Need help reading a file ~!

Question

Hi,
I cant seem to read this file. It compiles without errors, but i get a java.nullPointerException when i run it. My data file looks like this:
5
class1
class2
class3
class4
class5
1-2 1-3 2-4 3-4 4-5
here is my code to read the file:         public void Read(String fileName) {
                try {
                        String num; //number of cells
                        String cells; //cell data
                        FileReader file = new FileReader(fileName);
                        BufferedReader in = new BufferedReader (file);
                        num = in.readLine();
                        number = Integer.valueOf(num).intValue(); //converts string to int
                        co = new ClassObject[number];
                        System.out.println("There are " + number + " total classes");
//## PROBLEM OCCURS IN THIS FOR LOOP which reads in the 5 names of classes
                        for (int b=0; b<number; b++){
                               co.className = in.readLine();
} //#### end of problem
while ((cells = in.readLine()) != null) {
StringTokenizer st1 = new StringTokenizer(cells, " ");
while (st1.hasMoreTokens()) {
String ST1 = st1.nextToken();
StringTokenizer st2 = new StringTokenizer(ST1, "-");
String ST2 = st2.nextToken();
co[x] = new ClassObject();
co[x].classNumber = Integer.valueOf(ST2).intValue();
ST2 = st2.nextToken();
co[x].classRelation = Integer.valueOf(ST2).intValue();
x++;
} catch (IOException e) {
System.out.println("Warning: Cannot Read File");
System.exit(0);
setPositions();
thanks for any help!

Answer 1

Sorry, I didn't notice your comment in the code.
for (int b=0; b<number; b++){
  co[ b]= new ClassObject();
  co[ b].className = in.readLine();
}