public void insertString(int offset, String str, AttributeSet attr)
			throws BadLocationException
	{
		if (maxLength > 0 && getLength() + str.length() > maxLength)
		{
			Toolkit.getDefaultToolkit().beep();
		}
		else
		{
			try
			{
				Integer.parseInt(str);
				super.insertString(offset, str, attr);
			}
			catch (NumberFormatException exp)
			{
				Toolkit.getDefaultToolkit().beep();
			}
		}
	}