Calculate the difference between two java.util.Date objects

package com.takecargo.utils;

import java.util.Calendar;
import java.util.Date;
import java.util.concurrent.TimeUnit;

public class TCDateUtils {

    // a general method, independent of unit of time--it's specified as a parameter. see here for possible values: http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/TimeUnit.html
    // e.g.: TimeUnit.DAYS, TimeUnit.HOURS
    public static long getDateDiff(Date date1, Date date2, TimeUnit timeUnit) {
        long diffInMillies = date2.getTime() - date1.getTime();
        return timeUnit.convert(diffInMillies,TimeUnit.MILLISECONDS);
    }

    // http://stackoverflow.com/a/10650881/557194
    public static long getDateDiffInDays(Date date1, Date date2) {
        long diffInMillis = date2.getTime() - date1.getTime();
        return TimeUnit.MILLISECONDS.toDays(diffInMillis);  // http://stackoverflow.com/a/7829642/557194
    }

    // find out the number of hours (remainder) after the diffInDays value between date1 and date2
    public static int getHoursRemainderFromDateDiffInDays(Date date1, Date date2) {
        Calendar c1 = Calendar.getInstance();
        c1.setTime(date1);
        int hr1 = c1.get(Calendar.HOUR_OF_DAY);

        Calendar c2 = Calendar.getInstance();
        c2.setTime(date2);
        int hr2 = c2.get(Calendar.HOUR_OF_DAY);

        return Math.abs(hr2-hr1);
    }


    // find the "to date" calculated from today's date; return value should be equal to date2, above
    // @param days: will come from getDateDiffInDays()
    // @param hours: will come from getHoursRemainderFromDateDiffInDays()
    public static Date getToDateInXDaysAndXHours(long days, int hours) {
        Calendar toDate = Calendar.getInstance();
        toDate.add(Calendar.DAY_OF_YEAR, (int) days);
        toDate.add(Calendar.HOUR_OF_DAY, (int) ++hours);    // ++hours because HOUR_OF_DAY is zero-based
        return toDate.getTime();
    }



    // ########### TEST CODE ###############

    public static void main(String[] args) {
        Calendar today = Calendar.getInstance();
        Calendar tomorrow = Calendar.getInstance();
        tomorrow.add(Calendar.DAY_OF_YEAR, 1);

        System.out.println(getDateDiffInDays(today.getTime(), tomorrow.getTime())); // OUTPUT: 1
        System.out.println(getDateDiff(today.getTime(), tomorrow.getTime(), TimeUnit.DAYS));    // OUTPUT: 1
        System.out.println(getDateDiff(today.getTime(), tomorrow.getTime(), TimeUnit.HOURS));   // OUTPUT: 24

        // add 6 hours to "tomorrow"'s point in time
        tomorrow.add(Calendar.HOUR_OF_DAY, 6);

        System.out.println(getDateDiff(today.getTime(), tomorrow.getTime(), TimeUnit.HOURS));   // OUTPUT: 30

        Date toDate = getToDateInXDaysAndXHours(
                getDateDiffInDays(  // value: 1
                    today.getTime(),
                    tomorrow.getTime()
                ),
                getHoursRemainderFromDateDiffInDays(    // value: 6
                    today.getTime(),
                    tomorrow.getTime()
                )
        );
        System.out.println(toDate); // OUTPUT (e.g. today == "Tue Jun 10 11:41:13 CEST 2013"): Tue Jun 11 17:41:13 CEST 2013
    }
}