java当前日期上个月 java 当前日期的后一天

public String getNextDay(String startdate) throws ParseException{
 Date date = (new SimpleDateFormat("yyyy-MM-dd")).parse(startdate);
 Calendar cal = Calendar.getInstance();
 cal.setTime(date);
 cal.add(Calendar.DATE,1);
 date =cal.getTime();
 startdate=(new SimpleDateFormat("yyyy-MM-dd")).format(date);
 return startdate;
 }

 public String getLastDay(String startdate) throws ParseException{
 Date date = (new SimpleDateFormat("yyyy-MM-dd")).parse(startdate);
 Calendar cal = Calendar.getInstance();
 cal.setTime(date);
 cal.add(Calendar.DATE,-1);
 date =cal.getTime();
 startdate=(new SimpleDateFormat("yyyy-MM-dd")).format(date);
 return startdate;
 }