* {@code A -> B}.
   *
   * @since 9.0 (in 1.0 as {@code com.google.common.base.Service.State})
   */
  enum State {
    /** A service in this state is inactive. It does minimal work and consumes minimal resources. */
    NEW,

    /** A service in this state is transitioning to {@link #RUNNING}. */
    STARTING,

    /** A service in this state is operational. */