static class JavaXClassLoader extends URLClassLoader {
  S progID;
  Set<File> files = syncLinkedHashSet();
  Set<S> triedToLoad = synchroSet();
  Set<Class> loadedClasses = synchroSet();
  bool retired;
  O retiredMarker;
  IF1<S, Class> findClass_extension;
  S mainClassName;
  bool verbose;
  
  *(S progID, L<File> files) {
    this(progID, files, getSystemClassLoader());
  }
  
  *(S progID, L<File> files, ClassLoader parent) {
    super(new URL[0], parent, vm_globalACC());
    this.progID = progID;

    fOr (File f : files)
      addFile(f);
  }
  
  Class<?> super_findClass(S name) throws ClassNotFoundException {
    ret super.findClass(name);
  }
  
  protected Class<?> findClass(S name) throws ClassNotFoundException {
    if (verbose) System.out.println(this + " findClass: " + name);
    if (findClass_extension != null) {
      Class<?> c = findClass_extension.get(name);
      if (verbose) System.out.println("extension returned: " + c);
      if (c != null) ret c;
    }
    bool triedBefore = !triedToLoad.add(name);
    try {
      Class<?> c = super.findClass(name);
      if (verbose) System.out.println("super.findClass returned: " + c);
      loadedClasses.add(c);
      if (eq(name, mainClassName()))
        callOpt(javax(), 'registerAMainClass, c);
      ret c;
    } catch (ClassNotFoundException e) {
      if (verbose) System.out.println(getStackTrace(e));
      throw new ClassNotFoundException("Class " + name + " not found in " + joinWithComma(map(f f2s, files)) + " (progID=" + progID + ")"
        + (triedBefore ? ", tried to load before" : ""), e);
    }
  }
  
  toString {
    ret shortClassName(this) + "[" + systemHashCodeHex(this) + "] - " + progID;
  }
  
  S mainClassName() {
    if (mainClassName == null)
      mainClassName = or2(trim(loadTextFileResource(this, "main-class")), "main");
    ret mainClassName;
  }
  
  bool addFile(File f) ctex {
    if (!files.add(f)) false;
    addURL(f.toURI().toURL());
    mainClassName(); // calculate early. no good loading text files later
    true;
  }
}