Thread: Why do my changes not show up?

Hey everyone!

I have some problem i don't really understand the source.

Unfortunately i don't have a runnable example because this is part of a more complex structure but maybe it is self-explaining.
My problem is: i want a red area to appear when i click the button start, which doesn't work. And i don't really understand why it doesn't work, because i know (i tested it with a simple system output) that my testroutine is invoked by clicking my start-menuitem. When i add the same three lines (as in the method) in my constructor i get the visual result i want, so i figured that those 3 lines are not the problem. i tried a repaint in my testroutine which didn't work either.

i'm thankful for help

this is my code for this class:

    public class RTwindow extends MenuWindow {
	public RTwindow(){
		this.setExtendedState(MAXIMIZED_BOTH);
		JMenu mainmenu = new JMenu();
		JMenuItem start = new JMenuItem();
		this.addmenu(mainmenu,"Mainmenu");     
		this.addmenuitem(mainmenu, start, "Start");
//addmenu and addmenuitem are methods of my class MenuWindow
		start.addActionListener(new ActionListener(){
			public void actionPerformed(ActionEvent AE){
				testroutine();
			}
		});		
	}
 
	public void testroutine(){
		JPanel mainpanel = new JPanel();
		mainpanel.setBackground(Color.red);
		add(mainpanel);
	}
}

It's easy enough to create a short, runnable example to demonstrate a problem you're having with code. Saying it's too complex is just laziness. Here's 1) an example of how to do that, and 2) a demonstration of what I suspect is the source of your problem. Note the comment in the method buildJPanel(). If not, come back with a small, runnable example that demonstrates what you're seeing.

import java.awt.Color;
import java.awt.Dimension;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
 
// a simple class to demonstrate the effect of opacity on background color
public class TestClass
{
	public TestClass()
	{
		JFrame mainFrame = new JFrame( "Test Frame" );
		mainFrame.add( buildJPanel() );
		mainFrame.setLocationRelativeTo( null );
		mainFrame.pack();
		mainFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
		mainFrame.setVisible( true );
	}
 
	public JPanel buildJPanel()
	{
		JPanel mainPanel = new JPanel();
 
		// change the 'false' in the next line to 'true' to see what happens
		mainPanel.setOpaque( false );
		mainPanel.setBackground(Color.red);
		mainPanel.setPreferredSize( new Dimension( 100, 100 ) );
		return mainPanel;
	}
 
	// to launch TestClass on the EDT
	public static void main( String[] args )
	{
		SwingUtilities.invokeLater( new Runnable()
		{
			public void run()
			{
				new TestClass();
			}
		});
	}
}