static L<Method> findNonDefaultInterfaceMethods(Class intrface) {
  if (!isInterface(intrface)) null;
  new L<Method> l;
  _MethodCache cache = getMethodCache(intrface);
  
  Class c = intrface;
  do {
    for (Method m : c.getDeclaredMethods())
      if (m.getDeclaringClass() != O.class
        && !m.isDefault() && !isStaticMethod(m))
        l.add(m);

    c = c.getSuperclass();
  } while (c != null);
  
  ret l;
}

Began life as a copy of #1027670