Understanding NullPointerException when checking for Null after removing elements in 2D array

Question

Upon checking for Null values in a 2D array, do I keep getting the java.lang.NullPointerException error?

Here's my 2D array:

String[][] userInfo = new String[10][4];

Here's a method for deleting an entire entry in the array based on user input:

private void removeUser(String userInfo[][]) {
        String first = "";
        String last = "";
        Scanner searchUserinput = new Scanner(System.in);
        String searchUser;
        System.out.println("Which user would you like to search for? Please enter their first and last name");
        searchUser = searchUserinput.nextLine();
        /*System.out.println(searchUser); */

        String[] words = searchUser.split("\\s+");

        if (words.length > 2) {
            System.out.println("Please enter only the first and last name");
        }
        else {
            for (int i = 0; i < words.length; i++) {
               first = words[0];
               last = words[1];
            }
        }

        outerloop:
        for (int row = 0; row < userInfo.length;) {
            for (int column = 0; column < userInfo[row].length;) {
                  if (userInfo[row][column]!= null) {
                      if (userInfo[row][0].equals(first) && userInfo[row][1].equals(last)) {
                        System.out.println("We found this user's contact info the database.");
                        System.out.println("Removing now...");
                        userInfo[row][0] = null;
                        userInfo[row][1] = null;
                        userInfo[row][2] = null;
                        userInfo[row][3] = null;
                        break outerloop;
                      }

                   else{
                       column ++;
                       row ++;
                       break;
                    }
                   }

              }
               row++;
            }

    }

Let's say I have a number of rows and columns with data, like this:

Bill Smith 123 123 Jon Dude 234 23 Another Guy 2332 435 Some Person 1212 12

If I try to delete say Bill Smith, there's no error thrown, or if I try to delete Another Guy, still no issue. But If I, for example, delete Bill Smith, then try to delete Jon Dude, that's why I get the error. But Java is telling me the error is from the very line wherein I'm checking for a null value with: if (userInfo[row][column]!= null), not understanding why.

Exception in thread "main" java.lang.NullPointerException
    at Lab02.removeUser(Lab02.java:96)
    at Lab02.<init>(Lab02.java:32)
    at Lab02.main(Lab02.java:5)

Line 96 is where if (userInfo[row][column]!= null) is in the full script.

When asking questions about exceptions you MUST post a complete stack trace and clearly identify the statement in your code that threw the exception. Please update your post with this information. — Jim Garrison, Feb 17 '16 at 06:54
Unable to determine unless you provide your question in the following form: http://stackoverflow.com/help/mcve — STaefi, Feb 17 '16 at 07:07
For future reference: There are probably at most a dozen or so lines relevant for the error. Try to reduce your example as much as possible and you'll probably find the error yourself. — MikeMB, Feb 17 '16 at 07:32

score 1 · Accepted Answer · answered Feb 17 '16 at 07:18

I suspect the exception is actually thrown by this line:

if (userInfo[row][0].equals(first) && userInfo[row][1].equals(last)) {

The line prior to that just tests if userInfo[row][column] is null, but (userInfo[row][0] and/or (userInfo[row][1] might be null. So, you could be calling equals() on a null value.

Understanding NullPointerException when checking for Null after removing elements in 2D array

1 Answers1