code: public static Class findMethodParameterClass(Method method, int parm) {
      Class[] clzes = method.getParameterTypes();
  
      if (clzes.length <= parm)
        throw H2O.fail("Asked for the class of parameter number: " + parm + " of method: " + method + ", which only has: " + clzes.length + " parameters.");
  
      return clzes[parm];
    }
docs: Reflection helper which returns the actual class for a method's parameter.