JTextArea with freeze pane functionality

Question

Greetings. I am trying to implement a plain text viewer that has some sort of "freeze pane" functionality (like that found in MS Excel)
I took the approach of using 4 JTextArea and put them into a JScrollPane, its row header, column header and upper-left corner. All these text areas share the same document.
Everything works as expected. When I scroll the lower-right pane, the row and column headers scroll correspondingly. The problem I have is that the document in the lower-right pane now shows duplicate portion of the document that is already showing in the row and column headers.
Knowing that this should merely be a matter of shifting the Viewport on the document, I went through the documentation and java source, and just couldn't find a way to translate the view. SetViewPosition() works to a certain extent, but the scrollbars allow users to scroll back to the origin and reveal the duplicate data, which is undesirable.
Your help with find out a way to relocate the view to the desired location is much appreciated.
khsu

Answer 1

some sample code attached (with a quick hack in attempt to making it work, at least presentation-wise)
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
import javax.swing.plaf.*;
import javax.swing.plaf.basic.*;
import javax.swing.text.*;
public class SplitViewFrame extends JFrame {
    int splitX = 100;
    int splitY = 100;
    public static void main(String[] args) {
        // Create application frame.
        SplitViewFrame frame = new SplitViewFrame();
        // Show frame
        frame.setVisible(true);
     * The constructor.
     public SplitViewFrame() {
        JMenuBar menuBar = new JMenuBar();
        JMenu menuFile = new JMenu();
        JMenuItem menuFileExit = new JMenuItem();
        menuFile.setLabel("File");
        menuFileExit.setLabel("Exit");
        // Add action listener.for the menu button
        menuFileExit.addActionListener
            new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    SplitViewFrame.this.windowClosed();
        menuFile.add(menuFileExit);
        menuBar.add(menuFile);
        setTitle("SplitView");
        setJMenuBar(menuBar);
        setSize(new Dimension(640, 480));
        // Add window listener.
        this.addWindowListener
            new WindowAdapter() {
                public void windowClosing(WindowEvent e) {
                    SplitViewFrame.this.windowClosed();
        makeFreezePane();
    void makeFreezePane() {
        Container cp = getContentPane();
        Font font = new Font("monospaced", Font.PLAIN, 14);
        OffsetTextArea ta = new OffsetTextArea();
        ta.setSplit(splitX, splitY);
        ta.setOpaque(false);
        ta.setFont(font);
        // read doc
        readDocIntoTextArea(ta, "..\\afscheck.txt");
        JScrollPane jsp = new JScrollPane(ta);
        jsp.getViewport().setBackground(Color.white);
        Document doc = ta.getDocument();
        // dump doc
        //dumpDocument(doc);
        JViewport ulVP = makeViewport(doc, font, 0, 0, splitX, splitY);
        JViewport urVP = makeViewport(doc, font, splitX, 0, 20, splitY);
        JViewport llVP = makeViewport(doc, font, 0, splitY, splitX, 20);
        jsp.setRowHeader(llVP);
        jsp.setColumnHeader(urVP);
        jsp.setCorner(JScrollPane.UPPER_LEFT_CORNER, ulVP);
        jsp.setCorner(JScrollPane.UPPER_RIGHT_CORNER, new Corner());
        jsp.setCorner(JScrollPane.LOWER_LEFT_CORNER, new Corner());
        jsp.setCorner(JScrollPane.LOWER_RIGHT_CORNER, new Corner());
        cp.setLayout(new BorderLayout());
        cp.add(jsp, BorderLayout.CENTER);
    void readDocIntoTextArea(JTextArea ta, String filename) {
        try {
            File f = new File(filename);
            FileInputStream fis = new FileInputStream(f);
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            int br = 0;
            byte[] buf = new byte[1024000];
            while ((br = fis.read(buf, 0, buf.length)) != -1) {
                baos.write(buf, 0, br);
            fis.close();
            ta.setText(baos.toString());
        } catch (Exception e) {
            e.printStackTrace();
            ta.setText("Failed to load text.");
    protected void windowClosed() {
        System.exit(0);
    JViewport makeViewport(Document doc, Font f, int splitX, int splitY, int width, int height) {
        JViewport vp = new JViewport();
        OffsetTextArea ta = new OffsetTextArea();
        ta.setSplit(splitX, splitY);
        ta.setDocument(doc);
        ta.setFont(f);
        ta.setBackground(Color.gray);
        vp.setView(ta);
        vp.setBackground(Color.gray);
        vp.setPreferredSize(new Dimension(width, height));
        return vp;
    static void dumpDocument(Document doc) {
        Element[] elms = doc.getRootElements();
        for (int i = 0; i < elms.length; i++) {
            dumpElement(elms, 0);
static void dumpElement(Element elm, int level) {
for (int i = 0; i < level; i++) System.out.print(" ");
System.out.print(elm.getName());
if ( elm.isLeaf() && elm.getName().equals("content")) {
try {
int s = elm.getStartOffset();
int e = elm.getEndOffset();
System.out.println(elm.getDocument().getText(
s, e-s));
} catch (Exception e) {
System.out.println(e.getLocalizedMessage());
return;
System.out.println();
for (int i = 0; i < elm.getElementCount(); i++) {
dumpElement(elm.getElement(i), level+1);
class OffsetTextArea extends JTextArea {
int splitX = 0;
int splitY = 0;
public void setSplit(int x, int y) {
splitX = x;
splitY = y;
public void paint(Graphics g) {
g.translate(-splitX, -splitY);
super.paint(g);
g.translate( splitX, splitY);
/* Corner.java is used by ScrollDemo.java. */
class Corner extends JComponent {
protected void paintComponent(Graphics g) {
// Fill me with dirty brown/orange.
g.setColor(new Color(230, 163, 4));
g.fillRect(0, 0, getWidth(), getHeight());