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How to fix date in Gregorian Calendar

I want to fix the date to month/day/year in my class (Gregorian Calendar) so it works with my tester program. I get errors when running my tester program, I think it has to do with my string toString() method but I have tried to fix it but keep getting errors. I do not understand how having my string output to month + day + year would not work correctly in outputting mmmm/dd/yyyy. Thank you for your help.
Errors:
Exception in thread "main" java.lang.IllegalArgumentException
at Date.<init>(Date.java:15)
at Assign8B.main(Assign8B.java:14)
Class
public class Date {
private int day, month, year;
public Date() {
this.day = 1;
this.month = 1;
this.year = 1970;
}
public Date(int year, int month, int day) {
if (year < 1582) {
throw new IllegalArgumentException();
} else if (month <= 0 && month > 12) {
throw new IllegalArgumentException();
} else if (!isLeapYear(year) && (month == 2 && day == 29)) {
throw new IllegalArgumentException();
} else {
this.day = day;
this.month = month;
this.year = year;
}
}
public void addDays(int days) {
int[] daysOfMonth = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int step = 1;
if(days < 0)
step = -1;
if(isLeapYear(year))
daysOfMonth[1] = 29;
int d = 0;
while(d < days){
d++;
day += step;
if(day > daysOfMonth[month-1]){
day = 1;
month++;
if(month > 12){
year++;
month = 1;
if(isLeapYear(year))
daysOfMonth[1] = 29;
else
daysOfMonth[1] = 28;
}
}
else if(day < 1) {
month--;
if(month == 0) {
month = 12;
year--;
if(isLeapYear(year))
daysOfMonth[1] = 29;
else
daysOfMonth[1] = 28;
}
day = daysOfMonth[month-1];
}
}
}
public void addWeeks(int weeks) {
addDays(weeks * 7);
}
public int getDay() {
return day;
}
public void setDay(int day) {
this.day = day;
}
public int getMonth() {
return month;
}
public void setMonth(int month) {
this.month = month;
}
public int getYear() {
return year;
}
public void setYear(int year) {
this.year = year;
}
public boolean isLeapYear() {
return isLeapYear(this.year);
}
public boolean isLeapYear(int year) {
return(year % 400 == 0 || (year % 4 == 0 && year % 100 != 0));
}
public int daysTo(Date other) {
int days = 0;
int d1, m1, y1, d2, m2, y2;
int sign = 1;
if(this.toString().compareTo(other.toString()) > 0){
d1 = other.day;
m1 = other.month;
y1 = other.year;
d2 = day;
m2 = month;
y2 = year;
sign = -1;
} else {
d1 = day;
m1 = month;
y1 = year;
d2 = other.day;
m2 = other.month;
y2 = other.year;
}
int[] daysOfMonth = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
if(isLeapYear(y1))
daysOfMonth[1] = 29;
while(d1 != d2 || m1 != m2 || y1 != y2){
days++;
d1++;
if(d1 > daysOfMonth[m1-1]){
d1 = 1;
m1++;
if(m1 > 12){
y1++;
m1 = 1;
if(isLeapYear(y1))
daysOfMonth[1] = 29;
else
daysOfMonth[1] = 28;
}
}
}
days = days * sign;
return days;
}
public String longDate() {
String[] months = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
return months[month-1] + " " + day + ", " + year;
}
public String toString() {
String s = month + "/" + day + "/" + year;
return s;
}
public static int daysTo(Date one, Date two) {
return one.daysTo(two);
}
}
Tester Program
public class Assign8B {
// Part of the main method I'll use to test your class
// NO imports allowed from the JAVA API
public static void main(String[] a) {
Date one = new Date(10,15,1582); // start of Gregorian
Date two = new Date(1,28,2020); // 2020 is a leap year
one.addDays(1); // advance one day (negative subtracts days)
one.addWeeks(10); // advance one week (negative allowed, yes)
System.out.println(two.daysTo(one)); // -159645 days (negative)
System.out.println(one.getDay()); // day is now the 25th (advanced)
System.out.println(one.getMonth()); // returns 12, January is 1
System.out.println(one.getYear()); // still 1582 from start
System.out.println(one.isLeapYear()); // false for 1582
System.out.println(one.toString()); // style is 12/25/1582
try {
Date three = new Date(12,33,1956); // obviously illegal
Date four = new Date(2,29,2013); // illegal leap year
three.setDay(31); // fixes that day of month, OK
four.setMonth(3); // fixes the month, year still wrong
four.setYear(1929); // fixes the year, code not reached
} catch (IllegalArgumentException e) {
System.out.println("Illegal day attempted");
}
// Use UNIX zero of 01/01/70 for default, and create "longDate" output
// I thought a long date was dinner with a person you don't like?
Date five = new Date();
System.out.println(five.longDate()); // January 1, 1970
// Finally, let's understand what static methods are most commonly used for:
System.out.println(Date.daysTo(one, two)); // still 159645 days (positive)
}
}

As #madprogrammer mentioned in the comments, you have to change your Date call because of the order of year month day in your own class constructor, and then look at your add days function and change how you add years in your code.

Is their any simplified Java to find palindome dates between year 0000 and 9999?

import java.util.Arrays;
public class PalindromeDates {
static final int STARTINGYEAR = 0000;
static final int ENDINGYEAR = 9999;
public static void main(String[] args) {
int year, month, date;
int dateArray[];
boolean flag;
System.out.println(" Date --> Array Format\n");
for (year = STARTINGYEAR; year <= ENDINGYEAR; year++) {
for (month = 01; month <= 12; month++) {
for (date = 1; date <= 31; date++) {
if (checkValidDate(year, date, month)) {
dateArray = createDateArray(date, month, year);
flag = checkPalindrome(dateArray);
if (flag) {
System.out.print(year + "." + month + "." + date + " --> ");
System.out.println(Arrays.toString(dateArray));
}
}
}
}
}
}
public static int[] createDateArray(int date, int month, int year) { //Inserting the whole date to an array
int dateArray[] = new int[8];
dateArray[0] = year / 1000;
year = year % 1000;
dateArray[1] = year / 100;
year = year % 100;
dateArray[2] = year / 10;
dateArray[3] = year % 10;
dateArray[4] = month / 10;
dateArray[5] = month % 10;
dateArray[6] = date / 10;
dateArray[7] = date % 10;
return dateArray;
}
public static boolean checkPalindrome(int dateArray[]) {
for (int i = 0; i <= 3; i++) {
if (dateArray[i] == dateArray[7 - i]) {
} else {
return false;
}
}
return true;
}
public static boolean checkValidDate(int year, int month, int date) {
if (month == 2 && date == 30)
return false;
if ((month == 2 || month == 4 || month == 6 || month == 9 || month == 11) && (date == 31)) {
return false;
}
if ((month == 2) && (date == 29))
return (checkLeapYear(year));
return true;
}
public static boolean checkLeapYear(int year) {
if (year % 4 == 0) {
if (year % 100 == 0) {
if (year % 400 == 0)
return true;
else
return false;
} else
return true;
} else {
return false;
}
}
}
This program is written by me to find the palindrome dates since 0000 to 9999. Is their any simplifies program to do this?. What are the modifications for this code? And I want to know whether my leap year finding code is correct.
There is a method called createDateArray(). It is used to put the integer digits in year, month, date to an array. Is there any simple method to do that?

I am inferring from your code that a palindrome date is a date that formatted into yyyyMMdd format is a palindrome string. For example the day before yesterday, February 2, 2020, was a palindrome date because it’s formatted into 20200202, a palindrome.
Is their any simplifies program to do this? …
Yes there is. See below.
… And I want to know whether my leap year finding code is correct.
Yes, it is correct. I have tested its result against the result of Year.of(y).isLeap() for y ranging from 0 through 9999.
And the issue you didn’t ask about: as jrook hinted in a comment, beware of octal numbers.
static final int STARTINGYEAR = 0000;
While this works in this case, it works for reasons that I am afraid that you don’t fully understand. You will get surprises if some day you try 0500 for year 500 and get 320, or you use 0008 for year 8 and get a compile time error. When a Java integer literal begins with 0 (and has more digits following it), it is an octal number, not a number in the decimal number system. So in your code you should use 0 for the year that you want printed as 0000:
static final int STARTINGYEAR = 0;
java.time
On one side Andreas is correct in the other answer that this goes a lot more smoothly when using the date classes that are built into Java. On the other side the Calendar class used in that answer is poorly designed and long outdated. So I recommend we don’t use it and instead present a solution using java.time, the modern Java date and time API.
List<LocalDate> palindromeDates = Arrays.stream(Month.values())
.flatMap(m -> IntStream.rangeClosed(1, m.length(true)).mapToObj(d -> MonthDay.of(m, d)))
.map(md -> md.atYear(reverseStringToInt(md.format(monthDayFormatter))))
.sorted()
.collect(Collectors.toList());
palindromeDates.forEach(ld -> System.out.println(ld.format(dateFormatter)));
This code uses a few auxiliaries:
private static DateTimeFormatter monthDayFormatter = DateTimeFormatter.ofPattern("MMdd");
private static DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("uuuuMMdd");
private static int reverseStringToInt(String s) {
StringBuilder buf = new StringBuilder(s);
buf.reverse();
return Integer.parseInt(buf.toString());
}
Excerpt from the output:
01011010
01100110
01111110
01200210
…
20111102
20200202
20211202
…
92800829
92900929
The algorithm idea is stolen from Andreas’ answer since it is so well thought.
Link
Oracle tutorial: Date Time explaining how to use java.time.

DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("uuuuMMdd");
for (LocalDate d = LocalDate.of(0, 1, 1); d.isBefore(LocalDate.of(10000, 1, 1)); d = d.plusDays(1)) {
String dateString = dateFormatter.format(d);
if (dateString.equals(new StringBuilder(dateString).reverse().toString())) {
System.out.println(d);
}
}

Since the year can be any 4-digit year, there is no constraint there, so just go through all 3661 MMdd values of a year, reverse it and use as the year.
1) Since the leap date of 0229 reversed is 9220, it is a leap year, and hence a valid palindrome date.
As code, using Calendar, in year order:
List<String> palimdromeDates = new ArrayList<>();
Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("UTC"/*No DST*/));
cal.clear();
cal.set(2000/*Leap Year*/, Calendar.JANUARY, 1);
for (; cal.get(Calendar.YEAR) == 2000; cal.add(Calendar.DAY_OF_YEAR, 1)) {
int day = cal.get(Calendar.DAY_OF_MONTH);
int month = cal.get(Calendar.MONTH) + 1;
int year = 0; // Calculate: year = reverse(MMdd)
for (int i = 0, n = month * 100 + day; i < 4; i++, n /= 10)
year = year * 10 + n % 10;
palimdromeDates.add(String.format("%04d-%02d-%02d", year, month, day));
}
Collections.sort(palimdromeDates); // Sort by year
for (String date : palimdromeDates)
System.out.println(date);
Note that this code only loops 366 times, and does not create any unnecessary String objects or other type of objects, so it is very fast, and generates minimum garbage.
Output
0101-10-10
0110-01-10
0111-11-10
0120-02-10
0121-12-10
0130-03-10
0140-04-10
0150-05-10
0160-06-10
0170-07-10
0180-08-10
0190-09-10
0201-10-20
0210-01-20
0211-11-20
0220-02-20
0221-12-20
0230-03-20
0240-04-20
0250-05-20
0260-06-20
0270-07-20
0280-08-20
0290-09-20
0301-10-30
0310-01-30
0311-11-30
0321-12-30
0330-03-30
0340-04-30
0350-05-30
0360-06-30
0370-07-30
0380-08-30
0390-09-30
1001-10-01
1010-01-01
1011-11-01
1020-02-01
1021-12-01
1030-03-01
1040-04-01
1050-05-01
1060-06-01
1070-07-01
1080-08-01
1090-09-01
1101-10-11
1110-01-11
1111-11-11
1120-02-11
1121-12-11
1130-03-11
1140-04-11
1150-05-11
1160-06-11
1170-07-11
1180-08-11
1190-09-11
1201-10-21
1210-01-21
1211-11-21
1220-02-21
1221-12-21
1230-03-21
1240-04-21
1250-05-21
1260-06-21
1270-07-21
1280-08-21
1290-09-21
1301-10-31
1310-01-31
1321-12-31
1330-03-31
1350-05-31
1370-07-31
1380-08-31
2001-10-02
2010-01-02
2011-11-02
2020-02-02
2021-12-02
2030-03-02
2040-04-02
2050-05-02
2060-06-02
2070-07-02
2080-08-02
2090-09-02
2101-10-12
2110-01-12
2111-11-12
2120-02-12
2121-12-12
2130-03-12
2140-04-12
2150-05-12
2160-06-12
2170-07-12
2180-08-12
2190-09-12
2201-10-22
2210-01-22
2211-11-22
2220-02-22
2221-12-22
2230-03-22
2240-04-22
2250-05-22
2260-06-22
2270-07-22
2280-08-22
2290-09-22
3001-10-03
3010-01-03
3011-11-03
3020-02-03
3021-12-03
3030-03-03
3040-04-03
3050-05-03
3060-06-03
3070-07-03
3080-08-03
3090-09-03
3101-10-13
3110-01-13
3111-11-13
3120-02-13
3121-12-13
3130-03-13
3140-04-13
3150-05-13
3160-06-13
3170-07-13
3180-08-13
3190-09-13
3201-10-23
3210-01-23
3211-11-23
3220-02-23
3221-12-23
3230-03-23
3240-04-23
3250-05-23
3260-06-23
3270-07-23
3280-08-23
3290-09-23
4001-10-04
4010-01-04
4011-11-04
4020-02-04
4021-12-04
4030-03-04
4040-04-04
4050-05-04
4060-06-04
4070-07-04
4080-08-04
4090-09-04
4101-10-14
4110-01-14
4111-11-14
4120-02-14
4121-12-14
4130-03-14
4140-04-14
4150-05-14
4160-06-14
4170-07-14
4180-08-14
4190-09-14
4201-10-24
4210-01-24
4211-11-24
4220-02-24
4221-12-24
4230-03-24
4240-04-24
4250-05-24
4260-06-24
4270-07-24
4280-08-24
4290-09-24
5001-10-05
5010-01-05
5011-11-05
5020-02-05
5021-12-05
5030-03-05
5040-04-05
5050-05-05
5060-06-05
5070-07-05
5080-08-05
5090-09-05
5101-10-15
5110-01-15
5111-11-15
5120-02-15
5121-12-15
5130-03-15
5140-04-15
5150-05-15
5160-06-15
5170-07-15
5180-08-15
5190-09-15
5201-10-25
5210-01-25
5211-11-25
5220-02-25
5221-12-25
5230-03-25
5240-04-25
5250-05-25
5260-06-25
5270-07-25
5280-08-25
5290-09-25
6001-10-06
6010-01-06
6011-11-06
6020-02-06
6021-12-06
6030-03-06
6040-04-06
6050-05-06
6060-06-06
6070-07-06
6080-08-06
6090-09-06
6101-10-16
6110-01-16
6111-11-16
6120-02-16
6121-12-16
6130-03-16
6140-04-16
6150-05-16
6160-06-16
6170-07-16
6180-08-16
6190-09-16
6201-10-26
6210-01-26
6211-11-26
6220-02-26
6221-12-26
6230-03-26
6240-04-26
6250-05-26
6260-06-26
6270-07-26
6280-08-26
6290-09-26
7001-10-07
7010-01-07
7011-11-07
7020-02-07
7021-12-07
7030-03-07
7040-04-07
7050-05-07
7060-06-07
7070-07-07
7080-08-07
7090-09-07
7101-10-17
7110-01-17
7111-11-17
7120-02-17
7121-12-17
7130-03-17
7140-04-17
7150-05-17
7160-06-17
7170-07-17
7180-08-17
7190-09-17
7201-10-27
7210-01-27
7211-11-27
7220-02-27
7221-12-27
7230-03-27
7240-04-27
7250-05-27
7260-06-27
7270-07-27
7280-08-27
7290-09-27
8001-10-08
8010-01-08
8011-11-08
8020-02-08
8021-12-08
8030-03-08
8040-04-08
8050-05-08
8060-06-08
8070-07-08
8080-08-08
8090-09-08
8101-10-18
8110-01-18
8111-11-18
8120-02-18
8121-12-18
8130-03-18
8140-04-18
8150-05-18
8160-06-18
8170-07-18
8180-08-18
8190-09-18
8201-10-28
8210-01-28
8211-11-28
8220-02-28
8221-12-28
8230-03-28
8240-04-28
8250-05-28
8260-06-28
8270-07-28
8280-08-28
8290-09-28
9001-10-09
9010-01-09
9011-11-09
9020-02-09
9021-12-09
9030-03-09
9040-04-09
9050-05-09
9060-06-09
9070-07-09
9080-08-09
9090-09-09
9101-10-19
9110-01-19
9111-11-19
9120-02-19
9121-12-19
9130-03-19
9140-04-19
9150-05-19
9160-06-19
9170-07-19
9180-08-19
9190-09-19
9201-10-29
9210-01-29
9211-11-29
9220-02-29
9221-12-29
9230-03-29
9240-04-29
9250-05-29
9260-06-29
9270-07-29
9280-08-29
9290-09-29

How to recreate compareTo method in java?

How does the compareTo() method for Dates work here in java? I know that when you compare two dates the result will always be 0 if equal, 1 if the date being
compared inside the compareTo() parameter is older, and -1 if the date inside the parameter is more recent.
//Just an example
String[] da = {"01/14/1975", "08/20/1975", "08/20/1975"};
SimpleDateFormat f = new SimpleDateFormat("MM/dd/yyyy");
Date d1 = new Date();
Date d2 = new Date();
//this outputs 1 because d2 is older than d1
d1 = f.parse(da[1]);
d2 = f.parse(da[0]);
System.out.println(d1.compareTo(d2));
//this outputs 0 because dates are the same
d1 = f.parse(da[1]);
d2 = f.parse(da[2]);
System.out.println(d1.compareTo(d2));
//this outputs -1 because d2 is more recent than d1
d1 = f.parse(da[0]);
d2 = f.parse(da[1]);
System.out.println(d1.compareTo(d2));
Now I want to compare dates without using compareTo() method or any built-in method in java. As much as possible I want to use just the basic operators in java.
What is the computation or the algorithm of the compareTo() method in comparing dates that enable it to return -1, 0, and 1?
Edit:
In the case at the sample problem at my book, using java.util.Date is forbidden, what is supposed to be done is to create your own date object like this:
public class DatesObj
{
protected int day, month, year;
public DatesObj (int mm, int dd, int yyyy) {
month = mm;
day = dd;
year = yyyy;
}
public int getMonth() { return month; }
public int getDay() { return day; }
public int getYear() { return year; }
}
Now how do I compare this as if like they're int and determine which is old and which is newer??

If you want to compare two dates just as if they were just plain-old integers, you must first turn each date into a plain-old integer. The easiest way to turn a year/month/day representation of a date into a plain-old integer, that can be effectively compared with plain-old integers from other dates, is to line the pieces up in exactly that order: year first, month next, day last:
// in DateObj class....
public int getDateInt() {
return (yyyy * 10000) + (mm * 100) + dd;
}
So for March 19, 2019, you get 20190319, and for December 7, 1941 you get 19411207; by comparing the "integerized" versions of the dates you can see that:
19411207 < 20190319, just as December 7, 1941 is earlier than March 19, 2019;
20190319 > 19411207, just as March 19, 2019 is later than December 7, 1941;
19411207 != 20190319, just as December 7, 1941 and March 19, 2019 are different dates
You're limited to dates within the Common Era and no more than about 200,000 years into the future with this particular implementation. But with a little tweaking, you could easily easily handle dates outside these ranges, an exercise that I will, as the textbooks so often say, leave as an exercise for the reader.

Implement Comparable and override compareTo().
class DatesObj implements Comparable<DatesObj>{
protected int day, month, year;
public DatesObj(int mm, int dd, int yyyy) {
month = mm;
day = dd;
year = yyyy;
}
public int getMonth() {
return month;
}
public int getDay() {
return day;
}
public int getYear() { return year; }
#Override
public int compareTo(DatesObj o) {
int diff = this.year - o.year;
if(diff != 0) {
return diff;
}
diff = this.month - o.month;
if(diff != 0) {
return diff;
}
return this.day - o.day;
}
}

Compare the years. If the years of both the dates are same, compare the months.
If the months are same, compare the dates.
public int compareDate(DatesObj d) {
if (this.year != d.year) {
if (this.year > d.year)
return 1;
else
return -1;
}
if (this.month != d.month) {
if (this.month > d.month)
return 1;
else
return -1;
}
if (this.day != d.day) {
if (this.day > d.day)
return 1;
else
return -1;
}
return 0;
}

Ref : https://docs.oracle.com/javase/8/docs/api/java/lang/Comparable.html
Ref : https://developer.android.com/reference/java/util/Calendar
create own class with Interface Comparable
class DateCompare implements Comparable<Date>
{
protected int day, month, year;
public DateCompare(int mm, int dd, int yyyy) {
month = mm;
day = dd;
year = yyyy;
}
#Override
public int compareTo(Date o) {
Calendar cal = Calendar.getInstance();
cal.setTime(o);
int diff = this.year - cal.get(Calendar.YEAR);
if(diff != 0) {
return diff;
}
diff = this.month - cal.get(Calendar.MONTH);
if(diff != 0) {
return diff;
}
return this.day - cal.get(Calendar.DAY_OF_MONTH);
}
public int getMonth() {
return month;
}
public int getDay() {
return day;
}
public int getYear() { return year; }
}
And Other More Helpful
https://gist.github.com/Ashusolanki/fed3b6a680092985ac0ab93ed70fcd7c
private String postTime(Date date)
{
long postTime = date.getTime();
long atTime = System.currentTimeMillis();
long diff = atTime - postTime;
long sec = TimeUnit.SECONDS.convert(diff, TimeUnit.MILLISECONDS);
if (sec >= 60) {
long minit = TimeUnit.MINUTES.convert(diff, TimeUnit.MILLISECONDS);
if (minit >= 60) {
long hours = TimeUnit.HOURS.convert(diff, TimeUnit.MILLISECONDS);
if (hours >= 24) {
long days = TimeUnit.DAYS.convert(diff, TimeUnit.MILLISECONDS);
return days + " Days Ago";
} else {
return hours + " Hours Ago";
}
} else {
return minit + " Minutes Ago";
}
} else {
return sec + " Secounds Ago";
}
}

Method wont work when I create an object

I am building a Date class and when I try to create an object with it doesn't work. (errors in daysPerMonth)
However when I use setNewDay method outside of the object it does work.
Do you guys have any clues on what i'm doing wrong?
Here is my code:
public class Date{
private Dag day;
private Maand month;
private Jaar year;
private int maxday;
public Date(int day, int month, int year){
setDate(day, month, year);
}
public void setDate(int day, int month, int year){
this.month = new Maand(month);
setNewDay(day);
this.year = new Jaar(year);
}
private void daysPerMonth(){
int february;
if(year.getYear()%4 == 0) {
february = 29;
}else{
february = 28;
};
int[] daymonth={31,february,31,30,31,30,31,30,31,30,31,30};
maxday = daymonth[month.getMonth() -1];
}
public void setNewDay(int day){
daysPerMonth();
if(day > 0 && day <= maxday){
this.day = new Dag(day);
} else {
System.out.println("Wrong day");
}
}
}

I see a problem in the order of initialization :
public void setDate(int day, int month, int year){
this.month = new Maand(month);
setNewDay(day); // this method depends indirectly on this.year, which is not yet
// initialized (setNewDay calls daysPerMonth which calls
// year.getYear())
this.year = new Jaar(year);
}
Change it to :
public void setDate(int day, int month, int year){
this.year = new Jaar(year);
this.month = new Maand(month);
setNewDay(day);
}

Looking at the order of your calls, this
public void setDate(int day, int month, int year){
this.month = new Maand(month);
setNewDay(day);
this.year = new Jaar(year);
}
Should be
public void setDate(int day, int month, int year){
this.month = new Maand(month);
this.year = new Jaar(year);
setNewDay(day);
}
Because setNewDay() calls daysPerMonth() and that needs the year (Jaar).

Since you are calling the setNewDay() method before initialising the year ( which is by default null ). And setNewDay() method is instead calling the daysPerMonth() method which uses year but since year is currently null( which is by default value for every reference) You are getting NullPointerException
So you just need to initialise the year before calling the method setNewDay() :
public void setDate(int day, int month, int year){
this.month = new Maand(month);
this.year = new Jaar(year);
setNewDay(day); //call this method after setting up the year
}
So that when you call daysPerMonth() method your year contains valid data :
private void daysPerMonth(){
int february;
if(year.getYear()%4 == 0) { //now year is valid
february = 29;
}else{
february = 28;
}
int[] daymonth={31,february,31,30,31,30,31,30,31,30,31,30};
maxday = daymonth[month.getMonth() -1];
}

Depends on what year you try.
From memory you need three conditions to get February right: Isnot mod 100 & is mod 400

Count days between two dates with Java 8 while ignoring certain days of week

Below I have 3 methods. The first is very simple. It just counts the total number of days. The second, however, will not only count the days, but will ignore the days of the week that are passed in to the method.
My problem is that the third method is not always correct. It should match the second method. I am guessing it has something to do with leap years, because the difference is usually +=3|4 when it is incorrect.
Additional Info
I am attempting to mock Excel's weekday(serial_number,[return_type]) formula in a way.
serial_number = startDate:Date - daysOfWeekToInclude:Array<Integer>
Example
| A | B | C
+---------+----------------------------------------------------+-----------
1 | Start | =DATE(2014,9,7) | 9/7/2014
2 | End | =DATE(2025,6,13) | 6/13/2025
3 | Include | ={1,2,4,6} (Mon, Tue, Thu, & Sat) | <Disp Only>
4 | Days | =SUM(INT((WEEKDAY($B$1-{1,2,4,6},1)+$B$2-$B$1)/7)) | 2248
There is more information on this function here: How to count / calculate the number of days between two dates in Excel?
Raw Image
Methods
Simply count the number of days between two dates.
public static int simpleDaysBetween(final LocalDate start,
final LocalDate end) {
return (int) ChronoUnit.DAYS.between(start, end);
}
Count number of days, ignoring certain days of week, using a loop.
public static int betterDaysBetween(final LocalDate start,
final LocalDate end, final List<DayOfWeek> ignore) {
int count = 0;
LocalDate curr = start.plusDays(0);
while (curr.isBefore(end)) {
if (!ignore.contains(curr.getDayOfWeek())) {
count++;
}
curr = curr.plusDays(1); // Increment by a day.
}
return count;
}
Count number of days. again but without a loop.
public static int bestDaysBetween(final LocalDate start,
final LocalDate end, final List<DayOfWeek> ignore) {
int days = simpleDaysBetween(start, end);
if (days == 0) {
return 0;
}
if (!ignore.isEmpty()) {
int weeks = days / 7;
int startDay = start.getDayOfWeek().getValue();
int endDay = end.getDayOfWeek().getValue();
int diff = weeks * ignore.size();
for (DayOfWeek day : ignore) {
int currDay = day.getValue();
if (startDay <= currDay) {
diff++;
}
if (endDay > currDay) {
diff++;
}
}
if (endDay > startDay) {
diff -= endDay - startDay;
}
return days - diff;
}
return days;
}
Full code
import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
import java.util.Arrays;
import java.util.List;
public class DayCounter {
public static void main(String[] args) {
final LocalDate start = LocalDate.of(2014, 9, 7);
final LocalDate end = LocalDate.of(2025, 6, 13);
List<DayOfWeek> ignore = Arrays.asList(DayOfWeek.SUNDAY, DayOfWeek.WEDNESDAY, DayOfWeek.FRIDAY);
print(start);
print(end);
System.out.println(simpleDaysBetween(start, end));
System.out.println(betterDaysBetween(start, end, ignore));
System.out.println(bestDaysBetween(start, end, ignore));
}
public static void print(LocalDate date) {
System.out.printf("%s -> %s%n", date, date.getDayOfWeek());
}
public static int simpleDaysBetween(final LocalDate start,
final LocalDate end) {
return (int) ChronoUnit.DAYS.between(start, end);
}
public static int betterDaysBetween(final LocalDate start,
final LocalDate end, final List<DayOfWeek> ignore) {
int count = 0;
LocalDate curr = start.plusDays(0);
while (curr.isBefore(end)) {
if (!ignore.contains(curr.getDayOfWeek())) {
count++;
}
curr = curr.plusDays(1); // Increment by a day.
}
return count;
}
public static int bestDaysBetween(final LocalDate start,
final LocalDate end, final List<DayOfWeek> ignore) {
int days = simpleDaysBetween(start, end);
if (days == 0) {
return 0;
}
if (!ignore.isEmpty()) {
int weeks = days / 7;
int startDay = start.getDayOfWeek().getValue();
int endDay = end.getDayOfWeek().getValue();
int diff = weeks * ignore.size();
for (DayOfWeek day : ignore) {
int currDay = day.getValue();
if (startDay <= currDay) {
diff++;
}
if (endDay > currDay) {
diff++;
}
}
if (endDay > startDay) {
diff -= endDay - startDay;
}
return days - diff;
}
return days;
}
}

If we talk about a Java 8 API, why not use the Java 8 features consequently…
static long daysBetween(LocalDate start, LocalDate end, List<DayOfWeek> ignore) {
return Stream.iterate(start, d->d.plusDays(1))
.limit(start.until(end, ChronoUnit.DAYS))
.filter(d->!ignore.contains(d.getDayOfWeek()))
.count();
}
Starting with Java 9, we can use the even simpler
static long daysBetween(LocalDate start, LocalDate end, List<DayOfWeek> ignore) {
return start.datesUntil(end)
.filter(d->!ignore.contains(d.getDayOfWeek()))
.count();
}
Though, it might be worth using a Set with a better-than-linear lookup rather than the List:
static long daysBetween(LocalDate start, LocalDate end, List<DayOfWeek> ignore) {
if(ignore.isEmpty()) return start.until(end, ChronoUnit.DAYS);
EnumSet<DayOfWeek> set = EnumSet.copyOf(ignore);
return start.datesUntil(end)
.filter(d->!ignore.contains(d.getDayOfWeek()))
.count();
}
You may consider changing the parameter to Set<DayOfWeek>, as it is not only more efficient but better suited to the actual use cases. Instead of Arrays.asList(DayOfWeek.SUNDAY, DayOfWeek.WEDNESDAY, DayOfWeek.FRIDAY), you can pass EnumSet.of(DayOfWeek.SUNDAY, DayOfWeek.WEDNESDAY, DayOfWeek.FRIDAY), but you can also use constructs like EnumSet.range(DayOfWeek.MONDAY, DayOfWeek.FRIDAY), to denote the typical working days.
You can avoid iterating over all days, but it requires special care about corner cases and hence, thorough testing. And will only pay off for really large ranges. For completeness, this is the optimized variant:
static long daysBetween(LocalDate start, LocalDate end, Set<DayOfWeek> ignore) {
long d1 = start.toEpochDay(), d2 = end.toEpochDay();
if(d1 > d2) throw new IllegalArgumentException();
if(ignore.isEmpty()) return d2 - d1;
int incompleteWeek = 0;
DayOfWeek startDoW = start.getDayOfWeek(), endDoW = end.getDayOfWeek();
if(startDoW != endDoW) {
for(int v1 = startDoW.getValue(), v2 = endDoW.getValue();
v1 != v2 && d1 < d2; v1 = v1%7+1, d1++) {
if(!ignore.contains(DayOfWeek.of(v1))) incompleteWeek++;
}
}
return incompleteWeek + (d2 - d1) * (7 - ignore.size()) / 7;
}
Here, the performance of the ignore set’s lookup doesn’t matter, as we only look up at most six values, however, enforcing a Set, i.e. no duplicates, allows us to use the set’s size to calculate the number of days contained in complete weeks of the range. Complete weeks have the same day of week for the start and (exclusive) end date. So the code only needs to iterate the days, until the start and end day of week match.

You you are using wrong Excel formula. See the section "Using SUM and INT function to count the number of workdays" of the site that you have provided. It is stating the formula as:
=SUM(INT((WEEKDAY(A2-{2,3,4,5,6})+B2-A2)/7))
In Excel, Sunday is 1 and Saturday is 7. The numbers inside the curly braces indicates the day-of-weeks to be included. So for your case the formula will be:
=SUM(INT((WEEKDAY(A2-{2,3,5,7})+B2-A2)/7))
Please see the attached screenshot:
It is returning 2247 as the following code returns:
import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.Month;
import java.time.Year;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
public class SO25798876 {
public static void main(String[] args) {
String strStartDate = "09/07/2014";
String strEndDate = "06/13/2025";
String pattern = "MM/dd/yyyy";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
LocalDate startDate = LocalDate.parse(strStartDate, formatter);
LocalDate endDate = LocalDate.parse(strEndDate, formatter);
int count = 0;
while(startDate.isBefore(endDate) || startDate.isEqual(endDate)) { // you may want to not to use the isEqual method
DayOfWeek dayOfWeek = startDate.getDayOfWeek();
if(!(dayOfWeek == DayOfWeek.SUNDAY || dayOfWeek == DayOfWeek.WEDNESDAY || dayOfWeek == DayOfWeek.FRIDAY)) {
count++;
}
startDate = startDate.plusDays(1);
}
System.out.println(count);
}
}
You also have mentioned your doubt that the java.time may be not considering leap year, which is wrong, if you add the following piece of code
long year = startDate.getYear();
if(Year.isLeap(year)) {
Month month = startDate.getMonth();
if(month == Month.FEBRUARY && startDate.getDayOfMonth() == 29) {
System.out.println("Calculated 29th Feb for the year: " + year);
}
}
You will see that it is printing:
Calculated 29th Feb for the year: 2016
Calculated 29th Feb for the year: 2020
Calculated 29th Feb for the year: 2024
Lastly the count will be 2247 which matches the Excel result.
Happy coding.
-Tapas