AgeCalculator

Age.java

public class Age {

    private int days;
    private int months;
    private int years;

    public Age(int days, int months, int years) {
        this.days = days;
        this.months = months;
        this.years = years;
    }

    public int getDays() {
        return days;
    }

    public void setDays(int days) {
        this.days = days;
    }

    public int getMonths() {
        return months;
    }

    public void setMonths(int months) {
        this.months = months;
    }

    public int getYears() {
        return years;
    }

    public void setYears(int years) {
        this.years = years;
    }
}

AgeCalculator.java

   public static Age calculateAge(Date birthDate) {
        int years = 0;
        int months = 0;
        int days = 0;
        //create calendar object for birth day
        Calendar birthDay = Calendar.getInstance();
        birthDay.setTimeInMillis(birthDate.getTime());
        //create calendar object for current day
        long currentTime = System.currentTimeMillis();
        Calendar now = Calendar.getInstance();
        now.setTimeInMillis(currentTime);
        //Get difference between years
        years = now.get(Calendar.YEAR) - birthDay.get(Calendar.YEAR);
        int currMonth = now.get(Calendar.MONTH) + 1;
        int birthMonth = birthDay.get(Calendar.MONTH) + 1;
        //Get difference between months
        months = currMonth - birthMonth;
        //if month difference is in negative then reduce years by one and calculate the number of months.
        if (months < 0) {
            years--;
            months = 12 - birthMonth + currMonth;
            if (now.get(Calendar.DATE) < birthDay.get(Calendar.DATE))
                months--;
        } else if (months == 0 && now.get(Calendar.DATE) < birthDay.get(Calendar.DATE)) {
            years--;
            months = 11;
        }
        //Calculate the days
        if (now.get(Calendar.DATE) > birthDay.get(Calendar.DATE))
            days = now.get(Calendar.DATE) - birthDay.get(Calendar.DATE);
        else if (now.get(Calendar.DATE) < birthDay.get(Calendar.DATE)) {
            int today = now.get(Calendar.DAY_OF_MONTH);
            now.add(Calendar.MONTH, -1);
            days = now.getActualMaximum(Calendar.DAY_OF_MONTH) - birthDay.get(Calendar.DAY_OF_MONTH) + today;
        } else {
            days = 0;
            if (months == 12) {
                years++;
                months = 0;
            }
        }
        //Create new Age object
        return new Age(days, months, years);
    }