Java处理时间加减天数加减月

/**** 
 * 传入具体日期 ，返回具体日期增加一个月。 
 * @param date 日期(2017-04-13) 
 * @return 2017-05-13
 * @throws ParseException 
 */  
private  String calculateMonth(String date) throws ParseException {  
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");  
    Date dt = sdf.parse(date);  
    Calendar rightNow = Calendar.getInstance();  
    rightNow.setTime(dt);  
    rightNow.add(Calendar.MONTH, 1);  
    Date dt1 = rightNow.getTime();  
    String reStr = sdf.format(dt1);  
    return reStr;  
}


/**** 
  * 传入具体日期 ，返回具体日期减少一天 
  * @param date 日期(2017-04-13) 
  * @return 2017-04-12
  * @throws ParseException 
  */  
 private  String calculateDay(String date) throws ParseException {  
     SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");  
     Date dt = sdf.parse(date);  
     Calendar rightNow = Calendar.getInstance();  
     rightNow.setTime(dt);  
     rightNow.add(Calendar.DATE, -1);  
     Date dt1 = rightNow.getTime();  
     String reStr = sdf.format(dt1);  
     return reStr;  
 }

/**
 * 传入具体日期 ，返回具体日期增加或者减少天数，传出日期
 * @author wjk
 * @Date 2021-09-27
 */
private  Date calculateDay(Date date,int day){
    Calendar rightNow = Calendar.getInstance();
    rightNow.setTime(date);
    rightNow.add(Calendar.DATE, day);
    Date date1  = rightNow.getTime();
    return date1;
}


/**
 * 传入具体日期 ，返回具体日期增加或者减少月数，传出日期
 * @author wjk
 * @Date 2021-09-27
 */
private  Date calculateMonth(Date date,int month){
    Calendar rightNow = Calendar.getInstance();
    rightNow.setTime(date);
    rightNow.add(Calendar.MONTH, month);
    Date date1  = rightNow.getTime();
    return date1;
}

/**
 * 传入具体日期 ，返回当月的天数
 * @author wjk
 * @Date 2021-09-28
 */
public static int getDaysOfMonth(Date date) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    return calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
  }

/**
 * 获取当月最后几天
 * @param days
 * @return
 */
    private static List<String> getLastDays(int days) {
  SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
  Calendar calendar = Calendar.getInstance();
  List<String> list=new ArrayList<String>();
  for(int i=1;i<=days;i++){
  calendar.add(Calendar.MONTH, 1);
  calendar.set(Calendar.DATE, 1);
  calendar.add(Calendar.DATE, -i);
  Date theDate = calendar.getTime();
  String s = df.format(theDate);
  list.add(s);
  }
  return list;
    }}