Find Previous Day From a Given Day

Question

Hey guys, I'm new here and I just recently started working with Java, I am trying to figure out how to find the previous day for the 1st day and month of a year_. I.E. if passed the date (1,1,2000) in the mm/dd/yyyy format then the output would be (12,31,1999). I have everything worked out except I have to figure out how to find the last day of the previous month. I am trying to write this all from scratch to better understand Java, so i do not want to use the Calendar class or anything involved with it.
This is a handful of code that may not be formatted a bit sloppily, but if anyone has the time, I would greatly appreciate the help. (Also, I am aware that Java autmatically puts "this." if it is missing before a variable, I put mine in order to clearly see what's going on.) I made a test Class as well is anyone is interested in seeing it.
Also, how come the Java formatting does not show in the post?
* Date calculates the date and gives other information requested such as the birthday of someone, the
* previous and next days, whether the date is valid or not, and whether the year is a leap year
* @author Vlad Khmarsky
* @version 1.1
public class Date
/** The month */
int month = 00;
/** The day */
int day = 00;
/** The year */
int year = 0000;
/** First month of the year */
int firstMonth = 1;
/** Last month of the year */
int lastMonth = 12;
/** Asks for the day, month, and year upon creting an instance of dates
* @day asks for the day
* @month asks for the month
* @year asks for the year
Date( int month_, int day_, int year_) {
this.month = month_;
this.day = day_;
this.year = year_;
/** Gets the month passed in initially
* @return The month that is currently stored in the month field
int getMonth() {
return this.month;
/** Gets the day passed in initially
* @return The day that is currently stored in the month field
int getDay() {
return this.day;
/** Gets the year passed in initially
* @return The year that is currently stored in the month field
int getYear() {
return this.year;
/** Gets the number of days in the given month
* @return the number of days in the given month
int getDaysInTheMonth() {
return this.daysInTheMonth();
/** Returns the date in Gregorian format
* @return Returns the date in Gregorian format
* Test Cases:
* this.Dates(12, 10, 1989) = "12/10/1989"
* this.Dates(54, 67, 9999) = "54/67/9999"
* this.Dates(-1, -9, -900) = "-1/-9/-900"
String toPrettyString() {
return month + "/" + day + "/" + year;
/** Checks whether the passed in date is valid or not
* @return A true or false whether the date is valid
* Test Cases:
* this.Dates(12, 10, 1989) = true
* this.Dates(54, 67, 9999) = false
* this.Dates(-1, -9, -900) = false
boolean isValid() {
if (this.getDay() >= 0
&& this.getDay() <= 31
&& this.getMonth() >= 0
&& this.getMonth() <= 12) {
return true;
else {
return false;
/** Calculates the age of a person given the date
* @return The age of the person
* Test Cases:
* this.Dates(12, 10, 1990), dateMarked.Dates(12, 10, 0) = 1990
* this.Dates( 4, 25, 1000), dateMarked.Dates(12, 10, -990) = 1990
* this.Dates( 1, 1, 2578), dateMarked.Dates(12, 10, 1989) = 589
int calculateAge( Date birthday ) {
return (this.getYear() - birthday.getYear());
/** Do two dates represent the exact same day?
* @param other The date to compare this Date against.
* @return true if (and only if) this Date represents the same day as other.
* (that is, the same year, month, day-of-month).
* Test Cases:
* this.Dates(12, 10, 1989), other.Dates(12, 10, 1989) = true
* this.Dates(12, 10, 1989), other.Dates(11, 10, 1989) = false
* this.Dates(12, 10, 1989), other.Dates(12, 9, 1989) = false
* this.Dates(12, 10, 1989), other.Dates(12, 10, 1988) = false
boolean isEqualTo( Date otherDate ) {
if (this.getDay() == otherDate.getDay()
&& this.getMonth() == otherDate.getMonth()
&& this.getYear() == otherDate.getYear()) {
return true;
else {
return false;
/** Does one Date precede another?
* @param other The date to compare this Date against.
* @return true if (and only if) this Date comes before other.
* this.Dates( 5, 5, 2000), other.Dates( 5, 6, 2000) = true
* this.Dates( 5, 5, 2000), other.Dates( 6, 5, 2000) = true
* this.Dates( 5, 5, 2000), other.Dates( 5, 5, 2001) = true
* this.Dates( 5, 5, 2000), other.Dates( 5, 4, 2000) = false
* this.Dates( 5, 5, 2000), other.Dates( 5, 5, 1999) = false
* this.Dates( 5, 5, 2000), other.Dates( 4, 5, 2000) = false
boolean isBefore( Date otherDate ) {
if (this.getYear() <= otherDate.getYear()
&& this.getMonth() <= otherDate.getMonth()
&& this.getDay() < otherDate.getDay()) {
return true;
else if (this.getYear() <= otherDate.getYear()
&& this.getMonth() < otherDate.getMonth()) {
return true;
else if (this.getYear() < otherDate.getYear()) {
return true;
else {
return false;
/** Determines how many days there are in the month, given the instance's specified month and year
* @Return returns the number of days in the month
int daysInTheMonth () {
if (this.isValid() == true) {
if (this.getMonth() == 2) {
if (this.isLeapYear() == true) {
return 29;
else {
return 28;
else if (this.getMonth() == 1
|| this.getMonth() == 3
|| this.getMonth() == 5
|| this.getMonth() == 7
|| this.getMonth() == 8
|| this.getMonth() == 10
|| this.getMonth() == 12) {
return 31;
else {
return 30;
else {
return 0;
/** Return the day after `this`. (`this` must be a valid date.)
* @return the day after `this`. The result will be valid if `this` is valid.
Date nextDay() {
if (this.getDay() == this.getDaysInTheMonth() && this.getMonth() == 12) {
return new Date(1, 1, this.getYear() + 1);
else if (this.getDay() == this.getDaysInTheMonth()) {
return new Date(this.getMonth() + 1, 1, this.getYear());
else {
return new Date(this.getMonth(), this.getDay() + 1, this.getYear());
/** Return the day before `this`. (`this` must be a valid date.)
* @return the day before `this`. The result will be valid if `this` is valid.
Date previousDay() {
if (this.getDay() == 1 && this.getMonth() == 1) {
return new Date(12, this.getDaysInTheMonth(), this.getYear() - 1);
//Need to fix the days in the previous month and previous month
else if (this.getDay() == 1) {
return new Date(this.getMonth() - 1, this.getDaysInTheMonth() - 1,
this.getYear()); //need to fix the days in the previous month
else {
return new Date(this.getMonth() - 1, this.getDaysInTheMonth(), this.getYear());
/** Returns a true or false depending on whether the year is a leap year or not
* @return a true or false depending on whether the year is a leap year or not
* Test Cases:
* this.Dates( 5, 5, 2000) = true
* this.Dates(12, 6, 2004) = true
* this.Dates( 1, 1, 2001) = false
* this.Dates( 7, 9, 2006) = false
boolean isLeapYear () {
if (this.getYear() % 400 == 0) {
return true;
else if (this.getYear() % 100 == 0) {
return false;
else if (this.getYear() % 4 ==0) {
return true;
else {
return false;
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Edited by: THE_Russian on Sep 28, 2007 4:35 PM

Answer 1

Yeahhhh... that's exactly what I was trying not to do, I know that method, I don't want any associations with the Calendar class, thanks though
Aw crap, you can't edit the original post? Sorry everyone for the unformatted code, here's the formatted version
* Date calculates the date and gives other information requested such as the birthday of someone, the
*  previous and next days, whether the date is valid or not, and whether the year is a leap year
* @author Vlad Khmarsky
* @version 1.1
public class Date
/** The month */
    int month = 00;
/** The day */
    int day = 00;
/** The year */
    int year = 0000;
/** First month of the year */
    int firstMonthInYear = 1;
/** Last month of the year */
    int lastMonthInYear = 12;
/** First day of the month */
    int firstDayInMonth = 1;
/** Asks for the day, month, and year upon creting an instance of dates
   * @day asks for the day
   * @month asks for the month
   * @year asks for the year
    Date( int month_, int day_, int year_) {
        this.month = month_;
        this.day = day_;
        this.year = year_;
/** Gets the month passed in initially
   * @return The month that is currently stored in the month field
    int getMonth() {
        return this.month;
/** Gets the day passed in initially
   * @return The day that is currently stored in the month field
    int getDay() {
        return this.day;
/** Gets the year passed in initially
   * @return The year that is currently stored in the month field
    int getYear() {
        return this.year;
/** Gets the number of days in the given month
   * @return the number of days in the given month
    int getDaysInTheMonth() {
        return this.daysInTheMonth();
/** Returns the date in Gregorian format
   * @return Returns the date in Gregorian format
   * Test Cases:
   *    this.Dates(12, 10, 1989) = "12/10/1989"
   *    this.Dates(54, 67, 9999) = "54/67/9999"
   *    this.Dates(-1, -9, -900) = "-1/-9/-900"
    String toPrettyString() {
        return month + "/" + day + "/" + year;
/** Checks whether the passed in date is valid or not
   * @return A true or false whether the date is valid
   * Test Cases:
   *    this.Dates(12, 10, 1989) = true
   *    this.Dates(54, 67, 9999) = false
   *    this.Dates(-1, -9, -900) = false
    boolean isValid() {
        if (this.getDay() >= 0
            && this.getDay() <= 31
            && this.getMonth() >= 0
            && this.getMonth() <= 12) {
            return true;
        else {
            return false;
/** Calculates the age of a person given the date
   * @return The age of the person
   * Test Cases:
   *    this.Dates(12, 10, 1990), dateMarked.Dates(12, 10,    0) = 1990
   *    this.Dates( 4, 25, 1000), dateMarked.Dates(12, 10, -990) = 1990
   *    this.Dates( 1,  1, 2578), dateMarked.Dates(12, 10, 1989) =  589
    int calculateAge( Date birthday ) {
        return (this.getYear() - birthday.getYear());
/** Do two dates represent the exact same day?
   * @param other The date to compare this Date against.
   * @return true if (and only if) this Date represents the same day as other.
   *  (that is, the same year, month, day-of-month).
   *  Test Cases:
   *    this.Dates(12, 10, 1989), other.Dates(12, 10, 1989) = true
   *    this.Dates(12, 10, 1989), other.Dates(11, 10, 1989) = false
   *    this.Dates(12, 10, 1989), other.Dates(12,  9, 1989) = false
   *    this.Dates(12, 10, 1989), other.Dates(12, 10, 1988) = false
    boolean isEqualTo( Date otherDate ) {
        if (this.getDay() == otherDate.getDay()
            && this.getMonth() == otherDate.getMonth()
            && this.getYear() == otherDate.getYear()) {
            return true;
        else {
            return false;
/** Does one Date precede another?
   * @param other The date to compare this Date against.
   * @return true if (and only if) this Date comes before other.
   *    this.Dates( 5,  5, 2000), other.Dates( 5,  6, 2000) = true
   *    this.Dates( 5,  5, 2000), other.Dates( 6,  5, 2000) = true
   *    this.Dates( 5,  5, 2000), other.Dates( 5,  5, 2001) = true
   *    this.Dates( 5,  5, 2000), other.Dates( 5,  4, 2000) = false
   *    this.Dates( 5,  5, 2000), other.Dates( 5,  5, 1999) = false
   *    this.Dates( 5,  5, 2000), other.Dates( 4,  5, 2000) = false
    boolean isBefore( Date otherDate ) {
        if (this.getYear() <= otherDate.getYear()
            && this.getMonth() <= otherDate.getMonth()
            && this.getDay() < otherDate.getDay()) {
            return true;
        else if (this.getYear() <= otherDate.getYear()
            && this.getMonth() < otherDate.getMonth()) {
            return true;
        else if (this.getYear() < otherDate.getYear()) {
            return true;
        else {
            return false;
/** Determines how many days there are in the month, given the instance's specified month and year
   * @Return returns the number of days in the month
    int daysInTheMonth () {
        if (this.isValid() == true) {
            if (this.getMonth() == 2) {
                if (this.isLeapYear() == true) {
                    return 29;
                else {
                    return 28;
            else if (this.getMonth() == 1
                     || this.getMonth() == 3
                     || this.getMonth() == 5
                     || this.getMonth() == 7
                     || this.getMonth() == 8
                     || this.getMonth() == 10
                     || this.getMonth() == 12) {
                return 31;
            else {
                return 30;
        else {
            return 0;
/** Return the day after `this`.  (`this` must be a valid date.)
   * @return the day after `this`.  The result will be valid if `this` is valid.
  Date nextDay() {
      if (this.getDay() == this.getDaysInTheMonth() && this.getMonth() == 12) {
          return new Date(firstMonthInYear, firstDayInMonth, this.getYear() + 1);
      else if (this.getDay() == this.getDaysInTheMonth()) {
          return new Date(this.getMonth() + 1, firstDayInMonth, this.getYear());
      else {
          return new Date(this.getMonth(), this.getDay() + 1, this.getYear());
/** Return the day before `this`.  (`this` must be a valid date.)
   * @return the day before `this`.  The result will be valid if `this` is valid.
  Date previousDay() {
      if (this.getDay() == 1 && this.getMonth() == 1) {
          return new Date(lastMonthInYear, this.getDaysInTheMonth(), this.getYear() - 1); //Need to fix the days in the previous month and previous month
      else if (this.getDay() == 1) {
          return new Date(this.getMonth() - 1, this.getDaysInTheMonth() - 1, this.getYear()); //need to fix the days in the previous month
      else {
          return new Date(this.getMonth() - 1, this.getDaysInTheMonth(), this.getYear());
/** Returns a true or false depending on whether the year is a leap year or not
   * @return a true or false depending on whether the year is a leap year or not
   * Test Cases:
   *    this.Dates( 5,  5, 2000) = true
   *    this.Dates(12,  6, 2004) = true
   *    this.Dates( 1,  1, 2001) = false
   *    this.Dates( 7,  9, 2006) = false
    boolean isLeapYear () {
        if (this.getYear() % 400 == 0) {
            return true;
        else if (this.getYear() % 100 == 0) {
            return false;
        else if (this.getYear() % 4 ==0) {
            return true;
        else {
            return false;
}null