Thread: Problem w/ Hashmap. Null Pointer?

So basically, I have written this class to define a hashmap, with a method to access the values.
This is pretty explanatory, it is used as an answer key for a larger "quiz" program.
Whenever I try and run this, I get a "NullPointerException".
The parameter I am giving is an int (that SHOULD correspond with the key in the hashmap no?)
Any idea what is going wrong here?

package jQuiz;
import java.util.*;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
 
public class QuizAnswers {
 
	//create our map
  private static final Map<Integer,Character> mp = DefineAnswers();
 
  private static Map<Integer, Character> DefineAnswers(){
	   Map<Integer, Character> question = new HashMap<Integer, Character>();
	   // Create our answer key 
	   question.put(0,'B');
	   question.put(1,'D');
	   question.put(2,'C');
	   question.put(3,'A');
	   question.put(4,'A');
	   question.put(5,'B');
	   question.put(6,'D');
	   question.put(7,'B');
	   question.put(8,'C');
	   question.put(9,'A');
	   return Collections.unmodifiableMap(mp);
    }
 
   public static char getAnswer(int QuestionNum) {
	   //return our result
	   return mp.get(QuestionNum);
    }
 
}

Also, I should probably state. I am aware that an Array would be a viable solution to my problem, but this is a school assignment and I want to push my studies a little.
atm though, I am at a complete loss as to why the following has a null reference:

QuizAnswers.getAnswer(1)
QuizAnswers.getAnswer(2)
QuizAnswers.getAnswer(3)

should it not return the value that corresponds with the Integer key as defined in my map?
note I have tried both "Integer" and "int" for the parameter of getAnswer, to no avail.

this is the line where I am getting the exception

System.out.println("Question1:" + QuizAnswers.getAnswer(0));

it was a test line I added a while back to see if I could retrieve the values.

So this is saying that the 0 is invalid? Could it be that I am somehow creating my hashmap wrong?

One thought that just popped in to my head is that the:

question.put(0,'B');

is not even being added to the hashmap for some reason?

Obviously I am very new to the implementation of map/hashmap so it is very possible I am doing it wrong, and just don't see where my mistake is.

Think I may have nailed it! in the following line:

return Collections.unmodifiableMap(mp);

Instead of using the var mp (the var assigned to MAP), I tried the variable "question" (the var assigned to the HASHMAP). I am now able to successfully acquire the values from my hashmap.

I think I was just assuming that the mp var would somehow reference the hashmap.
thx fr the help.


note: the QuizAnswers is the class I posted in my OriginalPost.