Class reloading

[Supamagier]

Hello, I have this class to reload classes:

// Ripped from http://tutorials.jenkov.com/java-reflection/dynamic-class-loading-reloading.html

import java.io.*;
import java.net.*;

public class MyClassLoader
             extends ClassLoader
{

    public MyClassLoader(final ClassLoader parent) {
        super(parent);
    }

    public Class loadClass(final String name) throws ClassNotFoundException {
        if (!name.equals("BotMethods"))
            return super.loadClass(name);
        System.out.println("IN");
        try {
            String url = "file:BotMethods.class";
            URL myUrl = new URL(url);
            URLConnection connection = myUrl.openConnection();
            InputStream input = connection.getInputStream();
            ByteArrayOutputStream buffer = new ByteArrayOutputStream();
            int data = input.read();

            while(data != -1) {
                buffer.write(data);
                data = input.read();
            }

            input.close();

            byte[] classData = buffer.toByteArray();

            System.out.println("OUT1");

            return defineClass("BotMethods",classData,0,classData.length);

        }
        catch (MalformedURLException e) {
            e.printStackTrace();
        }
        catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println("OUT2");
        return null;
    }

}

the class BotMethods:

import java.net.*;
import java.io.*;

public class BotMethods
{

    // Only methods
    
}

And the main class:

import java.net.*;
import java.io.*;
import java.awt.*;
import java.lang.reflect.*;


public class JavaBot
{

  
    private JavaBot() {
        reloadMethods();
    }
    
    public void reloadMethods() {
        try {
            ClassLoader parentClassLoader = MyClassLoader.class.getClassLoader();
            MyClassLoader classLoader = new MyClassLoader(parentClassLoader);
            Class myClass = classLoader.loadClass("BotMethods");
            
            BotMethods bm1 = (BotMethods)myClass.newInstance(); // Error here

            //create new class loader so classes can be reloaded.
            classLoader = new MyClassLoader(parentClassLoader);
            myClass = classLoader.loadClass("BotMethods");

            bm1 = (BotMethods)myClass.newInstance();
            bm = bm1;
            //bm = new BotMethods();
        }
        catch (Exception e) {
            System.out.println("Could not reload methods");
            e.printStackTrace();
            //BotMethods.say(bout,"Matt","Could not reload methods: "+e);
        }
    }

    public static void main(String[] args) {
        new JavaBot();
    }
}

Which throws this error:

java.lang.ClassCastException: BotMethods cannot be cast to BotMethods

Why does it throw this error and how to fix it?

To clarify things: I want the class BotMethods to be reloaded without having to restart the application, so that I can add methods and such while running, which can be executed right after I called the reloadMethods method. I know this is possible, I'm just not sure how.

Please help. :)

Thanks,

~Matt

[OrangeDog]

If you change the methods of a class, it becomes a different class, and you cannot use the new class as if it were the old one.

What you are doing is incredibly bad practice, and I doubt it is possible. If it is then it shouldn't be.

If you need this kind of functionality, then explicitly create new classes that subclass BotMethods. This would prevent some of the more heinous type-safety crimes.

[Supamagier]

It would be great if it would work.

Why would I need to subclass BotMethods?

[OrangeDog]

To make explicit what you are doing and allow the type system to recognise it.

When you change BotMethods by adding new methods, you are effectively making a new subclass, but you haven't told the JVM this so it won't allow the casts.