141-java-refactoring-with-modern-features

# Modern Java Development Guidelines (Java 8+) Identify and apply modern Java (Java 8+) refactoring opportunities to improve readability, maintainability, and performance. **What is covered in this Skill?** - Lambda expressions and method references (over anonymous classes) - Stream API for declarative collection processing - `Optional` for null-safe APIs - `java.time` API (replacing `Date`/`Calendar`) - Default interface methods, `var` type inference - Unmodifiable collection factory methods (`List.of()`, `Set.of()`, `Map.of()`) - Text blocks for multi-line strings - Java 25 Flexible Constructor Bodies (JEP 513) - Java 25 Module Import Declarations (JEP 511) **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 modern Java refactoring, ensure the project compiles. If compilation fails, stop immediately — do not proceed until the project compiles successfully. After applying improvements, run full verification. - **MANDATORY**: Run `./mvnw compile` or `mvn compile` before applying any changes - **SAFETY**: If compilation fails, stop immediately — do not proceed until the project compiles successfully - **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 modern Java feature - **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 modern Java development - Apply best practices for modern Java development in Java code ## Workflow 1. **Compile project before modernization** Run `./mvnw compile` or `mvn compile` and stop immediately if compilation fails. 2. **Read modern-Java reference and identify candidates** Read `references/141-java-refactoring-with-modern-features.md` and identify high-value opportunities to adopt modern Java features. 3. **Apply modern Java refactorings** Refactor incrementally using appropriate language/library features while preserving behavior and readability. 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/141-java-refactoring-with-modern-features.md](references/141-java-refactoring-with-modern-features.md).