How many JComboBox in my panel?

Question

Hi,
I'm writing a simple JPanel which contains three JComboBox, one for the day, one for the month and one for the year. It works fine and the constructor is the following:
public class DatePanel extends JPanel implements ItemListener{
     * The combobox for the day.
    protected JComboBox comboDay = null;
     * The combobox for the month.
    protected JComboBox comboMonth = null;
     * The year.
    protected JComboBox comboYear = null;
     * A flag that indicates if the user has manually changed the date.
    protected boolean dateHasChanged = false;
     * Creates and set up each component of this panel.
    protected void setUpGUI(){
     // get the current date
     Calendar today = Calendar.getInstance();
     // create the components
     this.comboDay = new JComboBox();
     for(int i=1; i<=31; i++)
         this.comboDay.addItem(i);
     this.comboMonth = new JComboBox();
     for(int i=1; i<=12; i++)
         this.comboMonth.addItem(i);
     this.comboYear = new JComboBox();
     int currentYear = today.get(Calendar.YEAR);
     for( int i= (currentYear - 60); i< (currentYear + 5); i++)
         this.comboYear.addItem(i);
     // add the null values
     this.comboDay.addItem("--");
     this.comboMonth.addItem("--");
     this.comboYear.addItem("--");
     this.comboDay.setSelectedItem("--");
     this.comboMonth.setSelectedItem("--");
     this.comboYear.setSelectedItem("--");
     // add the listener
     this.comboDay.addItemListener(this);
     this.comboMonth.addItemListener(this);
     this.comboYear.addItemListener(this);
     // display components
     this.setLayout( new FlowLayout() );
     this.add(this.comboDay);
     this.add(this.comboMonth);
     this.add(this.comboYear);
     * Builds a panel without initializing it with a specific date.
    public DatePanel(){
     super();
     this.setUpGUI();
    }then I've got a subclass of the above panel which adds two comboes, one for the hour and one for minute. This is also working fine, and I've got a flag that says if the above three comboes should appear or not in the panel:
public class TimePanel extends DatePanel {
     * The comboHour selection combo box.
    protected JComboBox comboHour = null;
     * The comboMinute selection combo box.
    protected JComboBox comboMinute = null;
     * Builds the time panel with the specific comboboxes.
     * @param alsoDates true if also the dates should be visibles
    public TimePanel(boolean alsoDates){
     super();
     this.setUpGUI();
     // shuld the dates be available?
     if( ! alsoDates ){
         this.comboDay.setEnabled(false);
         this.comboMonth.setEnabled(false);
         this.comboYear.setEnabled(false);
         this.remove(this.comboDay);
         this.remove(this.comboMonth);
         this.remove(this.comboYear);
     * Sets up the components.
    @Override
    protected void setUpGUI() {
     super.setUpGUI();
     // add the time components
     this.comboHour = new JComboBox();
     for( int i=0; i<24; i++ )
         this.comboHour.addItem(i);
     this.comboHour.addItemListener(this);
     this.comboMinute = new JComboBox();
     for(int i=0; i<60; i++)
         this.comboMinute.addItem(i);
     this.comboMinute.addItemListener(this);
     this.add(new JLabel("hh:"));
     this.add(this.comboHour);
     this.add(new JLabel("mm:"));
     this.add(this.comboMinute);
    }As you can see, when I pass false to the constructor of the TimePanel, the comboes of the date panel are removed from the layout of the panel itself, thus showing only the hour and minute ones.
Now I was writing a JUnit test for this, and surprisingly when I run a code like the following:
     TimePanel tp1 = timePanel = new TimePanel(false);
     Component[] components = tp1.getComponents();
     int comboCount = 0;
     // count how many jcombobox there are, since it has been initialized
     // with the time only, it should contain only 2 combobox (hour and minutes)
     for(int i=0;i<components.length; i++ )
         if( components[i] instanceof JComboBox )
          comboCount ++;I found that the number of comboes on my panel are 7[, that is more than the max (5) when all the components are displayed. What is wrong here?
Thanks,
Luca

Answer 1

I found that the problem seems to be in the setUpGui method, that is called from the parent constructor and from the child constructor, thus displaying 7 comboes. But if I remove the call from the child constructor then it seems as the parent comboes are uninitialized and thus I got a nullpointer exception.
If I modify the constructor of the TimePanel into this:
   public TimePanel(boolean alsoDates){
     this.setUpGUI();
     // shuld the dates be available?
     if( ! alsoDates ){
         this.comboDay.setEnabled(false);
         this.comboMonth.setEnabled(false);
         this.comboYear.setEnabled(false);
         this.remove(this.comboDay);
         this.remove(this.comboMonth);
         this.remove(this.comboYear);
    }and explicity call the super.setupgui into the setupgui method
  protected void setUpGUI() {
     super.setUpGUI();
     // add the time components
     this.comboHour = new JComboBox();
     for( int i=0; i<24; i++ )
         this.comboHour.addItem(i);
     this.comboHour.addItemListener(this);
     this.comboMinute = new JComboBox();
     for(int i=0; i<60; i++)
         this.comboMinute.addItem(i);
     this.comboMinute.addItemListener(this);
     this.add(new JLabel("hh:"));
     this.add(this.comboHour);
     this.add(new JLabel("mm:"));
     this.add(this.comboMinute);
    }I got that the hour and minute comboes are added twice, and moreover the day,month and year are not removed. What is the right way to call the setupgui method to do what I'd like?
Luca