Extend JTextField to create integer JTextField in Java

import java.awt.Toolkit;
/*from   w  w w .  j av a 2  s  .c om*/
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.PlainDocument;

public class Main {
  public static void main(String[] argv) {
    IntegerField tf = new IntegerField();

    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLayout(new java.awt.GridLayout(0, 1));

    frame.add(tf);
    frame.setSize(150, 150);
    frame.setVisible(true);
    tf.requestFocus();
  }
}

/**
 * This class is a <CODE>TextField</CODE> that only allows integer values to be
 * entered into it.
 * 
 * @author <A HREF="mailto:colbell@users.sourceforge.net">Colin Bell</A>
 */
class IntegerField extends JTextField {
  /**
   * Default ctor.
   */
  public IntegerField() {
    super();
  }

  /**
   * Ctor specifying the field width.
   * 
   * @param cols
   *          Number of columns.
   */
  public IntegerField(int cols) {
    super(cols);
  }

  /**
   * Retrieve the contents of this field as an <TT>int</TT>.
   * 
   * @return the contents of this field as an <TT>int</TT>.
   */
  public int getInt() {
    final String text = getText();
    if (text == null || text.length() == 0) {
      return 0;
    }
    return Integer.parseInt(text);
  }

  /**
   * Set the contents of this field to the passed <TT>int</TT>.
   * 
   * @param value
   *          The new value for this field.
   */
  public void setInt(int value) {
    setText(String.valueOf(value));
  }

  /**
   * Create a new document model for this control that only accepts integral
   * values.
   * 
   * @return The new document model.
   */
  protected Document createDefaultModel() {
    return new IntegerDocument();
  }

  /**
   * This document only allows integral values to be added to it.
   */
  static class IntegerDocument extends PlainDocument {
    public void insertString(int offs, String str, AttributeSet a)
        throws BadLocationException {
      if (str != null) {
        try {
          Integer.decode(str);
          super.insertString(offs, str, a);
        } catch (NumberFormatException ex) {
          Toolkit.getDefaultToolkit().beep();
        }
      }
    }
  }
}

/*
 * Copyright (C) 2001-2003 Colin Bell colbell@users.sourceforge.net
 * 
 * This library is free software; you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation; either version 2.1 of the License, or (at your option)
 * any later version.
 * 
 * This library is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
 * details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */