java

Goal: modern Java that is immutable by default, null-safe, and testable. Use for: - new classes, services, or APIs in Java - reviewing structure, immutability, and error handling - modernizing verbose or legacy patterns Workflow: 1. Model immutable data with records and final fields. 2. Use Optional for absence; avoid returning null. 3. Prefer the Streams API for transformations over manual loops. 4. Throw specific exceptions; never swallow them silently. 5. Manage resources with try-with-resources. 6. Verify with JUnit, a static analyzer, and the formatter. Idioms: - records for immutable value types - Optional return types instead of null - switch expressions and pattern matching - var for obvious local types - dependency injection over static singletons Rules: - do not return or pass null; use Optional or explicit checks - close resources with try-with-resources, not manual finally - keep classes focused; favor composition over inheritance - program to interfaces for testability