code: public Class<?> getClass(final String key) {
      try {
        if (containsKey(key)) {
          return Class.forName(get(key));
        } else {
          throw new UndefinedPropertyException("Missing required property '"
              + key + "'");
        }
      } catch (final ClassNotFoundException e) {
        throw new IllegalArgumentException(e);
      }
    }
docs: Attempts to return the Class that corresponds to the Props value. If the class doesn't exit, an
  IllegalArgumentException will be thrown.