JScrollPane with JPanel inside doesn't show scroll bar when picture is bigger

Question

I'm making an utility to define footholds in a map for my game and i am displaying the preview of the map inside a JPanel that's inside a JScrollPane. I would like to be able to scroll when the map is bigger than the JScrollPane. How should i do that?

Here's a picture

Bigger version

The image of the map fits inside of the scrollpane but the image is actually larger so we don't get to see the whole map.

Some code:

The JPanel class which holds the image inside of the scrollPane

public class MapDisplay extends JPanel {

public MapDisplay() {
}

@Override
protected void paintComponent(Graphics g) {
    super.paintComponents(g);
    Graphics2D g2d = (Graphics2D) g;
    g2d.setColor(new Color(0xDFDFDF));
    g2d.fillRect(0, 0, 2000, 2000);
    if (mapinfo != null) {
    if (mapinfo.img != null) {
        g2d.drawImage(mapinfo.img, 0, 0, null);
    }
    }
    repaint();
}
}

the scrollPane's declaration

final JScrollPane scrollPane_1 = new JScrollPane(mapDisplay);

scrollPane_1.setBounds(10, 11, 989, 553);
getContentPane().add(scrollPane_1);
add(scrollPane_1);

Answer 1

The MapDisplay has to 'tell' the JScrollPane how big it wants to be. You can do so by implementing the getPreferredSize method of MapDisplay.

public Dimension getPreferredSize() {
    return new Dimension(widthOfMap, heightOfMap);
}

Further, do not call repaint() from inside the paintComponent() method, as this results in an infinite loop.