Another question about custom JComponents and JPanels

Question

Okay, so new issue now. I will be researching this as best I can while I wait for a reply.
So I made a custom Component, and added it to a custom Panel. The Panel only contains this Component.
If in the JFrame I create a JScrollPane and add the custom panel to it, then the scrollbar works exactly right. But, if I add the custom panel to another panel, it doesn't work. It just puts a one pixel border around the panel and centers it. I'm gonna go and read all about ScrollPanes and what it uses as a basis.
Any help will be greatly appreciated.

Answer 1

import java.awt.*;
import javax.swing.*;
public class WDF extends JFrame
    WDF()
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(500, 300);
        WaveFormPanel test = new WaveFormPanel(500, 100);
        add(test);
        setLocationRelativeTo(null);
        setVisible(true);
    public static void main(String[] args) {
        new WDF();
class WaveFormPanel extends JPanel
    LineComponent myLine;
    public WaveFormPanel(int width, int height)
        // to ... have the scrollpane constrained
        // to be a certain size, i.e., 400 by 100
        // no matter how large the LineComponent is.
        // You can use GridBagLayout to have scrollPane
        // shown centered and at its preferredSize.
        // The default FlowLayout will also show the
        // scrollPane at its preferredSize.
        setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        myLine = new LineComponent(width, height);
        JScrollPane sPane = new JScrollPane(myLine);
        sPane.setPreferredSize(new Dimension(400, 100));
        add(sPane, gbc);
class LineComponent extends JComponent
    int lineWidth;
    int lineHeight;
    public LineComponent(int width, int height)
        lineWidth = width;
        lineHeight = height;
        this.setPreferredSize(new Dimension(width, height));  
    @Override
    protected void paintComponent(Graphics g)
        super.paintComponent(g);
        g.drawLine(0, 0, lineWidth, lineHeight);
}