java 获取周、月、年的第一天以及最后一天的详细代码

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public class MyCalendar {


public static Date getDate(Calendar c) {  
   return new Date(c.getTimeInMillis());  
}  
/**
* 得到本周第一天
* @return
*/
public static Calendar getFirstDayOfWeek() {  
   Calendar monday = Calendar.getInstance();  
   return getADayOfWeek(monday, Calendar.MONDAY);  
}  
/**
* 得到本周第一天
* @param day
* @return
*/
public static Calendar getFirstDayOfWeek(Calendar day) {  
   Calendar monday = (Calendar) day.clone();  
   return getADayOfWeek(monday, Calendar.MONDAY);  
}  
/**
 * 得到本周最后一天
 * @return
 */
public static Calendar getLastDayOfWeek() {  
   Calendar sunday = Calendar.getInstance();  
   return getADayOfWeek(sunday, Calendar.SUNDAY);  
}  
/**
 * 得到本周最后一天
 * @param day
 * @return
 */
public static Calendar getLastDayOfWeek(Calendar day) {  
   Calendar sunday = (Calendar) day.clone();  
   return getADayOfWeek(sunday, Calendar.SUNDAY);  
}  
 
private static Calendar getADayOfWeek(Calendar day, int dayOfWeek) {  
   int week = day.get(Calendar.DAY_OF_WEEK);  
   if (week == dayOfWeek)  
       return day;  
   int diffDay = dayOfWeek - week;  
   if (week == Calendar.SUNDAY) {  
       diffDay -= 7;  
   } else if (dayOfWeek == Calendar.SUNDAY) {  
       diffDay += 7;  
   }  
   day.add(Calendar.DATE, diffDay);  
   return day;  
}  

/**   
* 得到本月的第一天   
* @return   
*/    
public static Calendar getMonthFirstDay() {     
   Calendar calendar = Calendar.getInstance();     
   calendar.set(Calendar.DAY_OF_MONTH, calendar     
           .getActualMinimum(Calendar.DAY_OF_MONTH));     
   
   return calendar;    
}     
   
/**   
* 得到本月的最后一天   
*    
* @return   
*/    
public static Calendar getMonthLastDay() {     
   Calendar calendar = Calendar.getInstance();     
   calendar.set(Calendar.DAY_OF_MONTH, calendar     
           .getActualMaximum(Calendar.DAY_OF_MONTH));     
   return calendar;       
}     
/**
* 得到本年度第一天
* @return
*/
public static Calendar getYearFristDay(){
Calendar calendar =Calendar.getInstance();
int year=calendar.get(Calendar.YEAR);
calendar.clear();
calendar.set(Calendar.YEAR, year);
return calendar;
}
/**
* 得到本年度最后一天
* @return
*/
public static Calendar getYearLastDay(){
Calendar calendar =Calendar.getInstance();
int year=calendar.get(Calendar.YEAR);
calendar.clear();
calendar.set(Calendar.YEAR, year);
calendar.roll(Calendar.DAY_OF_YEAR, -1);
return calendar;
}
public static void main(String[] args){
Calendar day=Calendar.getInstance();
int month=day.get(Calendar.DAY_OF_MONTH);
System.out.println("month:"+month);
SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd 00:00:00");
String dates=format.format(MyCalendar.getDate(MyCalendar.getFirstDayOfWeek()));
String datee=format.format(MyCalendar.getDate(MyCalendar.getLastDayOfWeek()));
String months=format.format(MyCalendar.getDate(MyCalendar.getMonthFirstDay()));
String monthe=format.format(MyCalendar.getDate(MyCalendar.getMonthLastDay()));
String years=format.format(MyCalendar.getDate(MyCalendar.getYearFristDay()));
String yeare=format.format(MyCalendar.getDate(MyCalendar.getYearLastDay()));
System.out.println("weekday :"+dates+"=========== end:"+datee);
System.out.println("months :"+months+"=========== end:"+monthe);
System.out.println("years :"+years+"=========== end:"+yeare);
}
}

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