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Answer 1

+1 A:

null is a valid value for an array. Both the pointer to the array and the contents in the array may be null. I took the time to read your too-long code. It looks like your code is not filling the arrays completely. For one thing, you do not put anything in slot 0 (questions[0] is always null).

Also, your code should be a for loop. And you should allocate the arrays to the number of questions allowed, not a fixed number. This way you will be certain that your arrays have no null elements (assuming JOptionPane doesn't return null if the user doesn't enter any value).

String[] questions = new String[x];
String[] answers = new String[x];
String[] a = new String[x];
String[] b = new String[x];
String[] c = new String[x];
String[] d = new String[x];

for (int i = 0; i < x; i++)
{

  questions[i] = JOptionPane.showInputDialog(null,"Please Enter Question Number "+i);
  a[i] = JOptionPane.showInputDialog(null,"What is the answer for a?");
  b[i] = JOptionPane.showInputDialog(null,"What is the answer for b?");
  c[i] = JOptionPane.showInputDialog(null,"What is the answer for c?");
  d[i] = JOptionPane.showInputDialog(null,"What is the answer for d?");
  answers[i] = JOptionPane.showInputDialog(null,"What is the correct answer to the question. \nType in lowercase a - d.");
}

Mr. Shiny and New 2010-06-02 16:31:12

Well its the user types in a question and it stores is in array[10]...then at the bottom it randomizes a number 1 - 10 and whichever it lands on depends on which question is pulled. So if it randomized a 7...question 7 would show in that format. Yet only null shows.

Nick Gibson 2010-06-02 16:42:38

@mdma: The original question didn't specify Java.

Mr. Shiny and New 2010-06-02 16:45:24

So then I can refer to i later down in the code as to display the correct value within the array?

Nick Gibson 2010-06-02 16:47:06

@Nick Gibson: No, `i` is only valid while you are in the `for` loop. But later on if you want a new `i` you can create one. Once the arrays are filled you can see how many questions there are by doing `questions.length`.

Mr. Shiny and New 2010-06-02 16:51:46

Ok well one more question, are the values still in the array after the for loop, so as to call them out and send them to a value during the later part of the code for testing.

Nick Gibson 2010-06-02 16:53:47

@Nick Gibson: The arrays are declared outside the loop, and the loop merely writes data into the array. The `int i` is declared inside the foor loop (well... sorta) and disappears afterwards. So the data should be there. Even in your original code the data is still there. I debugged it and saw it for myself.

Mr. Shiny and New 2010-06-02 17:04:06

Answer 2

A:

Your arrays, a,b,c,d, questions, answers are initialized to size 25. This will mean that they all hold null values initially - 25 of them. Your code fills in indexes 1..10, and then reviews a random question.

EDIT: The root cause is how you are genering random numbers, which can be 0, and index 0 is not filled. The array elements 1..10 are filled, but 0 and 11..24 are not. If the random number comes out as 0, you'll get a NullPointerException.

The fix is to set your question numbers starting from 0, and instead of Math.round(), cast the random number to an int which truncates the frantional part, so the range is 0..9.

mdma 2010-06-02 16:39:44

@mdma, "10..24 are not" as a typo. Should be: *11..24* are not

JohnB 2010-06-02 17:30:51

thanks! - fixed.

mdma 2010-06-02 18:25:00

Answer 3

+1 A:

JohnB 2010-06-02 16:48:54

Yeah I knew 1 - 10, I guess I forgot about including 0 in there since I had nothing in the 0 section. I was zero-indexing to start with but it was confusing when the user inserted 25 questions to add and it said Question #0 lol

Nick Gibson 2010-06-02 16:51:06

Also thank you very much on the Math help. the Math class was giving me problems since it generates a number as a data type of long, and was trying to make it an int. I never got into converting numeric data types, so I parsed the long into a String and then parsed the string into an int.

Nick Gibson 2010-06-02 16:57:10

@Nick Gibson, yes `Math.round(Math.random()*10);` could generate a **0** 9% of the time, and as you just realized, the `[0]` index of the array has nothing in it. If this is the answer to your question, you should click on the check mark. Good luck with you program.

JohnB 2010-06-02 17:05:48

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