Java Interop Performance in Clojure

Most Java interop is fast enough. The performance problems show up when:

• reflection happens repeatedly inside hot code paths
• you cross the Java/Clojure boundary per-element in a large loop
• you allocate conversions over and over instead of converting once

The engineering approach is the same as in Java: measure, profile, and then pick the right tool. This section highlights the common interop costs so you know what to look for when something feels “surprisingly slow.”

In this section

• Reflection and Performance Overheads in Clojure and Java Interoperability
  Understand when Clojure uses reflection for Java calls, why repeated reflective dispatch can hurt hot paths, and how to identify the exact call sites that need type information.
• Type Hinting and Avoiding Reflection in Clojure for Java Interoperability
  Use Clojure type hints surgically around Java interop calls so the compiler can emit direct method calls without turning idiomatic code into noisy pseudo-Java.
• Benchmarking and Profiling Interop Code
  Benchmark and profile Clojure code that calls Java so reflection, allocation, conversion, and boundary-crossing costs are measured before they are optimized.