I am writing some code to help teach me how code in java and I have been using arrays. I have an error that I can't work out why it is occurring. The Code:
import java.util.Scanner;
public class pubQuizArray {
private static Scanner kb = new Scanner (System.in);
static String[] questions;
static String[][] answers;
static char[] realAnswers;
static char ans;
static char yn;
static int questionNum;
static int questionNumArray;
static int numQ;
static int score = 0;
public static void writeQuiz()
{
getQNum();
getQ();
}
public static void getQNum()
{
System.out.println("How many Questions?");
numQ = kb.nextInt();
questions = new String[numQ];
}
public static void getAns()
{
questionNumArray = questionNum - 1;
answers = new String[numQ][];
System.out.println("What are the answers?");
System.out.println("a: ");
answers[questionNumArray][0] = kb.nextLine();
System.out.println("b: ");
answers[questionNumArray][1] = kb.nextLine();
System.out.println("c: ");
answers[questionNumArray][2] = kb.nextLine();
System.out.println("d: ");
answers[questionNumArray][4] = kb.nextLine();
realAnswers = new char[numQ];
System.out.println("What is the correct Answer?");
realAnswers[questionNum] = kb.next().charAt(0);
}
public static void getQ()
{
questionNum = 0;
System.out.println("What is the First Question?");
questions[questionNum] = kb.nextLine();
getAns();
questionNum ++;
while(questionNum < numQ)
{
System.out.println("What is the next Question?");
questions[questionNum] = kb.nextLine();
getAns();
questionNum ++;
}
}
public static void askQ()
{
questionNum = 0;
while(questionNum < numQ)
{
System.out.println("Q1: " + questions[questionNum]);
System.out.println("a: " + answers[questionNum][0]);
System.out.println("b: " + answers[questionNum][1]);
System.out.println("c: " + answers[questionNum][2]);
System.out.println("d: " + answers[questionNum][3]);
ans = kb.next().charAt(0);
if(ans == realAnswers[questionNum])
{
System.out.println("That was correct");
score ++;
}
}
}
public static void menu()
{
System.out.println("Would you like to write a new Quiz? y/n");
yn = kb.next().charAt(0);
while(yn == 'y')
{
writeQuiz();
System.out.println("Would you like to play the Quiz? y/n");
yn = kb.next().charAt(0);
while(yn == 'y')
{
askQ();
System.out.println("Would you like to play again? y/n");
yn = kb.next().charAt(0);
}
}
}
public static void main(String[] args)
{
menu();
}
}
The error is this:
Would you like to write a new Quiz? y/n
y
How many Questions?
10
What is the First Question?
What are the answers?
a:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
at pubQuizArray.getAns(pubQuizArray.java:34)
at pubQuizArray.getQ(pubQuizArray.java:56)
at pubQuizArray.writeQuiz(pubQuizArray.java:17)
Thanks in advance for any help that you can give. Please bear in mind that this is just a trial program and that I am still learning java.
OK I have another problem this time it says:
Would you like to write a new Quiz? y/n
y
How many Questions?
1
What is the First Question?
and
What are the answers?
a: a
Exception in thread "main" java.lang.NullPointerException
at pubQuizArray.getAns(pubQuizArray.java:34)
at pubQuizArray.getQ(pubQuizArray.java:57)
at pubQuizArray.writeQuiz(pubQuizArray.java:17)
at pubQuizArray.menu(pubQuizArray.java:96)
at pubQuizArray.main(pubQuizArray.java:110)
and i've updated the other previous code.
At this point, inside getAns()
questionNumArray = questionNum - 1;
answers = new String[numQ][];
System.out.println("What are the answers?");
System.out.println("a: ");
answers[questionNumArray][0] = kb.nextLine();
questionNumArray
contains the value -1
which is an invalid index for an array.
It comes from
public static void getQ()
{
questionNum = 0; // set to 0
System.out.println("What is the First Question?");
questions[questionNum] = kb.nextLine();
getAns(); // still 0
questionNum ++; // too late
...
}
Edit
The NPE you are getting boils down to
System.out.println("a: ");
answers[questionNumArray][0] = kb.nextLine();
you haven't initialized answers[questionNumArray]
so it is null
. Do the following first
answers[questionNumArray] = new String[someSize]; // someSize should probably be 5 looking at your code
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