Help sorting an array of objects needed please.

Question

I am trying to sort the array Students[] in descending order of Fees due. Using the code below I get a null pointer error at runtime. The array is not completely full, it has 20 cells, but the variable studentArrayCounter holds the number of used cells. The 'getFeesDue()' code returns an integer value.
Any help is appreciated.
     // Sort Student Records Method
           public void sortStudentRecords()
            int loopCount = 0;
           for (loopCount = 1; loopCount < studentArrayCounter; loopCount ++)
          if(Students[loopCount].getFeesDue()>Students[loopCount-1].getFeesDue())
               SortStudents[0]=Students[loopCount-1];
               Students[loopCount-1]=Students[loopCount];
               Students[loopCount]=SortStudents[0];
     }

Answer 1

Also, unless the excersize is to write a sort algorigthm (which I kinda doubt) you should use Arrays.sort
Arrays.sort(Students, new Comparator() {
  public int compare(Object o1, Object o2) {
    Student s1 = (Student) o1;
    Student s2 = (Student) o2;
    return s1.getFeesDue() - s2.getFeesDue();
});