Sorting array with non initialised elements

Question

I have code which sorts my first array of names alphabetically and then sorts the corresponding marks array so they correct student has the correct marks. The problem I have is a nullPointerException error. From what I understand this error is due to some of the array elements not being initialised, is there any way that I can still sort the array if some of the indices have not been initialised?

  static String[] studentNamesArray = new String[10];
  static int[][] studentMarksArray = new int[10][3];

  static void sortAlphabetical() { 
    String nameSwap;
    int [] markSwap;
    boolean flag = false;
    while (!flag) {
      flag = true;
      for (int i = 0;i < 9;i++) {
        if (studentNamesArray[i].compareTo(studentNamesArray[i + 1]) > 0) {
          nameSwap = studentNamesArray[i];
          studentNamesArray[i] = studentNamesArray[i + 1];
          studentNamesArray[i + 1] = nameSwap;
          markSwap = studentMarksArray[i];
          studentMarksArray[i] = studentMarksArray[i + 1];
          studentMarksArray[i + 1]= markSwap;
          flag = false;
        }
      }
    }
  }

Answer 1

Yes. Instead of

if (studentNamesArray[i].compareTo(studentNamesArray[i + 1]) > 0) {

Try using a ternary, or you could use an if else - this is a ternary.

int compare = (studentNamesArray[i] == null) ? -1 :  
               studentNamesArray[i].compareTo(studentNamesArray[i + 1]);
if (compare > 0) {

The ternary is equivalent to

int compare;
if (studentNamesArray[i] == null) { 
  compare = 1;
} else { 
  compare = studentNamesArray[i].compareTo(studentNamesArray[i + 1]);
}

A more complex if else is left as an exercise to the reader(s).

Answer 2

To get it working I made a global variable to keep check of how many elements have been entered in the array and then modified my code as below:

  static void sortAlphabetical() {
    String nameSwap;
    int [] markSwap;
    boolean flag = false;
    while (!flag) {
      flag = true;
      for (int i = 0;i < nameArrayCount-1;i++) {
        if (studentNamesArray[i].compareTo(studentNamesArray[i + 1]) > 0) {
          nameSwap = studentNamesArray[i];
          studentNamesArray[i] = studentNamesArray[i + 1];
          studentNamesArray[i + 1] = nameSwap;
          markSwap = studentMarksArray[i];
          studentMarksArray[i] = studentMarksArray[i + 1];
          studentMarksArray[i + 1]= markSwap;
          flag = false;
        }
      }
    }
  }