clojure gen-class generated classes invocation issue

Question

I defined the following MyCache.clj

(ns abcd.MyCache
  (:gen-class
   :name "abcd.MyCache"
   :init "init"
   :constructors { [java.text.DateFormat][] }
   :methods [ [now [] void] [myformat [long] String] ]
   :state "state"
   :main false))

(defn -init[format]
  ([[] (atom {:format format})]))



(defn -now[this] ( (:format @(.state this)) (System/currentTimeMillis)))

(defn -myformat[this time]
    ( (:format @(.state this) (new java.util.Date time))))

I compiled the above file using (compile 'abcd.MyCache) successfully.

When I am trying to use the generated classes as shown below..I am getting errors. Please help.

user=> (new abcd.MyCache (new java.text.SimpleDateFormat "mmDDyyyy"))
IllegalArgumentException Key must be integer  clojure.lang.APersistentVector.invoke (APersistentVector.java:265)

What do you think this is doing? ([[] (atom {:format format})]) — Chiron, Sep 02 '13 at 16:04

Chiron · Accepted Answer · 2013-09-02T15:23:51.803

1

I don't feel well about this:

(defn -init[format]
  ([] [atom {:format format}]))

You are trying to get an element from a vector and it is expects an index (number).

What is correct is to deref the atom and get its value as the index of the vector. But again in your case, you are trying to query an empty vector.

Notice also, that [atom {:format format}] isn't the correct way to create an atom. You should use:

(atom {:format format})

And by the way, the following form is the preferred one to create Java objects (nothing wrong with (new) of course):

(Date.)
(DateFormat.)

edited Sep 02 '13 at 15:23

answered Sep 02 '13 at 15:10

Chiron

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(defn -init[format] ([[] (atom {:format format})])) user=> (abcd.MyCache. (java.text.SimpleDateFormat. "mmDDyyyy")) ArityException Wrong number of args (0) passed to: PersistentVector clojure.lang.AFn.throwArity (AFn.java:437) – psaradhi Sep 02 '13 at 16:01
I realized my mistake. init should be defined as (defn -init[format] [ [] (atom {:format format})]). I have extra parentheses surrounding the returning array causing this error. Thanks Chiron – psaradhi Sep 02 '13 at 16:10
you mean "the returned vector" :) not array – Chiron Sep 02 '13 at 16:13

clojure gen-class generated classes invocation issue

1 Answers1