java中关于时间日期操作的常用函数

java中关于时间日期操作的常用函数

文章分类:Java编程

1.计算某一月份的最大天数

Java代码







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

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

Java代码







Calendar cal=Calendar.getInstance();

Date date=cal.getTime();

Calendar cal=Calendar.getInstance();
Date date=cal.getTime();

(2) Date转化为Calendar

Java代码







Date date=new Date();

Calendar cal=Calendar.getInstance();

cal.setTime(date);

Date date=new Date();
Calendar cal=Calendar.getInstance();
cal.setTime(date);

3.格式化输出日期时间

Java代码







import java.util.Date;

Date date=new Date();

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

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

import java.util.Date;
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

Java代码







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);

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

Java代码







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()));

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

Java代码







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));

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

Java代码







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));

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

Java代码







/** *//**计算两个时间之间相隔天数

* @param startday 开始时间

* @param endday 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

long sl=startday.getTimeInMillis();

long el=endday.getTimeInMillis();

long ei=el-sl;

//根据毫秒数计算间隔天数

return (int)(ei/(1000*60*60*24)); }

/** *//**计算两个时间之间相隔天数
* @param startday  开始时间
* @param endday 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
long sl=startday.getTimeInMillis();
long el=endday.getTimeInMillis();

long ei=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

Java代码







/** *//**计算两个时间之间相隔天数

* @param startday 开始时间

* @param endday 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

long sl=startday.getTime();

long el=endday.getTime();

long ei=el-sl;

//根据毫秒数计算间隔天数

return (int)(ei/(1000*60*60*24));

}

/** *//**计算两个时间之间相隔天数
* @param startday  开始时间
* @param endday 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
long sl=startday.getTime();
long el=endday.getTime();

long ei=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"

Java代码







//只要格式正确，直接比较字符串就可以了呀，精确到秒的也一样

String s1 = "2003-12-12 11:30:24";

String s2 = "2004-04-01 13:31:40";

int res = s1.compareTo(s2);

//求日期差：

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

Date begin=df.parse("2004-01-02 11:30:24");

Date end = df.parse("2004-03-26 13:31:40");

long between=(end.getTime()-begin.getTime())/1000;//除以1000是为了转换成秒

int day=between/(24*3600);

int hour=between%(24*3600)/3600;

int minute=between%3600/60;

int second=between%60/60;

//只要格式正确，直接比较字符串就可以了呀，精确到秒的也一样
String   s1   =   "2003-12-12   11:30:24";
String   s2   =   "2004-04-01   13:31:40";
int   res   =   s1.compareTo(s2);

//求日期差：
SimpleDateFormat   df   =   new   SimpleDateFormat("yyyy-MM-dd   HH:mm:ss");
Date   begin=df.parse("2004-01-02   11:30:24");
Date   end   =   df.parse("2004-03-26   13:31:40");
long   between=(end.getTime()-begin.getTime())/1000;//除以1000是为了转换成秒
int   day=between/(24*3600);
int   hour=between%(24*3600)/3600;
int   minute=between%3600/60;
int   second=between%60/60;

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

Java代码







public int getDaysBetween (Calendar d1, Calendar d2) ...{

if (d1.after(d2)) ...{ // swap dates so that d1 is start and d2 is end

java.util.Calendar swap = d1;

d1 = d2;

d2 = swap;

}

int days = d2.get(Calendar.DAY_OF_YEAR) - d1.get(Calendar.DAY_OF_YEAR);

int y2 = 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);

}

return days;

}

public int getDaysBetween (Calendar d1, Calendar d2) ...{
if (d1.after(d2)) ...{  // swap dates so that d1 is start and d2 is end
java.util.Calendar swap = d1;
d1 = d2;
d2 = swap;
}
int days = d2.get(Calendar.DAY_OF_YEAR) - d1.get(Calendar.DAY_OF_YEAR);
int y2 = 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);
}
return days;
}

得到明天的算法

Java代码







GregorianCalendar gc = new GregorianCalendar();

gc.add(GregorianCalendar.DATE,1);

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

System.out.println(ymdf.format(new Date(gc.getTimeInMillis())));

转自/article/4375847.html