Java 获取上一个月的月份的正确写法

         SimpleDateFormat format = new SimpleDateFormat("yyyy-MM");
        Date date = new Date();
        System.out.println(nowSdf.format(date));
        Calendar calendar = Calendar.getInstance();
        // 设置为当前时间
        calendar.setTime(date);
        // 设置为上一个月
        calendar.set(Calendar.MONTH, calendar.get(Calendar.MONTH) - 1);
        date = calendar.getTime();

 
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM");
        Date date = new Date();
        System.out.println(nowSdf.format(date));
        Calendar calendar = Calendar.getInstance();
        // 设置为当前时间
        calendar.setTime(date);
        // 设置为上一个月
        //calendar.set(Calendar.MONTH, calendar.get(Calendar.MONTH) - 1);
        calendar.add(Calendar.MONTH,-1);
        date = calendar.getTime();

 SimpleDateFormat  sd=new    SimpleDateFormat("yyyy-MM");
        try {
            String payoffYearMonth = "2018-06";
            Date  currdate = sd.parse(payoffYearMonth);
            Calendar   calendar= Calendar.getInstance();
            calendar.setTime(currdate);
            calendar.set(Calendar.MONTH,calendar.get(Calendar.MONTH)-1);
            System.out.println(sd.format(calendar.getTime()));
        } catch (ParseException e) {
            e.printStackTrace();
        }