Develop Reference

java.lang.NullPointerException when setting value of attributes within a loop

Trying to make it so if the user types "end", in the second input which is "Enter the first name of student", the loop automatically assigns each object in the array the attributes of "null" for id and name, and 0 for age and id, as well as breaking the outerloop. However, I get the error java.lang.NullPointerException.
Any help would be appreciated.
import java.util.*;
class Main {
public static void main(String[] args) {
Scanner myObj = new Scanner(System.in);
System.out.println("Enter number of students");
int numberof = myObj.nextInt();
System.out.println("Number of students is " + numberof);
Student Studentz[] = new Student[numberof];
outerloop:
for (int i = 0; i < numberof; ++i) {
Studentz[i] = new Student();
System.out.println("Enter first name of student " + (i + 1));
Scanner myObj1 = new Scanner(System.in);
String firstname = myObj1.nextLine();
System.out.println("Firstname is: " + firstname);
if (firstname.equals("end")) {
for (int g = i; g < numberof; ++g) {
Studentz[g].Setfirst("null");
Studentz[g].Setlast("null");
Studentz[g].Setage(0);
Studentz[g].Setid(0);
}
break outerloop;
} else {
Studentz[i].Setfirst(firstname);
System.out.println("Enter last name of student " + (i + 1));
Scanner myObj2 = new Scanner(System.in);
String lastname = myObj2.nextLine();
System.out.println("Last name is: " + lastname);
Studentz[i].Setlast(lastname);;
System.out.println("Enter age of student " + (i + 1));
Scanner myObj3 = new Scanner(System.in);
int nazca = myObj3.nextInt();
System.out.println("Age is: " + nazca);
Studentz[i].Setage(nazca);
System.out.println("Enter ID of student " + (i + 1));
Scanner myObj4 = new Scanner(System.in);
int nazca1 = myObj4.nextInt();
System.out.println("ID is: " + nazca1);
Studentz[i].Setid(nazca1);
}
for (int c = 0; c < numberof; ++c) {
System.out.println(Studentz[c].Snake());
}
}
}
}
public class Student {
private String first;
private String last;
private int age;
private int id;
public int getid() {
return
this.id;
}
public void Studentss(String f, String l, int a, int i) {
first = f;
last = l;
age = a;
id = i;
}
public void Setfirst(String z) {
this.first = z;
}
public void Setlast(String za) {
this.last = za;
}
public void Setage(int zb) {
this.age = zb;
}
public void Setid(int zc) {
this.id = zc;
}
public String Snake() {
String snek = "Name is " + this.first + " " + this.last + " , Age is " + this.age + " ,ID is " + this.id;
return snek;
}
}

you fail here because you try to print students data before you initialized all elements of Studentz array:
for (int c = 0; c < numberof; ++c) {
System.out.println(Studentz[c].Snake());
}
also your code fails here by the same reason:
for (int g = i; g < numberof; ++g) {
Studentz[g].Setfirst("null"); // NPE - no Student created yet in the array

Some Possibly Helpful Tips:
Follow Java naming rules for your variables and method names, Studentz should be studentz, even for your Arrays. I know...your tired of reading that but as you progress, you'll see how beneficial it really is.
If you can, don't use multiple Scanner objects, there is no need for that in your use-case. Declare one Scanner object and stick with it. You're probably doing this because you are using the nextLine() method after the nextInt() method and you're finding that it skips the first name prompt and provides a Null String (""). This happens because the nextInt() method does not consume the newline character when the Enter key is hit. To solve this problem you would either, place the code line myObj.nextLine(); directly under the int numberof = myObj.nextInt(); code line:
int numberof = myObj.nextInt();
myObj.nextLine(); // Consume ENTER key hit
or don't use the nextInt() method at all. Instead just stick with the nextLine() method and not worry about consumption:
Scanner myObj = new Scanner(System.in);
int numberof = 0;
String val = "";
while (val.equals("")) {
System.out.println("Enter number of students");
val = myObj.nextLine();
if (!val.matches("\\d+")) {
System.err.println("Invalid number supplied!");
val = "";
continue;
}
numberof = Integer.parseInt(val);
}
System.out.println("Number of students is " + numberof);
Student[] studentz = new Student[numberof];
It's always a good idea to validate any input from the User (as shown above), even if they're in a for loop. Give the User an opportunity to make a correct entry, after all, typo's do happen.
Get rid of the outerLoop: label. As a matter of fact, try avoid ever using them if you can....and you can. It would only be on a relatively rare occasion where you might ever need one.
Give your variables meaningful names, at least to some extent. This can benefit you later on down the road when you want to read your old code in the future.
In your Student class you made yourself a this real nice method named Studentss(). Well, I think it should be a constructor instead and save yourself a lot of code entry for calls to Setter methods. After all, that's mostly what the constructor is for. Your Student class constructor can look like this:
public Student(String firstName, String lastName, int age, int id) {
this.first = firstName;
this.last = lastName;
this.age = age;
this.id = id;
}
And be used like this. You will notice that upon each iteration of the outer for loop, all the prompt answers are placed within variables then at the end of all those prompts the constructor is used instantiate a student object, for example:
studentz[i] = new Student(firstname, lastname, age, id);
Doing it this way mean that there is no need to make calls to Setter methods. There is nothing wrong with making setter calls, it's just easier using the constructor. This is demonstrated below:
Scanner myObj = new Scanner(System.in);
int numberof = 0;
String val = "";
while (val.equals("")) {
System.out.println("Enter number of students");
val = myObj.nextLine();
if (!val.matches("\\d+")) {
System.err.println("Invalid number supplied!");
val = "";
continue;
}
numberof = Integer.parseInt(val);
}
System.out.println("Number of students is " + numberof);
Student[] studentz = new Student[numberof];
for (int i = 0; i < numberof; ++i) {
String firstname = "null";
String lastname = "null";
int age = 0;
int id = 0;
boolean exitOuterForLoop = false;
// Student First Name Prompt:
// (with option to End and default remaining to null's and 0's)
while (firstname.equals("null")) {
System.out.println("Enter first name of student " + (i + 1) + " (End to stop):");
firstname = myObj.nextLine();
if (firstname.equalsIgnoreCase("end")) {
firstname = "null";
//Make all remaining Student instances null and 0
for (int g = i; g < numberof; ++g) {
studentz[g] = new Student(firstname, lastname, age, id); // Use Student class constructor
}
exitOuterForLoop = true;
break; // Exit this 'while' loop
}
// Validate first name (no numbers or crazy characters)
if (!firstname.matches("(?i)[a-z']+")) {
System.err.println("Invalid First Name! (" + firstname + ") Try Again...");
firstname = "null";
}
}
if (exitOuterForLoop) {
break; // Exit this outer 'for' loop.
}
System.out.println("Firstname is: " + firstname);
// Student Last Name Prompt
while (lastname.equals("null")) {
System.out.println("Enter last name of student " + (i + 1));
lastname = myObj.nextLine();
// Validate last name (no numbers or crazy characters)
if (!lastname.matches("(?i)[a-z']+")) {
System.err.println("Invalid Last Name! (" + lastname + ") Try Again...");
lastname = "null";
}
}
System.out.println("Last name is: " + lastname);
// Student Age Prompt
val = "";
while (val.equals("")) {
System.out.println("Enter age of student " + (i + 1));
val = myObj.nextLine();
// Validate age (digits 0 to 9 only)
if (!val.matches("\\d+")) {
System.err.println("Invalid Age Supplied! (" + val + ") Try Again...");
val = "";
}
}
age = Integer.parseInt(val);
System.out.println("Student age is: " + age);
// Student ID Prompt
val = "";
while (val.equals("")) {
System.out.println("Enter ID of student " + (i + 1));
val = myObj.nextLine();
// Validate age (digits 0 to 9 only)
if (!val.matches("\\d+")) {
System.err.println("Invalid ID Supplied! (" + val + ") Try Again...");
val = "";
}
}
id = Integer.parseInt(val);
System.out.println("Student ID is: " + id);
studentz[i] = new Student(firstname, lastname, age, id); // Use Student class constructor
}
// Display the instances of Student contained within the 'studentz[]' array.
for (int c = 0; c < numberof; ++c) {
System.out.println(studentz[c].toString());
}
The snake() method is actually just another toString() method and there is nothing wrong with that however you might want to consider using StringBuilder class to create the returned string rather than doing concatenations, for example:
public String snake() {
return new StringBuilder("Name is ").append(this.first).append(" ").append(this.last)
.append(" , Age is ").append(this.age).append(" , ID is ")
.append(this.id).toString();
}
Not overly important here but it can save you memory if you do a lot concatenating with many large strings.

Issue dropping credits from course in Java dropCourse Method

What I have is a two snippets of code. The question I have in particular is about my dropCourse method within the student driver. Everything in my code seems to work fine except when I drop a course it does not drop the courses credits. For example, if I drop a course named "Computer101" which had four credits, it will remove "Computer101" From the schedule, but will not remove the "4" credits when I choose option 5 to print the total credits. So if we have a full schedule of:
Computer101 in position 0 worth 4 credits
Physics105 in position 1 worth 4 credits
Art101 in position 2 worth 4 credits
Chem101 in position 3 worth 4 credits
And I decide to drop Computer101 from the schedule, all other classes will move up in their position in the array as they are supposed to, when printing the schedule that class will no longer show up and when it is searched for it will not be found, but the amount of credits it was worth will still be there. I feel like the solution is right in front of me, but I am so burned out I am not seeing it. I would really appreciate any help and I hope I was clear with what I am asking.
Here is where my dropCourse method will be found:
public class Student
{
//Instance Data
String studentName;
String studentID;
String streetAddress;
String city;
String state;
String zipCode;
String major;
final int MAX_CREDITS = 18;
int courseNumber = 0; //start out with no courses
int totalCredits;
final int SIZE = 6;
String [ ] schedule = new String [SIZE];
//Create Constructor:
//Initializes the student data at instantiation time.
//-------------------------------------------------------
// Sets up the student's information.
//-------------------------------------------------------
public Student (String name, String id, String address, String cityName, String stateName, String zip, String area )
{
studentName = name;
studentID = id;
streetAddress = address;
city = cityName;
state = stateName;
zipCode = zip;
major = area;
}//end Student Constructor
//Method to Return student information as string:
//-------------------------------------------------------
// Returns the student information as a formatted string.
//-------------------------------------------------------
public String toString()
{
String studentInfo;
studentInfo = "Name:\t\t\t" + studentName + "\n" + "ID:\t\t\t" + studentID + "\n" + "Address:\t\t" + streetAddress
+ "\n" + "City:\t\t\t" + city + "\n" + "State:\t\t\t" + state + "\n" + "Zip Code:\t\t" + zipCode
+ "\n" + "Major:\t\t\t" + major + "\n";
return studentInfo;
}// end toString
//Method to determine if maximum allowed credits have been exceeded
//-------------------------------------------------------
// Returns true if total credits does not exceed 18.
//-------------------------------------------------------
private boolean checkCredits(int numCredits)
{
if (numCredits + totalCredits <= MAX_CREDITS) //make sure max credits not exceeded
{
return true; //return a true if still less than 18 credits
}
else
{
return false; //return a false if 18 credit limit is exceeded
}//end numCredits
}//checkCredits
//Method to add a course to the student’s schedule
//-------------------------------------------------------
// Adds a course to the array if total credits does not exceed 18.
//-------------------------------------------------------
public void addCourse(String course, int numCredits)
{
if (courseNumber < SIZE ) //make sure array is not full.
{
if (checkCredits(numCredits) == true) //if we’re under 18 credits
{
//add course
schedule [courseNumber] = course + ":\t\t" + numCredits + "\tCredits\n";
//increment number of credits
totalCredits = totalCredits + numCredits;
//increment number of courses
courseNumber = courseNumber + 1;
System.out.println("The course has been added!");
}
else //oops – can’t do more than 18 credits
{
System.out.println("You have exceeded the maximum allowed credits.");
}//end checkCredits
}
else //oops – can’t do more than 6 courses
{
System.out.println("You have exceeded 6 courses.");
}//end courseNumber
}//addCourse
public void displaySchedule( )
{
for (int index = 0; index < courseNumber; index++)
{
System.out.println("Course #" + (index + 1) + " " + schedule[index] + "\n");
}//end for
}//end display schedule
public int searchCourse(String courseName)
{
String course;
boolean flag = false;
int index = 0;
while(index < courseNumber && flag == false)
{
String extract = schedule[index].substring(0,6);
if (extract.contains(courseName) == true)
{
flag = true;
}
else
{
index++;
}
}
if (flag == false)
{
return -1;
}
else
{
return index++;
}
}
public void dropCourse(String courseName)
{
int found;
found = searchCourse(courseName);
int index = 0;
if (found == -1)
{
System.out.println("Course not in schedule");
}
else
{
if (found == 5)
{
courseNumber = courseNumber -1;
}
else
{
for (index = found; index < courseNumber; index ++)
{
schedule[index] = schedule[index + 1];
}
courseNumber = courseNumber -1;
System.out.println("The course has been dropped!");
}
}
}
public int totalCredits()
{
System.out.println("The total credits are " + totalCredits);
return totalCredits;
}
}//end class Student
This is where my menu that works with the above code is:
//This is a Driver program to test the external Class named Student
import java.util.Scanner;
public class TheMenu //BEGIN Class Definition
{
//**************** Main Method*************************
static Scanner scan = new Scanner(System.in);
public static void main (String[] args)
{
//Data Definitions:
//Instance Data
String name;
String id;
String street;
String city;
String state;
String zip;
String major;
String courseName;
int courseCredits;
int menu = 0;
//Initialize first Student
name = "Florence Welch";//look her up
id = "7777";
street = "777 Heaven Street";
city = "Witchville";
state = "NY";
zip = "12345";
major = "Arts";
//instantiate the Student object
Student student1 = new Student(name, id, street, city, state, zip, major);
while (menu < 6)//begin while for menu options
{
System.out.println("1. Add a course ");
System.out.println("2. Search for a course");
System.out.println("3. Drop a course");
System.out.println("4. Print out a student's schedule");
System.out.println("5. Print out total credits");
System.out.println("6. Exit");
System.out.println("Enter an option: ");
menu = scan.nextInt();
if (menu == 1)//option to add course
{
System.out.println("Please enter the name of the course: ");
courseName = scan.next();
System.out.println("How many credits is the course? ");
courseCredits = scan.nextInt();
student1.addCourse(courseName, courseCredits);//uses method to store course information in array
}
else if (menu == 2)//option to search for course
{
int x;
System.out.println("Please enter the name of the course: ");
courseName = scan.next();
student1.searchCourse(courseName);
x = student1.searchCourse(courseName);
if (x == -1)//course is not found if value returns -1
{
System.out.println("Course not found");
}
else
{
System.out.println("Course found in position " + student1.searchCourse(courseName));//shows user the position of course
}
}
else if (menu == 3)//will drop course from users schedule
{
System.out.println("Please enter the course you wish to drop: ");
courseName = scan.next();
student1.dropCourse(courseName);
}
else if (menu == 4)//displays the users schedule
{
System.out.println(name + "'s Schedule:\n\n");
student1.displaySchedule();
}
else if (menu == 5)//will display users credits for semester
{
student1.totalCredits();
}
else
{
System.out.println("Enjoy your semester!");//option 6 will exit program
}
}
}
}

How Do I Get Customer Input To Display?

I am in an Object-Oriented Programming course in college and I have to use Java to start a program that will eventually incorporate a full on GUI by the end of the course. For the beginning of this project, I have to basically use message boxes to set up how a customer would order a sub to be delivered to their home.
Here's what I have so far:
This is the main class
import javax.swing.*;
//Here is the main class
public class Subs {
public static void main(String[] args) {
// Begin Main Method
char letter;
String input;
String input1, input2, input3, input4, input6, input8;
int input5, input7;
int subL; //length of sub in inches
int cup; //size of drink in ounces
JFrame frame = new JFrame("Message");
JOptionPane.showMessageDialog(frame, "Welcome to Famous Subs! ");
input1 = JOptionPane.showInputDialog(frame, "Please Enter Your Name: ");
input2 = JOptionPane.showInputDialog(frame, "Please Enter Your Address: ");
do {
input3 = JOptionPane.showInputDialog(frame, "What kind of sub would "
+ "you like? " +
"\n Turkey Club" +
"\n Philly" +
"\n Meatball" +
"\n Chicken Parm");
input4 = JOptionPane.showInputDialog(frame, "What type of bread? " +
"\n White" +
"\n Wheat" +
"\n Rosemary" +
"\n Italian Herb");
subL = getValidLength();
input6 = JOptionPane.showInputDialog(frame, "What would you like to "
+ "to drink? " +
"\n Water" +
"\n Soda" +
"\n Juice");
cup = getValidCup ();
input8 = JOptionPane.showInputDialog(frame, "Do you wish to continue?\n "+
"'y' or 'Y' for YES\n"+
"'n' or 'N' for NO\n");
Order firstOrder = new Order(input1, input2, input3, input4, input6, subL, cup);
JOptionPane.showMessageDialog(frame, firstOrder.toString());
letter = input1.charAt(0);
}
while (letter == 'Y'|| letter == 'y');
System.exit(0);
}
private static int getValidLength()
{
int s;
String input5;
do{
input5 = JOptionPane.showInputDialog(null, "What size of sub do you wish "
+ "to order? "+
"\n 6 inch"+
"\n 12 inch");
s = Integer.parseInt(input5);
} while (!(s==6 || s==12));
return s;
}
private static int getValidCup()
{
int c;
String input8;
do{
input8 = JOptionPane.showInputDialog(null, "What size drink? " +
"\n Small 12oz." +
"\n Medium 24oz." +
"\n Large 36oz.");
c = Integer.parseInt(input8);
}
while (!(c==12 || c==24 || c==36));
return c;
}
}
This is my subclass
//This is the class for the order
public class Order {
//creating my variables
private String Customer;
private String Address;
private String name;
private String bread;
private String drink;
private int length; //in inches
private int size; //in ounces
private double SubPrice;
private double DrinkPrice;
private double total;
//blank constructor
public Order(){}
//Create a constructor to hold variables
public Order (String Customer, String Address, String name, String bread, String drink, int subL, int cup){
this.Customer = Customer;
this.Address = Address;
this.name = name;
this.bread = bread;
this.drink = drink;
subL = length;
cup = size;
}
//create the getters and setters for the variables
public String getCustomer(){
return Customer;
}
public void setCustomer(String Customer){
this.Customer = Customer;
}
public String getAddress(){
return Address;
}
public void setAddress(String Address){
this.Address = Address;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
public String getBread(){
return bread;
}
public void setBread(String bread){
this.bread = bread;
}
public String getDrink(){
return drink;
}
public void setDrink(String drink){
this.drink = drink;
}
public int getLength(){
return length;
}
public void setLength (int length){
this.length = length;
}
public int getSize(){
return size;
}
public void setSize (int size){
this.size = size;
}
public void setSubPrice (int subL, double SubPrice){
if (subL == 6)
SubPrice = 7.95;
else if (subL == 12)
SubPrice = 12.75;
}
public void setDrinkPrice(int cup, double DrinkPrice){
if (cup == 12)
DrinkPrice = 2.00;
else if (cup == 24)
DrinkPrice = 4.00;
else if (cup == 36);
DrinkPrice = 6.00;
}
public void setTotal(){
total = SubPrice + DrinkPrice;
}
#Override
public String toString(){
String grandOrder = "Greetings " + Customer +
"\nHere is your order: " +
"\n" + name +
"\n" + bread +
"\n" + drink +
"\nThe length of your sub is: " + length +
"\nThe size of your drink is: " + size +
"\nThe Price for your sub is: " + SubPrice +
"\nThe Price for your drink is: " + DrinkPrice +
"\nHere is your total: $" + calculateTotal(DrinkPrice, SubPrice) +
"\nThis will be delivered to: " + Address;
return grandOrder;
}
}
Everything runs just fine except the fact that the last box to show up returns all the string fields as null and the int and double variables as 0 or 0.0.
How do I return the values for what the user inputs on each dialog box? In addition, how do I get he customer's name and address to appear on this final screen? Thanks.

You never initialize fields of your Order. You call constructor without parameters public Order(){}. So you see the default values of the fields.
What you should do:
Be sure that you keep in a variable the value for the name of the client. (input = JOptionPane.showInputDialog(frame, "Please Enter Your Name: ");)
Be sure that you keep in variable user's input after "input = JOptionPane.showInputDialog(frame, "What kind of sub would "
+ "you like? " ...".
After get all inputs from the user, create Order object passing user's values
Order firstOrder = new Order(name, bread,drink,int subL, cup);
Change the constructor with parameters like that:
public Order (String name, String bread, String drink, int subL, int cup). You should not pass subPrice and drinkPrice because you Order class already know these values (see setdrinkPrice()). You determine the price of a cup based on the int cup. BTW, can you change the name of the method? Something like setDrinkPrice().
You never call setDrinkPrice() and setsubPrice()(should be setSubPrice(). You can do this when you calculate the total.
Start with these changes and if you have more problems ask .

Okay, a few things are going on here.
Order firstOrder;
firstOrder = new Order();
Can just be written as
Order firstOrder = new Order();
there's no need to do that on two lines. But, more importantly, you've not giving it any parameters, so Java is linking that to the empty constructor (the one that doesn't assign anything.) All of that nice constructor code you have isn't getting called.
To do that, you need to actually do something with those input fields you keep assigning (at the moment you're just ignoring them and writing over them); specifically, you should store them in local variables, and then pass them to the constructor like:
firstOrder = new Order(arg1, arg2, ...)
Also, Order isn't a subclass; it isn't extending anything. (Except Object, but we don't generally call something a subclass just for that.

input = JOptionPane.showInputDialog(frame, "Please Enter Your Name: ");
input = JOptionPane.showInputDialog(frame, "Please Enter Your Address: ");
On the first line above, you get the customer's name. then you call the second line, throwing away the customer's name without saving it anywhere.

Java NullPointerException why is the array null?

I can output the details from the student, but always when i do it displays
Exception in thread "main" java.lang.NullPointerException
at client.Client.main(Client.java:126)
and the program crashes.
The array is null , I don't why and I don't know how to fix that. Please help me to understand, the problem should be around here..
if (choice == 3) {
for (int a = 0; a < list.length; a++) { //To Display all current Student Information.
// list[i] = new student();
list[a].DisplayOutput();
}
Anyways here comes my code.
package client;
import java.util.Scanner;
public class Client {
//my infos
public static void AuthorInformation() {
System.out.print("__________________________________________\n"
+ "Student Name: xxxxxx xxxxxx\n"
+ "Student ID-Number: xxxxxx\n"
+ "Tutorial Timing: Wednesday 9:30 - 12:30 \n"
+ "Tutor Name: Mr xxxxxx\n\n"
+ "__________________________________________\n");
}
This is my client Class
public static void main(String[] args) {
AuthorInformation(); //calls the method for my information
student[] list = new student[20]; //my array
student student = new student();
int choice = 0; //variable for the choise of the menu
Scanner keyboard = new Scanner(System.in); //Scanner class
do { //MY menu in the do-while, so that it runs at least once while user enters 7(quit)
student.DisplayQuestions();
choice = keyboard.nextInt(); //takes the entered value from the user
if (choice == 1) {
System.out.println("Enter the Number of Students you want to store: ");//Enter amount of students to be stored
int studentNumber = keyboard.nextInt();
// student.addStudent();
for (int i = 0; i < studentNumber; i++) { //for loop is till the student number is achieved
list[i] = new student();
System.out.println("\nTitle of the student (eg, Mr, Miss, Ms, Mrs etc): ");
list[i].SetTitle(keyboard.next());
System.out.println("First name (given name)");
list[i].SetFirstName(keyboard.next());
System.out.println("A last name (family name/surname)");
list[i].SetFamilyName(keyboard.next());
System.out.println("Student number (ID):");
list[i].SetStudentID(keyboard.nextInt());
System.out.println("Enter the Day of birth(1-31): ");
list[i].SetDay(keyboard.nextInt());
System.out.println("Enter the Month of birth (1-12): ");
list[i].SetMonth(keyboard.nextInt());
System.out.println("Enter The Year of birth: ");
list[i].SetYear(keyboard.nextInt());
System.out.println("Students First Assignment Mark (0 - 100): ");
list[i].SetFirstMark(keyboard.nextInt());
System.out.println("Students Second Assignment Mark (0 - 100): ");
list[i].SetSecondMark(keyboard.nextInt());
System.out.println("Enter the mark of Student weekly practical work (0-10) ");
list[i].SetWeeklyMarks(keyboard.nextInt());
System.out.println("Please Enter the Marks for the final Exam(0 - 100): ");
list[i].SetFinalMark(keyboard.nextInt());
/* System.out.println("- - - - - - - - - - - - -");
System.out.println("Do you want to add another Student? (Yes/No)");
String a = keyboard.next();
if (a.equalsIgnoreCase("yes")) {
} else if (a.equalsIgnoreCase("no")) {
i = list.length + 1;
}*/
}
}
if (choice == 2) {
int x = 2;
double AverageNum = 0;
for (int p = 0; p < x; p++) { //This is to take the Average OverallMarks of all students
AverageNum += list[p].OverallMarking();
}
System.out.println("Total Average Of Overall Marks is :" + AverageNum / 2);
}
if (choice == 3) {
for (int a = 0; a < list.length; a++) { //To Display all current Student Information.
// list[i] = new student();
list[a].DisplayOutput();
}
}
if (choice == 4) { //To Display the distribution of grades awarded.
System.out.println("\nGrade Distribution: \n" + student.GetCounterHD() + " HDs\n" + student.GetCounterD() + " Ds\n" + student.GetCounterC() + " Cs\n" + student.GetCounterP() + " Ps\n" + student.GetCounterN() + " Ns\n");
}
if (choice == 5) {
System.out.println("Enter Student's ID Number to search for: "); // to take the id number from the user
int FindID = keyboard.nextInt();
boolean Found = false;
// to find with the student ID Number details of the student.
for (int i = 0; i < 10; i++) {
if (FindID == list[i].GetStudentID()) {
list[i].DisplayOutput();
Found = true;
break;
}
}
}
if (choice == 6) { //
System.out.println("Enter Student's Name to search for: ");
String SearchStudentName = keyboard.next(); //take the name of the student
boolean Found = false;
//To find the name of the student it loops till it has it or the limit of studentnumbers are achieved.
for (int i = 0; i < list.length; i++) {
if (SearchStudentName.equalsIgnoreCase(list[i].GetFirstName())) {
list[i].DisplayOutput();
Found = true;
break;
}
}
}
} while (choice != 7);
{ //while statement quit the program
System.out.println("\nYou Quit.");
}
}
}
And here is my student class
package client;
import java.util.Scanner;
public class student {
//The instance vriables for students (Title, first name, family name,
Student ID, date of birth in day month and year, first and second
assignment mark, mark of weekly practical work and final exam
private String Title;
private String FirstName;
private String FamilyName;
private long StudentID;
private int Day;
private int Month;
private int Year;
private float FirstMark;
private float SecondMark;
private float WeeklyMarks;
private float FinalMark;
//those private instance variables are for the calculation of (first and
second assignment mark, mark of weekly practical work and exam mark, final
mark and overall mark)
private float FirstMarkPercentage;
private float SecondMarkPercentage;
private float WeeklyMarksPercentage;
private float ExamPercentage;
private String FinalGrade;
private float OverallMarks = 0;
//those private instance variables are to count the the marks(
private int CounterN = 0;
private int CounterP = 0;
private int CounterC = 0;
private int CounterD = 0;
private int CounterHD = 0;
public student(String Title, String FirstName, String FamilyName, long StudentID, int Day, int Month, int Year, float FirstMark, float SecondMark, float WeeklyMarks, float FinalMark) {
this.Title = Title;
this.FirstName = FirstName;
this.FamilyName = FamilyName;
this.StudentID = StudentID;
this.Day = Day;
this.Month = Month;
this.Year = Year;
this.FirstMark = FirstMark;
this.SecondMark = SecondMark;
this.WeeklyMarks = WeeklyMarks;
this.FinalMark = FinalMark;
this.FinalGrade = FinalGrade;
}
//This Method is to display (Title, first name, family name, Student ID, date of birth in day month and year, first and second assignment mark, mark of weekly practical work and final exam)
public student() {
Title = "";
FirstName = "";
FamilyName = "";
StudentID = 0;
Day = 0;
Month = 0;
Year = 0;
FirstMark = 0;
SecondMark = 0;
WeeklyMarks = 0;
FinalMark = 0;
}
//The methods starting with Get...(), are to return the (Title, first name, family name, Student ID, date of birth in day month and year, first and second assignment mark, mark of weekly practical work and final exam and the marks N, P, C, D & HD)
public String GetTitle() {
return Title;
}
public String GetFirstName() {
return FirstName;
}
public String GetFamilyName() {
return FamilyName;
}
public long GetStudentID() {
return StudentID;
}
public int GetDay() {
return Day;
}
public int GetMonth() {
return Month;
}
public int GetYear() {
return Year;
}
public float GetFirstMark() {
return FirstMark;
}
public float GetSecondMark() {
return SecondMark;
}
public float GetWeeklyMarks() {
return WeeklyMarks;
}
public float GetFinalMark() {
return FinalMark;
}
public String GetFinalGrade() {
return FinalGrade;
}
public int GetCounterHD() {
return CounterHD;
}
public int GetCounterD() {
return CounterD;
}
public int GetCounterC() {
return CounterC;
}
public int GetCounterP() {
return CounterP;
}
public int GetCounterN() {
return CounterN;
}
public float GetOverallMarks() {
return OverallMarks;
}
//The methods starting with Set...(), are to set the (Title, first name, family name, Student ID, date of birth in day month and year, first and second assignment mark, mark of weekly practical work and final exam and the marks N, P, C, D & HD)
public void SetTitle(String Title) {
this.Title = Title;
}
public void SetFirstName(String FirstName) {
this.FirstName = FirstName;
}
public void SetFamilyName(String FamilyName) {
this.FamilyName = FamilyName;
}
public void SetStudentID(int StudentID) {
this.StudentID = StudentID;
}
public void SetDay(int Day) {
this.Day = Day;
}
public void SetMonth(int Month) {
this.Month = Month;
}
public void SetYear(int Year) {
this.Year = Year;
}
public void SetFirstMark(float FirstMark) {
this.FirstMark = FirstMark;
}
public void SetSecondMark(float SecondMark) {
this.SecondMark = SecondMark;
}
public void SetWeeklyMarks(float WeeklyMarks) {
this.WeeklyMarks = WeeklyMarks;
}
public void SetFinalMark(float FinalMark) {
this.FinalMark = FinalMark;
}
public void SetFinalGrade(String FinalGrade) {
this.FinalGrade = FinalGrade;
}
public void SetOverallMarks(float OverallMarks) {
this.OverallMarks = OverallMarks;
}
public boolean equals(student OtherStudent) {
return (this.FirstName.equalsIgnoreCase(OtherStudent.FirstName)) && (this.FamilyName.equalsIgnoreCase(OtherStudent.FamilyName));
}
//this method is for the calculation of (first and second assignment mark, mark of weekly practical work and exam mark, final mark and overall mark)
public float OverallMarking() {
FirstMarkPercentage = ((FirstMark / 100) * 20);
SecondMarkPercentage = ((SecondMark / 100) * 20);
WeeklyMarksPercentage = ((WeeklyMarks / 10) * 10);
ExamPercentage = ((FinalMark / 100) * 50);
OverallMarks = FirstMarkPercentage + SecondMarkPercentage + WeeklyMarksPercentage + ExamPercentage; //for the overall mark returns
return OverallMarks;
}
//this function arranges the grade calculations and returns the final grade
public String GradeCalculations() {
if (OverallMarks >= 80 && OverallMarks <= 100) { // if grade lies within this range print HD
FinalGrade = "HD";
CounterHD++;
} else if (OverallMarks >= 70 && OverallMarks < 80) { // if grade lies within this range print D
FinalGrade = "D";
CounterD++;
} else if (OverallMarks >= 60 && OverallMarks < 70) { // if grade lies within this range print C
FinalGrade = "C";
CounterC++;
} else if (OverallMarks >= 50 && OverallMarks < 60) { // if grade lies within this range print P
FinalGrade = "P";
CounterP++;
} else if (OverallMarks < 50 && OverallMarks >= 0) { // if grade lies within this range print N
FinalGrade = "N";
CounterN++;
}
return FinalGrade;
}
public void DisplayQuestions() {
System.out.println("\n Welcome to the Menu to perform one of the following operations (You must enter a number between 1-7):");
System.out.println("(1) To add the Student Information.");
System.out.println("(2) To Display the Output from the Average Overall Mark for students.");
System.out.println("(3) To Display all current Student Information.");
System.out.println("(4) To Display the distribution of grades awarded.");
System.out.println("(5) for entering a student ID Number To view all details of the student.");
System.out.println("(6) for entering a student name To view all details of the student.");
System.out.println("(7) Quit");
System.out.println("\n__________________________________________");
}
//This function displays the details of the student with before calculated marks.
public void DisplayOutput() {
System.out.println("\nName: " + GetTitle() + " " + GetFirstName() + " " + GetFamilyName());
System.out.println("Student ID: " + GetStudentID());
System.out.println("Date of Birth: " + GetDay() + "/" + GetMonth() + "/" + GetYear());
System.out.println("Assignment 1 Marks: " + GetFirstMark());
System.out.println("Assignment 2 Marks: " + GetSecondMark());
System.out.println("Weekly Practical Marks: " + GetWeeklyMarks());
System.out.println("Final Exam Marks: " + GetFinalMark());
System.out.println("Final Marks & Grade: " + OverallMarking() + "/" + GradeCalculations());
}
public void addStudent() {
/*Scanner keyboard = new Scanner(System.in);
for (int i = 0; i < list.length; i++) { //for loop is till the student number is achieved
list[i] = new student();
System.out.println("\nTitle of the student (eg, Mr, Miss, Ms, Mrs etc): ");
list[i].SetTitle(keyboard.next());
System.out.println("First name (given name)");
list[i].SetFirstName(keyboard.next());
System.out.println("A last name (family name/surname)");
list[i].SetFamilyName(keyboard.next());
System.out.println("Student number (ID):");
list[i].SetStudentID(keyboard.nextInt());
System.out.println("Enter the Day of birth(1-31): ");
list[i].SetDay(keyboard.nextInt());
System.out.println("Enter the Month of birth (1-12): ");
list[i].SetMonth(keyboard.nextInt());
System.out.println("Enter The Year of birth: ");
list[i].SetYear(keyboard.nextInt());
System.out.println("Students First Assignment Mark (0 - 100): ");
list[i].SetFirstMark(keyboard.nextInt());
System.out.println("Students Second Assignment Mark (0 - 100): ");
list[i].SetSecondMark(keyboard.nextInt());
System.out.println("Enter the mark of Student weekly practical work (0-10) ");
list[i].SetWeeklyMarks(keyboard.nextInt());
System.out.println("Please Enter the Marks for the final Exam(0 - 100): ");
list[i].SetFinalMark(keyboard.nextInt());
System.out.println("- - - - - - - - - - - - -");
System.out.println("Do you want to add another Student? (Yes/No)");
String a = keyboard.next();
if (a.equalsIgnoreCase("yes")) {
addStudent();
} else if (a.equalsIgnoreCase("no")) {
i=list.length+1;
}
}*/
}
}

The array isn't null.
The exception is thrown when you try to call a method on a null member of the array.
You iterate over the full array, but have not necessarily filled the entire array. Members that you have not assigned to reference an object are null.
for (int a = 0; a < list.length; a++) { //To Display all current Student Information.
// list[i] = new student();
list[a].DisplayOutput();
}
One fix would be to stop iterating after you've hit the first null.
for (int a = 0; a < list.length; a++) { //To Display all current Student Information.
// list[i] = new student();
student student = list[a];
if ( null == student ) {
break;
}
else {
list[a].DisplayOutput();
}
}
Another fix would be to remember in case 1 how many students were stored, and change the loop condition to reflect that.
for (int a = 0; a < cntStudents; a++) { //To Display all current Student Information.
By the way, in Java code it is almost universally accepted that:
Class names begin with an uppercase character.
Method names begin with a lowercase character.

Error with next int versus next line

The other question I asked was excellently answered, but at the end the person mentioned an issue with taking an int and not clearing to the next line in the file. I tried a few different things (the commented out stuff in my code that you will see) and nothing seems to work. I always get the same error no matter what I changed. Here is the error, my code, my class code, then the file in that order.
The error:
Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Scanner.java:864)
at java.util.Scanner.next(Scanner.java:1485)
at java.util.Scanner.nextInt(Scanner.java:2117)
at java.util.Scanner.nextInt(Scanner.java:2076)
at HuntowskiSamuel.main(HuntowskiSamuel.java:25)
The code section:
import java.util.Scanner; //I'm only gonna need scanner for this project I think
import java.io.*;
public class HuntowskiSamuel //This is what the file name should be as well as the class name
{
public static void main (String [] args) throws IOException
{
File cFile = new File("cipcs115.txt"); //This will be the file and scanner variable used to pull the data for the candidates
Scanner scan = new Scanner(cFile);
File cFileReadIn = new File("cipcs115.txt"); //While this file and scanner will be used to pull the number of candidates from the same file...hopefully
Scanner scanReadIn = new Scanner(cFileReadIn);
String StateName = "No name yet"; //This is where the state value will be held, that controls the input of the file
int NumberOfCandidates = 0; // This will pull the number of candidates for the array size
String garbage = "Empty"; //This is where the ReadIn scanner can dump excess stuff
StateName = scanReadIn.next(); //The prime read for the while loop
//garbage = scan.nextLine(); //Consuming the newline character
int NumberOfLettersEntered [] = new int [8]; //Since we only have the letters L, C, V, S, D, P, Q, and X (others/errors) that were entered, IN THAT ORDER. Its not graceful but it works
while(StateName != "END_OF_FILE") //While we haven't reached the end of the file
{
int i = scanReadIn.nextInt();
garbage = scan.nextLine(); //Getting rid of the whitespace after the int is taken
for(i=i; i > 0; i--) //Read in the number of candidates, then run the loop that number of times
{
NumberOfCandidates++; //Every time this loop runs, it means there is one more candidate for the total amount
garbage = scanReadIn.nextLine(); //This will take all the important info and dump it, seeing as we only need the number of candidates and the state name
}
StateName = scanReadIn.next(); //Pull the next state name
//garbage = scan.nextLine(); //Consuming the newline after the state pull
}
Candidate_Info candidates [] = new Candidate_Info [NumberOfCandidates]; //This creates an array of the exact size of the number of candidates in the file
for(int i = 0; i < NumberOfCandidates; i++) //Running the constructor for each and every candidate created
{
candidates[i] = new Candidate_Info();
}
StateName = scan.next(); //Prime read for the data taking loop
//garbage = scan.nextLine(); //Getting rid of the whitespace after the state
while(StateName != "END_OF_FILE") //The same as the other loop, only using the real file and scanner variables
{
int CandidateNumber = 0; //This will keep the array number straight from 0 to however many candidates - 1
int candidatesPerState = scan.nextInt();
garbage = scan.nextLine(); //To get rid of the rest of the whitespace after the int return
for(int i = 0; i < candidatesPerState; i++) //This will loop for each of the candidates in ONE STATE, it pulls the number of candidates as an int
{
candidates[CandidateNumber].setState(StateName);
candidates[CandidateNumber].setName(scan.next());
candidates[CandidateNumber].setOffice(scan.next());
candidates[CandidateNumber].setParty(scan.next().charAt(0)); //This might not work because it is just a single character versus the string that it would be passed
candidates[CandidateNumber].setVotes(scan.nextInt());
candidates[CandidateNumber].setSpent(scan.nextDouble());
candidates[CandidateNumber].setMotto(scan.nextLine());
CandidateNumber++;
}
StateName = scan.next();
//garbage = scan.nextLine(); //To get rid the whitespace after taking the state value
}
}
}
The class code:
//Samuel James Huntowski
// started: 11-18-2014
// last modified: 11-18-2014
public class Candidate_Info
{
private String State; //All the variables that were given to me in the specification
private String Name_of_Candidate;
private String Election_Office;
private char Party;
private int Number_of_Votes;
private double Dollars_Spent;
private String Motto;
private final double DOLLARS_SPENT_MIN = 0.0; //Mutator method for Dollars_Spent must check to see if greater then this value
private final int NUMBER_OF_ATTRIBUTES = 7; //for use in the equals method
public Candidate_Info()
{
State = "No state assigned"; //Giving empty values to all of the variables
Name_of_Candidate = "No name yet";
Election_Office = "No office assigned";
Party = 'X';
Number_of_Votes = 0;
Dollars_Spent = 0.0;
Motto = "No motto yet";
}
//These are all of the Accessor Methods
public String getState()
{
return State;
}
public String getName()
{
return Name_of_Candidate;
}
public String getOffice()
{
return Election_Office;
}
public char getParty()
{
return Party;
}
public int getVotes()
{
return Number_of_Votes;
}
public double getSpent()
{
return Dollars_Spent;
}
public String getMotto()
{
return Motto;
}
//Mutator methods will go here
public void setState(String newState)
{
State = newState;
System.out.println("The candidate's state is now set to " + newState + ".");
}
public void setName(String newName)
{
Name_of_Candidate = newName;
System.out.println("The candidate's name is now set to " + newName + ".");
}
public void setOffice(String newOffice)
{
Election_Office = newOffice;
System.out.println("The candidate's office is now set to " + newOffice + ".");
}
public void setParty(char newParty)
{
if(!((newParty == 'd') || (newParty == 'r') || (newParty == 'i') || (newParty == 'o'))) //If the value of newParty DOES NOT EQUAL 'o', 'd', 'r', or 'i' then do the next set of code
{
System.out.println("Invalid party input. Candidate's party remains unchanged. Please try again.");
}
else
{
Party = newParty;
System.out.println("The candidate's party is now set to " + newParty + ".");
}
}
public void setVotes(int newNumberOfVotes)
{
Number_of_Votes = newNumberOfVotes;
System.out.println("The candidate's number of votes is now set to " + newNumberOfVotes + ".");
}
public void setSpent(double newDollarsSpent)
{
if(newDollarsSpent < DOLLARS_SPENT_MIN) //If the amount of money spent is less then zero (Which just wouldn't make sense, so that's why I set the variable to zero)
{
System.out.println("New amount of dollars spent is invalid. Candidate's dollars spent remains unchanged. Please try again.");
}
else
{
Dollars_Spent = newDollarsSpent;
System.out.println("The candidate's dollars spent is now set to " + newDollarsSpent + ".");
}
}
public void setMotto(String newMotto)
{
Motto = newMotto;
System.out.println("The candidate's motto is now set to \"" + newMotto + "\"");
}
public void displayAll()
{
System.out.println(State + "\t" + Name_of_Candidate + "\t"
+ Election_Office + "\t" +
Party + "\t" + Number_of_Votes +
"\t" + Dollars_Spent + "\t" + Motto); //Display all info separated by tabs
}
public String toString()
{
String ReturnThis = (State + "\t" + Name_of_Candidate + "\t" +
Election_Office + "\t" + Party +
"\t" + Number_of_Votes + "\t" +
Dollars_Spent + "\t" + Motto); //same as displayAll() just in one string
return ReturnThis;
}
public boolean equals(Candidate_Info PassedCandidate)
{
boolean TF [] = new boolean [NUMBER_OF_ATTRIBUTES]; //An array of booleans that match the number of attributes above
boolean finalResult; //This will hold the final boolean result of all the below calculations
if(State.equals(PassedCandidate.getState())) TF[0] = true; //This isn't the most graceful method of doing this, but it works
else TF[0] = false;
if(Name_of_Candidate.equals(PassedCandidate.getName())) TF[1] = true;
else TF[1] = false;
if(Election_Office.equals(PassedCandidate.getOffice())) TF[2] = true;
else TF[2] = false;
if(Party == PassedCandidate.getParty()) TF[3] = true;
else TF[3] = false;
if(Number_of_Votes == PassedCandidate.getVotes()) TF[4] = true;
else TF[4] = false;
if(Dollars_Spent == PassedCandidate.getSpent()) TF[5] = true;
else TF[5] = false;
if(Motto.equals(PassedCandidate.getMotto())) TF[6] = true;
else TF[6] = false;
if(TF[0] && TF[1] && TF[2] && TF[3] && TF[4] && TF[5] && TF[6]) finalResult = true; //If ALL OF THE ATTRIBUTES equal the attributes of the passed candidate, therefore making all the TF variables true, then they are equal
else finalResult = false;
return finalResult;
}
}
And the file:
Illinois
3
Obama President d 131313 19.21 Great in 2008!
Daley Mayor d 5678 89000.45 My dad was good!
Stevenson Governor d 2367 43877.45 My hair is bad!
Wisconsin
6
Smith Mayor r 3 5.98 You can count on me daily!
Bush President r 11004 1222888.44 My dad was good too!
Gore President d 11003 54.34 Hear my Gore-y details!
Kim Governor r 111 3212.16 I'm the other Guy!
Hanrath Instructor i 6 0.12 What, me worry?
Jones Instructor o 9 14.56 You'd better worry!
Alaska
4
Nader President o 2 50.00 Nader's Raiders!
Alexander Mayor i 13 13.13 What am I doing?
Thompson Governor o 1 0.00 And you thought I was gone!
Schwarzenegger President o 123 1233377.94 I'll be back!
Delaware
2
Allen Instructor i 147 16.71 No exams in cs105!
Stewart President o 3 27367.67 I'm a good thing!
END_OF_FILE
Each of the data values of the file is seperated by a tab, but I didn't think that would matter as the methods that I use stop at the whitespace. Was I wrong? Where did I screw up? This is all happening at run time by the way. It compiles fine after you guys helped me earlier.