java swing - layout oddness when using different layout managers

Question

Bit of oddness, seen if I do the following:

import javax.swing.*;
public class FunkyButtonLayout {
    public static void main(String[] args) {
        JFrame frame = new JFrame("");
        JPanel j0 = new JPanel();     // j0 gets added to the root pane
        j0.setLayout(null);
        JPanel j1 = new JPanel();     // j1 gets added to j0 
        j1.setLayout(null);
        JButton b1 = new JButton(""); // b1 gets added to j1
        j1.add(b1);
        b1.setBounds(0, 0, 40, 32);   // b1 is big
        j0.add(j1);
        j1.setBounds(0, 0, 32, 32);   // j1 is not so big - b1 gets 'trimmed'
        frame.getContentPane().setLayout(null); // <- seems to be needed :-(
        frame.getContentPane().add(j0);             
        j0.setBounds(10, 10, 32, 32); // end result: a 32x32 button with
        frame.setSize(125, 125);      // a trimmed right border
        frame.setVisible(true);       // in the top-left corner
    }
}

I get pretty much what I'm looking for, apart from the ability to position j0 in the root pane with a layout manager. If I change the

        frame.getContentPane().setLayout(null);

line to

        frame.getContentPane().setLayout(new java.awt.FlowLayout());

I see j0 draw as a 1x1 pixel @ the middle of the screen :-(

Any ideas why? Note that this isn't just a FlowLayout thing - pretty much every layout manager messes this up.

I really want to have the net effect of the 'border trimmed on one side' button - it allows me to do the toolbar-button-cluster thing (the kind of thing that cage fighter tries to get rid of) with native-looking button controls - I cannot see another way of doing this, thanks to OS-level skins. So any ideas appreciated :-)

Answer 1

If you set the layout manager to null, you have to explicitly set the container's preferred size (that's why it's showing up so small).

If you are using setBounds on a component, you are over-riding the work that the layout manager for the parent container does.

I would remove all calls to setBounds and all calls to setLayout(null) and try to achieve the effect you are after using just layout managers.

Answer 2

For a really good explanation of how layout managers work, check out an old article I wrote at Sun

http://developer.java.sun.com/developer/onlineTraining/GUI/AWTLayoutMgr/

It's old, but talks about preferredSize and layout nesting pretty well.

Enjoy, -- Scott