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How can we display the line numbers inside a JTextArea in Java?
A JTextArea is a subclass of JTextComponent and it is a multi-line text component to display the text or allow the user to enter a text. A JTextArea can generate a CaretListener interface, which can listen to caret update events. By default, JTextArea does not display the line numbers, we have to customize the code by using a DocumentListener interface.
Example
import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.Element;
public class LineNumberTextAreaTest extends JFrame {
private static JTextArea textArea;
private static JTextArea lines;
private JScrollPane jsp;
public LineNumberTextAreaTest() {
setTitle("LineNumberTextArea Test");
jsp = new JScrollPane();
textArea = new JTextArea();
lines = new JTextArea("1");
lines.setBackground(Color.LIGHT_GRAY);
lines.setEditable(false);
// Code to implement line numbers inside the JTextArea
textArea.getDocument().addDocumentListener(new DocumentListener() {
public String getText() {
int caretPosition = textArea.getDocument().getLength();
Element root = textArea.getDocument().getDefaultRootElement();
String text = "1" + System.getProperty("line.separator");
for(int i = 2; i < root.getElementIndex(caretPosition) + 2; i++) {
text += i + System.getProperty("line.separator");
}
return text;
}
@Override
public void changedUpdate(DocumentEvent de) {
lines.setText(getText());
}
@Override
public void insertUpdate(DocumentEvent de) {
lines.setText(getText());
}
@Override
public void removeUpdate(DocumentEvent de) {
lines.setText(getText());
}
});
jsp.getViewport().add(textArea);
jsp.setRowHeaderView(lines);
add(jsp);
setSize(400, 275);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
setVisible(true);
}
public static void main(String[] args) {
new LineNumberTextAreaTest();
}
}Output
Updated on: 10-Feb-2020
622 Views
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