hvad er der galt her!

JEg kan ikke lige få det her til at gå op, der kommer ikke andet frem end en tom JFrame.


import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.*;
import javax.swing.*;
import java.awt.*;


public class JCalendarPanel extends JFrame
    implements ActionListener
{
   
    private static final int BUTTON_COUNT = 42;
    private static final int LABEL_COUNT = 7;
    private JButton days[];
    private JLabel dayOfWeekLabel[];
    private JButton selectedButton;
    private JComboBox monthChoice;
    private JLabel yearLabel;
    private int selectedMonth;
    private int selectedYear;
    private int selectedDay;
    private int cellHeight;
    private int cellWidth;
    private int sundayColumnIndex;
    private JPanel headerPanel;
    private JPanel calendarGridPanel;
    private JButton nextYearButton;
    private JButton prevYearButton;
    private JButton nextMonthButton;
    private JButton prevMonthButton;
    private static final int numDays[] = {
        31, 28, 31, 30, 31, 30, 31, 31, 30, 31,
        30, 31};
    private Vector months;
    private Date selectedDate;
    private PropertyChangeSupport changes;
   

    public JCalendarPanel()
    {
        super("dav Gamli");
        setSize(500,500);
        setVisible(true);
       
       
        days = new JButton[42];             //knap array
        dayOfWeekLabel = new JLabel[7];     //Label array
        selectedButton = null;
        sundayColumnIndex = 0;
        months = new Vector(12);             //månedsvektor 12 måneder som udgangspunkt
       
        selectedDate = new Date();
             
        setFont(new Font("Dialog", 0, 12));
        FontMetrics fontmetrics = getFontMetrics(getFont());
        cellHeight = fontmetrics.getHeight() + 10;
        cellWidth = fontmetrics.stringWidth("WWW") + 10;
        setLayout(new BorderLayout());
       
        headerPanel = new JPanel();         //lav JPanel, bestem layout og tilføj nord
        headerPanel.setLayout(new FlowLayout());
        //headerPanel.Opaque(Color.BLUE);
     
       
        calendarGridPanel = new JPanel();     //lav JPanel, bestem layout og tilføj center
        calendarGridPanel.setLayout(new GridLayout(7, 7));
       
       
        Insets insets = new Insets(1, 1, 1, 1);
        yearLabel = new JLabel("");
       
        //knapper får billede, placering margen og actionlistener
        nextMonthButton = new JButton("ja tryk");
        nextMonthButton.setAlignmentY(0.5F);
        nextMonthButton.setMargin(insets);
        nextMonthButton.addActionListener(this);
       
        prevMonthButton = new JButton("ja tryk her");
        prevMonthButton.setAlignmentY(0.5F);
        prevMonthButton.setMargin(insets);
        prevMonthButton.addActionListener(this);
       
        nextYearButton = new JButton("tryk nu");
        nextYearButton.setAlignmentY(0.5F);
        nextYearButton.setMargin(insets);
        nextYearButton.addActionListener(this);
       
        prevYearButton = new JButton("halloo");
        prevYearButton.setAlignmentY(0.5F);
        prevYearButton.setMargin(insets);
        prevYearButton.addActionListener(this);
       
        buildMonths();                                 //kalder metoden buildmonths
       
        monthChoice = new JComboBox(months);         //laver en combobox
        monthChoice.addActionListener(this);
       
        headerPanel.add(prevYearButton);            //tilføjer knapper og combobox
        headerPanel.add(prevMonthButton);
        headerPanel.add(monthChoice);
        headerPanel.add(yearLabel);
        headerPanel.add(nextMonthButton);
        headerPanel.add(nextYearButton);
       
        Container contentPane = super.getContentPane();
       
        contentPane.add(headerPanel, "North");
        contentPane.add(calendarGridPanel, "Center");
       
        buildDays();
        buildCells();
        Date date = new Date();
        setSelectedDate(date);
        updateDisplay();
       
    }//construkteren

(det hele er ikke med her)