I am planning to make an airline system. I have initialized the array using initSeats but it still throws back the NPE error. It happens when i call the seatChecker() from bookMenu.
public void initSeats(){
for(int b = 0; b < seatList.length; b++)
{
initC.setName("null");
initC.setEmail("null");
initC.setCreditNo(0);
initC.setAddress("null");
initC.setPassportNo("null");
seatList[b] = new Seat('A', 0, "null", 0.0, "Available", initC);
}
for(int d = 0; d <= 24; d++)
{
seatList[d].setSeatLetter('A');
seatList[d].setSeatNo(d);
}
for(int n = 25; n <= 48; n++)
{
seatList[n].setSeatLetter('B');
seatList[n].setSeatNo(n);
}
for(int m = 49; m <= 72; m++)
{
seatList[m].setSeatLetter('C');
seatList[m].setSeatNo(m);
}
for(int t = 73; t <= 96; t++)
{
seatList[t].setSeatLetter('D');
seatList[t].setSeatNo(t);
}
for(int q = 97; q <= 120; q++)
{
seatList[q].setSeatLetter('E');
seatList[q].setSeatNo(q);
}
for(int v = 121; v < 144; v++)
{
seatList[v].setSeatLetter('F');
seatList[v].setSeatNo(v);
}
for(int x = 0; x <= 48; x++)
{
seatList[x].setSection("Front");
seatList[x].setPrice(500);
}
for(int j = 49; j <= 96; j++)
{
seatList[j].setSection("Middle");
seatList[j].setPrice(250);
}
for(int u = 97; u < 144; u++)
{
seatList[u].setSection("Back");
seatList[u].setPrice(100);
}
}
public void seatChecker(int index)
{
String status = seatList[index].getStatus();
if(status.equalsIgnoreCase("Available")){
System.out.println("Seat is Available.");
}else{
System.out.println("Seat is not Available. Please Pick Another Seat.");
bookMenu();
}
}
public void bookMenu()
{
int choice1 = 0;
int index;
System.out.println("Where do you want to be seated?");
System.out.println("[1] Front");
System.out.println("[2] Middle");
System.out.println("[3] Back");
choice1 = sc.nextInt();
sc.nextLine();
if(choice1 == 1){
System.out.print("Choose a seat number (0 - 48): ");
index = sc.nextInt();
sc.nextLine();
seatChecker(index);
}else if(choice1 == 2){
System.out.println("Choose a seat number (49 - 96): ");
index = sc.nextInt();
sc.nextLine();
seatChecker(index);
}else if(choice1 == 3){
System.out.println("Choose a seat number (97 - 144): ");
index = sc.nextInt();
sc.nextLine();
seatChecker(index);
}else
{
System.out.println("Invalid Choice. Going back to Menu.");
MainMenu();
}
}
Null Pointer Exception Code
Exception in thread "main" java.lang.NullPointerException
at pkg.Airlines.AirlineUI.seatChecker(AirlineUI.java:132)
Seat Class
public class Seat{
private char seatLetter;
private int seatNo;
private String section;
private double price;
private String status;
private Customer customerDetails;
public Seat(char seatLetter, int seatNo, String section, double price, String status, Customer details)
{
this.seatLetter = seatLetter;
this.seatNo = seatNo;
this.section = section;
this.price = price;
this.status = status;
this.customerDetails = details;
}
public Customer getCustomerDetails() {
return customerDetails;
}
public void setCustomerDetails(Customer customerDetails) {
this.customerDetails = customerDetails;
}
public char getSeatLetter() {
return seatLetter;
}
public void setSeatLetter(char seatLetter) {
this.seatLetter = seatLetter;
}
public String getStatus() {
return status;
}
public void setStatus(String status) {
this.status = status;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public int getSeatNo() {
return seatNo;
}
public void setSeatNo(int seatNo) {
this.seatNo = seatNo;
}
public String getSection() {
return section;
}
public void setSection(String section) {
this.section = section;
}
}
Probably the problems are this two line :
String status = seatList[index].getStatus();
if(status.equalsIgnoreCase("Available"))
First thing could be seatList[index] is not initialized . Once you declare an array of references as :
Seat[] array = new Seat[10];
The array contains 10 null references for Seat object . You need to instantiate them before using them :
Seat[0] = new Seat();
Second potential problem will be, this check :
if(status.equalsIgnoreCase("Available"))
Replace it to :
if("Available".equalsIgnoreCase(status))
to avoid any NullPointerException in case status is null.
P.S. Please show us the Seat class to understand your problem better.
Well is quite simple resolve a Null Pointer Exception.
Probably in one of the index of seatList there isn't a value.
Related
Make an array of integer (score) with 10 members. Randomize the
content with value between 0-100. For each of the member of array,
visualize the value using “-” for each ten. For example: score[0] = 55 will be visualized as “-----" (Using Java).
public class w9lab1 {
public static void main(String args[]) {
double[] temperature = new double[7];
for (int i = 0; i < 7; i++) {
temperature[i] = Math.random()*100;
}
for (int i = 0; i < 7; i++) {
System.out.println(temperature[i]);
}
double totalTemperature = 0;
for (int i = 0; i < 7 ; i++) {
totalTemperature += temperature[i];
}
double maxTemperature = temperature[0];
for (int i = 1; i < 7; i++){
if (temperature[i] > maxTemperature){
maxTemperature = temperature[i];
}
}
System.out.println("Temperatur maximum adalah " + maxTemperature);
}
}
import java.util.Random;
import java.util.Arrays;
public class w9lab1 {
public static void main(String[] args) {
Random random = new Random();
int[] score = new int[10];
for (int i = 0; i < score.length; i++) {
score[i] = random.nextInt(101);
for (int n = 1; n <= score[i] / 10; n++)
System.out.print('-');
System.out.println();
}
System.out.println(Arrays.toString(score));
}
}
I'm trying to make a 9x9 grid of Spaces with 1-10 int values. I'm using the java n-ide app, and am getting a successful compilation, but it's not printing any values.
class Space {
int one = 1;
int two = 2;
...
int ten = 10;
}
class green {
Space[][] board = new Space[9][9];
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[i].length; j++) {
board[i][j] = new Space();
System.out.println(board[i][j].one);
}
}
}
I think you can just refactor your Space class to just hold a primitive integer value:
class Space {
private int value;
private static final String MSG = "Space values must be between 1 and 10 inclusive";
public Space() { }
public Space(int value) {
// prevent spaces from being created with illegal values
if (value < 1 || value > 10) {
throw new IllegalArgumentException(MSG);
}
this.value = value;
}
public int getValue() {
return value;
}
}
Then, in your consuming class, use the Space class:
class Green {
private Space[][] board = new Space[9][9];
for (int i=0; i < board.length; i++) {
for (int j=0; j < board[i].length; j++) {
// maybe get a value from somewhere and use it below
board[i][j] = new Space();
}
}
}
Regarding your exact question about values not printing, the bigger problem than above is that you don't have any logic for assigning values.
Here is the task I have been set with:
Create a text file named Names_ages.txt with the following content:
Jones 14
Abrams 15
Smith 19
Jones 9
Alexander 22
Smith 20
Smith 17
Tippurt 42
Jones 2
Herkman 12
Jones 11
Each line is a person’s last name followed by a space and then his age. We want to sort these names alphabetically and in the case of duplicate names, sort by age in an ascending fashion. A properly sorted list will appear as follows:
Abrams, 15
Alexander, 22
Herkman, 12
Jones, 2
Jones, 9
Jones, 11
Jones, 14
Smith, 17
Smith, 19
Smith, 20
Tippurt, 42
Here are my (working) selection sort methods for Strings and ints respectively:
private static void sort(String[] a) {
String min;
int minIndex;
for (int i = 0; i < a.length; i++) {
min = a[i];
minIndex = i;
// find minimum
for (int j = i + 1; j < a.length; j++) {
// salient feature
if (a[j].charAt(0) < min.charAt(0)) {
min = a[j];
minIndex = j;
}
}
a[minIndex] = a[i]; // swap
a[i] = min;
}
}
private static void sort(int[] a) {
int min, minIndex;
for (int i = 0; i < a.length; i++) {
min = a[i];
minIndex = i;
// find minimum
for (int j = i + 1; j < a.length; j++) {
// salient feature
if (a[j] < min) {
min = a[j];
minIndex = j;
}
}
a[minIndex] = a[i]; // swap
a[i] = min;
}
}
I can sort the names in the text file and then the numbers after, but the ages end up corresponding with incorrect people. Here is my class with the main method:
Scanner scanner = new Scanner(new File("/Users/Krish/IdeaProjects/Lessons/src/Lesson40/MultipleKey/NamesAges.txt"));
String text[] = new String[100];
int index = 0;
while (scanner.hasNext()) {
text[index++] = scanner.nextLine();
}
scanner.close();
String name;
String[] names = new String[index];
int age;
int[] ages = new int[index];
for (int i = 0; i < index; i++) {
Scanner line = new Scanner(text[i]);
name = line.next();
names[i] = name;
age = line.nextInt();
ages[i] = age;
}
sort(names);
sort(ages);
for (int i = 0; i < index; i++) {
System.out.println(names[i] + ", " + ages[i]);
}
Any help is appreciated, thanks.
Create a POJO class Person implementing Comparable<Person>
After parsing, store Person instances in a collection, say List<Person>
Sort the collection
-
public class PersonTest {
static class Person implements Comparable<Person> {
private static final Comparator<Person> COMPARATOR = Comparator
.comparing(Person::getName)
.thenComparingInt(Person::getAge);
final String name;
final int age;
public static Person parse(String rec) {
final String[] parts = rec.split(" ");
return new Person(parts[0], Integer.valueOf(parts[1]));
}
Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
#Override
public int compareTo(Person o) {
return COMPARATOR.compare(this, o);
}
}
#Test
public void testSorting() throws Exception {
final Person[] sortedPersons = Files.lines(Paths.get("/path/to/file.txt"))
.map(Person::parse)
.sorted() // sort it here
.toArray(Person[]::new);
// or instead, sort it here with your custom algorithm
// using Person.COMPARATOR for comparison
}
}
public static void main(String[] args) throws IOException {
Scanner scanner = new Scanner(new File("/Users/Krish/IdeaProjects/Lessons/src/Lesson40/MultipleKey/NamesAges"));
String[] text = new String[100];
int index = -1;
while (scanner.hasNext()) {
text[++index] = scanner.nextLine();
}
scanner.close();
Scanner line;
String[] name = new String[100];
int[] age = new int[100];
for (int i = 0; i <= index; i++) {
line = new Scanner(text[i]);
name[i] = line.next();
age[i] = line.nextInt();
}
String minName;
int minAge;
int minIndex;
for (int i = 0; i <= index; i++) {
minName = name[i];
minAge = age[i];
minIndex = i;
for (int j = i + 1; j <= index; j++) {
if (name[j].compareTo(minName) == 0) {
if (age[j] < minAge) {
minName = name[j];
minAge = age[j];
minIndex = j;
}
} else if (name[j].compareTo(minName) < 0) {
minName = name[j];
minAge = age[j];
minIndex = j;
}
}
name[minIndex] = name[i];
name[i] = minName;
age[minIndex] = age[i];
age[i] = minAge;
}
for (int j = 0; j <= index; j++) {
System.out.println(name[j] + ", " + age[j]);
}
}
I need to write a function that receives the number generated in fillArray and determine if it has already been generated. I need to return a true or false thus determining if the random number must be put into the array.
Here's what I am working on. Thanks for any help. I've searched for anything similar but unfortunately cannot find anything.
public class RandomGenerator {
int Arr[] = new int[6];
int size;
public void fillArray() {
int randNum = (int) (Math.random() * 49) + 1;
for (int i = 0; i < size; i++) {
Arr[i] = randNum;
alreadyThere(randNum);
}
size++;
}
public int alreadyThere(int randNum) {
int find = randNum;
boolean found = false;
int i = 0;
while (!found && i < size) {
if (Arr[i] == find) {
found = true;
}
i++;
}
if (!found) {
}
return randNum;
}
The purpose of this code is is to define the root of the sum of the squares.
I cant figure out how to put i into j. Please help.
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
int input, som, i=0;
int j = 0;
double answer;
Boolean gaDoor= true;
int [] array = new int [24];
while (gaDoor)
{
Console.Write("Specify a positive integer");
input = Convert.ToInt32(Console.ReadLine());
if (input == -1)
{
gaDoor = false;
}
else
{
if (input >= 0)
{
array[i] = input;
i++;
}
else
{
Console.WriteLine("Specify a positive integer ");
}
}
}
while (j<i)
{
sum = array [j] ^ 2;
answer = Math.Sqrt(sum);
Console.Write(answer);
}
Console.ReadKey();
}
}
}
using System;
namespace Test
{
class MainClass
{
public static void Main (string[] args)
{
int[] invoer = new int[24];
double[] resultaat = new double[24];
double totaal = 0;
double wortel = 0;
int commando = 0;
int teller = -1;
try {
// Keep going until a negative integer is entered (or a 0)
while ((commando = Convert.ToInt32 (Console.ReadLine ())) > 0) {
teller++;
invoer [teller] = commando;
}
} catch (FormatException) {
// Not a number at all.
}
teller = -1;
foreach (int i in invoer) {
teller++;
resultaat [teller] = Math.Pow (invoer [teller], 2);
totaal += resultaat [teller];
if (invoer [teller] > 0) {
Console.WriteLine ("Invoer: {0}, Resultaat: {1}", invoer [teller], resultaat [teller]);
}
}
wortel = Math.Sqrt (totaal);
Console.WriteLine ("Totaal: {0}, Wortel: {1}", totaal, wortel);
}
}
}