Clojure Exception in thread main - clojure

Question

I'm trying to learn Clojure, for this I installed the latest Clojure and Leiningen, so I created a new lein project and add the :main helloclojure.core entry in to project.clj but when I try to run the project I get the following error:
Exception in thread "main" java.lang.ClassNotFoundException: helloclojure.core
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at clojure.lang.DynamicClassLoader.findClass(DynamicClassLoader.java:61)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:249)
at clojure.lang.RT.classForName(RT.java:2039)
at clojure.lang.Reflector.invokeStaticMethod(Reflector.java:199)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at clojure.lang.Reflector.invokeMatchingMethod(Reflector.java:93)
at clojure.lang.Reflector.invokeStaticMethod(Reflector.java:207)
at user$eval12.invoke(NO_SOURCE_FILE:1)
at clojure.lang.Compiler.eval(Compiler.java:6511)
at clojure.lang.Compiler.eval(Compiler.java:6501)
at clojure.lang.Compiler.eval(Compiler.java:6477)
at clojure.core$eval.invoke(core.clj:2797)
at clojure.main$eval_opt.invoke(main.clj:297)
at clojure.main$initialize.invoke(main.clj:316)
at clojure.main$null_opt.invoke(main.clj:349)
at clojure.main$main.doInvoke(main.clj:427)
at clojure.lang.RestFn.invoke(RestFn.java:421)
at clojure.lang.Var.invoke(Var.java:419)
at clojure.lang.AFn.applyToHelper(AFn.java:163)
at clojure.lang.Var.applyTo(Var.java:532)
at clojure.main.main(main.java:37)
But I have no idea what is wrong.
Here is my project.clj file:
(defproject helloclojure "0.1.0-SNAPSHOT"
:description "FIXME: write description"
:main helloclojure.core
:url "http://example.com/FIXME"
:license {:name "Eclipse Public License"
:url "http://www.eclipse.org/legal/epl-v10.html"}
:dependencies [[org.clojure/clojure "1.4.0"]])
Any help will be much appreciated.

Answer 1

When you add the :main keyword to your project.clj like this, it is expected to point to a namespace that includes a function named -main. This namespace should generate a real Java class, and you can do this using the :gen-class keyword in your namespace definition.
So for this to work I would expect you to have a source file at:
src/helloclojure/core.clj
that contains at least this content:
(ns helloclojure.core
(:gen-class))
(defn -main [& args]
(println args))