java获取指定日期的前一天和后一天

@Test
    public void getDay() {
        String day = "2018-03-19";
        Calendar c = Calendar.getInstance();
        Date date = null;
        try {
            date = new SimpleDateFormat("yy-MM-dd").parse(day);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        c.setTime(date);
        int day1 = c.get(Calendar.DATE);
        c.set(Calendar.DATE, day1 - 1);
 
        String dayAfter = new SimpleDateFormat("yyyy-MM-dd").format(c.getTime());
        System.out.println(dayAfter);
    }
后一天同前一天，c.set(Calendar.DATA,day1+1)