日期相差月和日期加月

/**
  * 计算给定日期+几月      假如当前日期是1月31号  月份：1   那么得到的日期就是2月28号
  * @param date
  * @param month
  * @return
  */
 public String nextTime(Date date,int month){
  SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");  
  Date smdate = null;
       try {
   smdate=sdf.parse(sdf.format(date));
  } catch (ParseException e) {
   e.printStackTrace();
  }  
       Calendar cal = Calendar.getInstance();    
       cal.setTime(smdate);    
       cal.add(Calendar.MONTH, month);
       return sdf.format(cal.getTime());
 }

 

 

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   /* 计算两个日期之间相差的月(自然月==天数不满30天也算成是一个月，即向上取整) 

    * 假如最小时间为1.30 较大时间为2.28  相差的月份为2月

    * 假如最小时间为1.29 较大时间为2.28  相差的月份为2月

    * 假如最小时间为1.31 较大时间为6.30  相差的月份为6月
    * @param smdate 较小的时间 
    * @param bdate  较大的时间 
    * @return 相差月份 
    * @throws ParseException  
    */    
   public void monthsBetween(Date smdate,Date bdate)    
   {    
      SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
     Date smdate = null;
     Date bdate = null;
        try {
    smdate=sdf.parse("2013-01-20");
    bdate=sdf.parse("2013-04-21");  
   } catch (ParseException e) {
    e.printStackTrace();
   }  
        Calendar cal = Calendar.getInstance();    
        cal.setTime(smdate);
        long yeartime1 = cal.get(Calendar.YEAR);
        long time1 = cal.get(Calendar.MONDAY)+1;              
        long daytime1= cal.get(Calendar.DAY_OF_MONTH);
        cal.setTime(bdate);    
        long yeartime2 = cal.get(Calendar.YEAR);
        long time2 = cal.get(Calendar.MONDAY)+1;         
        long daytime2= cal.get(Calendar.DAY_OF_MONTH);
        long between_year = Math.abs(yeartime2-yeartime1);
        long between_months = 0;
        if(time2-time1>=0){
         between_months=time2-time1;
        }else{
         between_year--;
         between_months = 12-time1+time2;
        }
        if(daytime2-daytime1>0){
         between_months++;
        }
        if(between_year>0){
         between_months+=between_year*12;
        }

        Calendar call = Calendar.getInstance();    
              call.setTime(smdate);    
              call.add(Calendar.MONTH, Integer.parseInt(String.valueOf(between_months)));
              long addDate = call.get(Calendar.DAY_OF_MONTH);
              if(addDate == daytime2){
                  between_months++;
              }
        System.out.println(between_months);          
   }