修改时间（年月日时分）

public static void main(String[] args) throws ParseException {
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

Calendar nowTime = Calendar.getInstance();

       //添加时间不增加时间为当前默认

                 String q ="2018-02-05";

Date d = ym.parse(q);

cal.setTimeInMillis(d.getTime());  

//正数为加，负数为减                

                nowTime.add(Calendar.YEAR,-1); //修改年

         nowTime.add(Calendar.MONTH,-1); //修改月

nowTime.add(Calendar.DATE,0); //修改天
nowTime.add(Calendar.HOUR_OF_DAY,0);//修改小时
nowTime.add(Calendar.MINUTE, 0);//修改分钟
System.out.println(format.format(nowTime.getTime()));

}