java-code-review

Run a structured checklist review covering null safety, exception handling, concurrency, and performance. The Skill scans the changed code and returns findings grouped by severity with line references and suggested fixes.

A thorough checklist covers null safety and Optional usage, swallowed or overly broad exceptions, collection modification during iteration, thread safety and race conditions, equals/hashCode contracts, try-with-resources, API design, and performance pitfalls like N+1 queries.

Look for shared mutable state without synchronization, check-then-act patterns like containsKey followed by put, and missing volatile on shared fields. Replace them with ConcurrentHashMap, computeIfAbsent, or java.util.concurrent utilities.

It works best on focused changes such as a single class or pull request diff rather than entire repositories. Narrowing scope keeps findings specific and avoids repeating obvious issues across files.

Each += creates a new String object, causing O(n²) copying in loops. Use StringBuilder for repeated appends, pre-compile regex patterns outside loops, and batch database queries to avoid N+1 patterns.