Referencing coordinates of a JPanel in a JFrame

Question

Hi I am having trouble with referencing the origin of a JPanel within my JFrame. My JPanel was set up like so in the constructor I want to add a line that is on the left edge of my JPanel.

table = new JPanel();                    
table.setBackground(Color.green);                   
table.setBounds(10,10, 600, 600);
table.setSize(width.getValue(), height.getValue());
add(table);                                     

Then the paint method...

public void paint(Graphics g){
    super.paint(g);
    Graphics2D g2d = (Graphics2D)g;
    g2d.drawLine(table.getX(), table.getY(), table.getX(), (table.getY() + table.getHeight()));
    g2d.drawLine(100, 100, (int)Math.round(cueBall.getPositionX()), (int)Math.round(cueBall.getPositionY()));   
}

The last command in the paint method is unrelated to my problem... The code appears to be getting the origin as (10, 10) but applying it to the JFrame as a whole rather than the contentPane. I don't completely understand the contentPane but I thought that add() adds to the content pane and from then on you are referencing coordinates from the contentPane only...I just don't see why setBounds() added the JPanel where I wanted it which was (10,10) in relation to only the contentPane but when I paint() it appears to get the coordinates in relation to the contentPane but paint those coordinates in reference to the JFrame. I realize I could just add a value to move the line down but I suspect that is a poor solution.

Do I need to add a contentPane with it's own paint() method or something along those lines?

Answer 1

You should override and do your painting in JPanel.paintComponent(). Checkout Painting in AWT and Swing.

Not sure what is the reason for the use of setbounds(), are you trying to go with absolute positioning of your components? I'd recommend to get familiar with java layouts, here is a good start - A Visual Guide to Layout Managers.