I've created a program with an object called CarlysCatering. I'm trying to sort the CarlysCatering objects by number of guests.
I've tried using a bubble sort but I get an error message.
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
CarlysCatering[] event = new CarlysCatering[100];
event[0] = new CarlysCatering(10, "A547", "6874714145", 0);
event[1] = new CarlysCatering(100, "B527", "6874874945", 2);
event[2] = new CarlysCatering(50, "C546", "6874785145", 3);
event[3] = new CarlysCatering(40, "L577", "6874321485", 1);
event[4] = new CarlysCatering(70, "A111", "6874714145", 4);
event[5] = new CarlysCatering(90, "K222", "6874974855", 2);
event[6] = new CarlysCatering(11, "F798", "6875555555", 3);
event[7] = new CarlysCatering(17, "T696", "6474763898", 0);
//SORT
int selection = 0;
do {
System.out.println("1 - sort by eventID. 2 - sort by number of guests. 3 - sort by event type. 4 - quit");
selection = input.nextInt();
input.nextLine();
if(selection == 1) {
}
if(selection == 2) {
int n = event.length;
for (int i = 0; i < n - 1; i++) {
for (int j = 0; j < n - i - 1; j++) {
if (event[j].getGuests() > event[j + 1].getGuests()) {
// swap arr[j+1] and arr[i]
CarlysCatering temp = event[j];
event[j] = event[j + 1];
event[j + 1] = temp;
}
}
}
}
} while (selection != 4);
//Print totals
event[0].getTotals(); event[1].getTotals(); event[2].getTotals(); event[3].getTotals(); event[4].getTotals(); event[5].getTotals(); event[6].getTotals(); event[7].getTotals();
}
////////////////////////////////////////////////////// STATIC METHODS //////////////////////////////////////////////////////////////////////
}
public class CarlysCatering {
public static final int PRICE_PER_GUEST_HIGH = 35;
public static final int PRICE_PER_GUEST_LOW = 32;
public static final int CUTOFF_VALUE_LARGE = 49;
private int guests;
private int totalPrice;
private String eventID;
private String phoneNumber;
private String eventType;
private boolean largeEvent;
///////////////////////////////////////////////////// CONSTRUCTORS //////////////////////////////////////////////////////////////////
CarlysCatering() {
this.guests = 0;
this.eventID = "A000";
this.phoneNumber = "0000000000";
}
CarlysCatering(int guests, String eventID, String phoneNumber, int eventType) {
this.guests = guests;
this.eventID = eventID;
//Phone Number formatting
String phoneNumber2 = "";
int count = 0;
for(int i = 0; i < phoneNumber.length(); i++) {
if (Character.isDigit(phoneNumber.charAt(i))) {
phoneNumber2 += phoneNumber.charAt(i);
count += 1;
}
}
if (count != 10) {
this.phoneNumber = "0000000000";
} else {
String phoneNumber3 = "(" + phoneNumber2.substring(0,3) + ") " + phoneNumber2.substring(3,6) + "-" + phoneNumber2.substring(6,10);
this.phoneNumber = phoneNumber3;
}
//Event type formatting
final String[] eventString = new String[5];
eventString[0] = "wedding"; eventString[1] = "baptism"; eventString[2] = "birthday"; eventString[3] = "corporate"; eventString[4] = "other";
if(eventType > -1 && eventType < 5) {
this.eventType = eventString[eventType];
} else {
this.eventType = eventString[4];
}
}
///////////////////////////////////////////////////////// SETTERS AND GETTERS /////////////////////////////////////////////////
//Setters
public void setEventID(String eventID) {
this.eventID = eventID;
}
public void setGuests(int guests) {
this.guests = guests;
}
public void setPhoneNumber(String phoneNumber) {
String phoneNumber2 = "";
int count = 0;
for (int i = 0; i < phoneNumber.length(); i++) {
if (Character.isDigit(phoneNumber.charAt(i))) {
phoneNumber2 += phoneNumber.charAt(i);
count += 1;
}
}
if (count != 10) {
this.phoneNumber = "0000000000";
} else {
String phoneNumber3 = "(" + phoneNumber2.substring(0, 3) + ") " + phoneNumber2.substring(3, 6) + "-" + phoneNumber2.substring(6, 10);
this.phoneNumber = phoneNumber3;
}
}
public void setEventType(String eventType) {
this.eventType = eventType;
}
//Getters
public int getTotalPrice() {
return totalPrice;
}
public int getGuests() {
return guests;
}
public String getEventID() {
return eventID;
}
public String getPhoneNumber() {
return phoneNumber;
}
public String getEventType() {
return eventType;
}
/////////////////////////////////////////////////////// ADDITIONAL METHODS ///////////////////////////////////////////////////////////////////
public void isLargeEvent() {
if (this.guests > CUTOFF_VALUE_LARGE) {
largeEvent = true;
System.out.println("Yes this is a large event.");
} else {
largeEvent = false;
System.out.println("This is not a large event");
}
}
public void getTotals() {
boolean largeEvent = false;
if(this.guests > CUTOFF_VALUE_LARGE) {
largeEvent = true;
this.totalPrice = this.guests * PRICE_PER_GUEST_HIGH;
} else {
largeEvent = false;
this.totalPrice = this.guests * PRICE_PER_GUEST_LOW;
}
System.out.println("The number of guests attending event " + this.eventID + " " + this.eventType + " is: " + this.guests + ". The total price is $" + this.totalPrice);
System.out.println("Large event: " + largeEvent);
System.out.println("The phone number on file is " + this.phoneNumber);
}
// Static methods
public static void showMotto() {
System.out.println("*****Carly's makes the food that makes it a party.*****");
}
}
The error message I get when I try to sort by guests is Exception in thread "main" java.lang.NullPointerException and then error code exit -1. The line that's causing the error is:
if (event[j].getGuests() > event[j + 1].getGuests()) {
You create an Array with the size 100.
After that, you fill it from index 0 to 7.
Every other place of the array remains null but the length is 100.
Then, you try to sort the array.
This throws a NullPointerException when you try to dereference (access) the 8. element:
event[j+1].getGuests()
I think you should use a smaller array(size 8) or a List.