code: private void checkRunnable(Class<?> type) {
      if(Runnable.class.isAssignableFrom(type)) {
        try{
          this.method = type.getMethod("run");
        } catch(Exception e) {
          throw new RuntimeException("Cannot get run method of runnable class.", e);
        }
      }
    }
docs: Checks if the type is a Runnable and gets the run method.
  
  @param type