如何限制JTextField中的字符数？

http://www.rgagnon.com/javadetails/java-0198.htmlimport javax.swing.text.Plaindocument;import javax.swing.text.AttributeSet;import javax.swing.text.BadLocationException;public class JTextFieldLimit extends Plaindocument {  private int limit;  JTextFieldLimit(int limit) {   super();   this.limit = limit;   }  public void insertString( int offset, String  str, AttributeSet attr ) throws BadLocationException {    if (str == null) return;    if ((getLength() + str.length()) <= limit) {      super.insertString(offset, str, attr);    }  }}

然后

import java.awt.*;import javax.swing.*; public class DemoJTextFieldWithLimit extends JApplet{   JTextField textfield1;   JLabel label1;   public void init() {     getContentPane().setLayout(new FlowLayout());     //     label1 = new JLabel("max 10 chars");     textfield1 = new JTextField(15);     getContentPane().add(label1);     getContentPane().add(textfield1);     textfield1.setdocument        (new JTextFieldLimit(10));     }}

（谷歌的第一个结果）