Custom text layout

Question

Hello follow coders.
I have been trying my hands at this for quite some time now, and I thought it is time to ask for some help. =)
I'm looking to create a text component in which the text is presented organized in columns, of an arbitrary width, with spaces between the columns. The spaces would not be a space character, but rather just some pixel distance.
Think Hex editor.
ex.
0000 0000 0000 0000
0000 0000 0000 0000
0000 0000 0000 0000.. where the spaces between the sets of zeros would not be treated as characters, just spacing.
The caret should be able to move fluidly within the rows of text, automatically skipping the spaces, without counting them to the offset
ex. the caretpositions would be
Text: 0000 0000 00
Pos:  0123 4567 89So, logically, in the eyes of the component the contents would really just be a large row of characters, only they're displayed as if they had spaces.
I hope my desciption is satisfying, and I hope someone can help me.
My conclusion this far is that the solution would involve overiding the actual paint that paints the text within the text component, but my problem is that I don't really understand the inner workings of the text component...
Cheers
/D

Answer 1

If you want to change the painting behavior in a JTextArea you might start with the
BasicTextUI and View classes.
Here's another approach using a DocumentFilter and a NavigationFilter. Since you indicated
an interest in the painting approach I stopped short of implementing cut, copy and paste
which would be the next step.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
public class Navigate {
    private JScrollPane getContent() {
        JTextArea textArea = new JTextArea() {
            { enableEvents(AWTEvent.KEY_EVENT_MASK); }
            protected void paintComponent(Graphics g) {
                ((Graphics2D)g).setRenderingHint(
                        RenderingHints.KEY_TEXT_ANTIALIASING,
                        RenderingHints.VALUE_TEXT_ANTIALIAS_ON
                super.paintComponent(g);
            protected void processKeyEvent(KeyEvent e) {
                if(e.getKeyCode() == KeyEvent.VK_BACK_SPACE) {
                    try {
                        int pos = getCaretPosition();
                        String s = getDocument().getText(pos-1, 1);
                        if(s.equals(" ")) {
                            e.consume();   // Don't back up.
                            return;
                    } catch(BadLocationException ble) {
                        System.out.printf("BadLocation: %s%n", ble.getMessage());
                super.processKeyEvent(e);
        textArea.setMargin(new Insets(2,5,2,5));
        textArea.setLineWrap(true);
        textArea.setFont(textArea.getFont().deriveFont(18f));
        textArea.setNavigationFilter(new ColumnNavFilter());
        AbstractDocument doc = (AbstractDocument)textArea.getDocument();
        doc.setDocumentFilter(new ColumnDocFilter());
        return new JScrollPane(textArea);
    public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setContentPane(new Navigate().getContent());
        f.setSize(400,200);
        f.setLocation(600,400);
        f.setVisible(true);
class ColumnNavFilter extends NavigationFilter {
    int maxLength = 19;
    // direction values:
    //     SwingConstants.NORTH = 1
    //     SwingConstants.EAST  = 3
    //     SwingConstants.SOUTH = 5
    //     SwingConstants.WEST  = 7
    public int getNextVisualPositionFrom(
                       JTextComponent text, int pos,
                       Position.Bias bias,  int direction,
                       Position.Bias[] biasRet
                                         ) throws BadLocationException {
        // format    0000 0000 0000 0000
        // pos       0123456789111111111  -> 19 places
        //                     012345678
        int next = text.getUI().getNextVisualPositionFrom(text, pos, bias,
                                                          direction, biasRet);
        //System.out.printf("pos = %d\tbias = %s\tdirection = %d\tnext = %d%n",
        //                    pos, bias.toString(), direction, next);
        // Number of new lines so far.
        int newLines = pos/maxLength;
        // Offset in this line: [0 <= lineOffset <= maxLength]
        int lineOffset = newLines > 0 ? pos%(maxLength+1) : pos;
        switch(lineOffset) {
            case 3:
                if(direction == SwingConstants.EAST)
                    next = pos+2;
                else if(direction == SwingConstants.WEST)
                    next = pos-1;
                break;
            case 5:
                if(direction == SwingConstants.WEST)
                    next = pos-2;
                break;
            case 8:
                if(direction == SwingConstants.EAST)
                    next = pos+2;
                break;
            case 10:
                if(direction == SwingConstants.WEST)
                    next = pos-2;
                break;
            case 13:
                if(direction == SwingConstants.EAST)
                    next = pos+2;
                break;
            case 15:
                if(direction == SwingConstants.WEST)
                    next = pos-2;
                break;
        return next;
    public void moveDot(NavigationFilter.FilterBypass fb,
                        int dot, Position.Bias bias) {
        //System.out.println("moveDot: dot = " + dot + "\tbias = " + bias);
        fb.moveDot(dot, bias);
    public void setDot(NavigationFilter.FilterBypass fb,
                       int dot, Position.Bias bias) {
        //System.out.println("setDot: dot = " + dot + "\tbias = " + bias);
        // Number of new lines so far.
        int newLines = dot/maxLength;
        // Offset in this line: [0 <= lineOffset <= maxLength]
        int lineOffset = newLines > 0 ? dot%(maxLength+1) : dot;
        if(lineOffset == 4) {
            if(bias == Position.Bias.Forward)
                fb.setDot(dot+1, bias);
            else if(bias == Position.Bias.Backward)
                fb.setDot(dot+2, bias);
        else if(lineOffset == 9) {
            if(bias == Position.Bias.Forward)
                fb.setDot(dot+1, bias);
            else
                fb.setDot(dot+2, bias);
        else if(lineOffset == 14) {
            if(bias == Position.Bias.Forward)
                fb.setDot(dot+1, bias);
            else
                fb.setDot(dot+2, bias);
        else
            fb.setDot(dot, bias);
class ColumnDocFilter extends DocumentFilter {
    String domain;
    int maxLength;
    Toolkit toolkit;
    public ColumnDocFilter() {
        domain = "0123456789 \n";
        maxLength = 19;
        toolkit = Toolkit.getDefaultToolkit();
    public void insertString(DocumentFilter.FilterBypass fb,
                             int offset,
                             String str,
                             AttributeSet attrs) throws BadLocationException {
        replace(fb, offset, 0, str, attrs);
    public void replace(DocumentFilter.FilterBypass fb,
                        int offset,
                        int length,               // selected text
                        String str,               // incoming string
                        AttributeSet attrs) throws BadLocationException {
        // format    0000 0000 0000 0000
        // pos       0123456789111111111  -> 19 places
        //                     012345678
        String text = fb.getDocument().getText(0, fb.getDocument().getLength());
        int docLength = text.length();
        //System.out.printf("offset = %d\tstr = %s%n", offset, str);
        // Build replacement string.
        char[] source = str.toCharArray();
        char[] result = new char[source.length + 3];
        int k = 0;
        for(int j = 0; j < source.length; j++) {
            if(domain.indexOf(source[j]) != -1) {
                // Number of new lines so far.
                int newLines = offset/maxLength;
                // Offset in this line: [0 <= lineOffset <= maxLength]
                int lineOffset = newLines > 0 ? offset%(maxLength+1) : offset;
                // Are we at the end of this line?
                boolean lineEnd = offset > 0 && lineOffset % maxLength == 0;
                if(lineEnd)
                    result[k++] = '\n';
                //System.out.printf("offset = %d\tnewLines = %d\tlineEnd = %b\t" +
                //                  "lineOffset = %s%n",
                //                   offset, newLines, lineEnd, lineOffset);
                if(offset > 0 && (lineOffset+1)%5 == 0 &&
                       lineOffset%maxLength != 0 && !str.equals(" ")) {
                    if(docLength > offset) {
                        fb.replace(offset, 2, " " + source[j], attrs);
                        continue;
                    else
                        result[k++] = ' ';
                result[k++] = source[j];
            else
                toolkit.beep();
        fb.replace(offset, length, new String(result, 0, k), attrs);
}