Java best practices

Skill ComeOnOliver/skillshub/skills/HoangNguyen0403/agent-skills-standard/java-best-practices

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Core Effective Java patterns for robust, maintainable Java code. Use when applying SOLID principles, choosing between inheritance and composition, refactoring Java code smells, or reviewing class design. (triggers: **/*.java, refactor, SOLID, builder, factory, composition, immutable, Optional, checked exception, clean code)

SKILL.md

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Java Best Practices

Priority: P1 (HIGH)

Core engineering principles for robust, maintainable Java systems.

Implementation Guidelines

Immutability: Prefer immutable objects (final fields, unmodifiable collections).
Access Modifiers: Minimize visibility. Default to package-private (no modifier). Use private for all fields. Only public for API contracts.
Composition > Inheritance: Favor Has-A over Is-A. Avoid deep hierarchies.
Constructors: Use Static Factory Methods (User.of()) over complex constructors.
Builder Pattern: Use for objects with 4+ parameters.
Exceptions: Recoverable → Checked; Programming error → Unchecked.
Fail Fast: Validate parameters (Objects.requireNonNull) at the method start.
Interfaces: Code to interfaces (List, Map), not implementations (ArrayList).
Dependency Injection: Inject dependencies via constructor; don't create them internally.
Method References: Use String::toUpperCase over s -> s.toUpperCase() where readable.

Anti-Patterns

No Null Returns: Return Optional<T> or empty collection instead.
No Empty Catch: Log or rethrow; never swallow exceptions silently.
No God Class: Split into focused classes following Single Responsibility Principle.
No Magic Numbers: Extract named constants with clear meaning.
No Mutable Statics: Avoid public static mutable fields (global state).

References

Static Factory & Composition Examples