/**
     * Tests if this sensor is currently on.
     *
     * @return <tt>true</tt> if the sensor is currently on;
     *         <tt>false</tt> otherwise.
     *
     */

    public boolean isOn() {

  {- -------------------------------------------
  (1) on フィールドの値をリターンするだけ.
      ---------------------------------------- -}

            synchronized (lock) {
                return on;
            }
        }