title: Name 'flight_Num' must match pattern '^[a-z][a-zA-Z0-9]*$'
body: <p>I keep getting this error when I run checkstyle on my program:</p>
  
  <pre><code>    NonRefundable.java:20:28: Name 'flight_Num' must match pattern '^[a-z][a-zA-Z0-9]*$'.
  </code></pre>
  
  <p>I'm not sure what I need to do to correct this. Here are the comments for this particular error:</p>
  
  <pre><code>/** Comments.
    *
    * @param flight_Num the flight number.
    * @param trip_Data the information stored in the Itinerary object.
    * @param base_Fare the double representing the initial cost of the trip.
    * @param fare_AdjustmentFactor the number factored into the baseFare and 
              discountFactor used to calculate totalFare.
    * @param discount_Factor the number factored into baseFare and 
    *         fare_AdjustmentFactor to calculate totalFare.
    */
    NonRefundable(String flight_Num, Itinerary trip_Data, double base_Fare,
              double fare_AdjustmentFactor, double discount_Factor) {
  
       super(flight_Num, trip_Data, base_Fare, fare_AdjustmentFactor);
       this.discountFactor = discount_Factor;
    }
  </code></pre>