private void setUpValueSelection(Instances format) {
    if (format.classIndex() < 0 || format.classAttribute().isNumeric()) {
      // cant do anything in this case
      return;
    }
    if (m_displayValNames == false) {
      remove(m_messageLabel);
    }
    
    int existingClassVal = m_classValuePicker.getClassValueIndex();
    String [] attribValNames = new String [format.classAttribute().numValues()];
    for (int i = 0; i < attribValNames.length; i++) {
      attribValNames[i] = format.classAttribute().value(i);
    }
    m_ClassValueCombo.setModel(new DefaultComboBoxModel(attribValNames));
    if (attribValNames.length > 0) {
      if (existingClassVal < attribValNames.length) {
	m_ClassValueCombo.setSelectedIndex(existingClassVal);
      }
    }
    if (m_displayValNames == false) {
      add(m_holderP, BorderLayout.CENTER);
      m_displayValNames = true;
    }
    validate(); repaint();
  }