Clojure: exit program when Window Frame is Closed

Question

I'd like my Clojure program to exit when a JFrame is closed.

I'm attempting to trap and handle the close event as such:

(def exit-action (proxy [WindowAdapter] []
               (windowClosing [event] (fn [] (System/exit 0)))
               )
)
(.addWindowListener frame exit-action)

This doesn't throw any obvious errors but it also doesn't appear to do what I want.

Assistance is appreciated.

Answer:

Adapting Rekin's answer did the trick:

(.setDefaultCloseOperation frame JFrame/EXIT_ON_CLOSE)

Note that that is:

setDefaultCloseOperation

not:

setDefaultOperationOnClose

Rekin · Answer 1 · 2011-06-22T07:48:49.337

3

In Java it's:

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

More elaborate examples can be found in official Java Swing tutorial about Frames

edited Jun 22 '11 at 07:48

answered Jun 22 '11 at 07:07

Rekin

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I'm not sure why but setDefaultCloseOperation failed with an error about not being able to find JFrame.EXIT_ON_CLOSE (nothing about the function not being found) setDefaultCloseOperation did what was needed with no such error about not finding EXIT_ON_CLOSE. I suppose it could be different JVM versions. Thanks again. – SMTF Jun 22 '11 at 07:42
Oh, sorry, that's because i wrote it from memory. I'm going to edit out the answer. – Rekin Jun 22 '11 at 07:48

amalloy · Answer 2 · 2011-06-23T22:28:00.527

3

I would use EXIT_ON_CLOSE, but the reason your first attempt didn't work is that the body of proxy should contain (System/exit 0), not (fn [] (System/exit 0)). Rather than exiting, you were returning (and then throwing away) a function that, when called, would exit.

edited Jun 23 '11 at 22:28

answered Jun 23 '11 at 03:25

amalloy

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Thanks for that clarification. I initially thought that I needed an ad-hock function to be sure that I was passing the proxy what it needed; it slipped my mind that the exit call would be a valid function itself. – SMTF Jun 29 '11 at 22:13

score 2 · Answer 3 · answered Jun 22 '11 at 14:10

Here's a short demonstration program I showed on my blog a while ago

(ns net.dneclark.JFrameAndTimerDemo
  (:import (javax.swing JLabel JButton JPanel JFrame Timer))
  (:gen-class))

(defn timer-action [label counter]
   (proxy 1 []
     (actionPerformed
      [e]
       (.setText label (str "Counter: " (swap! counter inc))))))

(defn timer-fn []
  (let [counter (atom 0)
        label (JLabel. "Counter: 0")
        timer (Timer. 1000 (timer-action label counter))
        panel (doto (JPanel.)
                (.add label))]
    (.start timer)
    (doto (JFrame. "Timer App")
      (.setContentPane panel)
      (.setDefaultCloseOperation JFrame/EXIT_ON_CLOSE)
      (.setLocation 300 300)
      (.setSize 200 200)
      (.setVisible true)))
  (println "exit timer-fn"))

(defn -main []
  (timer-fn))

Note the line in timer-fn[] that sets the default close operation. Just about like Java but with a little syntax fiddling.

The purpose of the blog entry was to show an example of a closure in Clojure.

Clojure: exit program when Window Frame is Closed

3 Answers3