Help with nullPointer exception

Question

Hi,
I would like some help identifying and error in the code below. Im getting a nullPointer exception at the location specified in the code. Im adding elements to a tableModel. What puzzles me is that the strings I add to the model does contain values. And it does not complain about adding them. Perhaps this is just a simple error, and you more experinced programmars are probably loughing at me ;)
void getTests() {
      String[] idNummer = getDirectory(); //gets filenames from a directory
      for (int i = 0; i < idNummer.length; i++) {
         idNummer[i] = idNummer.substring(idNummer[i].lastIndexOf(dataSeparetor) + 1, idNummer[i].length());
// just sorts out specific parts of the filenames
for (int i = 0; i < idNummer.length; i ++) {
System.out.println(idNummer[i]); //I print the sorted filenames and they not null
testModel.addElement(idNummer[i]); //I add them to the table model
testNr.setModel(testModel); //and gets a nullPoint exception here??

Answer 1

I'm sorry, you mean testNr. Don't pay any attention to the above post. it is also declared directly in the class:
public class GUI extends JFrame implements EventListener  {
  JList testModel;
}and creates an instance here:
public GUI {
testModel = new DefaultListModel();
getTests();
testNr = new JList(testModel);
      testNr.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
      testNr.setLayoutOrientation(JList.VERTICAL);
      testNr.setPreferredSize(new Dimension(80, 80));
      testNr.addListSelectionListener(new ListSelectionListener() {
         public void valueChanged(ListSelectionEvent event) {
      leftPanel.add(testNr, BorderLayout.EAST);
}