JSplitPane in JFrame class

Question

Hi all,
Sorry about the newbie question. I'm trying to place a split pane into a JFrame, but I'm not entirely clear how to implement it. The code is below. Ideally, I'd have one ImageJPanel on the left-hand side, to be populated with a BufferedImage, and one on the right, to be populated with a graphical representation of some data from that image (specifically RGB and HSV histograms). However, I'm just having trouble displaying the JSplitPane, although, admittedly, I don't know much about it. Any advice is appreciated. Thanks!
Joe
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;
import java.awt.image.*;
public class ImFrame extends JFrame implements ActionListener {
    ImageJPanel imgPanel = new ImageJPanel();
    ImageJPanel leftPanel = new ImageJPanel();
    ImageJPanel rightPanel = new ImageJPanel();
    JScrollPane imageScrollPane = new JScrollPane();
    JScrollPane leftPane = new JScrollPane();
    JScrollPane rightPane = new JScrollPane();
    private JSplitPane split;
    public ImFrame(){
        super("Image Display Frame");
        setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);
        JMenu fileMenu = new JMenu("File");
        fileMenu.add(makeMenuItem("Open"));
        fileMenu.add(makeMenuItem("Save Analysis Data"));
        fileMenu.add(makeMenuItem("Quit"));
        JMenu analyzeMenu = new JMenu("Analyze");
        analyzeMenu.add(makeMenuItem("Smooth"));
        analyzeMenu.add(makeMenuItem("Display RGB and HSV"));
        analyzeMenu.add(makeMenuItem("Display Second Image for Comparison"));
        JMenuBar menuBar = new JMenuBar();
        menuBar.add(fileMenu);
        menuBar.add(analyzeMenu);
        setJMenuBar(menuBar);
        split = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT,
                                leftPanel, rightPanel);
        split.setDividerLocation(150);
        split.setSize(300, 300);
        split.setRightComponent(rightPane);
        split.setLeftComponent(leftPane);
        setContentPane(split);
        setSize(300, 300);
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.CENTER)
            .addComponent(imageScrollPane, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, 400, Short.MAX_VALUE)
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(imageScrollPane, javax.swing.GroupLayout.DEFAULT_SIZE, 296, Short.MAX_VALUE)
        imageScrollPane.setViewportView(imgPanel);
        pack();
        //setVisible(true);
    public void actionPerformed(ActionEvent e){
        String command = e.getActionCommand();
        if(command.equals("Quit")) System.exit(0);
        else if (command.equals("Open")) loadFile();
    private void loadFile(){
        JFileChooser chooser = new JFileChooser();
        int result = chooser.showOpenDialog(this);
        if (result == JFileChooser.CANCEL_OPTION) return;
        try{
            File file = chooser.getSelectedFile();
            System.out.println("Loading..." + file.getAbsolutePath());
            BufferedImage buffImage = ImageIO.read(file);
            if (buffImage != null) {
            leftPanel.setImage(buffImage);
            imageScrollPane.setViewportView(leftPanel);
            } else {
                System.out.println("Problem loading image file.");
        } catch(Exception e){
            System.out.println("File error:" + e);
    private JMenuItem makeMenuItem(String name){
        JMenuItem m = new JMenuItem(name);
        m.addActionListener(this);
        return m;
    public static void main(String[] s){
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new ImFrame().setVisible(true);
}

Answer 1

split.setDividerLocation(150); // only works once the GUI is visible
split.setSize(300, 300);Don't use setSize() it has no effect when using a layout manager
split.setRightComponent(rightPane);
split.setLeftComponent(leftPane);You are adding an ImagePanel. Presumably ImagePanel extends JPanel. I don't know what you code is like but I'm guessing that you are doing custom painting. When you do custom painting the panel does not have a preferred size (unless you specifically set it). So when you do a pack(), the preferred size of each panel is (0, 0) and therefore the preferred size of the split pane is (0, 0) plus the divideer size, so you frame is really small.
setContentPane(split);Just use getContentPane().add(split);
setSize(300, 300);Has no effect since the pack method will recalculate the preferred size as described above.
Here is a simple example:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class SplitPaneBasic extends JFrame
     JSplitPane splitPane;
     public SplitPaneBasic()
          JPanel red = new JPanel();
          red.setBackground( Color.RED );
          red.setPreferredSize( new Dimension(100, 100) );
//          red.setMinimumSize( new Dimension(0, 0) );
          JPanel blue = new JPanel();
          blue.setBackground( Color.BLUE );
          blue.setPreferredSize( new Dimension(100, 100) );
          splitPane = new JSplitPane();
          splitPane.setOneTouchExpandable(true);
          splitPane.setLeftComponent( red );
          splitPane.setRightComponent( blue );
//          splitPane.setDividerLocation(1.0);
//          splitPane.setResizeWeight(0.5);
          getContentPane().add(splitPane, BorderLayout.CENTER);
          splitPane.setDividerLocation(1.0);
     public static void main(String[] args)
          SplitPaneBasic frame = new SplitPaneBasic();
          frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
          frame.pack();
          frame.setLocationRelativeTo( null );
          frame.splitPane.setDividerLocation(0.75);
          frame.setVisible(true);
//          frame.splitPane.setDividerLocation(1.0);
}