Here is some code to set up a masked text field using JClass Field:

    JCTextField textField = new JCTextField();
    JCStringValidator validator = new JCStringValidator();
    validator.setMask( "(@@@) @@@-@@@@" );
    validator.setPlaceHolderChars( "(000) 000-0000" );
    validator.setAllowNull( false );
    textField.setValueModel( new StringValueModel() );
    textField.setValidator( validator );

   #    Any digit, minus sign, comma, decimal point, or plus sign.
   @    Any digit.
   H    Any hexadecimal digit.
   U    Any alphabetic character. Lower case characters will be converted
        to upper case.
   L    Any alphabetic character. Upper case characters will be converted
        to lower case.
   A    Any alphabetic character. No case conversion.
   *    Any character.
   ^    Any alphanumeric character, that is, any character from the set
        {0-9a-zA-Z}.
   \\   The next character that follows is to be treated as a literal,
        even if it is one of the above characters.