How to make a JPanel with a GridLayout scroll

Question

I am using a JPanel to hold around 100 buttons. The JPanel is using GridLayout to organise these buttons in rows of 3 buttons per row. i.e. buttonPanel.setLayout(new GridLayout(33,3)); As there are so many buttons they obviously don't all fit in the viewable area of the screen. To get around this I am trying to use a JScrollPane on the buttonPanel to make it scroll but I can't get it to work. I have tried both creating a seperate JScrollPane object and adding the buttonPanel to it
JScrollPane buttonScroll = new JScrollPane();
buttonPanel.setLayout(new GridLayout(33,3));
buttonPanel.setPreferredSize(new Dimension(380,400));
buttonPanel.setMaximumSize(new Dimension(380,400));
buttonScroll.add(buttonPanel);and also embeding everything into a new JPanel like:
buttonHolder.add(new JScrollPane(buttonPanel),BorderLayout.CENTER);Neither way works. Any ideas. I've read about view port but not exactly sure what this is or if this will fix my problem.
Help urgently required.

Answer 1

Fixed layouts have their perils.
We need to figure the size for the buttonScroll. Here's one way to approach this:
    topPanel
        messagePanel 400 x 400    buttonScroll unknown size
    inputPanel
        previewPane  600 x  80    sendButton   icon size (55 x 68, duke)
    For a fixed layout, find the size required for the buttonScroll by commenting out the
    two lines that add the buttons to buttonPanel and calling pack on the frame:
    frame size (pack w/no buttons)     743 x 570
    topPanel size                      735 x 400
    therefore, required size for
        buttonScroll is                335 x 400     (735 - 400, 400)
After adding the buttons back in the final sizes become
C:\jexp>java GUI
frame width = 763       height = 570
topPanel width = 755    height = 400I substituted a Duke image for your sendIcon so the sizes may differ but this should get you started...
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.Container.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.text.*;
public class GUI extends JFrame
    Icon sendIcon = new ImageIcon(getClass().getResource("images/T4.gif"));
    Icon deleteIcon = new ImageIcon(getClass().getResource("images/T6.gif"));
    JButton sendButton = new JButton("Send",sendIcon);
    JButton deleteButton = new JButton("Delete",deleteIcon);
    JLabel statusBar = new JLabel();
    JMenu optionsMenu = new JMenu("Options");
    JMenu helpMenu = new JMenu("Help");
    JMenuBar menuBar = new JMenuBar();
    JMenuItem connectMenuItem = new JMenuItem("Connect");
    JMenuItem disconnectMenuItem = new JMenuItem("Disconnect");
    JMenuItem exitMenuItem = new JMenuItem("Exit");
    JMenuItem helpMenuItem = new JMenuItem("Online Help");
    JMenuItem aboutMenuItem = new JMenuItem("About");
    JPanel buttonPanel = new JPanel();
    JPanel inputPanel = new JPanel();
    JPanel messagePanel = new JPanel();
    JPanel topPanel = new JPanel();
    JPanel buttonHolder = new JPanel();
    JScrollPane buttonScroll = new JScrollPane(buttonPanel,20,30);
    JTextPane messageArea = new JTextPane();
    JTextPane previewPane = new JTextPane();
    public GUI()
        super("Chat Program");
        String userName = "user";
        statusBar.setText("Connected: " + userName);
        menuBar.add(optionsMenu);
        menuBar.add(helpMenu);
        setJMenuBar(menuBar);
        optionsMenu.add(connectMenuItem);
        optionsMenu.add(disconnectMenuItem);
        optionsMenu.add(exitMenuItem);
        helpMenu.add(helpMenuItem);
        helpMenu.add(aboutMenuItem);
        buttonPanel.setLayout(new GridLayout(0,3));
        for(int i = 0; i < 100; i++)
            buttonPanel.add(new JButton("Button " + (i + 1)));
        messageArea.setEditable(false);
        previewPane.setEditable(false);
        previewPane.setPreferredSize(new Dimension(600,80));
        previewPane.setMaximumSize(new Dimension(600,80));
        messagePanel.setLayout(new BorderLayout(10,10));
        messagePanel.add(new JScrollPane(messageArea),BorderLayout.CENTER);
        messagePanel.setPreferredSize(new Dimension(400,400));
        messagePanel.setMaximumSize(new Dimension(400,400));
        // w = 735 - 400, h = 400
        // does not take into account the width of the vertical scrollBar
        buttonScroll.setPreferredSize(new Dimension(335,400));       // *
        Box box = new Box(BoxLayout.X_AXIS);
        box.add(new JScrollPane(previewPane));
        box.add(sendButton);
        inputPanel.add(box,BorderLayout.CENTER);
        statusBar.setBorder(new BevelBorder(BevelBorder.LOWERED));
        topPanel.setLayout(new BorderLayout(10,10));
        topPanel.add(messagePanel, BorderLayout.WEST);
        topPanel.add(buttonScroll, BorderLayout.EAST);
        Container content = getContentPane();
        content.add(topPanel,   BorderLayout.NORTH);
        content.add(inputPanel, BorderLayout.CENTER);
        content.add(statusBar,  BorderLayout.SOUTH);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();
//        setSize(?,?);       // 763, 570 (now we know)
        setLocation(200,200);
        setVisible(true);
        // collect size information
        System.out.println("frame width = " + getWidth() + "\t" +
                           "height = " + getHeight() + "\n" +
                           "topPanel width = " + topPanel.getWidth() + "\t" +
                           "height = " + topPanel.getHeight());
    public static void main(String[] args)
        new GUI();
}