java-performance-smell-detection

Review code for common smells like regex compilation in loops, string concatenation in loops, boxing in hot paths, and unbounded collections. Always measure with JMH or a profiler before optimizing, since modern JVMs already handle many patterns well.

Since Java 9, simple concatenation with + uses invokedynamic and is well optimized by the JVM. However, concatenation inside loops still creates a new String each iteration, so StringBuilder or String.join remains the right choice there.

Parallel streams help only for CPU-intensive work on large collections, typically over 10,000 items. Avoid them on small collections where overhead exceeds benefit, and never use them with shared mutable state due to race conditions.

No, database concerns like N+1 queries, lazy loading, and pagination are explicitly out of scope and handled by the java-jpa-patterns skill. This skill focuses only on code-level smells such as streams, collections, boxing, and regex.

Skip optimization when the code is not a hot path, when no measured problem exists, when readability would suffer, or when collections are small. Clear code usually matters more than micro-optimizations that save microseconds.