How to implement Line number in JTextArea

Question

Hi
I have seen some JTextArea with Line numbers How to do it
Thankx

Answer 1

I'm playing around with trying to make a Line Number component that will work with JTextArea, JTextPane, JTable etc. I'm not there yet, but this version works pretty good with JTextArea. At least it will give you some ideas.
Good luck.
import java.awt.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.text.*;
public class LineNumber extends JComponent
     private final static Color DEFAULT_BACKGROUND = new Color(230, 163, 4);
     private final static Color DEFAULT_FOREGROUND = Color.black;
     private final static Font DEFAULT_FONT = new Font("monospaced", Font.PLAIN, 12);
     // LineNumber height (abends when I use MAX_VALUE)
     private final static int HEIGHT = Integer.MAX_VALUE - 1000000;
     // Set right/left margin
     private final static int MARGIN = 5;
     // Line height of this LineNumber component
     private int lineHeight;
     // Line height of this LineNumber component
     private int fontLineHeight;
     private int currentRowWidth;
     // Metrics of this LineNumber component
     private FontMetrics fontMetrics;
     *     Convenience constructor for Text Components
     public LineNumber(JComponent component)
          if (component == null)
               setBackground( DEFAULT_BACKGROUND );
               setForeground( DEFAULT_FOREGROUND );
               setFont( DEFAULT_FONT );
          else
               setBackground( DEFAULT_BACKGROUND );
               setForeground( component.getForeground() );
               setFont( component.getFont() );
          setPreferredSize( 9999 );
     public void setPreferredSize(int row)
          int width = fontMetrics.stringWidth( String.valueOf(row) );
          if (currentRowWidth < width)
               currentRowWidth = width;
               setPreferredSize( new Dimension(2 * MARGIN + width, HEIGHT) );
     public void setFont(Font font)
          super.setFont(font);
          fontMetrics = getFontMetrics( getFont() );
          fontLineHeight = fontMetrics.getHeight();
     * The line height defaults to the line height of the font for this
     * component. The line height can be overridden by setting it to a
     * positive non-zero value.
     public int getLineHeight()
          if (lineHeight == 0)
               return fontLineHeight;
          else
               return lineHeight;
     public void setLineHeight(int lineHeight)
          if (lineHeight > 0)
               this.lineHeight = lineHeight;
     public int getStartOffset()
          return 4;
     public void paintComponent(Graphics g)
          int lineHeight = getLineHeight();
          int startOffset = getStartOffset();
          Rectangle drawHere = g.getClipBounds();
//          System.out.println( drawHere );
// Paint the background
g.setColor( getBackground() );
g.fillRect(drawHere.x, drawHere.y, drawHere.width, drawHere.height);
          // Determine the number of lines to draw in the foreground.
g.setColor( getForeground() );
          int startLineNumber = (drawHere.y / lineHeight) + 1;
          int endLineNumber = startLineNumber + (drawHere.height / lineHeight);
          int start = (drawHere.y / lineHeight) * lineHeight + lineHeight - startOffset;
//          System.out.println( startLineNumber + " : " + endLineNumber + " : " + start );
          for (int i = startLineNumber; i <= endLineNumber; i++)
               String lineNumber = String.valueOf(i);
               int width = fontMetrics.stringWidth( lineNumber );
               g.drawString(lineNumber, MARGIN + currentRowWidth - width, start);
               start += lineHeight;
          setPreferredSize( endLineNumber );
     public static void main(String[] args)
          JFrame frame = new JFrame("LineNumberDemo");
          frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
          JPanel panel = new JPanel();
          frame.setContentPane( panel );
          panel.setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
          panel.setLayout(new BorderLayout());
          JTextArea textPane = new JTextArea();
          JScrollPane scrollPane = new JScrollPane(textPane);
          panel.add(scrollPane);
          scrollPane.setPreferredSize(new Dimension(300, 250));
          LineNumber lineNumber = new LineNumber( textPane );
          lineNumber.setPreferredSize(99999);
          scrollPane.setRowHeaderView( lineNumber );
          frame.pack();
          frame.setVisible(true);