How to make JPanel scrollable?

Question

I'm creating GUI for my university project and I 'm trying to understand how JScrollPane works.

I have successfully written simple program which shows picture in a scrollable way:

public class ScrollPaneTest{
    public static void main(String[] args){
        JFrame testFrame = new JFrame("ramka testowa");
        testFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JLabel picture = new JLabel(new ImageIcon("JavaSwingCompoentsList.PNG"));
        JScrollPane scrollPane = new JScrollPane(picture);

        testFrame.add(scrollPane, BorderLayout.CENTER);
        testFrame.setSize(400, 400);
        testFrame.setVisible(true);
    }
}

Although, in my final GUI, I would like to apply JScrollPane only to a part of it, e.g. single JPanel. To test this idea I have written following code, which unfortunately does not work:

public class ScrollPaneTest{
    public static void main(String[] args){
        JFrame testFrame = new JFrame("ramka testowa");
        testFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JLabel picture = new JLabel(new ImageIcon("JavaSwingCompoentsList.PNG"));
        JScrollPane scrollPane = new JScrollPane(picture);

        JPanel insidePanel = new JPanel();
        insidePanel.add(scrollPane);
        testFrame.add(insidePanel, BorderLayout.CENTER);

        testFrame.setSize(400, 400);
        testFrame.setVisible(true);

    }
}

I have read numerous tutorials, as well as Stack and CodeRanch articles and I still fail to grasp the idea of how the JScrollPane work. I suspect, that my mistake has something to do with specifying the dimension of JPanel-to-scroll, but every single approach I have tried gave me no scrollbars or no picture at all.

If you could show me the right solution to this problem and most importantly, show me where I was wrong I would be very grateful.

Answer 1

1. Initialize JPanel, not JScrollPane with picture

2. To add the JPanel to JScrollPane, do:

   scrollPane.setViewportView (panel)
   

3. Add the JScrollPane, not JPanel to the JFrame

Answer 2

The simplest way is to create your JPanel and specify it when creating the JScrollPane:

 JPanel myPanel = ...;
 JScrollPane scroller = new JScrollPane( myPanel );

Then just add the scroller to your GUI (instead of adding myPanel ).