Thread: I can''t understand this error

The code works fine, but at the end of the quiz, I get an error for some unknown reason and any help pinpointing why I have this error would be much appreciated.

The code...

public class Student  {
	private String studentName;
	public void Setname(String name){
		studentName=name;
			}
 
	public String getName() {
		return studentName;
	}
 
	public void saying(){
		System.out.printf("Your test starts now, you have 5 minutes, you may begin %s", getName());
	}
}
 
 
 
public class Group 
 
{
	private String studentGroup;
	public void Setgroup(String name){
		studentGroup=name;
 
	}
 
	public String getGroup() {
		return studentGroup;
 
}
 
		public void groupsaying(){
			System.out.printf(" from %s", getGroup());
 
		}
		}
 
 
 
// basic question
 
 
public class SimpleQuestion {
 
 
	private String text;
	private String answer;
 
	public SimpleQuestion(String questionText)
	{
		text = questionText;
		answer = "";
 
	}
 
	// sets the answer
 
	public void setAnswer(String correctResponce)
	{
		answer = correctResponce;
 
	}
 
	// checks given responce
 
	public boolean checkAnswer(String responce)
	{
		return responce.equals(answer);
	}
 
	// displays the question
 
	public void display()
	{
		System.out.println(text);
	}
 
}
 
 
 
import java.util.ArrayList;
 
// Multiple choice question class
 
public class MultipleQuestion extends SimpleQuestion {
 
	private ArrayList<String> choices;
 
 
	public MultipleQuestion(String questionText)
	{
		super(questionText);
		choices = new ArrayList<String>();
 
	}
 
	// correct answer
 
	public void addChoice (String choice, boolean correct)
	{
		choices.add(choice);
		if (correct)
		{
			//Convert choice.size to string
			String choiceString = "" + choices.size();
			   setAnswer(choiceString);
 
		}
	}
 
		public void display()
		{
			//displays the text for the question
			super.display();
			// Display the answer choices
			 for (int i = 0; i < choices.size(); i++)
			{
				int choiceNumber = i + 1;
				System.out.println(choiceNumber + ": " +choices.get(i));
 
			}
		}
 
}
 
 
import java.util.Scanner;
 
 
 
 
class quizDemon{
	public static void main(String[] args) {
		int count = 0;
 
		Scanner input = new Scanner(System.in);
		Scanner inputgroup = new Scanner(System.in);
		Student studentObject = new Student();
		Group groupObject = new Group();
		System.out.println("\nEnter your name here : ");
		String studentnamesave = input.nextLine();
		System.out.println("\nEnter your group here : ");
		String groupnamesave = inputgroup.nextLine();
		studentObject.Setname(studentnamesave);
		groupObject.Setgroup(groupnamesave);
		studentObject.saying();
		groupObject.groupsaying();
 
		SimpleQuestion[] quiz = new SimpleQuestion[9];
 
			quiz[0] = new SimpleQuestion ("\nWho sang Stairway to Heaven");
 
				quiz[0].setAnswer("Led Zepplin");
 
 
		MultipleQuestion question = new MultipleQuestion(
				"Which of the following are Car manufactures");
					question.addChoice("Saab", true);
					if(true){
						++count;
					}
					question.addChoice("R8", false);
					question.addChoice("Accord",false);
					question.addChoice("Weetos", false);
					question.addChoice("FF10", false);
				quiz[1] = question;
 
		MultipleQuestion question2 = new MultipleQuestion(
				"Which one of the following is a programming language");
 
					question2.addChoice("Diamond", false);
					question2.addChoice("C++", true);
				quiz[2]	= question2;
 
 
 
		Scanner in = new Scanner(System.in);
			for (SimpleQuestion q : quiz)
			{
				q.display();
				System.out.print("Please insert your answer here: ");
				String responce = in.nextLine();
					System.out.println(q.checkAnswer(responce));
					System.out.println("Your current score is");
					System.out.println(count);
 
			}
 
 
	}
}

//
The error message

Exception in thread "main" java.lang.NullPointerException
at quizDemon.main(QuizTest.java:54)







Thanks again

When posting code, make sure you use the CODE tags. And make sure you boil your code down to the smallest form possible, an SSCCE (that's a link, click it). Point out any line numbers referenced in the Exception's stack trace so we don't have to count them ourselves.

Please use [highlight=java]your java code here[*/highlight] while posting your code.

Remove the * from [*/highlight] while posting the code actually.

That would help us understand it better.

Goldest

See: Common Java Mistakes: Forgetting to initialize a variable

Step through your code in debug mode to find out which variable didn't get initialized (or didn't get initialized to be non-null).

Hmmmm..how about this:

public class Student  {
    private String studentName;
 
public Student(String studentName)
{
this.studentName = studentName;
Setname(studentName);
}
    public void Setname(String name){
        studentName=name;
            }
 
    public String getName() {
        return studentName;
    }
 
    public void saying(){
        System.out.printf("Your test starts now, you have 5 minutes, you may begin %s", getName());
    }
}

public class Group
 
{
    private String studentGroup;
public Group(String studentGroup)
{
this.studentGroup = studentGroup;
Setgroup(studentGroup);
}
    public void Setgroup(String name){
        studentGroup=name;
 
    }
 
    public String getGroup() {
        return studentGroup;
 
}
 
        public void groupsaying(){
            System.out.printf(" from %s", getGroup());
 
        }
        }

Also, it'd be best if you had Student and Group in two separate java files.