Java Day of Week weeksBetween(Date early, Date late)

Description

Returns the weeks between two dates.

License

Open Source License

Parameter

Parameter	Description
early	the "first date"
late	the "second date"

Return

the weeks between the two dates

Declaration

public static final int weeksBetween(Date early, Date late) 

Method Source Code

//package com.java2s;
//License from project: Open Source License 

import java.util.Calendar;
import java.util.Date;

public class Main {
    /**/* w  w w.  j  av  a 2 s  .c o m*/
     * Returns the weeks between two dates.
     * 
     * @param early
     *            the "first date"
     * @param late
     *            the "second date"
     * @return the weeks between the two dates
     */
    public static final int weeksBetween(Date early, Date late) {
        Calendar c1 = Calendar.getInstance();
        Calendar c2 = Calendar.getInstance();
        c1.setTime(early);
        c2.setTime(late);
        int days = daysBetween(c1, c2) + 1;
        int earlyweek = c1.get(Calendar.DAY_OF_WEEK);
        int lateweek = c2.get(Calendar.DAY_OF_WEEK);
        int weeks = days / 7;
        int weekst = days % 7;
        if (weekst == 0) {
            return weeks;
        } else if (lateweek >= earlyweek) {
            return weeks + 1;
        } else {
            return weeks + 2;
        }
    }

    public static final int daysBetween(Calendar early, Calendar late) {
        return (int) (toJulian(late) - toJulian(early));
    }

    public static final int daysBetween(Date early, Date late) {
        Calendar c1 = Calendar.getInstance();
        Calendar c2 = Calendar.getInstance();
        c1.setTime(early);
        c2.setTime(late);
        return daysBetween(c1, c2);
    }

    /**
     * Return a Julian date based on the input parameter. This is based from
     * calculations found at
     * 
     * <pre>
     * <a href="http://quasar.as.utexas.edu/BillInfo/JulianDatesG.html">Julian Day
     * Calculations (Gregorian Calendar)</a>, provided by Bill Jeffrys.
     * </pre>
     * 
     * @param c
     *            a calendar instance
     * @return the julian day number
     */
    public static final float toJulian(Calendar c) {
        int Y = c.get(Calendar.YEAR);
        int M = c.get(Calendar.MONTH);
        int D = c.get(Calendar.DATE);
        int A = Y / 100;
        int B = A / 4;
        int C = 2 - A + B;
        float E = (int) (365.25f * (Y + 4716));
        float F = (int) (30.6001f * (M + 1));
        float JD = C + D + E + F - 1524.5f;

        return JD;
    }
}

Related

1. weekDay(final Date date)
2. weekDaysBetween(final Date a, final Date b)
3. WeekOfTheYear(Date dt)
4. weekOfYear(Date date)
5. weeksBetween(Date date1, Date date2)
6. weekStart(Date date)
7. weekStart(Date date)