Performance Smell Detection

This helps you spot Java performance smells like regex compilation in loops, string concatenation inefficiencies, and boxing overhead, but it's opinionated about modern Java realities. The author correctly notes that string concatenation with + is fine in Java 9+ for simple cases thanks to invokedynamic, and that streams are often acceptable except in tight loops with huge datasets. The guidance on regex pre-compilation and StringBuilder in loops remains valid. What I appreciate is the "measure first" philosophy throughout, acknowledging that readability often trumps micro-optimizations and that JVMs have gotten really good at optimization. It explicitly scopes itself to code-level issues and punts JPA/database problems to the jpa-patterns skill, which is the right call.