我无法弄清楚 getTotalFlightTime()

Question

The Itinerary class stores the information about itinerary with the following members:

• A private ArrayList data field named flights that contains the flights for the itinerary in increasing order of departureTime. (Hint: You do not need to do the sorting.)

• A constructor that creates an itinerary with the specified flights in ArrayList type.

• A method named getTotalFlightTime() that returns the total flight time of the itinerary in minutes. (Hint: Invoke the getFlightTime() method for each Flight object.)

• A method named getTotalTravelTime() that returns the total travel time in minutes from the departure time of the first flight to the arrival time of the last flight in the itinerary. Assume all the times are in the same time zone.

package que6;

/**
 *
 * @author vpi764
 */


import java.util.ArrayList;
import java.util.GregorianCalendar;
public class TestFlightItinerary {


    public static void main(String[] args) {

  lic static void main(String[] args) {
        ArrayList<Flight>flights = new ArrayList<>();
  Flight F1 =  new Flight("US230", new GregorianCalendar(2014, 5, 5, 5, 5, 0), new GregorianCalendar(2014, 5, 5, 6, 15, 0));
    Flight F2 =  new Flight("US235", new GregorianCalendar(2014, 5, 5, 6, 55, 0), new GregorianCalendar(2014, 5, 5, 7, 45, 0));
      Flight F3 =  new Flight("US237", new GregorianCalendar(2014, 5, 5, 9, 35, 0), new GregorianCalendar(2014, 5, 5, 12, 55, 0));

      flights.add(F1);
      flights.add(F2);
      flights.add(F3);

 }

}

class Flight{

        private String flightNo;
        private GregorianCalendar departureTime;
        private GregorianCalendar arrivalTime;


        //Constructor
        Flight(String SpecNo,GregorianCalendar SpecDtime ,GregorianCalendar SpecAtime ){
            this.flightNo = SpecNo;
            this.departureTime = SpecDtime;
            this.arrivalTime = SpecAtime;
        }
        //Getters
        public String GetFlightNo() {
            return flightNo;
        }
        public GregorianCalendar GetDtime() {
            return departureTime;
        }
        public GregorianCalendar GetAtime() {
            return arrivalTime;
        }

        //setters
        // If we don't use setter the could would still work because we are getting input in constructor with parameters
        public void SetFlightNo(String Number) {
            flightNo = Number;
        }
        public void SetDtime(GregorianCalendar Dtime) {
            departureTime = Dtime;
        }
        public void SetAtime(GregorianCalendar Atime) {
            arrivalTime = Atime;
        }

        public long getTimeinMillis() {
                return (arrivalTime.getTimeInMillis() - departureTime.getTimeInMillis());
                }
                // getFlightTime method
                public long getFlightTime() {
                return getTimeinMillis() / (60 * 1000);
                }
    }

class Itinerary {


    ArrayList<Flight> flights = new ArrayList<>();

   public Itinerary(){
           this.flights = flights;
    }
    public long getTotalFlightTime(ArrayList<Flight> flights){

    }
    public long getTotalTravelTime(){

    }


}

Answer 1

ArrayList maintain the order in which elements are added. May be thats the cue.

Answer 2

You can use either Comparable or Comparator on class flight. For compareTo and compare function use departure time as deciding factor for sorting.

You will need to call Collections.sort in order to sort arraylist. It does not get done by default. On how to use, please read https://www.geeksforgeeks.org/comparator-interface-java/

For total flight time you need to find difference of list.get(list.size()-1).GetDtime() list.get(0).GetDtime()

For travel time. You will need to loop through arraylist and do sum of getTimeinMillis() for each flight object.

I hope this will help.

Answer 3

If I am understanding the instructions correctly, you do not need to do the sorting of the ArrayList. All you are required to do is define a constructor that accepts an ArrayList of flights.

Your Itinerary class should be:

class Itinerary {
    ArrayList<Flight> flights; // no need to instantiate, flights passed in as arg

    public Itinerary(ArrayList<Flight> flights) {
        this.flights = flights;
    }

    public long getTotalFlightTime(){
        // Do stuff
    }
    public long getTotalTravelTime(){
        // Do Stuff
    }
}

In your main method you would then add the following:

ArrayList<Flight> flights = new ArrayList<>();
flights.addAll(F1, F2, F3);
Itinerary myItinerary = new Itinerary(flights);