Re: empty interfaces via reflection

 Daniel Pitts <>
Tue, 16 Oct 2007 00:21:00 -0000
On Oct 14, 12:17 pm, "Aryeh M. Friedman" <>

On Oct 14, 6:01 pm, Steven Simpson <s...@domain.invalid> wrote:

Aryeh M. Friedman wrote:

Then how do you handle the return type?!?!?!? Namely I can't do:

Class<?> testClass = loadTestClass();
Object testInstance = testClass.newInstance();
Result res=new Result();

for (Method method: testClass.getDeclaredMethods())
     res.merge((Result) method.invoke(testInstance, new
Object[0])); // cast exception

The reason why it is not possible is any Result object created by a
test is <MyClassLoader>.Result and all the results here are

Looking back at an earlier post, your custom MyClassLoader goes like this:

public class MyClassLoader extends ClassLoader
        public Class loadClass(String name)
                try {
                                return super.loadClass(name);

A custom ClassLoader is expected to override findClass(String) rather
than loadClass(String), as the latter (indirectly) accomplishes this


"When requested to find a class or resource, a ClassLoader instance will
delegate the search for the class or resource to its parent class loader
before attempting to find the class or resource itself."

MyClassLoader is loading Result instead of delegating to its parent
first, which should always find it first.

I just tested:import*;
import java.lang.reflect.*;

public class MyClassLoader extends ClassLoader
        public Class findClass(String name)
                try {
                        // return super.loadClass(name);

                        FileInputStream fis=new FileInputStream(name
                        byte[] b=new byte[fis.available()];


                        return defineClass(name,b,0,b.length);
                } catch(Throwable e) {

                return null;


and now the class loader no longer honors recompiled classes:

Script started on Sun Oct 14 15:09:05 2007
jtest@monster:/home/jtest% java Main
jtest@monster:/home/jtest% cat foo
import java.lang.reflect.*;

public class MyClass
        public MyClass()
                ack=new Integer(2);

        public Integer getAck()
                return ack;

        private int foo;
        private Integer ack;}

jtest@monster:/home/jtest% cp foo
jtest@monster:/home/jtest% javac
jtest@monster:/home/jtest% fg
java Main

jtest@monster:/home/jtest% exit
Script ends on Sun Oct 14 15:09:45 2007

Just for ref here is the new main():

public class Main
        public static void main(String[] args)
                throws Throwable
                while(true) {
                        ClassLoader loader=new MyClassLoader();
                        Class klass=loader.loadClass("MyClass");

                        MyClass m=(MyClass) klass.newInstance();



You should simply use UrlClassLoader and have the system classpath not
include your code that needs to be reloaded, and the URLClassLoader
have the path that DOES need to be reloaded (creating a new instance
of that class loader every time you need to reload the class)

That way, Result will be properly loaded by the System class loader,
and your reloadable class wont.

Hoep this helps,

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