code: public static String className(Class<?> clazz) {
          if (CoreUtils.classNames.isLoggable(Level.FINER)) {
              return clazz.getName();
          } else {
              return simpleClassName(clazz);
          }
      }
docs: Returns the full name or simple name of the class depending
  on the log level.
  
  @param clazz the class
  @return the name