Help needed with simple code

Question

Hi,
Im doing a project for my module at uni. Not being a programmer I find it very hard to design application as Im required to. Anyway I have to design booking application for bikeshop.
User selects bike from 3 types: MTB,Kids and racing. each bike has its price so cost of booking must be calculated.There are extra options like helmet which may rented as well. Some customer info must be collected (name,address etc).
Bookings has to be written into file. Report of past booking must be available-simple printouts.
No databases as use of arrays is required.
Im stuck and trying to figure it out how to read from array which contains bike types and prices and extra features. Then combine several bookings for on customes on a form/interface.
Any ideas how to start it? I mean at least on design level.
Thanks in advance for any help

Answer 1

Hi
I managed to produced some code to extend my app but when I run it I get:
Exception in thread "main" java.lang.NullPointerException
     at ReservationSystem.main(ReservationSystem.java:22)
Im really stuck
Will somebody give me any idea?
Below is the code...
Thanks
whale
mport java.util.ArrayList;
import javax.swing.JOptionPane;
public class ReservationSystem {
     static ArrayList<Booking> Bookings;
     public static void main(String[] args) {
          int BikeType = 0;
          do {
               BikeType = Integer.parseInt(JOptionPane.showInputDialog("0 - Mountain bike, 1 - Racing Bike, 2 - Childrens Bike, 3 - Finish?"));
               String Surname = JOptionPane.showInputDialog("Surname?");
               String Date = JOptionPane.showInputDialog("Date?");
               int Number_of_days = Integer.parseInt(JOptionPane.showInputDialog("Number of days?"));
               switch (BikeType) {
               case 0:
                    String Sex = JOptionPane.showInputDialog("Sex (M/F)?");
                    String Frame_size = JOptionPane.showInputDialog("Frame size (S/M/L)?");
                    boolean Helmet = JOptionPane.showConfirmDialog(null, "Is a helmet required?", "Helmet", JOptionPane.YES_NO_OPTION) == 0;
                    Bicycle Bike = new MountainBike(Sex, Frame_size, Helmet);
                    Bookings.add(new Booking(Surname, Date, Number_of_days, Bike));
               case 1:
               case 2:
               default:
          } while (BikeType != 3);
          int Length = Bookings.size();
          int i;
          for (i = 0; i < Length; i++) {
           Bookings.get(i).print_booking();
     }Booking class
public class Booking {
  //Date start_date;
  int Number_of_days;
  Bicycle Bike;
  String Surname;
  String Date;
  Booking(String Surname, String Date, int Number_of_days, Bicycle Bike) {
       this.Surname = Surname;
       this.Number_of_days = Number_of_days;
       this.Bike = Bike;
       this.Date = Date;
  public void print_booking() {
       System.out.print(this.Surname + ": " + this.Date + "/" + " for " + this.Number_of_days);
       this.Bike.print_bike();
  }}class Bicycle
public class Bicycle {
  int Price;
  boolean Helmet;
     public void print_bike() {
class MountainBike extends Bicycle {
     String Frame_size;
     String Sex;
     public MountainBike(String Sex, String Frame_size, boolean Helmet) {
          this.Sex = Sex;
          this.Frame_size = Frame_size;
          this.Helmet = Helmet;
          this.Price = 20;
          if (Helmet) {
               this.Price += 5;
     public void print_bike() {
          System.out.println("Mountain bike (" + this.Sex + ", " + this.Frame_size + ") "
                    + (this.Helmet ? " with helmet" : "") + " price " + this.Price);
class RacingBike extends Bicycle {
     boolean Panniers;
     String Frame_size;
     String Sex;
     public RacingBike(String Sex, String Frame_size, boolean Panniers) {
          this.Sex = Sex;
          this.Frame_size = Frame_size;
          this.Panniers = Panniers;
          this.Price = 25;
          if (Panniers) {
               this.Price += 10;
               this.Helmet = true;
     public void print_bike() {
          System.out.println("Racing bike (" + this.Sex + ", " + this.Frame_size + ") "
                    + (this.Panniers ? " with panniers" : "") + " price " + this.Price);
class ChildrensBike extends Bicycle {
     int Age;
     public ChildrensBike(int Age) {
          this.Age = Age;
          this.Helmet = true;
          this.Price = 15;
     public void print_bike() {
          System.out.println("Mountain bike (" + this.Age + ") "
                    + (this.Helmet ? " with helmet" : "") + " price " + this.Price);
}