基礎知識:
公元1年1月1日是星期一
一年有365天/366天(閏年)
閏年規則:原則上4年1閏,但逢百時(shí)400才閏
算法推理:
365/7=52余1
也就是說(shuō)公元2年1月1日是星期二.....
當然閏年會(huì )多過(guò)1天
算法總結:A年B月C日
1、每過(guò)去1年多1天,閏年再多1天,到上一年為止多了幾天能算了吧。
int count=(A-1)+(A-1)/4+(A-1)/400-(A-1)/100;
2、從1月到上月今年過(guò)去的總天數,列個(gè)全年的數組能行吧(沒(méi)考慮今年的閏月)
int[] M={31,28,31,30,31,30,31,31,30,31,30,31};
for(int i=1;i<B;i++){
count+=M[i];
}
3、如果今年是閏年且B>2
count++
4、到本月今天總天數
count+=C;
5、由于公元1年1月1日是星期一,再扣一天除7取余
(count-1)%7
0為星期天,以此類(lèi)推
根據日期獲得星期幾
import java.util.Calendar;
import java.util.Date;
public class CountWeek {
public static String getWeekOfDate(Date dt){
String[] weekDays={"星期日","星期一","星期二","星期三","星期四","星期五","星期六"};
Calendar cal=Calendar.getInstance();
cal.setTime(dt);
int w=cal.get(Calendar.DAY_OF_WEEK)-1;
if(w<0)w=0;
return weekDays[w];
}
public static void main(String[] args) {
System.out.println("今天是:"+CountWeek.getWeekOfDate(new Date()));
}
}
public class ManageWeek {
//判斷兩個(gè)日期是否在同一周
boolean isSameWeekDates(Date date1, Date date2) {
Calendar cal1 = Calendar.getInstance();
Calendar cal2 = Calendar.getInstance();
cal1.setTime(date1);
cal2.setTime(date2);
int subYear = cal1.get(Calendar.YEAR) - cal2.get(Calendar.YEAR);
if (0 == subYear) {
if (cal1.get(Calendar.WEEK_OF_YEAR) == cal2.get(Calendar.WEEK_OF_YEAR))
return true;
}
else if (1 == subYear && 11 == cal2.get(Calendar.MONTH)) {
// 如果12月的最后一周橫跨來(lái)年第一周的話(huà)則最后一周即算做來(lái)年的第一周
if (cal1.get(Calendar.WEEK_OF_YEAR) == cal2.get(Calendar.WEEK_OF_YEAR))
return true;
}
else if (-1 == subYear && 11 == cal1.get(Calendar.MONTH)) {
if (cal1.get(Calendar.WEEK_OF_YEAR) == cal2.get(Calendar.WEEK_OF_YEAR))
return true;
}
return false;
}
//產(chǎn)生周序列
public static String getSeqWeek(){
Calendar c = Calendar.getInstance(Locale.CHINA);
String week = Integer.toString(c.get(Calendar.WEEK_OF_YEAR));
if(week.length()==1)week = "0" + week;
String year = Integer.toString(c.get(Calendar.YEAR));
return year+week;
}
//獲得周一的日期
public static String getMonday(Date date){
Calendar c = Calendar.getInstance();
c.setTime(date);
c.set(Calendar.DAY_OF_WEEK,Calendar.MONDAY);
return new SimpleDateFormat("yyyy-MM-dd").format(c.getTime());
}
//獲得周五的日期
public static String getFriday(Date date){
Calendar c = Calendar.getInstance();
c.setTime(date);
c.set(Calendar.DAY_OF_WEEK,Calendar.FRIDAY);
return new SimpleDateFormat("yyyy-MM-dd").format(c.getTime());
}
//當前日期前幾天或者后幾天的日期
public static String afterNDay(int n){
Calendar c=Calendar.getInstance();
DateFormat df=new SimpleDateFormat("yyyy-MM-dd");
c.setTime(new Date());
c.add(Calendar.DATE,n);
Date d2=c.getTime();
String s=df.format(d2);
return s;
}
public static void main(String[] args){
}
}
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