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How to handle invalid input

Can anyone suggest an example on how to handle invalid inputs, I have got the logic wrong for input from the keyboard. So, I need !myScanner.hasNextInt() or to put that loop in a method which I can reuse for ever.
package dayoftheyear;
import java.util.Scanner;
/**
*
* #author abdal
*/
public class DayOfTheYear {
/**
* Ask the user to enter a month, day, and year as integers
* separated by spaces then display the number of the days since the
* beginning of the year.
* Don’t forget about leap year.
* Sample: user inputs ‘3 1 2000’, output is ‘61’.
* #param args Unused.
*/
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
String enter = "A-z";
int a=31;
int b=1;
boolean dateCheck;
int month;
int day;
int year;
do {
System.out.print("Enter a valid month day year separated by spaces");
if (s.hasNextInt()) {
month= s.nextInt();
day=s.nextInt();
year=s.nextInt();
if (month >= b && month <= a || day>=b && day<=a || year>=b) {
int numberOfDay = countDays(month, day, year);
System.out.println(+ month + "/" + day + "/" + year + " is a day number "
+ numberOfDay + " of that year");
dateCheck = true;
} else {
System.out.println("Enter a valid month day year separated by spaces");
dateCheck = false;
}
} else {
System.out.println("Not a date");
month = 0;
day=0;
year=0;
s.next();
dateCheck = false;
}
} while (!dateCheck);
/**
* Get the number of days since the start of the year.
* Declare a 12 element array and initialize it with the number of
* days in each month.
* #param month Month to count from.
* #param day Day of the month to count to.
* #param year The year to count from.
* #return Days since the start of the given year.
*/
} public static int countDays(int month, int day, int year) {
int monthLength[] = {
31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};
int days = 0;
if (isLeapYear(year) && month > 2)
days += 1;
for (int i = 0; i < month - 1; i++)
days += monthLength[i];
return days += day;
}
/**
* Check if a year is a leap year.
* #param year Year to check.
* #return True if the year is a leap year.
*/
public static boolean isLeapYear(int year) {
if (year % 4 != 0) return false;
else if (year % 100 != 0) return true;
else return year % 400 == 0;
}
}

Replace
if (month >= b && month <= a || day>=b && day<=a || year>=b)
with
if (month >= 1 && month <= 12 && day >= 1 && day <= 31 && year >= 1)
A sample run after this change:
Enter a valid month day year separated by spaces: 13 1 2000
Enter a valid month day year separated by spaces
Enter a valid month day year separated by spaces: 3 32 2000
Enter a valid month day year separated by spaces
Enter a valid month day year separated by spaces: 3 1 2
3/1/2 is a day number 60 of that year
Update1: the following condition will hold good also for February
if ((month == 2 && day >= 1 && day <= 28 && year >= 1 && !isLeapYear(year))
|| (month == 2 && day >= 1 && day <= 29 && year >= 1 && isLeapYear(year))
|| (month != 2 && month >= 1 && month <= 12 && day >= 1 && day <= 31 && year >= 1))
A sample run:
Enter a valid month day year separated by spaces: 2 29 2001
Enter a valid month day year separated by spaces
Enter a valid month day year separated by spaces: 13 2 2001
Enter a valid month day year separated by spaces
Enter a valid month day year separated by spaces: 1 32 2001
Enter a valid month day year separated by spaces
Enter a valid month day year separated by spaces: 1 2 3
1/2/3 is a day number 2 of that year
Update2: the following code addresses all the issues raised in the comments
int monthLength[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
if ((month == 2 && day >= 1 && day <= 28 && year >= 1 && !isLeapYear(year))
|| (month == 2 && day >= 1 && day <= 29 && year >= 1 && isLeapYear(year))
|| (month != 2 && month >= 1 && month <= 12 && day >= 1 && day <= monthLength[month-1] && year >= 1))
A sample run:
Enter a valid month day year separated by spaces: 2 29 2001
Enter a valid month day year separated by spaces
Enter a valid month day year separated by spaces: 13 2 2001
Enter a valid month day year separated by spaces
Enter a valid month day year separated by spaces: 1 32 2001
Enter a valid month day year separated by spaces
Enter a valid month day year separated by spaces: 6 31 2020
Enter a valid month day year separated by spaces
Enter a valid month day year separated by spaces: 7 31 2020
7/31/2020 is a day number 213 of that year

Since date format is not subject to change in real world, it should be appropriate to use some hard coding. Dividing the problem into several methods is always recommended.
You could add following methods to your class:
private static boolean validDate(int month, int day, int year) {
if (year < 1) {
return false; // no B.C.
}
if (month > 1 && month < 13) {
if (month == 2) { // handle February
return validFeb(day, year);
} else if (month % 2 == 1 && month < 8
|| month % 2 == 0 && month >= 8) { // 31-day months
return valid31(day);
} else { // 30 day months
return valid30(day);
}
}
return false;
}
Validate 30-day months:
private static boolean valid30(int day) {
if (day > 1 && day < 31) {
return true;
}
return false;
}
Validate 31-day months
private static boolean valid31(int day) {
if (day > 1 && day < 32) {
return true;
}
return false;
}
Validate February
private static boolean validFeb(int day, int year) {
if (isLeapYear(year)) {
if (day > 1 && day < 30) {
return true;
}
} else {
if (day > 1 && day < 29) {
return true;
}
}
return false;
}
Then your do-while loop should look something like so:
do {
System.out.print("Enter a valid month day year separated by spaces\n");
if (s.hasNextInt()) month = s.nextInt();
else s.next();
if (s.hasNextInt()) day = s.nextInt();
else s.next();
if (s.hasNextInt()) year = s.nextInt();
else s.next();
int numberOfDaysSinceStart = 0;
if (validDate(month, day, year)) {
dateCheck = true;
numberOfDaysSinceStart = countDays(month, day, year);
System.out.println(month + "/" + day + "/" + year + " is a day number "
+ numberOfDaysSinceStart + " of that year");
} else {
dateCheck = false;
}
} while (!dateCheck);

You can add edge cases forever. There is a reason why time-related calculations are nightmare outsourced to libraries written by some poor souls that are paid to try to cover them all. Java has such built in, take a look at java.util.Calendar (Gregorian implementation).
You set it to year/month/day, and it will puke out an exception if anything is wrong while trying to get the result.
Calendar c = Calendar.getInstance();
c.set(year, month, day);
try {
c.getTime();
} catch (Exception e) {
// wrong date format
}

I think the code below can help you, comment if you have any questions.
while(true) {
try{
System.out.print("Enter a valid month day year separated by spaces");
month= s.nextInt();
day=s.nextInt();
year=s.nextInt();
if (month >= 1 && month <= 12 || day>=1 && day<=31 || year>=1) {
System.out.println(+ month + "/" + day + "/" + year + " is a day number "+ " of that year");
break;
} else {
System.out.println("Enter a valid month day year separated by spaces");
}
} catch(InputMismatchException e) {
System.out.println("Enter a valid month day year separated by spaces");
}
s.next();
}

thanks I updated my program and it is working;
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
int year = 0;
int month = 0;
int day = 0;
boolean dateCheck;
do {
System.out.print("Enter a valid month day year separated by spaces\n");
if (s.hasNextInt()) month = s.nextInt();
else s.next();
if (s.hasNextInt()) day = s.nextInt();
else s.next();
if (s.hasNextInt()) year = s.nextInt();
else s.next();
int numberOfDaysSinceStart = 0;
if (month >= 1 && month <= 12 && day >= 1 && day <= 31 && year >= 1) {
dateCheck = true;
numberOfDaysSinceStart = countDays(month, day, year);
System.out.println(month + "/" + day + "/" + year + " is a day number "
+ numberOfDaysSinceStart + " of that year");
} else {
dateCheck = false;
}
} while (!dateCheck);
/**
* Get the number of days since the start of the year.
* Declare a 12 element array and initialize it with the number of
* days in each month.
* #param month Month to count from.
* #param day Day of the month to count to.
* #param year The year to count from.
* #return Days since the start of the given year.
*/
} public static int countDays(int month, int day, int year) {
int monthLength[] = {
31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};
int days = 0;
if (isLeapYear(year) && month > 2)
days += 1;
for (int i = 0; i < month - 1; i++)
days += monthLength[i];
return days += day;
}
/**
* Check if a year is a leap year.
* #param year Year to check.
* #return True if the year is a leap year.
*/
public static boolean isLeapYear(int year) {
if (year % 4 != 0) return false;
else if (year % 100 != 0) return true;
else return year % 400 == 0;
}
}

Date calculator: Tell what day of the week a certain date is

I am trying to write a program in Java (this is a school assignment that tells you what day of the week a certain date is. (The date should be written on the form yyyy-mm-dd.) I thought I had come up with a solution with the code below, but then I found an error.
When you run the code, and type in 1999-12-31 in the dialog, the program tells you that the entered date (1999-12-31) is a Friday. But when you type in the date 2000-01-01 (which is one day after 1999-12-31), the program tells you that the day is a Sunday! What happened with Saturday? A similar problem happens when you type in 2000-02-29 and 2000-03-01, they both give Wednesday as an answer!
What I have yet noticed, this error appears only when you enter a date between 2000-01-01 and 2000-02-29. I would be very grateful if someone could please help me to find the cause of the error and to solve the problem!
import static javax.swing.JOptionPane.*;
import static java.lang.Math.*;
public class DateCalc {
// Here, between the DateCalc class declaration and the main method, several methods used in the program are
// constructed.
// The method isLeapYear tests whether the entered year is a leap year or not.
private static boolean isALeapYear(int year) {
// If the year is a multiple of 4 and not a multiple of 100, or a multiple of 400, then it is a leap year.
if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
return true;
}
else {
return false;
}
}
// A method that tests whether a given string is written as a valid date.
private static boolean isAValidDate(int year, int month, int day) {
int maxValidYear = 9999;
int minValidYear = 1754;
if (year > maxValidYear || year < minValidYear) {
return false;
}
if (month < 1 || month > 12) {
return false;
}
if (day < 1 || day > 31) {
return false;
}
// Handle the February Month
if (month == 2) {
if (isALeapYear(year)) {
return (day <= 29); // This statement is true if the value of the day is less than or equal to 29 if the month is February within a leap year.
// Otherwise the statement is false and the method will return the boolean value false.
}
else {
return (day <= 28); // This statement is true if the value of the day is less than or equal to 28 if the month is February within a non-leap year.
// Otherwise the statement is false and the method will return the boolean value false.
}
}
// Month of April, June, September and November must have number of days less than or equal to 30.
if (month == 4 || month == 6 || month == 9 || month == 11) {
return (day <= 30);
}
return true;
}
// A method that calculates the day number within the year.
private static int dayNumberWithinYear(int year, int month, int day) {
// An array which stores the number of days in the different months (when the year is not a leap year).
// (Index 0 is the number of days in January, index 1 is the number of days in February, etc.)
int[] monthStructure = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
// If the entered year is a leap year, then the monthStructure array will be initialized with an extra day in February, i.e the leap day.
if (isALeapYear(year)) {
monthStructure[1] = 29;
}
int sumDaysInPreviousMonths = 0;
int daysInTheCurrentMonth = day;
int dayNumber = 0;
// Loops through all the months (index 0 is January, index 1 is February, etc.).
for (int i = 0; i < month - 1; i++) {
sumDaysInPreviousMonths += monthStructure[i];
}
dayNumber = sumDaysInPreviousMonths + daysInTheCurrentMonth;
return dayNumber;
}
// A method that decides the day of the week of an entered date.
private static void weekDay(int year, int month, int day) {
// The number of days that have passed since January 1, 1754, excluding the days of the entered year and
// excluding the leap days.
int sumDaysInOrdinaryYears = (year - 1754) * 365;
int sumLeapDaysInLeapYears = 0;
// Suppose the entered year is n. The for-loop goes through all the years from year n-1 to year 1754, and
// checks if the current year in the loop is a leap year. The number of leap years between year 1754 and n-1
// is equal to the number of days that will get added (beside from the days in ordinary years) to the total
// days from January 1, 1754 to the entered date.
for (; year > 1754; year -= 1) {
if (isALeapYear(year)) {
sumLeapDaysInLeapYears += 1;
}
}
// The sum of all days from year 1754 to year n-1 (if the entered year is n), is equal to the sum of days in
// the ordinary years and the leap days in the years.
int sumDaysInEveryYearExcludingTheEntered = sumDaysInOrdinaryYears + sumLeapDaysInLeapYears;
int sumDaysInTotalYears = sumDaysInEveryYearExcludingTheEntered + dayNumberWithinYear(year, month, day);
int weekDay = sumDaysInTotalYears % 7;
if (weekDay == 0) {
showMessageDialog(null, "The date is a monday.");
}
else if (weekDay == 1) {
showMessageDialog(null, "The date is a tuesday.");
}
else if (weekDay == 2) {
showMessageDialog(null, "The date is a wednesday.");
}
else if (weekDay == 3) {
showMessageDialog(null, "The date is a thursday.");
}
else if (weekDay == 4) {
showMessageDialog(null, "The date is a friday.");
}
else if (weekDay == 5) {
showMessageDialog(null, "The date is a saturday.");
}
// If weekDay == 6
else {
showMessageDialog(null, "The date is a sunday.");
}
}
public static void main(String[] args) {
// This is step 3 in the laboratory instruction.
while (true) {
String date = showInputDialog("Please, enter a date on the form yyyy-mm-dd");
// If the user clicks 'Cancel' or clicks 'OK' when the dialog box is empty, the program will exit.
if (date == null || date.length() == 0) {
break;
}
int y = Integer.parseInt(date.substring(0,4));
int m = Integer.parseInt(date.substring(5,7));
int d = Integer.parseInt(date.substring(8));
if (!isAValidDate(y, m, d)) {
showMessageDialog(null, "Error! The entered date is invalid. " +
" Please enter a valid date on the form yyyy-mm-dd");
}
else {
weekDay(y, m, d);
}
}
}
}

Instead of asking us to debug through your entire code, perhaps consider LocalDate to get the desired result:
LocalDate ldt = LocalDate.parse("1999-12-31");
System.out.println(ldt.getDayOfWeek());
LocalDate ldt2 = LocalDate.parse("2000-01-01");
System.out.println(ldt2.getDayOfWeek());
Output:
FRIDAY
SATURDAY

The Problem is with finding the number of leap year. Your logic is counting the year 2000 also. The number of leap years should be same for 1999-12-31 and 2000-01-01. You need to consider year 2000 only if the month is greater than February. Increment the sumLeapDaysInLeapYears only if the input date is greater than Feb 28th

how to return the number of days according on its month using java [duplicate]

This question already has answers here:
Number of days in particular month of particular year?
(22 answers)
Closed 7 years ago.
I was given this assignment for my homework:
create a program in java that accepts an unsigned integer n and return the number of days according to its month. For example if n = 6, the return value is 30 because 6th month of june has 30 days. Assume no leap year.
This is my attempt, but it doesn't work as expected. Can anyone give me pointers as to why.
public class daysmonths {
public static void main(String []args) {
for (int i = 1; i<=12; i++){
int e = f(i);
System.out.println(i + " = " + e + " days ");
}
}
public static int f(int i){
if ((i == 1)|(i == 3)|(i == 5)|(i == 7)|(i == 8)|(i == 10)|(i == 12))
return 31;
else if ((i == 4)|(i == 6)|(i == 9)|(i == 11))
return 30;
else
return 28;
}
}

The below code uses the java Calendar class by setting it's month to the input month and getting its max date by getActualMaximum() method. Also it will return 29 for leap years.
public static void main(String args[]){
int month = 6;
Calendar cal = Calendar.getInstance();
cal.set(Calendar.MONTH, month-1);
System.out.println(cal.getActualMaximum(Calendar.DATE));
}

Method working with days in a month not behaving

So basically we have this question to do : Write a method dayNumber that determines the number of days in a year up to and including the current day. The method should have three int parameters: year, month, and day. If the value of any parameter is invalid, the method should print a warning message and return the value zero. The table gives some examples of the action of the method. Accept any non-negative year as being valid. You may want to assume the existence of a method numberOfDays that returns the number of days in a given month of a given year. And you should have a method call isLeapYear, if the user enter a year that is a leap year.
This is what I did so far....
class dayMonthYear {
public static void main(String[] args) {
System.out.println("Enter a year");
int year = In.getInt();
System.out.println("Enter the month for '1' to be January - '12' to be december");
int month = In.getInt();
System.out.println("Enter the day");
int day = In.getInt();
dayNumber(year, month, day);
System.out.println(dayNumber(year, month, day));
}
public static int dayNumber(int year, int month, int day) {
int total = 0;
for (int m = 1; m < month; m++)
total += (numberOfDays(month, year));
return total + day;
}
public static boolean isLeapYear(int yearB) {
return (yearB % 4 == 0 && yearB % 100 != 0) || yearB % 400 == 0;
}
public static int numberOfDays(int monthA, int yearA) {
int days = 0;
if (monthA == 4 || monthA == 6 || monthA == 9 || monthA == 11)
days = 30;
if (monthA == 1 || monthA == 3 || monthA == 5 || monthA == 7
|| monthA == 8 || monthA == 10 || monthA == 12)
days = 31;
else if (monthA == 2 && isLeapYear(yearA))
days = 29;
else if (monthA == 2)
days = 28;
return days;
}
}
It works and compiles but my problem is that: let say I enter "12" for December and December has 31 days, so what my program will do since December has 31 days, it thinks each month has 31 days and add them up which will give me 372 when it's suppose to give me 365. How do I make it that it won't do that and that it will work if the year is a leap year too.

Basically, this...
for (int m= 1; m < month; m++)
total += (numberOfDays(month, year));
is wrong, you are passing the value of month to this method each time it is called (12 for example), meaning that each time you call it, it thinks the number of days in the month is 31 (because it is)...
Instead, pass m
for (int m= 1; m < month; m++)
total += (numberOfDays(m, year));

Week day Finder in Java

I'm doing a project that consists on: 'Write a program that prompts for a date (month, day, year) and reports the day of the week for that date. It might be
helpful to know that January 1, 1601 was a Monday.'. This is an exercise of 'Building Java Programs - A Back to Basics Approach, 2nd Edition', a book which I bought to teach myself Java. Any feedback is highly appreciated, but I do ask that you explain why you would do something another/a certain way. Thanks!
So, my problem is that while for the dates nearer to 1600's it's giving the correct day (I believe), the same is not true for more recent days, with them having an offset of three days (at least the ones I checked). Why does this happen and how do I fix it? Thanks!
My code:
// finds the day of the week of the given date
public static String dayFinder(int month, int day, int year) {
// handle invalid input
if (month > 12 || month < 1 || day > 31 || day < 1) {
throw new IllegalArgumentException("Month must be between "
+ "1 and 12 and Day must be between 1 and 31.");
}
// convert to "absolute" day, covering day and month
int absoluteDay = monthToDay(month, day, year);
// convert year to days and add to "absolute" day
absoluteDay += yearToDay(year);
if (absoluteDay % 7 == 1) {
return "Monday";
} else if (absoluteDay % 7 == 2) {
return "Tuesday";
} else if (absoluteDay % 7 == 3) {
return "Wednesday";
} else if (absoluteDay % 7 == 4) {
return "Thursday";
} else if (absoluteDay % 7 == 5) {
return "Friday";
} else if (absoluteDay % 7 == 6) {
return "Saturday";
} else { // absoluteDay % 7 == 0
return "Sunday";
}
}
// calculates the number of days present in a given
// date since the beginning of the year
public static int monthToDay(int month, int day, int year) {
// convert to "absolute" day
int absoluteDay = 0, daysTo31 = 0;
// iterate through months
for (int i = 0, loopMonth = month; i < month; i++) {
if (loopMonth == 1 || loopMonth == 3 || loopMonth == 5
|| loopMonth == 7 || loopMonth == 8 || loopMonth == 10
|| loopMonth == 12) {
absoluteDay += 31;
daysTo31 = 0;
} else if (loopMonth == 2) {
if (year % 4 != 0) {
absoluteDay += 28;
daysTo31 = 3;
} else { // leap year
absoluteDay += 29;
daysTo31 = 2;
}
} else { // month = 4, 6, 9 or 10
absoluteDay += 30;
daysTo31 = 1;
}
loopMonth--;
}
// adjust to specific day
absoluteDay -= (31 - day - daysTo31);
return absoluteDay;
}
// calculates the number of days between
// (the beginning of) the given year and
// (the beginning of) the reference year 1601
public static int yearToDay(int year) {
// convert to "absolute" day
int absoluteDay = 0;
year -= 1601;
// iterate through years
for (int i = 0, loopYear = year; i < year; i++) {
if (loopYear % 4 != 0) {
absoluteDay += 365;
} else { // leap year
absoluteDay += 366;
}
loopYear--;
}
return absoluteDay;
}
// Year 1604 (MDCIV) was a leap year starting on Thursday

Your problem is probably connected with the leap years.
Due to Wikipedia:
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100; the centurial years that are exactly divisible by 400 are still leap years. For example, the year 1900 is not a leap year; the year 2000 is a leap year. [link]
It's the reason why you have three day too much (1700, 1800, 1900).

Java.util date/calendar functionality is fraught with craziness. I think Java7 has improved it a bit (I've heard, but not investigated), but I recommend a 3rd party library Joda-Time. To do what you're trying to do with Joda would be:
DateTime anyDateTime = new DateTime(
1800, //year
4, //month
19, //day
0, //hour
0); // minutes
System.out.println("DOW = " + anyDateTime.dayOfWeek().getAsText());
prints "DOW = Saturday"
I realize your goal is to learn Java, but it's not always necessary to reinvent the wheel.

tl;dr
int dayOfWeekNumber =
LocalDate.of( 2016 , 12 , 22 ) // A date-only object, no time-of-day nor time zone.
.getDayOfWeek() // `DayOfWeek` enum object.
.getValue() ; // 1-7 for Monday-Sunday.
java.time
The Question is really about algorithm. But FYI, this functionality is built into Java with the java.time classes.
LocalDate
The LocalDate class represents a date-only value without time-of-day and without time zone.
LocalDate ld = LocalDate.of( 2016 , 12 , 22 );
DayOfWeek
The DayOfWeek enum defines seven objects for each day of the week.
DayOfWeek dow = ld.getDayOfWeek() ;
Generally best to use the DayOfWeek object. But if you absolutely need an integer number, you can ask for one. Numbered 1-7 for Monday-Sunday per ISO 8601.
int dowNumber = dow.getValue();
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old date-time classes such as java.util.Date, .Calendar, & java.text.SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to java.time.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations.
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport and further adapted to Android in ThreeTenABP (see How to use…).
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

import java.util.*;
This code is working for any date.
Maybe it will help someone.
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner console = new Scanner(System.in);
System.out.println("Give me a special date !!!");
System.out.print("Month: ");
int month = console.nextInt();
System.out.print("Day: ");
int day = console.nextInt();
System.out.print("Year:");
int year = console.nextInt();
String date = dayFinder(month, day, year);
System.out.println("It is the date " + month + "/" + date + "/" + year);
console.close();
}
public static String dayFinder(int month, int day, int year) {
// handle invalid input
if (month > 12 || month < 1 || day > 31 || day < 1) {
throw new IllegalArgumentException("Month must be between "
+ "1 and 12 and day must be between 1 and 31");
} else {
// convert to "absolute" day, covering day and month
int absoluteDay = monthToDay(month, day, year);
// convert year to days and add to "absolute" day
absoluteDay += yearToDay(year);
if (absoluteDay % 7 == 2) {
return "Monday";
} else if (absoluteDay % 7 == 3) {
return "Tuesday";
} else if (absoluteDay % 7 == 4) {
return "Wednesday";
} else if (absoluteDay % 7 == 5) {
return "Thursday";
} else if (absoluteDay % 7 == 6) {
return "Friday";
} else if (absoluteDay % 7 == 0) {
return "Saturday";
} else { // absoluteDay % 7 == 1
return "Sunday";
}
}
}
// calculates the number of days between
// (the beginning of) the given year
// (the beginning of) the reference year 1601;
public static int yearToDay(int years) {
// covert to "absolute" day;
int absoluteDay = 0;
int leapYears = 0;
// iterate through years;
for (int i = 0; i < years; i++) {
if (((i % 4) == 0) && ((i % 100) != 0)) {
leapYears +=1;
} else if (i % 400 == 0) {
leapYears ++;
}
}
absoluteDay = (leapYears * 366) + (((years - 1) - leapYears) * 365);
return absoluteDay;
}
// Calculates the numbers of days present in a given
// date since the beginning of the year;
public static int monthToDay (int month, int day, int year) {
// convert to absolute day;
int absoluteDay = 0;
// iterate through months
for (int i = 1; i < month; i++) {
if ((i == 4) || (i == 6) || (i == 9) || (i == 11)) { // 30 day
absoluteDay += 30;
} else if (i == 2) {
if ((year % 4 == 0) && (year % 100 != 0)) {
absoluteDay += 29;
} else if (year % 400 == 0) {
absoluteDay += 29;
} else {
absoluteDay += 28;
}
} else {
absoluteDay += 31; // 1,3,5,7,8,10,12 months
}
}
return absoluteDay + day;
}
}