Extend java class in clojure: how to override only one of two similar methods?

Question

I have the following java class.

public class Toto { public void aMethod(A a) { System.out.println("A " + a); } public void aMethod(B b) { System.out.println("B " + b); } }

I want to override aMethod(A a) but not aMethod(B b). The only way I could do that was:

(ns titi (:gen-class :extends Toto :exposes-method {aMethod parentMethod})) (defn- -aMethod [this x] (if (= (type x) A) (println "ok do something here") (.parentMethod this x)))

Is there a better way to do this? (I mean without checking type of x myself).

circlespainter · Accepted Answer · 2014-09-01 16:49:27Z

According to http://dishevelled.net/Tricky-uses-of-Clojure-gen-class-and-AOT-compilation.html, with :gen-class it is possible to override by signature but I couldn't find documentation on that, so I guess it can be considered "internals" and it may break in the future.

Anyway, supposing you have your Toto class in package jpkg together with two empty classes A and B, this works for me:

(ns Titi (:import [jpkg A]) (:gen-class :extends jpkg.Toto :exposes-method [aMethod])) (defn- -aMethod-A [this x] (println "clj a"))

As the following main namespace:

(ns main (:import [jpkg A B])) (set! *warn-on-reflection* true) (defn -main [] (. (new Titi) aMethod (new A)) (. (new Titi) aMethod (new B)))

prints:

clj a B jpkg.B@6631f5ca

instead of:

clj a clj a

Type hints instead seem not to help here.

Collectives™ on Stack Overflow

Extend java class in clojure: how to override only one of two similar methods?

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related