Re: ClassLoader not loading recompiled classes

Daniel Pitts <>
Tue, 02 Oct 2007 23:03:02 -0700
Aryeh M. Friedman wrote:

Try look at the super simple example attached below.




public class DoubleDynmaic {
    private static void dynno(int n) {
       (new File("test")).mkdir();
       try {
          OutputStream os = new FileOutputStream("test/");
          PrintStream ps = new PrintStream(os);
          ps.println("public class Test {");
          ps.println(" public Test() {");
          ps.println(" System.out.println(" + n + ");");
          ps.println(" }");
          Runtime.getRuntime().exec("javac -d test
          URL[] url = new URL[1];
          url[0] = new URL("file:test/");
          URLClassLoader cl = new URLClassLoader(url);
          Class.forName("Test", true, cl).newInstance();
       } catch (Exception e) {
    public static void main(String[] args) {
       for(int i = 0; i < 10; i++) {

Works fine *IF* the code is compiled from within the class but if it
is externally compliled it does the same thing as just straight class


Please don't top post, it makes it hard to understand whats going on...

Anyway, my guess is that you're casting the class (MyClass). Doing this
actually loads the class with the same class loader. You can't know
about a class at the Java level without that class being loaded. You're
going to have to use reflection all the way through. While your
application may be a good candidate, there are dangers of using reflection:


Hope this helps,
Daniel Pitts' Tech Blog: <>

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