DateField - Work with weeks, dateFormat problem

Vaadin 6 / 7 / 8
1

Hi,
I’m trying to work with weeks DateField, setting ISOweekNumber.
The problem seems to be formatting, because with passing String
“w”
 to
setDateFormat(String)
, he does not want to know anything.

Instead, overriding setDateFormat as below, It is formatted correctly.
the problem recurs when the user change the value.
P.S= The field is an String but is treaty as Date.

DateField dateMonthYear = new DateField(){
    private static final long serialVersionUID = 1L;

   @Override
      public void setDateFormat(String dateFormat) {
         super.setDateFormat(new SimpleDateFormat("w-Y").format(propertyDate));
   }
};