java中年月日的加减法，年月的加减法使用

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java计算两个年月日之间相差的天数：
 public static int daysBetween(String smdate,String bdate) throws ParseException{
        int daysInterval=0;
        if(StringUtils.isNoneBlank(smdate)&&StringUtils.isNoneBlank(bdate)){
            SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");  
            Calendar cal = Calendar.getInstance();    
            cal.setTime(sdf.parse(smdate));    
            long time1 = cal.getTimeInMillis();                 
            cal.setTime(sdf.parse(bdate));    
            long time2 = cal.getTimeInMillis();         
            long between_days=(time2-time1)/(1000*3600*24);
            daysInterval = Integer.parseInt(String.valueOf(between_days));
        }
            
       return daysInterval;     
    }  
    
java计算年月之间的加法和减法：
public static void main(String[] args) throws ParseException
    {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");   
        String time=sdf.format(new Date());
        Calendar cd = Calendar.getInstance();
        cd.setTime(sdf.parse(time));
        cd.add(Calendar.MONTH, 0);//往前一月，，如果是整数则进行加法，如果是负数，则进行减法    
        Date date=cd.getTime();  
        String endTimeString = sdf.format(date);
        cd.add(Calendar.MONTH, -7);//往后7个月
        String startTimeString = sdf.format(cd.getTime());
        String startTime = startTimeString.replaceAll("-", "");//格式日期yyyyMM
        String endTime  = endTimeString.replaceAll("-", "");//格式日期yyyyMM
        System.out.println(startTime);
        System.out.println(endTime);
    }    
        
        
获取一个月中的第一天和最后一天：
public static void main(String[] args)
    {
        // 获取当前年份、月份、日期  
        Calendar cale = null;  
        cale = Calendar.getInstance();  
        // 获取当月第一天和最后一天  
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");  
        // 获取前月的第一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, -6);  
        cale.set(Calendar.DAY_OF_MONTH, 1);  
        String startTimeString = format.format(cale.getTime());  
        // 获取前月的最后一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, 0);  
        cale.set(Calendar.DAY_OF_MONTH, 0);  
        String endTimeString = format.format(cale.getTime());  
        String startTime =startTimeString.replaceAll("-", "");//格式日期yyyyMMdd
        String endTime  =endTimeString.replaceAll("-", "");//格式日期yyyyMMdd
        String layerTime = startTimeString +"至"+endTimeString;
        System.out.println(layerTime);
    }
    
    
计算两个月份之间相差的月份个数：
     public int getMonthInterval(String str1,String str2) throws ParseException{
        int monthLength = 0;
        if(StringUtils.isNoneBlank(str1)&& StringUtils.isNoneBlank(str2)){
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
            Calendar bef = Calendar.getInstance();
            Calendar aft = Calendar.getInstance();
            bef.setTime(sdf.parse(str1));
            aft.setTime(sdf.parse(str2));
            int result = aft.get(Calendar.MONTH) - bef.get(Calendar.MONTH);
            int month = (aft.get(Calendar.YEAR) - bef.get(Calendar.YEAR)) * 12;
            monthLength = Math.abs(month + result);
        }
       return monthLength;
    }
    
java对当前月份进行传值计算：
  public static Map<String,Object> getMonth(int length) throws ParseException{
        Map<String, Object> map = new HashMap<>();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");   
        String time=sdf.format(new Date());
        Calendar cd = Calendar.getInstance();
        cd.setTime(sdf.parse(time));
        cd.add(Calendar.MONTH, -length);//往前一月    
        Date date=cd.getTime();  
        String monthFormat= sdf.format(date);
//        System.out.println(monthFormat);
        String monthString =monthFormat.replaceAll("-", "");//格式日期yyyyMM
        map.put("monthFormat", monthFormat);
        map.put("monthString", monthString);
        return map;
    }    
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