How to draw a white rectangle at the bottom of a JComponent?

Question

In my code i have:

A Gui with a JScrolledPane containing a Box which contains some JPanel (they could be refactor as JComponent if needed).

See Image 1 :

I am trying to:

Find the best way to add a white space between them.

I tried with the Box.createVerticalStruct, but it complicates the managment. I don't want to add a new white panel to my object representing the coloredPanel too, so i googled it and it seems to me that there are other 2 ways: using inset or overriding the paint method.

What do you think is the best way in my case? in case you'd suggest to use the paintComponent method, how do i retrieve the bottom corner position to draw a white rectangle of a certain height?

The final results should be something like this:

Here is some code you can use to make some try (which has been written on purpose, so don't take too much care on good writing techniques):

public class TheMotherPuckerGlue2 {

    public static void main(String [] a) {
        final JFrame frame = new JFrame();
        frame.setSize(500, 500);
        frame.setTitle("myCode");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());

        JScrollPane myPane = new JScrollPane();
        myPane.setPreferredSize(new Dimension(350,200));
        myPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

        JPanel viewPort = new JPanel(new BorderLayout());
        viewPort.setBackground(Color.WHITE);

        Box myBox = Box.createVerticalBox(); 
        myBox.setBorder(BorderFactory.createEmptyBorder(3, 3, 3, 3));

        viewPort.add(myBox,BorderLayout.PAGE_START);

        class ColoredPanel extends JPanel{
            public ColoredPanel(Color aColor){
                super.setBackground(aColor);
                super.setPreferredSize(new Dimension(100,60));
            }

        }

        ColoredPanel panel1 = new ColoredPanel(Color.green);
        ColoredPanel panel2 = new ColoredPanel(Color.yellow);
        ColoredPanel panel3 = new ColoredPanel(Color.red);

        myBox.add(panel1);
        myBox.add(panel2);
        myBox.add(panel3);

        viewPort.add(myBox,BorderLayout.PAGE_START);


        myPane.setViewportView(viewPort);

        frame.add(myPane);

        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                frame.setVisible(true);
            }
        });
   }

}

Thanks

Answer 1

I found a great way to do that by rewriting the paintComponent that way:

public void paintComponent(Graphics g){
    super.paintComponent(g);
    drawWhiteSpace(g);
    drawBorder(g);
}

drawWhiteSpace method will draw a white rectangle which start at the bottom-left corner -6 pixel, and go to the bottom rightcorner

private void drawWhiteSpace(Graphics g) {
    int x1 = 0;
    int y1 = this.getSize().height-6;
    int x2 = this.getSize().width;
    int y2 = this.getSize().height;
    g.setColor(Color.WHITE);
    g.fillRect(x1, y1, x2, y2);     
}   

however the border was not fine, so i had to remove it and to draw it myself by drawing it from the top-left corner to the top-right corner of the white space

private void drawBorder(Graphics g) {
    int x1 = 0;
    int y1 = 0;
    int x2 = this.getSize().width-1;
    int y2 = this.getSize().height-6;
    g.setColor(Color.GRAY);
    g.drawRect(x1, y1, x2, y2); 
}