write a DayTester program that constructs a Day object representing today, adds ten days to it, and then computes the difference between that day and today. Print the difference and the expected value.

HAVE TO USE THIS SOURCE CODE.

/**

A Day object represents a day in the Julian/Gregorian calendar.

*/

import java.util.GregorianCalendar;

public class Day

{

private int year;

private int month;

private int date;

private static final int[] DAYS_PER_MONTH

= { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

private static final int GREGORIAN_START_YEAR = 1582;

private static final int GREGORIAN_START_MONTH = 10;

private static final int GREGORIAN_START_DAY = 15;

private static final int JULIAN_END_DAY = 4;

private static final int JANUARY = 1;

private static final int FEBRUARY = 2;

private static final int DECEMBER = 12;

/**

Constructs a day object representing today's date.

*/

public Day()

{

GregorianCalendar today = new GregorianCalendar();

year = today.get(GregorianCalendar.YEAR);

month = today.get(GregorianCalendar.MONTH) + 1;

date = today.get(GregorianCalendar.DAY_OF_MONTH);

}

/**

Constructs a day with a given year, month, and day

of the Julian/Gregorian calendar. The Julian calendar

is used for all days before October 15, 1582

@param aYear a year != 0

@param aMonth a month between 1 and 12

@param aDate a date between 1 and 31

*/

public Day(int aYear, int aMonth, int aDate)

{

year = aYear;

month = aMonth;

date = aDate;

}

/**

Returns the year of this day.

@return the year

*/

public int getYear()

{

return year;

}

/**

Returns the month of this day.

@return the month

*/

public int getMonth()

{

return month;

}

/**

Returns the day of the month of this day.

@return the day of the month

*/

public int getDate()

{

return date;

}

/**

Returns a day that is a certain number of days away from

this day.

@param n the number of days, can be negative

@return a day that is n days away from this one

*/

public Day addDays(int n)

{

Day result = this;

while (n > 0)

{

result = result.nextDay();

n--;

}

while (n < 0)

{

result = result.previousDay();

n++;

}

return result;

}

/**

Returns the number of days between this day and another

day.

@param other the other day

@return the number of days that this day is away from

the other (>0 if this day comes later than other)

*/

public int daysFrom(Day other)

{

int n = 0;

Day d = this;

while (d.compareTo(other) > 0)

{

d = d.previousDay();

n++;

}

while (d.compareTo(other) < 0)

{

d = d.nextDay();

n--;

}

return n;

}

public String toString()

{

return String.format("%04d-%02d-%02d", year, month, date);

}

/**

Compares this day with another day.

@param other the other day

@return a positive number if this day comes after the

other day, a negative number if this day comes before

the other day, and zero if the days are the same

*/

private int compareTo(Day other)

{

if (year > other.year) return 1;

if (year < other.year) return -1;

if (month > other.month) return 1;

if (month < other.month) return -1;

return date - other.date;

}

/**

Computes the next day.

@return the day following this day

*/

private Day nextDay()

{

int y = year;

int m = month;

int d = date;

if (y == GREGORIAN_START_YEAR

&& m == GREGORIAN_START_MONTH

&& d == JULIAN_END_DAY)

d = GREGORIAN_START_DAY;

else if (d < daysPerMonth(y, m))

d++;

else

{

d = 1;

m++;

if (m > DECEMBER)

{

m = JANUARY;

y++;

if (y == 0) y++;

}

}

return new Day(y, m, d);

}

/**

Computes the previous day.

@return the day preceding this day

*/

private Day previousDay()

{

int y = year;

int m = month;

int d = date;

if (y == GREGORIAN_START_YEAR

&& m == GREGORIAN_START_MONTH

&& d == GREGORIAN_START_DAY)

d = JULIAN_END_DAY;

else if (d > 1)

d--;

else

{

m--;

if (m < JANUARY)

{

m = DECEMBER;

y--;

if (y == 0) y--;

}

d = daysPerMonth(y, m);

}

return new Day(y, m, d);

}

/**

Gets the days in a given month.

@param y the year

@param m the month

@return the last day in the given month

*/

private static int daysPerMonth(int y, int m)

{

int days = DAYS_PER_MONTH[m - 1];

if (m == FEBRUARY && isLeapYear(y))

days++;

return days;

}

/**

Tests if a year is a leap year.

@param y the year

@return true if y is a leap year

*/

private static boolean isLeapYear(int y)

{

if (y % 4 != 0) return false;

if (y < GREGORIAN_START_YEAR) return true;

return (y % 100 != 0) || (y % 400 == 0);

}

}