Calling Java from Clojure

Calling Java from Clojure is direct: you are still on the JVM. The main differences from Java are syntactic and ergonomic, not “capability” differences.

Common shapes you will see:

1(.substring "hello" 1 3)  ;; instance method => "el"
2(Math/abs -3)             ;; static method   => 3

The practical gotcha is reflection: if Clojure cannot infer the target type for an interop call, it may reflect at runtime. That is usually fine at the edges, but it can become a real cost inside tight loops. This section helps you recognize the call forms and know when type hints are worth it.

In this section

• Java Interop Syntax in Clojure
  Learn the core forms for calling Java from Clojure: static calls, instance calls, field access, constructors, and the type hints that keep hot paths away from reflection.
• Accessing Java Fields and Properties in Clojure
  Access Java fields and JavaBean-style getters and setters from Clojure without confusing object state with the plain data model used in idiomatic Clojure code.
• Java Constructors from Clojure
  Create Java objects with Clojure constructor forms, compare them with Java new expressions, and keep object construction localized at interop boundaries.