Add document listener to a JTextField in Java

import java.awt.FlowLayout;
//from   ww  w . java2 s . co  m
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;

public class Main {
  public static void main(String[] argv) {
    JTextField tf = new JTextField(20);
    DocumentListener dl = new T1();
    tf.getDocument().addDocumentListener(dl);
    
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLayout(new FlowLayout());
    frame.add(tf);
    frame.setSize(300, 150);
    frame.setVisible(true);
  }
}

class T1 implements DocumentListener {
  public void changedUpdate(DocumentEvent e) {
  }

  public void insertUpdate(DocumentEvent e) {
    System.out.println(e);
  }

  public void removeUpdate(DocumentEvent e) {
    System.out.println(e);
  }
}