show how the same Class file loaded by two classloaders become "incompatible"

F.java

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

public class F {
  static F instance;
  
  public static void main(String[] args) throws Exception {
    ClassLoader l = new URLClassLoader(new URL[] { new File(".").toURI().toURL()}, null);
    Class<?> clazz = l.loadClass("F");
    F.class.getDeclaredField("instance").set(null, clazz.newInstance());
  }
}

gistfile2.txt

D:\code>java F
Exception in thread "main" java.lang.IllegalArgumentException: Can not set static F field F.instance to F
        at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(Unknown Source)
        at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(Unknown Source)
        at sun.reflect.UnsafeStaticObjectFieldAccessorImpl.set(Unknown Source)
        at java.lang.reflect.Field.set(Unknown Source)
        at F.main(F.java:10)