defrecord_interop.clj

(ns defrecord-interop)

(defrecord Kitten []
  java.lang.Runnable
  (run [this] (println "Kitten")))

(deftype Puppy []
  java.lang.Runnable
  (run [this] (println "Puppy")))

HelloWorldApp.java

import defrecord_interop.Kitten;
import defrecord_interop.Puppy;

class HelloWorldApp {
    public static void main(String[] args) {
        (new Kitten()).run();
        (new Puppy()).run();
    }
}