java simple JPanel management (see screenshot)

Question

I have a JPanel that encapsulates two JPanels, one on top of the other.

The first holds two JLabels which hold the playing cards.

The second holds the player's text (name and score).

However, when I remove the player's cards, the lower JPanel moves up to the top, which i would prefer that it not do. Is there a way to keep it in place regardless of whether the top JPanel is occupied or not?

Thanks

Answer 1

What layout managers are you using? The default layout manager for a JPanel is a FlowLayout which render child components one after the other.

Maybe you could set the root JPanel to have a BorderLayout. Then set the top JPanel to the root panel's "top" spot:

JPanel rootPanel = ...;
JPanel topPanel = ...;
rootPanel.add(topPanel, BorderLayout.TOP);

Then set a minimum size for your top JPanel:

topPanel.setMinimumSize(new Dimension(someWidth, someHeight));

And add the second panel to the bottom or middle spot:

rootPanel.add(secondPanel, BorderLayout.CENTER);

Check out http://java.sun.com/docs/books/tutorial/uiswing/layout/border.html

Answer 2

I had time to do an example:

public class TestJpanel extends JFrame {


    public TestJpanel() {
        this.setLayout( new BorderLayout() );

        final JLabel card1 = new JLabel( "card1" );
        final JLabel card2 = new JLabel( "card2" );

        final JPanel topPanel = new JPanel();
        topPanel.setPreferredSize( new Dimension( 1024, 100 ) );
        topPanel.add( card1 );
        topPanel.add( card2 );

        this.add( topPanel, BorderLayout.NORTH );

        JPanel centerPanel = new JPanel();
        final JButton hideCardsButton = new JButton( "Hide cards" );
        hideCardsButton.addActionListener( new ActionListener() {

            @Override
            public void actionPerformed( ActionEvent e ) {
                if ( topPanel.getComponentCount() == 0 ) {
                    topPanel.add( card1 );
                    topPanel.add( card2 );
                    hideCardsButton.setText( "Hide cards" );
                } else {
                    topPanel.removeAll();
                    hideCardsButton.setText( "Show cards" );
                }
                topPanel.validate();
                topPanel.repaint();
            }
        } );
        centerPanel.add( hideCardsButton );

        this.add( centerPanel, BorderLayout.CENTER );
    }

    public static void main( String[] args ) {
        TestJpanel window = new TestJpanel();
        window.setDefaultCloseOperation( JFrame.DISPOSE_ON_CLOSE );
        window.setSize( 1024, 768 );
        window.setVisible( true );
    }

}

Note that this code if full of bad practices but helps demonstrate what I want with a short number of lines.