电影 红色高跟鞋:一个初级java Applet问题，编译不通过

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

public class D2
{
public static void main(String[] arg)
{
TextFieldFrame frame = new TextFieldFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.show();
}
}
class TextFieldFrame extends JFrame
{

public TextFieldFrame()
{
setTitle("textdivide");
setSize(WIDTH,HEIGHT);

Container contentPane = getContentPane();
DocumentListener resultListener = new ResultListener();

JPanel textPanel = new JPanel();

originText = new JTextField("input interger",40);

originText.getDocument().addDocumentListener(resultListener);

resultText = new JTextField("能否被3和5整除",50);

resultText.setEditable(false);

textPanel.add(originText);
textPanel.add(resultText);

contentPane.add(textPanel);
}
public void getAnswer()
{
try
{
int n;
String s;
n = Integer.parseInt(originText.getText().trim());

if (n%3 == 0 && n%5 == 0)

s = new String("数字" + n+"能被3和5整除");

resultText.setText(s);
}
catch (NumberFormatException e)
{
}

}

private class ResultListener implements DocumentListener
{

public void insertUpdate(DocumentEvent e)
{
getAnswer();
}

public void removeUpdate(DocumentEvent e)
{
getAnswer();
}
}

public static final int WIDTH = 350;
public static final int HEIGHT = 150;
private JTextField originText;

private JTextField resultText;

}

错误出现在最后一个类：private class ResultListener implements DocumentListener
错误如下：
TextFieldFrame.ResultListener is not abstract and does not override abstract method changedUpdate(javax.swing.enent.Document) in javax.swing.event.DocumentListener
多谢！