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
• Model Java data with records and pure functions
• Separate Java behavior from immutable data structures
• Validate data integrity with pure Java functions

Workflow

1. Compile project before data-oriented changes

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

1. 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.

1. Apply data-oriented refactorings

Implement selected improvements using records, pure transformation functions, flat structures, and explicit validation.

1. 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.