Step #1 of building the simplest ClassLoader is failing

Question

I am trying to build a URLClassLoader. I am not familiar, at all, with doing this. Of course, the below code will fail, but I am doing tiny steps. I have two fundamental questions:
public class Test {
  public static void main(String[] args) {
    try {
      URL[] urls = new URL[1];
      urls[0] = new URL("file://temp/ClassA.class");
      URLClassLoader loader = MyClassLoader.newInstance(urls);
      loader.loadClass("ClassA");  // takes 15-seconds
    }   catch(Exception e) {
            e.printStackTrace();
public class MyClassLoader extends URLClassLoader {
  public MyClassLoader(URL[] urls) {
    super(urls);
  protected Class<?> findClass(String name) throws ClassNotFoundException {
    return null;
}*(1)* this is the correct URL for my local file references?
URL[] urls = new URL[1];
urls[0] = new URL("file://temp/ClassA.class");
If relevant, the package for ClassA is "net.ropp".
*(2)* given the embassasingly stupid code above, why does it take +15-seconds+ for this stack trace to be produced? a deep file system traversal? Is every single available class loaded (as opposed to waiting to load until they are first referenced)?
ps. if my code bailed right away, and not wait 15-seconds, I would not be posting. sorry.
the stack trace is:
java.lang.ClassNotFoundException: ClassA
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at java.net.FactoryURLClassLoader.loadClass(URLClassLoader.java:592)
at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
at main.Test.main(Test.java:25)
Please help me get oriented with dynamic class loading. thanks.
Edited by: ichigoichi on Jan 31, 2010 8:37 PM

Answer 1

URLClassLoader loader = MyURLClassLoader.newInstance(urls);That calls URLClassLoader.newInstance(), because you haven't overridden it. So what you are getting back is a URLClassLoader, nor a MyURLClassLoader, whatever you think you need that for.
*(1)* this is the correct URL for my local file references?
URL[] urls = new URL[1];
urls[0] = new URL("file://temp/ClassA.class");No. The URL points to the directory where the package hierarchy starts. In this case assuming ClassA isn't in a package it is file://temp.