public IntervalleDate previousYear(){
  Calendar lower=null;
  if (lower_bound != null) {
    lower=Calendar.getInstance();
    lower.setTime(lower_bound);
    lower.add(Calendar.YEAR,-1);
  }
  Calendar upper=null;
  if (upper_bound != null) {
    upper=Calendar.getInstance();
    upper.setTime(upper_bound);
    upper.add(Calendar.YEAR,-1);
  }
  return new IntervalleDate(lower.getTime(),upper.getTime());
}

public IntervalleDate previousYear ( ) { Calendar lower = null ; if ( lower_bound != null ) { lower = Calendar . getInstance ( ) ; lower . setTime ( lower_bound ) ; lower . add ( Calendar . YEAR , - 1 ) ; } Calendar upper = null ; if ( upper_bound != null ) { upper = Calendar . getInstance ( ) ; upper . setTime ( upper_bound ) ; upper . add ( Calendar . YEAR , - 1 ) ; } return new IntervalleDate ( lower . getTime ( ) , upper . getTime ( ) ) ; }
compute the same intervalle ( same number of days ) but for previous year
