Line numbers in text area

Question

im using the class JTextArea of the swing class to view some text documents.
How i can vies the number of lines of each document:
i want the line numbers not in the document but as a part of the text area. for example:
1:line 1
2:something
3:something
4:sjdhfskjhsl
Please help.Thanx

Answer 1

You can do it in two ways.
Place a JLabel on left of your Text Area, Add a KeyListener to the text area. On each ENTER key press count lines of JTextArea.getLineCount(). and paint your JLabel as well. Secondly you will need to move the JLabel as soon as the ScrollBar of JScrollPane will move.
Second way is like:
<code>
import java.awt.Toolkit;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.text.BadLocationException;
public class MyTextArea extends JTextArea{
public MyTextArea(){
super("1: ");
setCaretPosition(3);
addKeyListener(new MyKeyListener());
class MyKeyListener extends KeyAdapter{
public void keyReleased(KeyEvent e){
try{
switch(e.getKeyCode()){
case KeyEvent.VK_ENTER:
int position=getCaretPosition();
int line=getLineOfOffset(position);
insert((line + 1) + ": ", position);
changeLineNos(line);
break;
case KeyEvent.VK_BACK_SPACE:
position=getCaretPosition();
line=getLineOfOffset(position);
if(line > 0){
int cLoc=getCollonLocation(position);
int diff=position - cLoc;
if(diff <= 2){
replaceRange("", getLineEndOffset(line - 1) - 1, cLoc + diff);
changeLineNos(line);
} else{
int cLoc=getCollonLocation(position);
int diff=position - cLoc;
if(diff <= 2){
if(getLineCount() > 1){
replaceRange("", 0, getLineEndOffset(0));
changeLineNos(0);
} else{
setText("1: ");
Toolkit.getDefaultToolkit().beep();
break;
} catch(BadLocationException ex){
ex.printStackTrace();
private void changeLineNos(int lineNo) throws BadLocationException{
int total=getLineCount();
if(total > lineNo){
while(lineNo < total){
int offset=getLineStartOffset(lineNo);
int collonLocation=getCollonLocation(offset, lineNo);
replaceRange("" + ++lineNo, offset, collonLocation);
private int getCollonLocation(int offset, int lineNo) throws BadLocationException{
return getText(offset, getLineEndOffset(lineNo) - offset).indexOf(':') + offset;
private int getCollonLocation(int caretPosition) throws BadLocationException{
int lineNo=getLineOfOffset(caretPosition);
int offset=getLineStartOffset(lineNo);
return getText(offset, getLineEndOffset(lineNo) - offset).indexOf(':') + offset;
public static void main(String argv[]){
JFrame frame=new JFrame();
MyTextArea area=new MyTextArea();
frame.getContentPane().add(new JScrollPane(area));
frame.setSize(300, 200);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
</code>
Regards,