programming.md](references/144-java-data-oriented-programming.md).