Re: JPanel will not show

Wed, 27 Apr 2011 15:29:03 GMT

Knute Johnson wrote: wrote:

So you can see my program in contxt

public class MainPanel extends JPanel implements ActionListener {

    JFrame parent;
// JFrame addPrinterFrame, deletePrinterFrame, changePrinterFrame;
    JButton addButton, changeButton, delButton;
    JTextArea jtarea;
    JScrollPane scrollPane;
    JPanel buttonPanel, scrollPanePanel;

    // View
    MainPanel(JFrame parent) throws IOException {
        Toolkit kit = Toolkit.getDefaultToolkit();
        Dimension screenSize = kit.getScreenSize();
        int screenHeight = screenSize.height;
        int screenWidth = screenSize.width;
        setSize(screenWidth / 2, screenHeight / 2);
        setLocation(screenWidth / 4, screenHeight / 4);
// snipping a bunch of stuff
// Here is my action

public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();
        if (command.equals("Add Printer")) {
            JPanel addPanel = createAddPanel();
            } else if (command.equals("Change Printer")) {
        // JPanel addPanel = createChangePanel();
        } else if (command.equals("Delete Printer")) {
            //JPanel addPanel = createDeletePanel();
// more snipped stuff
// Here is the method it calls

    private JPanel createAddPanel()
        JPanel box = new JPanel();
        JButton testButton = new JButton("test");
        box.setLayout(new BoxLayout(box, BoxLayout.PAGE_AXIS));
        JPanel pane = new JPanel(new BorderLayout());
        pane.add(box, BorderLayout.NORTH);
        pane.add(testButton, BorderLayout.SOUTH);
// I see this line in my eclipse console so I know that the code is
getting here!!
        System.out.println("returning pane");
        return pane;
// snipped stuff at the end

How do I make my panel appear? Do I need to add it to the main JFrame,
or is there a way to use the JPanel and have it a distinct window that
can be moved around and resized independantly of the main window....
ideas where I can look to figure this out? Will I find the answer in
the sun java swing tutorial or is there somewhere else I should be

You make your panel appear by adding it to a top level container and
then showing the container. A top level container is a Frame/JFrame or

The biggest problem you are going to face is layout managers. Either
you use one or you don't but you can't mix and match. If you want to
lay out your container manually then set it's layout manager to null.
Then every component you add will have to have a size and a location set
or it will not show up. I guarantee you that your life will be much
better if you don't do that and use an appropriate layout manager instead.

Since all of your code is not there it is difficult to tell exactly what
you want to do. And since you didn't really tell us we just have to
guess. It looks like you want to display a different panel depending on
a button selection. Here is a simple example of how to do that.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class test extends JFrame implements ActionListener {
     JPanel panel;
     JPanel redPanel,greenPanel,bluePanel;

     public test() {

         redPanel = new JPanel();
         redPanel.setPreferredSize(new Dimension(400,300));

         greenPanel = new JPanel();
         greenPanel.setPreferredSize(new Dimension(400,300));

         bluePanel = new JPanel();
         bluePanel.setPreferredSize(new Dimension(400,300));

         panel = redPanel;

         JPanel buttonPanel = new JPanel();

         JButton red = new JButton("Red");

         JButton green = new JButton("Green");

         JButton blue = new JButton("Blue");



     public void actionPerformed(ActionEvent ae) {
         String ac = ae.getActionCommand();
         if (ac.equals("Red")) {
            panel = redPanel;
         } else if (ac.equals("Green")) {
            panel = greenPanel;
         } else if (ac.equals("Blue")) {
            panel = bluePanel;

     public static void main(String[] args) {
         Runnable r = new Runnable() {
             public void run() {
                 new test();


Knute Johnson
email s/nospam/knute/

Ok... that's what I thought. I need to add the panel to the top level
container. Thanks for your help.

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