The document describes a Java class named 'date' that represents a date with fields for year, month, and day, along with methods for date manipulation such as adding days, checking for leap years, and forming string representations of dates. Additionally, it includes a 'birthday' class that calculates a person's age on a specific date based on user input. Key features include exception handling for invalid dates, methods for determining days in a month, and weekday calculations.

1. Date class that represents a date consisting of a year, month, and a day
import java.util.TimeZone;
public class Date {
// constants
private static final int JANUARY = 1;
private static final int FEBRUARY = 2;
private static final int DECEMBER = 12;
private static final int DAYS_PER_WEEK = 7;
private static final int DAYS_PER_YEAR = 365;
private static final int DAYS_PER_LEAP_YEAR = 366;
private static final String[] DAY_NAMES = {"SUNDAY", "MONDAY", "TUESDAY",
"WEDNESDAY", "THURSDAY", "FRIDAY", "SATRDAY"};
private static final int[] DAYS_PER_MONTH = { -1,
// 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31,
};
// fields
private int year;
private int month;
private int day;
/**
Constructs a new object representing the given year, month, and day.
@throws IllegalArgumentException if month is not between 1 and 12, or if day is not between 1
and the number of days in that month.
*/
public Date(int year, int month, int day) {
this.year = year;
this.month = month;
this.day = day;
if (month < 1 || month > 12 || day < 1 || day > getDaysInMonth()) {
throw new IllegalArgumentException("Invalid day or month: " + toString());
}
}

2. /** Constructs a new object representing today's date. */
public Date() {
this(2006, july
, 22);
int daysSinceEpoch = (int) ((System.currentTimeMillis() +
TimeZone.getDefault().getRawOffset()) / 1000 / 60 / 60 / 24);
for (int i = 0; i < daysSinceEpoch; i++) {
nextDay();
}
}
/**
Adds the given number of days to this Date.
@throws IllegalArgumentException if days < 0.
*/
public void addDays(int days) {
while (days > getDaysInYear()) {
days -= getDaysInYear();
year++;
}
for (int i = 1; i <= days; i++) {
nextDay();
}
}
/**
Returns whether o refers to a Date object representing the same
year, month, and day as this one.
*/
public boolean equals(Object o) {
Date other = (Date) o;
return day == other.day &&
month == other.month &&

3. year == other.year;
}
/**
Returns the day represented by this Date object.
@return the day, between 1 and the number of days in this Date's month
(which varies from 28 to 31)
*/
public int getDay() {
return day;
}
/** Returns the number of days in the month represented by the current Date. */
public int getDaysInMonth() {
int result = DAYS_PER_MONTH[month];
if (month == FEBRUARY && isLeapYear()) {
result++;
}
return result;
}
public int getDaysInYear() {
if (isLeapYear()) {
return 366;
} else {
return 365;
}
}
/**
Returns a string such as "Monday" representing what day of the week
this Date fell on.
@return the day as either "Sunday", "Monday", "Tuesday, "Wednesday", "Thursday",
"Friday", or "Satrday"
*/
public String getDayOfWeek() {
int index = 1;
Date temp = new Date(1753, JANUARY, 1);

4. while (temp != this) {
temp.nextDay();
index = (index + 1) % DAYS_PER_WEEK;
}
return DAY_NAMES[index];
}
/**
Returns the month represented by this Date object.
@return the month, between 1 and 12
*/
public int getMonth() {
return month;
}
/**
Returns the year represented by this Date object.
@return the year
*/
public int getYear() {
return year;
}
/**
Returns whether this Date falls on a leap year.
@return true if in a year divisible by 4 but not by 100 unless by 400
*/
public boolean isLeapYear() {
return (year % 400 == 0) || (year % 4 == 0 && year % 100 != 0);
}
/**
Advances this Date to the next day.
If necessary, wraps to the next month and/or year.
*/

5. public void nextDay() {
day++;
if (day > getDaysInMonth()) {
// wrap to next month
month++;
day = 1;
if (month > DECEMBER) {
// wrap to next year
year++;
month = JANUARY;
}
}
}
/**
Returns a String representation of this Date.
@return a String such as "2007/07/26" for July 26, 2007
*/
public String toString() {
return year + "/" + pad(month) + "/" + pad(day);
}
private String pad(int n) {
if (n < 10) {
return "0" + n;
} else {
return "" + n;
}
}
}
/* get a birthday and say how old the person will be on september 29, 2016
*/
import java.util.Scanner;
public class birthday
{

6. public static void main(String[] args)
{
String birthday, month;
int date, year, monthNum = 0;
Scanner kb = new Scanner(System.in);
int age;
int leapdays;
System.out.print("enter birthday (in english): ");
birthday = kb.nextLine();
Scanner readBday = new Scanner(birthday);
month = readBday.next();
String dateString = readBday.next();
dateString = dateString.substring(0,dateString.length()-1);
date = Integer.parseInt(dateString);
/* our logic was flawed here - leap year status applies to 2016, not to the birth year
however, we can use this code if we write a more general version of the program
year = readBday.nextInt();
if ((year % 4 == 0 && year %100 != 0) || year %400 == 0)
leapdays = 29; // is a leap year
else leapdays = 28; // not a leap year
*/
leapdays = 28; // 2016 is not a leap year
System.out.println("you entered: " + month + " "
+ date + ", " + year);
if (month.equalsIgnoreCase("january"))
monthNum = 1;
else if (month.equalsIgnoreCase("february"))
monthNum = 2;
else if (month.equalsIgnoreCase("march"))
monthNum = 3;

7. else if (month.equalsIgnoreCase("april"))
monthNum = 4;
else if (month.equalsIgnoreCase("may"))
monthNum = 5;
else if (month.equalsIgnoreCase("june"))
monthNum = 6;
else if (month.equalsIgnoreCase("july"))
monthNum = 7;
else if (month.equalsIgnoreCase("august"))
monthNum = 8;
else if (month.equalsIgnoreCase("september"))
monthNum = 9;
else if (month.equalsIgnoreCase("october"))
monthNum = 10;
else if (month.equalsIgnoreCase("november"))
monthNum = 11;
else if (month.equalsIgnoreCase("december"))
monthNum = 12;
System.out.println("you entered: " + monthNum + "/"
+ date + "/" + year);
int days = 0;
switch (monthNum) {
case 1: case 3: case 5:
case 7: case 8: case 10: case 12:
days += 31 - date;
break;
case 9: case 4: case 11: days += 30 - date;
break;
case 2: days += leapdays - date;
break;
default:
}

8. switch (monthNum) {
case 1: days += leapdays;
case 2: days += 31;
case 3: days += 30;
case 4: days += 31;
case 5: days += 30;
case 6: days += 31;
case 7: days += 31;
case 8: days += 30;
case 9: days += 31;
case 10: days += 30;
case 11: days += 31;
default:
}
System.out.print("on 9/30/2016 you will be: ");
age = 2016 - year - 1;
System.out.print(age + " year(s) and " + days + " day(s) old");
}
}
Solution
Date class that represents a date consisting of a year, month, and a day
import java.util.TimeZone;
public class Date {
// constants
private static final int JANUARY = 1;
private static final int FEBRUARY = 2;
private static final int DECEMBER = 12;
private static final int DAYS_PER_WEEK = 7;
private static final int DAYS_PER_YEAR = 365;
private static final int DAYS_PER_LEAP_YEAR = 366;
private static final String[] DAY_NAMES = {"SUNDAY", "MONDAY", "TUESDAY",
"WEDNESDAY", "THURSDAY", "FRIDAY", "SATRDAY"};
private static final int[] DAYS_PER_MONTH = { -1,

9. // 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31,
};
// fields
private int year;
private int month;
private int day;
/**
Constructs a new object representing the given year, month, and day.
@throws IllegalArgumentException if month is not between 1 and 12, or if day is not between 1
and the number of days in that month.
*/
public Date(int year, int month, int day) {
this.year = year;
this.month = month;
this.day = day;
if (month < 1 || month > 12 || day < 1 || day > getDaysInMonth()) {
throw new IllegalArgumentException("Invalid day or month: " + toString());
}
}
/** Constructs a new object representing today's date. */
public Date() {
this(2006, july
, 22);
int daysSinceEpoch = (int) ((System.currentTimeMillis() +
TimeZone.getDefault().getRawOffset()) / 1000 / 60 / 60 / 24);
for (int i = 0; i < daysSinceEpoch; i++) {
nextDay();
}
}
/**

10. Adds the given number of days to this Date.
@throws IllegalArgumentException if days < 0.
*/
public void addDays(int days) {
while (days > getDaysInYear()) {
days -= getDaysInYear();
year++;
}
for (int i = 1; i <= days; i++) {
nextDay();
}
}
/**
Returns whether o refers to a Date object representing the same
year, month, and day as this one.
*/
public boolean equals(Object o) {
Date other = (Date) o;
return day == other.day &&
month == other.month &&
year == other.year;
}
/**
Returns the day represented by this Date object.
@return the day, between 1 and the number of days in this Date's month
(which varies from 28 to 31)
*/
public int getDay() {
return day;
}
/** Returns the number of days in the month represented by the current Date. */
public int getDaysInMonth() {
int result = DAYS_PER_MONTH[month];

11. if (month == FEBRUARY && isLeapYear()) {
result++;
}
return result;
}
public int getDaysInYear() {
if (isLeapYear()) {
return 366;
} else {
return 365;
}
}
/**
Returns a string such as "Monday" representing what day of the week
this Date fell on.
@return the day as either "Sunday", "Monday", "Tuesday, "Wednesday", "Thursday",
"Friday", or "Satrday"
*/
public String getDayOfWeek() {
int index = 1;
Date temp = new Date(1753, JANUARY, 1);
while (temp != this) {
temp.nextDay();
index = (index + 1) % DAYS_PER_WEEK;
}
return DAY_NAMES[index];
}
/**
Returns the month represented by this Date object.
@return the month, between 1 and 12
*/
public int getMonth() {
return month;

12. }
/**
Returns the year represented by this Date object.
@return the year
*/
public int getYear() {
return year;
}
/**
Returns whether this Date falls on a leap year.
@return true if in a year divisible by 4 but not by 100 unless by 400
*/
public boolean isLeapYear() {
return (year % 400 == 0) || (year % 4 == 0 && year % 100 != 0);
}
/**
Advances this Date to the next day.
If necessary, wraps to the next month and/or year.
*/
public void nextDay() {
day++;
if (day > getDaysInMonth()) {
// wrap to next month
month++;
day = 1;
if (month > DECEMBER) {
// wrap to next year
year++;
month = JANUARY;
}
}
}

13. /**
Returns a String representation of this Date.
@return a String such as "2007/07/26" for July 26, 2007
*/
public String toString() {
return year + "/" + pad(month) + "/" + pad(day);
}
private String pad(int n) {
if (n < 10) {
return "0" + n;
} else {
return "" + n;
}
}
}
/* get a birthday and say how old the person will be on september 29, 2016
*/
import java.util.Scanner;
public class birthday
{
public static void main(String[] args)
{
String birthday, month;
int date, year, monthNum = 0;
Scanner kb = new Scanner(System.in);
int age;
int leapdays;
System.out.print("enter birthday (in english): ");
birthday = kb.nextLine();
Scanner readBday = new Scanner(birthday);
month = readBday.next();

14. String dateString = readBday.next();
dateString = dateString.substring(0,dateString.length()-1);
date = Integer.parseInt(dateString);
/* our logic was flawed here - leap year status applies to 2016, not to the birth year
however, we can use this code if we write a more general version of the program
year = readBday.nextInt();
if ((year % 4 == 0 && year %100 != 0) || year %400 == 0)
leapdays = 29; // is a leap year
else leapdays = 28; // not a leap year
*/
leapdays = 28; // 2016 is not a leap year
System.out.println("you entered: " + month + " "
+ date + ", " + year);
if (month.equalsIgnoreCase("january"))
monthNum = 1;
else if (month.equalsIgnoreCase("february"))
monthNum = 2;
else if (month.equalsIgnoreCase("march"))
monthNum = 3;
else if (month.equalsIgnoreCase("april"))
monthNum = 4;
else if (month.equalsIgnoreCase("may"))
monthNum = 5;
else if (month.equalsIgnoreCase("june"))
monthNum = 6;
else if (month.equalsIgnoreCase("july"))
monthNum = 7;
else if (month.equalsIgnoreCase("august"))
monthNum = 8;
else if (month.equalsIgnoreCase("september"))
monthNum = 9;
else if (month.equalsIgnoreCase("october"))
monthNum = 10;

15. else if (month.equalsIgnoreCase("november"))
monthNum = 11;
else if (month.equalsIgnoreCase("december"))
monthNum = 12;
System.out.println("you entered: " + monthNum + "/"
+ date + "/" + year);
int days = 0;
switch (monthNum) {
case 1: case 3: case 5:
case 7: case 8: case 10: case 12:
days += 31 - date;
break;
case 9: case 4: case 11: days += 30 - date;
break;
case 2: days += leapdays - date;
break;
default:
}
switch (monthNum) {
case 1: days += leapdays;
case 2: days += 31;
case 3: days += 30;
case 4: days += 31;
case 5: days += 30;
case 6: days += 31;
case 7: days += 31;
case 8: days += 30;
case 9: days += 31;
case 10: days += 30;
case 11: days += 31;
default:
}

16. System.out.print("on 9/30/2016 you will be: ");
age = 2016 - year - 1;
System.out.print(age + " year(s) and " + days + " day(s) old");
}
}