Thread: How to add scrollbar to a JPanel with Graphics

I have a JInternalFrame. Inside this frame I have a JPanel which is a drawing panel.
It implements the paint() method and draws something within the panel.
I want to add a scrollbar for this JPanel so that I can scroll down and see different parts of what I draw. I use the following code within a method in JInternalFrame:


jp = new DrawingPanel(); // DrawingPanel is a subclass of JPanel which implements paint();
JScrollPane scroller = new JScrollPane(jp);
scroller.setVerticalScrollBarPolicy(ScrollPaneCons tants.VERTICAL_SCROLLBAR_ALWAYS);
add(scroller);
add(jp);

The program can compile. and I can see the graphics inside the DrawingPanel.
But the problem is that the scrollbar doesn't even appear.
How can I fix this problem with the least modification to the whole structure of the program?