O (1) версия , которая работает и поддерживает различные шаблоны выходных и отрицательных дней:
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
public class DateUtil {
//Weekend patterns
public static final int WEEKEND_SAT_SUN = 0;
public static final int WEEKEND_FRI_SAT = 1;
public static final int WEEKEND_THU_FRI = 2;
public static final int WEEKEND_FRI_SUN = 3;
public static final int WEEKEND_FRI = 4;
public static final int WEEKEND_SAT = 5;
public static final int WEEKEND_SUN = 6;
//Weekend pattern by country
//@see https://en.wikipedia.org/wiki/Workweek_and_weekend
public static Map<String,Integer> weekendPatternByCountry = new HashMap<>();
static {
weekendPatternByCountry.put("CO",WEEKEND_SUN); //Colombia
weekendPatternByCountry.put("GQ",WEEKEND_SUN); //Equatorial Guinea
weekendPatternByCountry.put("IN",WEEKEND_SUN); //India
weekendPatternByCountry.put("MX",WEEKEND_SUN); //Mexico
weekendPatternByCountry.put("KP",WEEKEND_SUN); //North Korea
weekendPatternByCountry.put("UG",WEEKEND_SUN); //Uganda
weekendPatternByCountry.put("BN",WEEKEND_FRI_SUN); //Brunei Darussalam
weekendPatternByCountry.put("DJ",WEEKEND_FRI); //Djibouti
weekendPatternByCountry.put("IR",WEEKEND_FRI); //Iran
weekendPatternByCountry.put("AF",WEEKEND_THU_FRI); //Afghanistan
weekendPatternByCountry.put("NP",WEEKEND_SAT); //Nepal
weekendPatternByCountry.put("DZ",WEEKEND_FRI_SAT); //Algeria
weekendPatternByCountry.put("BH",WEEKEND_FRI_SAT); //Bahrain
weekendPatternByCountry.put("BD",WEEKEND_FRI_SAT); //Bangladesh
weekendPatternByCountry.put("EG",WEEKEND_FRI_SAT); //Egypt
weekendPatternByCountry.put("IQ",WEEKEND_FRI_SAT); //Iraq
weekendPatternByCountry.put("IL",WEEKEND_FRI_SAT); //Israel
weekendPatternByCountry.put("JO",WEEKEND_FRI_SAT); //Jordan
weekendPatternByCountry.put("KW",WEEKEND_FRI_SAT); //Kuwait
weekendPatternByCountry.put("LY",WEEKEND_FRI_SAT); //Libya
weekendPatternByCountry.put("MV",WEEKEND_FRI_SAT); //Maldives
weekendPatternByCountry.put("MR",WEEKEND_FRI_SAT); //Mauritania
weekendPatternByCountry.put("MY",WEEKEND_FRI_SAT); //Malaysia
weekendPatternByCountry.put("OM",WEEKEND_FRI_SAT); //Oman
weekendPatternByCountry.put("PS",WEEKEND_FRI_SAT); //Palestine
weekendPatternByCountry.put("QA",WEEKEND_FRI_SAT); //Qatar
weekendPatternByCountry.put("SA",WEEKEND_FRI_SAT); //Saudi Arabia
weekendPatternByCountry.put("SD",WEEKEND_FRI_SAT); //Sudan
weekendPatternByCountry.put("SY",WEEKEND_FRI_SAT); //Syria
weekendPatternByCountry.put("AE",WEEKEND_FRI_SAT); //United Arab Emirates
weekendPatternByCountry.put("YE",WEEKEND_FRI_SAT); //Yemen
}
//Adjustment vectors - precomputed adjustment
static int[][][] adjVector = new int[][][]{
{//WEEKEND_SAT_SUN
//Positive number of days
{1,0,-1,-2,-3,1,1},
{0,0},
{0,0,0,0,0,2,1},
//Negative number of days
{-1,3,2,1,0,-1,-1},
{0,0},
{-1,1,1,1,1,1,0}
},
{//WEEKEND_FRI_SAT
//Positive number of days
{0,-1,-2,-3,1,1,1},
{0,0},
{0,0,0,0,2,1,0},
//Negative number of days
{3,2,1,0,-1,-1,-1},
{0,0},
{1,1,1,1,1,0,-1}
},
{//WEEKEND_THU_FRI
//Positive number of days
{-1,-2,-3,1,1,1,0},
{0,0},
{0,0,0,2,1,0,0},
//Negative number of days
{2,1,0,-1,-1,-1,3},
{0,0},
{1,1,1,1,0,-1,1}
},
{//WEEKEND_FRI_SUN
//Positive number of days
{0,-1,-2,-3,-4,-4,0},
{1,0},
{0,0,0,0,0,-1,1},
//Negative number of days
{4,3,2,1,0,0,4},
{0,-1},
{1,1,1,1,1,0,2}
},
{//WEEKEND_FRI
//Positive number of days
{-1,-2,-3,-4,1,1,0},
{0},
{0,0,0,0,1,0,0},
//Negative number of days
{3,2,1,0,-1,-1,4},
{0},
{1,1,1,1,1,0,1}
},
{//WEEKEND_SAT
//Positive number of days
{0,-1,-2,-3,-4,1,1},
{0},
{0,0,0,0,0,1,0},
//Negative number of days
{4,3,2,1,0,-1,-1},
{0},
{1,1,1,1,1,1,0}
},
{//WEEKEND_SUN
//Positive number of days
{1,0,-1,-2,-3,-4,1},
{0},
{0,0,0,0,0,0,1},
//Negative number of days
{-1,4,3,2,1,0,-1},
{0},
{0,1,1,1,1,1,1}
}
};
//O(1) algorithm to add business days.
public static Date addBusinessDays(Date day, int days,int weekendPattern){
Calendar ret = Calendar.getInstance();
if(day != null) {
ret.setTime(day);
}
if(days != 0) {
int startDayofWeek = ret.get(Calendar.DAY_OF_WEEK)-1; //Zero based to use the vectors bellow.
int idx = days > 0 ? 0 : 3;
int howManyWeekendDays = 0;
int[][] adjV = adjVector[weekendPattern];
int numWeekendDaysInOneWeek = adjV[idx+1].length;
for(int i = 0; i < numWeekendDaysInOneWeek;i++){
int adjustmentA = adjV[idx][startDayofWeek]; //pattern shift
int adjustmentB = adjV[idx+1][i]; //day shift
howManyWeekendDays += (days-adjustmentA-adjustmentB)/(7-numWeekendDaysInOneWeek);
}
int adjustmentC = adjV[idx+2][startDayofWeek]; //f(0) adjustment
howManyWeekendDays += adjustmentC;
ret.add(Calendar.DATE,days + howManyWeekendDays);
//TODO: Extend to support holidays using recursion
// int numHolidays = getNumHolidaysInInterval(day,ret.getTime());
// if(numHolidays > 0) return addBusinessDays(ret.getTime,numHolidays);
}
return ret.getTime();
}
public static Date addBusinessDays(Date day, int days,String country){
Integer weekpat = weekendPatternByCountry.get(country);
return weekpat != null ? addBusinessDays(day,days,weekpat) : addBusinessDays(day,days,WEEKEND_SAT_SUN);
}
}