How can I add business days to the current date in Java?

Question

How can I add business days to the current date in Java?

public Calendar addBusinessDate(Calendar cal, int days) {
//
// code goes over here
//
}
         


        

Answer 1

O(1) version that works and supports different weekend patterns and negative days:

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 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);
}
}