使用gen-class时如何获取类的实例

Question

I want to use the instance of the class constructed via gen-class in a method of the class.

How do I access it? What do I have insert for "this" in the following example:

(ns example
  (:gen-class))

(defn -exampleMethod []
  (println (str this)))

Or is it impossible when using gen-class?

Answer 1

The first argument of Clojure functions corresponding to a method generated by gen-class takes the current object whose method is being called.

(defn -exampleMethod [this]
  (println (str this)))

In addition to this, you have to add a :methods option to gen-class when you define a method which comes from neither a superclass nor interfaces of the generated class. So a complete example would be as follows.

example.clj

(ns example)

(gen-class
 :name com.example.Example
 :methods [[exampleMethod [] void]])

(defn- -exampleMethod
  [this]
  (println (str this)))

REPL

user> (compile 'example)
example

user> (.exampleMethod (com.example.Example.))
com.example.Example@73715410
nil