JComponent problem

I am trying to create a custom calendar in Java. For this I am expanding javax.swing.JComponent

.

public class GMCalendar extends JComponent { ... }

      

        
        
        
      

    

In my constructor, I do basic setup and load an image:

calendarDay = Toolkit.getDefaultToolkit().createImage(getClass().getResource("/resources/images/calendar_day.png"));

      

        
        
        
      

    

And in paintComponent

he has to draw my calendar, but he will not draw anything that looks very strange.

public void paintComponent(Graphics g) {
    super.paintComponent(g);

    Calendar calendar = Calendar.getInstance();
    calendar.add(Calendar.MONTH, currentMonth);
    int numberOfWeeks = calendar.getActualMaximum(Calendar.WEEK_OF_MONTH);

    for (int i = 0; i < 7; i++) {
        for (int j = 0; j < numberOfWeeks; j++) {
            int x = i * (DAY_SIZE + DAY_SPACE);
            int y = j * (DAY_SIZE + DAY_SPACE);
            g.drawImage(calendarDay, x, y, null);
        }
    }
}

      

        
        
        
      

    

The result is nothing or something like this:

It seems to paintComponent

get called before the component size is greater than 1x1.

This is in my main()

:

GMContainerFrame cf = new GMContainerFrame();
cf.setMinimumSize(new Dimension(800,600));
cf.setVisible(true);

      

        
        
        
      

    

This is from the constructor GMContainerFrame

(which it doesn't use LayoutManager

!):

calendarFrame = new GMMiniFrame("Kalender", new GMCalendar(), 230);

      

        
        
        
      

    

GMMiniFrame

extends JSplitPane

.