Hashmap overwriting values

Question

Hey im trying to make a hashMap store for planes. But when i add, it will only print out one flight. Can anyone help me with this. Here is my code:

import java.util.Scanner;


public class MainApp 
{
    private Scanner keyboard = new Scanner(System.in);
    public static void main(String[] args)
    {
        new MainApp().start();  
    }

    public void start()
    {
        Airline aerLingus = new Airline("AerLingus");
        PlaneStore planeStore = new PlaneStore("Aer Lingus");

        Flight p1 = new Flight("Aer Lingus","A01", 150.5, 10.5, 500, Flight.AIRPLANETYPE.AIRBUS);
        Flight p2 = new Flight("Aer Lingus","B01", 50.3, 1.5, 91, Flight.AIRPLANETYPE.CORPORATE);
        Flight p3 = new Flight("Aer Lingus","C01", 12.2, -3.1, 56, Flight.AIRPLANETYPE.AIRBUS);


        Flight p4 = new Flight("Ryan Air","D01", 10.5, 1.5, 430, Flight.AIRPLANETYPE.PRIVATE);
        Flight p5 = new Flight("Ryan Air","E01", 0.3, 2.1, 101, Flight.AIRPLANETYPE.CORPORATE);
        Flight p6 = new Flight("Ryan Air","F01", 2.2, -3, 291, Flight.AIRPLANETYPE.AIRBUS);
        planeStore.addFlight("",p1);
        planeStore.addFlight("",p2);
        planeStore.addFlight("",p3);
        planeStore.print();

        aerLingus.add(planeStore);
        aerLingus.add(planeStore);
        aerLingus.add(planeStore);

        aerLingus.printPlane();
    }

}

import java.util.TreeMap;


public class PlaneStore 
{
    private String airlineName;
    private TreeMap<String,Flight> planeMap;


    public PlaneStore(String airlineName) 
    {
        this.airlineName = "";
        planeMap = new TreeMap<String,Flight>();
    }


    public String getAirlineName() {
        return airlineName;
    }


    public TreeMap<String, Flight> getFlightList() {
        return planeMap;
    }
    public void addFlight(String airline,Flight flight)
    {
        planeMap.put(airline, flight);
    }

    // ---------------------------------------------------------------------------------------
    // Name: Print.
    // ---------------------------------------------------------------------------------------
    public void print()
    {
        System.out.println("\n********Student's in the Company.********");
        for (Flight flight : planeMap.values()) {
            // System.out.println(employee); to print the toString of Employee
            // class
            // or:
            System.out.println("Airline:\t" + flight.getAirline());
            System.out.println("Flight Number:\t" + flight.getFlightNumber());
            System.out.println("Fuel Remaining:\t" + flight.getFuelRemaining());
        }

    }


}
public class Flight 
{
    private String airline;
    private String flightNumber;
    private double fuelRemaining;
    private double overdue;
    private int passengerNumber;
    private AIRPLANETYPE planeType;

    public enum AIRPLANETYPE
    {
        AIRBUS("1"), CORPORATE("2"), PRIVATE("3");

        private String planeName;

        private AIRPLANETYPE(String planeName)
        {
            this.planeName = planeName;
        }
    }


    public Flight(String airline, String flightNumber, double fuelRemaining,
            double overdue, int passengerNumber, AIRPLANETYPE planeType) 
    {
        super();
        this.airline = airline;
        this.flightNumber = flightNumber;
        this.fuelRemaining = fuelRemaining;
        this.overdue = overdue;
        this.passengerNumber = passengerNumber;
        this.planeType = planeType;
    }

    public String getAirline() {
        return airline;
    }

    public void setAirline(String airline) {
        this.airline = airline;
    }

    public String getFlightNumber() {
        return flightNumber;
    }

    public void setFlightNumber(String flightNumber) {
        this.flightNumber = flightNumber;
    }

    public double getFuelRemaining() {
        return fuelRemaining;
    }

    public void setFuelRemaining(double fuelRemaining) {
        this.fuelRemaining = fuelRemaining;
    }

    public double getOverdue() {
        return overdue;
    }

    public void setOverdue(double overdue) {
        this.overdue = overdue;
    }

    public int getPassengerNumber() {
        return passengerNumber;
    }

    public void setPassengerNumber(int passengerNumber) {
        this.passengerNumber = passengerNumber;
    }

    public AIRPLANETYPE getPlaneType() {
        return planeType;
    }

    public void setPlaneType(AIRPLANETYPE planeType) {
        this.planeType = planeType;
    }


    public String toString() 
    {
        return "Flight [airline=" + airline + ", flightNumber=" + flightNumber
                + ", fuelRemaining=" + fuelRemaining + ", overdue=" + overdue
                + ", passengerNumber=" + passengerNumber + ", planeType="
                + planeType + "]";
    }




}

Answer 1

EDIT in response to further code posting:

Every time you do PlaneStore.addPlane() you are providing a blank key. A Hashmap is only useful if you provide a unique key for every object. Otherwise every plane will overwrite the previous plane. This is why when you print you only see a single object. Give every plane a unique key, possibly a tail number or something related, and you should be able to retrieve every object.

Answer 2

HashMap is a data structure in which you are able to store key-value pairs. It essential that the key is unique. Otherwise you overwrite the value that has the same key.

With this data structure you are able to add and find values very quickly because the complexity of adding and finding values is constant. But the disadvantage is that you can only add a key one time.

Answer 3

You need to define your hashmap as follows:

Map<String, List<Flight>> map = new TreeMap<String, List<Flight>>();

and then for each flight name you need to create a new list of flights as follows:

map.get("foo") = new ArrayList<Flight>();

map.get("foo").add(Flight);

for above code, you need to be defensive, if there is no list, you need to create one, otherwise you ll get some exception. moreover, ensure that only one list will be created per flight key.