1. 计算两天之间相隔几天的Java函数

/**

* 计算两天之间相差几天

* @param startTime

* @param endTime

* @return

*

* 取得两个时间段的时间间隔

* return t2 与t1的间隔天数

* throws ParseException 如果输入的日期格式不是0000-00-00 格式抛出异常

*/

public static int betweenTwoDays(String startTime,String endTime){

String startYearStr = startTime.substring(0, 4);

String endYearStr = endTime.substring(0, 4);

String startMonthStr = startTime.substring(4, 6);

String endMonthStr = endTime.substring(4, 6);

String startDayStr = startTime.substring(6, 8);

String endDayStr = endTime.substring(6, 8);

String t1 = startYearStr+"-"+startMonthStr+"-"+startDayStr;

String t2 = endYearStr+"-"+endMonthStr+"-"+endDayStr;

DateFormat format = new SimpleDateFormat("yyyy-MM-dd");

int betweenDays = 0;

Date d1 = null;

Date d2 = null;

try {

d1 = format.parse(t1);

d2 = format.parse(t2);

Calendar c1 = Calendar.getInstance();

Calendar c2 = Calendar.getInstance();

c1.setTime(d1);

c2.setTime(d2);

int betweenYears = c2.get(Calendar.YEAR)-c1.get(Calendar.YEAR);

betweenDays = c2.get(Calendar.DAY_OF_YEAR)-c1.get(Calendar.DAY_OF_YEAR);

for(int i=0;i

c1.set(Calendar.YEAR,(c1.get(Calendar.YEAR)+1));

betweenDays += c1.getMaximum(Calendar.DAY_OF_YEAR);

}

} catch (ParseException e) {

e.printStackTrace();

}

return betweenDays;

}

2. 判断是否为闰年

/***

* 判断是否为闰年

* @param yearStr

* @return

*/

public static boolean isLoop(String yearStr){

int year = Integer.parseInt(yearStr);

boolean flag = false;

if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)){

flag = true;

}

return flag;

}

public static boolean isLoop(int year){

boolean flag = false;

if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)){

flag = true;

}

return flag;

}

3.判断前多少天是那一天的函数

/****

* 计算出day的before天之前是哪一天

* @param day

* @return

*/

public static String getDayBefore(String day,int beforeDay){

String resultDay = null;

String YearStr = day.substring(0, 4);

String MonthStr = day.substring(4, 6);

String DayStr = day.substring(6, 8);

int yearInt = Integer.parseInt(YearStr);

int monthInt = Integer.parseInt(MonthStr);

int dayInt = Integer.parseInt(DayStr);

int[] month;

if(isLoop(yearInt)){

month = new int[]{0,31,29,31,30,31,30,31,31,30,31,30,31};

}

else{

month = new int[]{0,31,28,31,30,31,30,31,31,30,31,30,31};

}

for(int i=0;i

dayInt--;

if(dayInt<=0){

monthInt--;

if(monthInt<=0){

yearInt--;

monthInt = 12;

dayInt = month[monthInt];

}

else{

dayInt = month[monthInt];

}

}

}

resultDay = ""+yearInt+String.format("%02d",monthInt)+String.format("%02d",dayInt);

return resultDay;

}

一些转载之作：

1.计算某一月份的最大天数

Calendar time=Calendar.getInstance();

time.clear();

time.set(Calendar.YEAR,year);

time.set(Calendar.MONTH,i-1);//注意,Calendar对象默认一月为0

int day=time.getActualMaximum(Calendar.DAY_OF_MONTH);//本月份的天数

注：在使用set方法之前，必须先clear一下，否则很多信息会继承自系统当前时间

2.Calendar和Date的转化

(1) Calendar转化为Date

Calendar cal=Calendar.getInstance();

Date date=cal.getTime();

(2) Date转化为Calendar

Date date=new Date();

Calendar cal=Calendar.getInstance();

cal.setTime(date);

3.格式化输出日期时间

Date date=new Date();

SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

System.out.println(df.format(date));

4.计算一年中的第几星期

(1)计算某一天是一年中的第几星期

Calendar cal=Calendar.getInstance();

cal.set(Calendar.YEAR, 2006);

cal.set(Calendar.MONTH, 8);

cal.set(Calendar.DAY_OF_MONTH, 3);

int weekno=cal.get(Calendar.WEEK_OF_YEAR);

(2)计算一年中的第几星期是几号

SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd");

Calendar cal=Calendar.getInstance();

cal.set(Calendar.YEAR, 2006);

cal.set(Calendar.WEEK_OF_YEAR, 1);

cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);

System.out.println(df.format(cal.getTime()));

输出:

2006-01-02

5.add()和roll()的用法

(1)add()方法

SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd");

Calendar cal=Calendar.getInstance();

cal.set(Calendar.YEAR, 2006);

cal.set(Calendar.MONTH, 8);

cal.set(Calendar.DAY_OF_MONTH, 3);

cal.add(Calendar.DATE, -4);

Date date=cal.getTime();

System.out.println(df.format(date));

cal.add(Calendar.DATE, 4);

date=cal.getTime();

System.out.println(df.format(date));

输出：

2006-08-30

2006-09-03

(2)roll方法

cal.set(Calendar.YEAR, 2006);

cal.set(Calendar.MONTH, 8);

cal.set(Calendar.DAY_OF_MONTH, 3);

cal.roll(Calendar.DATE, -4);

date=cal.getTime();

System.out.println(df.format(date));

cal.roll(Calendar.DATE, 4);

date=cal.getTime();

System.out.println(df.format(date));

输出：

2006-09-29

2006-09-03

可见，roll()方法在本月内循环，一般使用add()方法；

6.计算两个任意时间中间的间隔天数

(1)传进Calendar对象

/**计算两个时间之间相隔天数

     *@paramstartday  开始时间

     *@paramendday 结束时间

     *@return*/

public

int

getIntervalDays(Calendar startday,Calendar endday)

{

//确保startday在endday之前if(startday.after(endday)){

            Calendar cal=startday;

            startday=endday;

            endday=cal;

        }//分别得到两个时间的毫秒数longsl=startday.getTimeInMillis();

longel=endday.getTimeInMillis();

longei=el-sl;

//根据毫秒数计算间隔天数return(int)(ei/(1000*60*60*24));

    } (2)传进Date对象

/**计算两个时间之间相隔天数

     *@paramstartday  开始时间

     *@paramendday 结束时间

     *@return*/

public

int

getIntervalDays(Date startday,Date endday)

{

//确保startday在endday之前if(startday.after(endday)){

            Date cal=startday;

            startday=endday;

            endday=cal;

        }//分别得到两个时间的毫秒数longsl=startday.getTime();

longel=endday.getTime();

longei=el-sl;

//根据毫秒数计算间隔天数return(int)(ei/(1000*60*60*24));

    } 同理，可以用相同的方法计算出任意两个时间相隔的小时数，分钟数，秒钟数等

注：以上方法是完全按时间计算，有时并不能令人满意，如：

startday="2006-10-11 20:00:00"

endday="2006-10-12 8:00:00"

计算结果为0，但是我们也许相让计算结果变为1，此时可以用如下方法实现：

在传参之前，先设定endday的时间，如：

endday.set(Calendar.HOUR_OF_DAY, 23);

endday.set(Calendar.MINUTE, 59);

endday.set(Calendar.SECOND, 59);

endday.set(Calendar.MILLISECOND, 59);

这样再传进去startday,endday，则结果就如我们所愿了。不过，如果嫌以上方法麻烦，可以参考以下方法：

(3)改进精确计算相隔天数的方法

public

int

getDaysBetween (Calendar d1, Calendar d2)

{

if(d1.after(d2)){//swap dates so that d1 is start and d2 is endjava.util.Calendar swap=d1;

            d1=d2;

            d2=swap;

        }intdays=d2.get(Calendar.DAY_OF_YEAR)-d1.get(Calendar.DAY_OF_YEAR);

inty2=d2.get(Calendar.YEAR);

if(d1.get(Calendar.YEAR)!=y2){

            d1=(Calendar) d1.clone();

do{

                days+=d1.getActualMaximum(Calendar.DAY_OF_YEAR);//得到当年的实际天数d1.add(Calendar.YEAR,1);

            }while(d1.get(Calendar.YEAR)!=y2);

        }returndays;

    }