public static String getStartOfNextWeek(String DATE){

String format = "dd.MM.yyyy";SimpleDateFormat df = new SimpleDateFormat(format);

Date date = null;
try {
date = df.parse(DATE);
} catch (ParseException e) {
e.printStackTrace();
}

Calendar cal = Calendar.getInstance();

cal.setTime(date);
int week = cal.get(Calendar.WEEK_OF_YEAR);
int year = cal.get(Calendar.YEAR);

Calendar calendar = new GregorianCalendar();
calendar.clear();
calendar.set(Calendar.YEAR, year);
calendar.set(Calendar.WEEK_OF_YEAR, week);

//add 8 days to get next weeks Monday

calendar.add(Calendar.DAY_OF_WEEK, 8);

Date startDate = calendar.getTime();

SimpleDateFormat df2 = new SimpleDateFormat("dd.MM.yyyy");

String start = df2.format(startDate);

return start;

input: 15.12.2014
output: 22.12.2014 CORRECT
input: 22.12.2014
output: 29.12.2014 CORRECT
input: 29.12.2014
output: 6.1.2014 WRONG