Develop Reference

Oracle next_day function equivalent in JAVA

I wanted to make a method which works similar to as oracle's next_day() function, below is my code which accepts date n weekday in MONDAY,TUESDAY etc. and returns a date which falls on the next given day from the input date.
/**
* #param date
* #param weekDay
* #return Gives the date for next weekday specified in the parameter.
*/
public Date getNextDay(Date value, String weekday) {
Calendar date1 = Calendar.getInstance();
date1.setTime(value);
if (weekday.equalsIgnoreCase("MONDAY")) {
while (date1.get(Calendar.DAY_OF_WEEK) != Calendar.MONDAY) {
date1.add(Calendar.DATE, 1);
}
} else if (weekday.equalsIgnoreCase("TUESDAY")) {
while (date1.get(Calendar.DAY_OF_WEEK) != Calendar.TUESDAY) {
date1.add(Calendar.DATE, 1);
}
} else if (weekday.equalsIgnoreCase("WEDNESDAY")) {
while (date1.get(Calendar.DAY_OF_WEEK) != Calendar.WEDNESDAY) {
date1.add(Calendar.DATE, 1);
}
} else if (weekday.equalsIgnoreCase("THURSDAY")) {
while (date1.get(Calendar.DAY_OF_WEEK) != Calendar.THURSDAY) {
date1.add(Calendar.DATE, 1);
}
} else if (weekday.equalsIgnoreCase("FRIDAY")) {
while (date1.get(Calendar.DAY_OF_WEEK) != Calendar.FRIDAY) {
date1.add(Calendar.DATE, 1);
}
} else if (weekday.equalsIgnoreCase("SATURDAY")) {
while (date1.get(Calendar.DAY_OF_WEEK) != Calendar.SATURDAY) {
date1.add(Calendar.DATE, 1);
}
} else {
while (date1.get(Calendar.DAY_OF_WEEK) != Calendar.SUNDAY) {
date1.add(Calendar.DATE, 1);
}
}
return date1.getTime();
}
Please suggest a better way of doing this.

I recommend you do it using the modern java.time date-time API. Learn more about the modern date-time API from Trail: Date Time. The java.util date-time API and SimpleDateFormat are outdated and error-prone. In case you are not using Java-8, you can still use Java-8 date-time API through ThreeTenABP library.
import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;
public class Main {
public static void main(String[] args) {
// Tests
// Next occurrence
System.out.println(getNextDay(LocalDate.now(), "Monday"));
System.out.println(getNextDay(LocalDate.now(), "Wednesday"));
// Same (if date falls on the given day) or next occurrence
System.out.println(getSameOrNextDay(LocalDate.now(), "Monday"));
System.out.println(getSameOrNextDay(LocalDate.now(), "Wednesday"));
}
static LocalDate getNextDay(LocalDate value, String weekday) {
return value.with(TemporalAdjusters.next(DayOfWeek.valueOf(weekday.toUpperCase())));
}
static LocalDate getSameOrNextDay(LocalDate value, String weekday) {
return value.with(TemporalAdjusters.nextOrSame(DayOfWeek.valueOf(weekday.toUpperCase())));
}
}
Output:
2020-09-28
2020-09-30
2020-09-28
2020-09-23

If you are interested in the next day I'll suggest using a java.time.LocalDate instead of a java.util.Date.
The following code accepts such a LocalDate along with a String (that needs to be a full day of week in upper case letters) and returns the LocalDate representing the nearest future date which has the given day of week:
public static LocalDate nextDay(LocalDate sourceDay, String weekday) {
// parse the day of week to an enum value
DayOfWeek dayOfWeek = DayOfWeek.valueOf(weekday);
// check if the day is the same as the one of the given LocalDate
if (sourceDay.getDayOfWeek().equals(dayOfWeek)) {
// and return the LocalDate that's a week later
return sourceDay.plusWeeks(1);
} else {
// otherwise add a day to the given date
LocalDate nextDayOfWeek = sourceDay.plusDays(1);
// and do that until the day of week of the given date is reached
while (nextDayOfWeek.getDayOfWeek() != dayOfWeek) {
nextDayOfWeek = nextDayOfWeek.plusDays(1);
}
// then return the future date
return nextDayOfWeek;
}
}
You can use it in a main like this:
public static void main(String[] args) {
System.out.println(nextDay(LocalDate.now(), "FRIDAY")
.format(DateTimeFormatter.ofPattern("uuuu-MM-dd '('EEEE')'",
Locale.ENGLISH)));
}
Output (today ⇒ 2020-09-23):
2020-09-25 (Friday)

Use the "new" java.time.DayOfWeek and java.time.LocalDate classes:
public LocalDate getNextDay(
final LocalDate value,
final DayOfWeek day
)
{
int currentDay = value.getDayOfWeek().getValue();
int expectedDay = day.getValue();
if ( currentDay >= expectedDay )
{
expectedDay += 7;
}
return value.plusDays( expectedDay - currentDay );
}

Java Exercise: produce the output of the calendar for the current month in a grid

I am working on a small exercise to test myself. I made a small program to print the date/days in the current month. I assumed that you would be given the current date e.g. May 10th and the current day Thursday. My question, is it possible to do this exercise without being given the date today and the day? Here's my code:
public static void main(String [] args) {
int days = 31; // may
String arr[] = new String[]{"Mon", "Tue", "Wed", "Thur", "Fri","Sat", "Sun"};
int today_date = 10;
String today_day = "Thur";
int today_index = 0;
//get index of current day e.g. Thur = index 3
for(int i = 0; i<arr.length; i++) {
if(today_day.equals(arr[i])) {
today_index = i;
}
}
//count from today_day to 1, the purpose is to get the first day of the month
while(today_date > 1) {
if(today_index == 0) {
today_index = 6;
today_date--;
}
else {
today_date--;
today_index--;
}
}
//print each day of the month
for(int i = 1; i<=days; i++ ) {
if(today_index == 6) {
System.out.print(i+"("+ arr[today_index]+") \n");
today_index = 0;
}
else {
System.out.print(i+"("+ arr[today_index]+") | ");
today_index++;
}
}
}
Sample output:

Create key value pair for mapping "integer to name of month" and "integer to day in a week". (Switch case can also be used)
Use Calendar which is part of java.util package and get day of the week for given date, month and year.
Ex:
Calendar cal = new GregorianCalendar();
cal.set(Calendar.MONTH, 4);
cal.set(Calendar.DAY_OF_MONTH, 15);
cal.set(Calendar.YEAR, 2018);
System.out.println(cal.getTime());
System.out.println(cal.getDisplayName(2, 3, Locale.US));
Use "integer to day in a week" key value pair to print respective day and month in words.
Hope this helps.

JAVA - How to make custom holidays and keep track of them

Making a Calendar that allows you to add in specific holidays

You should use the java.time package. Specifically the MonthDay class to represent a holiday, as holidays are usually some fixed month + day (however you will need more complicated logic than a Set<MonthDay> if the holidays are "dynamic").
import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.Month;
import java.time.MonthDay;
import java.util.HashSet;
import java.util.Set;
public class CustomHolidays {
private final Set<MonthDay> holidays = new HashSet<>();
public void addHoliday(final MonthDay monthDay) {
holidays.add(monthDay);
}
public boolean isHoliday(final LocalDate localDate) {
return isWeekend(localDate) || holidays.contains(toMonthDay(localDate));
}
public int numberOfWorkdaysBetween(final LocalDate startInclusive, final LocalDate endInclusive) {
int c = 0;
for (LocalDate i = startInclusive; !i.isAfter(endInclusive); i = i.plusDays(1)) {
if (!isHoliday(i)) {
c++;
}
}
return c;
}
private boolean isWeekend(final LocalDate localDate) {
final DayOfWeek dow = localDate.getDayOfWeek();
return dow == DayOfWeek.SATURDAY || dow == DayOfWeek.SUNDAY;
}
private static MonthDay toMonthDay(final LocalDate localDate) {
return MonthDay.of(localDate.getMonth(), localDate.getDayOfMonth());
}
public static void main(String[] args) {
final CustomHolidays ch = new CustomHolidays();
ch.addHoliday(MonthDay.of(Month.MAY, 1));
ch.addHoliday(MonthDay.of(Month.MAY, 2));
ch.addHoliday(MonthDay.of(Month.MAY, 3));
System.out.println(ch.numberOfWorkdaysBetween(LocalDate.of(2018, 5, 1), LocalDate.of(2018, 5, 8)));
}
}
Output: 3

As recommended by others, you should go ahead and use java.time.LocalDate instead.
But if you are still curious as to why your current approach is not working, read ahead.
1st Problem: The following while condition will stop once the day is equal, even if months are different (because dayIndex!= yDay will evaluate to false)
while (monthIndex != yMonth && dayIndex != yDay)
Changing the while condition to below one will check for both the day and month. Also compare monthIndex to yMonth-1 since your monthIndex is initialised as xMonth-1
while (!(monthIndex == yMonth-1 && dayIndex == yDay))
2nd problem: Change int calMonth = xMonth; to int calMonth = xMonth-1; for the same reason as mentioned in problem 1.
3rd Problem: Initialise dayIndex to 0 instead of 1, because you are incrementing dayIndex after the if block. If you initialise it to 1, it will increment to 2 and hence 1st date of every month will be skipped.
if (dayIndex == numDaysInMonth+1) {
dayIndex = 0;
monthIndex++;
}
dayIndex++;
Check here for working fiddle

Calculate number of weekdays between two dates in Java

Can anyone point me to some Java snippet wherein i can get business (except Sat and Sun) days between two dates.

public static int getWorkingDaysBetweenTwoDates(Date startDate, Date endDate) {
Calendar startCal = Calendar.getInstance();
startCal.setTime(startDate);
Calendar endCal = Calendar.getInstance();
endCal.setTime(endDate);
int workDays = 0;
//Return 0 if start and end are the same
if (startCal.getTimeInMillis() == endCal.getTimeInMillis()) {
return 0;
}
if (startCal.getTimeInMillis() > endCal.getTimeInMillis()) {
startCal.setTime(endDate);
endCal.setTime(startDate);
}
do {
//excluding start date
startCal.add(Calendar.DAY_OF_MONTH, 1);
if (startCal.get(Calendar.DAY_OF_WEEK) != Calendar.SATURDAY && startCal.get(Calendar.DAY_OF_WEEK) != Calendar.SUNDAY) {
++workDays;
}
} while (startCal.getTimeInMillis() < endCal.getTimeInMillis()); //excluding end date
return workDays;
}
Start date and end date are exclusive, Only the days between given
dates will be counted. Start date and end date will not be included.

Solution without loop:
static long days(Date start, Date end){
//Ignore argument check
Calendar c1 = Calendar.getInstance();
c1.setTime(start);
int w1 = c1.get(Calendar.DAY_OF_WEEK);
c1.add(Calendar.DAY_OF_WEEK, -w1);
Calendar c2 = Calendar.getInstance();
c2.setTime(end);
int w2 = c2.get(Calendar.DAY_OF_WEEK);
c2.add(Calendar.DAY_OF_WEEK, -w2);
//end Saturday to start Saturday
long days = (c2.getTimeInMillis()-c1.getTimeInMillis())/(1000*60*60*24);
long daysWithoutWeekendDays = days-(days*2/7);
// Adjust days to add on (w2) and days to subtract (w1) so that Saturday
// and Sunday are not included
if (w1 == Calendar.SUNDAY && w2 != Calendar.SATURDAY) {
w1 = Calendar.MONDAY;
} else if (w1 == Calendar.SATURDAY && w2 != Calendar.SUNDAY) {
w1 = Calendar.FRIDAY;
}
if (w2 == Calendar.SUNDAY) {
w2 = Calendar.MONDAY;
} else if (w2 == Calendar.SATURDAY) {
w2 = Calendar.FRIDAY;
}
return daysWithoutWeekendDays-w1+w2;
}

Solution without loop in 5 lines of code
Days between are defined in the same way as ChronoUnit.DAYS.between(start, end) which means there are 4 days between Monday and Friday. Since we are only interested in weekdays we have to subtract weekends, therefore from Friday until Tuesday there will be 2 weekdays(just compute endDay - startDay and subtract 2 for the weekend). Add 1 to the result if you want an inclusive result, i.e. not days between.
I present two solutions.
First solution (5-liner, short and cryptic):
import java.time.*;
import java.time.temporal.*;
public static long calcWeekDays1(final LocalDate start, final LocalDate end) {
final DayOfWeek startW = start.getDayOfWeek();
final DayOfWeek endW = end.getDayOfWeek();
final long days = ChronoUnit.DAYS.between(start, end);
final long daysWithoutWeekends = days - 2 * ((days + startW.getValue())/7);
//adjust for starting and ending on a Sunday:
return daysWithoutWeekends + (startW == DayOfWeek.SUNDAY ? 1 : 0) + (endW == DayOfWeek.SUNDAY ? 1 : 0);
}
Second solution:
public static long calcWeekDays2(final LocalDate start, final LocalDate end) {
final int startW = start.getDayOfWeek().getValue();
final int endW = end.getDayOfWeek().getValue();
final long days = ChronoUnit.DAYS.between(start, end);
long result = days - 2*(days/7); //remove weekends
if (days % 7 != 0) { //deal with the rest days
if (startW == 7) {
result -= 1;
} else if (endW == 7) { //they can't both be Sunday, otherwise rest would be zero
result -= 1;
} else if (endW < startW) { //another weekend is included
result -= 2;
}
}
return result;
}

java.time
The modern way is with the java.time classes.
LocalDate
The LocalDate class represents a date-only value without time-of-day and without time zone.
LocalDate start = LocalDate.of( 2016 , 1 , 23 );
LocalDate stop = start.plusMonths( 1 );
DayOfWeek enum
The DayOfWeek enum provides a singleton instance for each of the sever days of the week.
DayOfWeek dow = start.getDayOfWeek();
if( dow.equals( DayOfWeek.SATURDAY ) || dow.equals( DayOfWeek.SUNDAY ) ) …
We can collect the desired dates in a List.
int initialCapacity = Duration.between( start , stop ).toDays() ;
List<LocalDate> dates = new ArrayList<>( initialCapacity );
…
if( dow.equals( DayOfWeek.SATURDAY ) || dow.equals( DayOfWeek.SUNDAY ) ) {
dates.add( date );
…
An EnumSet is an extremely efficient, fast and low-memory, implementation of Set. We can use an EnumSet instead of the if statement seen above.
Set<DayOfWeek> weekend = EnumSet.of( DayOfWeek.SATURDAY , DayOfWeek.SUNDAY ) ;
…
if( weekend.contains( dayOfWeek ) ) …
Put that all together.
LocalDate date = start ;
while( date.isBefore( stop ) ) {
if( ! weekend.contains( date.getDayOfWeek() ) ) { // If not weekend, collect this LocalDate.
dates.add( date ) ;
}
// Prepare for next loop.
date = date.plusDays( 1 ); // Increment to next day.
}
nextWorkingDay TemporalAdjuster
Another approach uses the ThreeTen-Extra project to add classes that work with java.time.
The Temporals class adds additional implementations of TemporalAdjuster for manipulating date-time values. We want the nextWorkingDay adjuster to increment the date while skipping over Saturday & Sunday.
LocalDate start = LocalDate.of( 2016 , 1 , 23 );
LocalDate stop = start.plusMonths( 1 );
int initialCapacity = Duration.between( start , stop ).toDays() ;
List<LocalDate> dates = new ArrayList<>( initialCapacity );
LocalDate date = start.minusDays( 1 ); // Start a day ahead.
while( date.isBefore( stop ) ) {
date = date.with( org.threeten.extra.Temporals.nextWorkingDay() );
// Double-check ending date as the `nextWorkingDay` adjuster could move us past the stop date.
if( date.isBefore( stop ) ) {
dates.add( date ) ;
}
}
Performance
I am curious about the performance of the various approach in various Answers on this page. I am considering only the modern java.time code, not the code using troublesome legacy Date/Calendar classes.
Here are four methods that each return the number of days elapsed.
One uses the clever math-based approach seen in the Answer by Roland.
private long countWeekDaysMath ( LocalDate start , LocalDate stop ) {
// Code taken from Answer by Roland.
// https://stackoverflow.com/a/44942039/642706
long count = 0;
final DayOfWeek startW = start.getDayOfWeek();
final DayOfWeek stopW = stop.getDayOfWeek();
final long days = ChronoUnit.DAYS.between( start , stop );
final long daysWithoutWeekends = days - 2 * ( ( days + startW.getValue() ) / 7 );
//adjust for starting and ending on a Sunday:
count = daysWithoutWeekends + ( startW == DayOfWeek.SUNDAY ? 1 : 0 ) + ( stopW == DayOfWeek.SUNDAY ? 1 : 0 );
return count;
}
Two use approaches seen in this Answer of mine: (a) Visit each date, incrementing one-by-one in a conventional loop.
private long countWeekDaysVisit ( LocalDate start , LocalDate stop ) {
// Code taken from Answer by Basil Bourque.
// https://stackoverflow.com/a/40369140/642706
long count = 0;
Set < DayOfWeek > weekend = EnumSet.of( DayOfWeek.SATURDAY , DayOfWeek.SUNDAY );
LocalDate ld = start;
while ( ld.isBefore( stop ) ) {
if ( ! weekend.contains( ld.getDayOfWeek() ) ) { // If not weekend, collect this LocalDate.
count++;
}
// Prepare for next loop.
ld = ld.plusDays( 1 ); // Increment to next day.
}
return count;
}
…and, (b) Using the TemporalAdjuster implementation org.threeten.extra.Temporals.nextWorkingDay().
private long countWeekDaysAdjuster ( LocalDate start , LocalDate stop ) {
// Code taken from Answer by Basil Bourque.
// https://stackoverflow.com/a/40369140/642706
long count = 0;
Set < DayOfWeek > weekend = EnumSet.of( DayOfWeek.SATURDAY , DayOfWeek.SUNDAY );
TemporalAdjuster nextWorkingDayTA = org.threeten.extra.Temporals.nextWorkingDay();
LocalDate ld = start;
if ( weekend.contains( ld.getDayOfWeek() ) ) {
ld = ld.with( nextWorkingDayTA );
}
while ( ld.isBefore( stop ) ) {
count++;
// Prepare for next loop.
ld = ld.with( nextWorkingDayTA ); // Increment to next working day (non-weekend day).
}
return count;
}
The last uses Java Streams approach seen in the Answer by Ravindra Ranwala.
private long countWeekDaysStream ( LocalDate start , LocalDate stop ) {
// Code taken from the Answer by Ravindra Ranwala.
// https://stackoverflow.com/a/51010738/642706
long count = 0;
Set < DayOfWeek > weekend = EnumSet.of( DayOfWeek.SATURDAY , DayOfWeek.SUNDAY );
final long weekDaysBetween = start.datesUntil( stop )
.filter( d -> ! weekend.contains( d.getDayOfWeek() ) )
.count();
return count;
}
And the test harness.
Caveats:
Well, the usual caveats about micro-benchmarking being untrustworthy, prone to unjustified or unrealistic conclusions.
I wish I'd learned to use the JMH micro-benchmarking framework.
I have not bothered to try optimizing any of this code. For example, in real work, the TemporalAdjuster could be cached outside our method.
Test harness.
LocalDate start = LocalDate.of( 2018 , Month.JANUARY , 1 );
LocalDate stop = start.plusYears( 1 );
int runs = 100_000;
long go = System.nanoTime();
for ( int i = 1 ; i <= runs ; i++ ) {
long count = this.countWeekDaysMath( start , stop );
}
long elapsedMath = ( System.nanoTime() - go );
go = System.nanoTime();
for ( int i = 1 ; i <= runs ; i++ ) {
long count = this.countWeekDaysVisit( start , stop );
}
long elapsedVisit = ( System.nanoTime() - go );
go = System.nanoTime();
for ( int i = 1 ; i <= runs ; i++ ) {
long count = this.countWeekDaysStream( start , stop );
}
long elapsedAdjuster = ( System.nanoTime() - go );
go = System.nanoTime();
for ( int i = 1 ; i <= runs ; i++ ) {
long count = this.countWeekDaysStream( start , stop );
}
long elapsedStream = ( System.nanoTime() - go );
System.out.println( "math: " + elapsedMath + " each: " + ( elapsedMath / runs ) );
System.out.println( "visit: " + elapsedVisit + " each: " + ( elapsedVisit / runs ) );
System.out.println( "adjuster: " + elapsedAdjuster + " each: " + ( elapsedAdjuster / runs ) );
System.out.println( "stream: " + elapsedStream + " each: " + ( elapsedStream / runs ) );
When run on my MacBook Pro (Sierra) with Oracle JDK 10.0.1 and ThreeTen-Extra version 1.3.2, I get results consistently close to the following. The math solution is a tiny fraction of the others at a couple hundred nanos versus several thousand, as we would expect obviously. Of the other three, the TemporalAdjuster is the longest, always over 10,000 nanos each. The visit and stream both come in well under that 10,000 nanos each, with visit being noticeably faster than streams. As seen in other examples around the internets, Java Streams usually make for nifty short code while often running significantly longer, about 20% longer in this case.
math: 18313309 each: 183
visit: 708420626 each: 7084
adjuster: 1002157240 each: 10021
stream: 924724750 each: 9247
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & 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. Specification is JSR 310.
Where to obtain the java.time classes?
Java SE 8 and SE 9 and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
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.

I used Shengyuan Lu's solution, but I needed to make a fix for the case where the method is called when one of the dates is on a Saturday and the other a Sunday - otherwise the answer is off by a day:
static long days(Date start, Date end){
//Ignore argument check
Calendar c1 = GregorianCalendar.getInstance();
c1.setTime(start);
int w1 = c1.get(Calendar.DAY_OF_WEEK);
c1.add(Calendar.DAY_OF_WEEK, -w1 + 1);
Calendar c2 = GregorianCalendar.getInstance();
c2.setTime(end);
int w2 = c2.get(Calendar.DAY_OF_WEEK);
c2.add(Calendar.DAY_OF_WEEK, -w2 + 1);
//end Saturday to start Saturday
long days = (c2.getTimeInMillis()-c1.getTimeInMillis())/(1000*60*60*24);
long daysWithoutSunday = days-(days*2/7);
if (w1 == Calendar.SUNDAY) {
w1 = Calendar.MONDAY;
}
if (w2 == Calendar.SUNDAY) {
w2 = Calendar.MONDAY;
}
return daysWithoutSunday-w1+w2;
}

Almost all the solutions are pretty much obsoleted and narrative. However here's a much condensed and readable solution.
This approach uses a Java Stream provided by the LocalDate::datesUntil method built into in Java 9 and later.
LocalDate startDate = LocalDate.of(2018, 5, 2);
LocalDate endDate = LocalDate.now();
Set<DayOfWeek> weekend = EnumSet.of(DayOfWeek.SATURDAY, DayOfWeek.SUNDAY);
final long weekDaysBetween = startDate.datesUntil(endDate)
.filter(d -> !weekend.contains(d.getDayOfWeek()))
.count();
.datesUntil returns a sequential ordered stream of dates. The
returned stream starts from this date (inclusive) and goes to
endExclusive (exclusive) by an incremental step of 1 day.
Then all the Saturdays and Sundays are filtered out. Final step is to get the count of the remaining week days.
Java-9 has been released one year ago, since using it now seems reasonable to me.

This thread is filled with failing solutions... I started by writing a little test file which met my needs, and saw that Roland's both solutions fails, Amir's too. I wanted a solution that uses java 8 and that does not uses loops because, do I have to say why ?
So here's the test file :
#Test
public void test() {
LocalDate d1 = LocalDate.of(2018, 8, 1);
LocalDate d2 = LocalDate.of(2018, 8, 2);
LocalDate d3 = LocalDate.of(2018, 8, 3);
LocalDate d4 = LocalDate.of(2018, 8, 4);
LocalDate d5 = LocalDate.of(2018, 8, 5);
LocalDate d6 = LocalDate.of(2018, 8, 6);
LocalDate d7 = LocalDate.of(2018, 8, 7);
LocalDate d8 = LocalDate.of(2018, 8, 8);
LocalDate d9 = LocalDate.of(2018, 8, 9);
LocalDate d10 = LocalDate.of(2018, 8, 10);
LocalDate d15 = LocalDate.of(2018, 8, 15);
LocalDate dsep = LocalDate.of(2018, 9, 5);
// same day : 0 days between
Assert.assertEquals(0, DateUtils.calcWeekDays1(d1, d1));
Assert.assertEquals(1, DateUtils.calcWeekDays1(d1, d2));
Assert.assertEquals(2, DateUtils.calcWeekDays1(d1, d3));
// end on week-end
Assert.assertEquals(2, DateUtils.calcWeekDays1(d1, d4));
Assert.assertEquals(2, DateUtils.calcWeekDays1(d1, d5));
// next week
Assert.assertEquals(3, DateUtils.calcWeekDays1(d1, d6));
Assert.assertEquals(4, DateUtils.calcWeekDays1(d1, d7));
Assert.assertEquals(5, DateUtils.calcWeekDays1(d1, d8));
Assert.assertEquals(6, DateUtils.calcWeekDays1(d1, d9));
Assert.assertEquals(7, DateUtils.calcWeekDays1(d1, d10));
// start on saturday
Assert.assertEquals(0, DateUtils.calcWeekDays1(d4, d5));
Assert.assertEquals(0, DateUtils.calcWeekDays1(d4, d6));
Assert.assertEquals(1, DateUtils.calcWeekDays1(d4, d7));
// start on sunday
Assert.assertEquals(0, DateUtils.calcWeekDays1(d5, d5));
Assert.assertEquals(0, DateUtils.calcWeekDays1(d5, d6));
Assert.assertEquals(1, DateUtils.calcWeekDays1(d5, d7));
// go to next week
Assert.assertEquals(10, DateUtils.calcWeekDays1(d1, d15));
// next month
Assert.assertEquals(25, DateUtils.calcWeekDays1(d1, dsep));
// start sat, go to next month
Assert.assertEquals(22, DateUtils.calcWeekDays1(d4, dsep));
}
And here is my proposed solution, quite simple. Just let java count the number of weeks, multiply by five, and add the number of days needed to compensate the difference ; the only trick is adjusting the start and end to avoid week-ends :
public static long calcWeekDays1(LocalDate start, LocalDate end) {
if (start.getDayOfWeek().getValue() > 5) {
start = start.with(TemporalAdjusters.next(DayOfWeek.MONDAY));
}
if (end.getDayOfWeek().getValue() > 5) {
end = end.with(TemporalAdjusters.previous(DayOfWeek.FRIDAY));
}
if (start.isAfter(end)) { // may happen if you start sat. and end sunday
return 0;
}
long weeks = ChronoUnit.WEEKS.between(start, end);
if (start.getDayOfWeek().getValue() > end.getDayOfWeek().getValue()) {
weeks += 1;
}
return 5 * weeks + end.getDayOfWeek().getValue() - start.getDayOfWeek().getValue();
}
And now I will look stupid if my code fails too :)

I don't have a Java based solution, but have a PHP one, hope it helps:
function getDate($days) {
for ($i = 0; $i < $days; $i ++) {
if (date('N' , strtotime('+' . ($i + 1) . ' days')) > 5) {
$days++;
}
}
return date('l, F jS', strtotime('+' . $days . ' days', time()));
}

This is my example without looping. Algorithm is same as 卢声远 Shengyuan Lus one but I used some features of JodaTime.
public static int getNumberOfBusinessDays(#Nonnull LocalDate from, #Nonnull LocalDate to) {
int fromDateDayOfWeek = from.getDayOfWeek();
int toDateDayOfWeek = to.getDayOfWeek();
int daysWithoutWeekends = 5 * Weeks.weeksBetween(
from.withDayOfWeek(DateTimeConstants.MONDAY), to).getWeeks();
if (fromDateDayOfWeek == DateTimeConstants.SUNDAY) {
fromDateDayOfWeek = DateTimeConstants.SATURDAY;
}
if (toDateDayOfWeek == DateTimeConstants.SUNDAY) {
toDateDayOfWeek = DateTimeConstants.SATURDAY;
}
return daysWithoutWeekends - (fromDateDayOfWeek - toDateDayOfWeek);
}

The do while in the solution of Piyush is wrong, it should be :
do {
if (startCal.get(Calendar.DAY_OF_WEEK) != Calendar.SATURDAY && startCal.get(Calendar.DAY_OF_WEEK) != Calendar.SUNDAY) {
++workDays;
}
startCal.add(Calendar.DAY_OF_MONTH, 1);
} while (startCal.getTimeInMillis() < endCal.getTimeInMillis());

The startCal.add should add onto the Calendar.DATE field, not the Calendar.DAY_OF_MONTH, I was getting weird results with over Decemeber / January period.

This is my example without looping. It is a class in this example because I serialize it in some JSON output. Basically I work out the number of days between the two dates, divide by 7 and assign to a long to have a integer value for the number of weeks. Take the original number of days and subtract the number of weekends*2. This isn't quite perfect - you need to work out if there is a 'hangover' where the start is close to the end of the week and goes over the weekend. To correct for this I find the day of the week at the start and find the remainder of the number of days, and add those together to find the 'hangover' - and if it is more than 5 it is a weekend. It isn't quite perfect, and does not account for holidays at all. And no Joda in sight. That said there is also a issue with timezones.
import java.io.Serializable;
import java.util.Date;
public class BusinessDayCalculator implements Serializable {
private static long DAY = 86400000l;
private Date startTime;
private Date endTime;
public void setStartTime(Date startTime) {
this.startTime = startTime;
}
public Date getStartTime() {
return startTime;
}
public void setEndTime(Date endTime) {
this.endTime = endTime;
}
public Date getEndTime() {
return endTime;
}
public long getHours() {
return (this.endTime.getTime() - this.startTime.getTime())/(1000*60*60);
}
public long getBusinessDays(){
long startDay = getDayFromDate(this.startTime);
long endDay = getDayFromDate(this.endTime);
long totalDays = endDay-startDay;
long totalWeekends = totalDays/7;
long day = getDay(this.startTime);
long hangover = totalDays % 7;
long intoWeekend = day + hangover;
if(intoWeekend>5){
totalWeekends++;
}
long totalBusinessDays = totalDays - (totalWeekends *2);
/*
System.out.println("Days = " + day );
System.out.println("Hangover = " + hangover );
System.out.println("Total Days = " + totalDays);
System.out.println("Total Weekends = " + totalWeekends);
System.out.println("Total Business Days = " + totalBusinessDays);
*/
return totalBusinessDays;
}
private long getDayFromDate( Date date ){
long d = date.getTime() / DAY;
return d;
}
private long getDay( Date date ){
long daysSinceEpoc = getDayFromDate(date);
long day = daysSinceEpoc % 7;
day = day + 4;
if(day>6) day = day - 7;
return day;
}
}

Solution for Java 8 without loop and INCLUSIVE intervals:
public long getDaysWithoutSundays(LocalDate startDate, LocalDate endDate) {
long numberOfDays = ChronoUnit.DAYS.between(startDate, endDate) + 1;
long numberOfSundays = numberOfDays / 7;
long rest = numberOfDays % 7;
if (rest > 0) {
int startToEnd = startDate.getDayOfWeek().getValue() - endDate.getDayOfWeek().getValue();
if (startToEnd > 0) {
numberOfSundays++;
}
else {
if (endDate.getDayOfWeek().equals(DayOfWeek.SUNDAY)) {
numberOfSundays++;
}
}
}
return numberOfDays - numberOfSundays;
}

import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
/**
*
* #author varun.vishwakarma
*
*/
public class FindWeekendsInDateRange {
static HashMap<Integer, String> daysOfWeek=null;
static {
daysOfWeek = new HashMap<Integer, String>();
daysOfWeek.put(new Integer(1), "Sun");
daysOfWeek.put(new Integer(2), "Mon");
daysOfWeek.put(new Integer(3), "Tue");
daysOfWeek.put(new Integer(4), "Wed");
daysOfWeek.put(new Integer(5), "Thu");
daysOfWeek.put(new Integer(6), "Fri");
daysOfWeek.put(new Integer(7), "Sat");
}
/**
*
* #param from_date
* #param to_date
* #return
*/
public static List<Date> calculateWeekendsInDateReange(Date fromDate, Date toDate) {
List<Date> listOfWeekends = new ArrayList<Date>();
Calendar from = Calendar.getInstance();
Calendar to = Calendar.getInstance();
from.setTime(fromDate);
to.setTime(toDate);
while (from.getTimeInMillis() < to.getTimeInMillis()) {
if (daysOfWeek.get(from.get(Calendar.DAY_OF_WEEK)) == "Sat") {
Date sat = from.getTime();
listOfWeekends.add(sat);
} else if (daysOfWeek.get(from.get(Calendar.DAY_OF_WEEK)) == "Sun") {
Date sun = from.getTime();
listOfWeekends.add(sun);
}
from.add(Calendar.DAY_OF_MONTH, 1);
}
return listOfWeekends;
}
public static void main(String[] args) {
String fromDate = "7-Oct-2019";
String toDate = "25-Oct-2019";
System.out.println(FindWeekendsInDateRange.calculateWeekendsInDateReange(new Date(fromDate), new Date(toDate)));
}
}

I'm surprised that every solution given here fails to account for business holidays, which occur in most countries every few months at least, so any span more than a few months will give an incorrect answer. Fortunately, Ravindra's answer using Streams is, despite the inconsequential (for spans under ~10 years) overhead, the best one because it is trivial to correct:
import java.time.*;
import java.util.*;
import static java.time.temporal.ChronoUnit.DAYS;
public class WeekDaysLeft {
public static void main(String[] args) {
LocalDate startDate = LocalDate.now(); // Early 2023
LocalDate endDate = LocalDate.of(2023, 6, 23);
Set<DayOfWeek> weekendDays =
EnumSet.of(DayOfWeek.SATURDAY, DayOfWeek.SUNDAY);
Set<LocalDate> holidays =
Set.of(LocalDate.of(2023,4,7),
LocalDate.of(2023,4,10));
final long weekDaysBetween =
startDate.datesUntil(endDate)
.filter(d -> !weekendDays.contains(
d.getDayOfWeek()))
.filter(d -> !holidays.contains(d))
.count();
System.out.println(weekDaysBetween);
}
}
In regard to my claim that the overhead is inconsequential:
Run my solution under time(1) on Unix/Linux
e.g., time java WeekDaysLeft.java
Change the end-date to 2033, and repeat step 1.
On my system, the user time went DOWN slightly (user time up trivially).
And, of course, if you're running this after June, 2023, bump all the years given.

This program considers loop approach but consider activities happened on after work hours to next working day office start hour
public class BusinessDayCalculator {
private final String DATE_FORMAT = "dd/MM/yyyy HH:mm:ss";
private final int OFFICE_START_HOUR = 9;
private final int OFFICE_CLOSE_HOUR = 17;
private final int TOTAL_MINS_IN_BUSINESS_DAY = (OFFICE_CLOSE_HOUR - OFFICE_START_HOUR)*60;
public void dateDifference(String start, String end){
Date startDate = validateStringToDate(start);
Date endDate = validateStringToDate(end);
System.out.println(startDate);
System.out.println(endDate);
Calendar startDay = convertDateToCalendar(startDate);
Calendar tempDay = (Calendar) startDay.clone();
Calendar endDay = convertDateToCalendar(endDate);
System.out.println(startDay.getTime());
System.out.println(endDay.getTime());
int workDays = -1;
int startDayDifference = 0;
int endDayDifference = 0;
int hours = 0;
int minsRemainder = 0;
if(!(startDay.get(Calendar.DAY_OF_YEAR) == endDay.get(Calendar.DAY_OF_YEAR)
&& startDay.get(Calendar.YEAR) == endDay.get(Calendar.YEAR))){
do{
tempDay.add(Calendar.DAY_OF_MONTH, 1);
if(tempDay.get(Calendar.DAY_OF_WEEK) != Calendar.SATURDAY
&& tempDay.get(Calendar.DAY_OF_WEEK) != Calendar.SUNDAY){
workDays++;
}
}while(tempDay.getTimeInMillis() <= endDay.getTimeInMillis());
if(workDays > 0){
workDays = workDays - 1;
}
}
startDayDifference = hourDifferenceInMinutesOfStartDay(startDay);
endDayDifference = hourDifferenceInMinutesOfEndDay(endDay);
minsRemainder = (startDayDifference + endDayDifference) % TOTAL_MINS_IN_BUSINESS_DAY;
workDays = workDays + ((startDayDifference + endDayDifference) / TOTAL_MINS_IN_BUSINESS_DAY);
hours = minsRemainder/60;
minsRemainder = minsRemainder % 60;
System.out.println(workDays + "d "+ hours + "hrs " + minsRemainder + " mins");
}
private int hourDifferenceInMinutesOfEndDay(Calendar endDay) {
long endTimestamp = endDay.getTimeInMillis();
System.out.println(endTimestamp);
endDay.set(Calendar.HOUR_OF_DAY, OFFICE_START_HOUR);
endDay.set(Calendar.MINUTE,0);
long endDayOfficeStartTimestamp = endDay.getTimeInMillis();
System.out.println(endDayOfficeStartTimestamp);
int difference = (int)((endTimestamp - endDayOfficeStartTimestamp) / 1000) / 60;
System.out.println(difference);
return difference;
}
private int hourDifferenceInMinutesOfStartDay(Calendar startDay) {
long starttimestamp = startDay.getTimeInMillis();
System.out.println(starttimestamp);
startDay.set(Calendar.HOUR_OF_DAY, OFFICE_CLOSE_HOUR);
startDay.set(Calendar.MINUTE,0);
long startDayOfficeCloseTimestamp = startDay.getTimeInMillis();
System.out.println(startDayOfficeCloseTimestamp);
int difference = (int)((startDayOfficeCloseTimestamp - starttimestamp) / 1000) / 60;
System.out.println(difference);
return difference;
}
public Calendar convertDateToCalendar(Date date){
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
if(calendar.get(Calendar.DAY_OF_WEEK) == Calendar.SATURDAY
|| calendar.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY){
calendar = handleActivityOnAfterWorkHoursOrWeekendOrHolidays(calendar);
}
if(calendar.get(Calendar.HOUR_OF_DAY) >= OFFICE_CLOSE_HOUR
&& calendar.get(Calendar.MINUTE) > 0){
calendar = handleActivityOnAfterWorkHoursOrWeekendOrHolidays(calendar);
}
if(calendar.get(Calendar.HOUR_OF_DAY) < OFFICE_START_HOUR){
calendar.set(Calendar.HOUR_OF_DAY, OFFICE_START_HOUR);
calendar.set(Calendar.MINUTE,0);
}
return calendar;
}
private Calendar handleActivityOnAfterWorkHoursOrWeekendOrHolidays(Calendar calendar) {
do{
calendar.add(Calendar.DAY_OF_MONTH, 1);
}while(isHoliday(calendar));
calendar.set(Calendar.HOUR_OF_DAY, OFFICE_START_HOUR);
calendar.set(Calendar.MINUTE,0);
return calendar;
}
private boolean isHoliday(Calendar calendar) {
if(calendar.get(Calendar.DAY_OF_WEEK) == Calendar.SATURDAY
|| calendar.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY){
return true;
}
return false;
}
public Date validateStringToDate(String input){
SimpleDateFormat dateFormat = new SimpleDateFormat(DATE_FORMAT);
Date date = null;
try{
date = dateFormat.parse(input);
}catch(ParseException exception){
System.out.println("invalid date format");
throw new RuntimeException("invalid date format");
}
return date;
}
public static void main(String[] args){
BusinessDayCalculator calc = new BusinessDayCalculator();
String startDate = "27/12/2016 11:38:00";
String endDate = "04/01/2017 12:38:00";
calc.dateDifference(startDate, endDate);
}
}

In groovy:
public static int getWorkingDaysBetweenDates (Date start, Date end) {
def totalDays = (Integer) (end.getTime() - start.getTime()) / (1000 * 60 * 60 * 24)
def int workingDays = 0
(0..totalDays).each { def dow = (start + it)[Calendar.DAY_OF_WEEK]; if(dow != Calendar.SATURDAY && dow != Calendar.SUNDAY){workingDays++} }
workingDays
}

Using java 8 it can be easily done, example function:
long getBusinessDaysDifference(LocalDate startDate, LocalDate endDate) {
EnumSet<DayOfWeek> weekend = EnumSet.of(DayOfWeek.SATURDAY, DayOfWeek.SUNDAY);
List<LocalDate> list = Lists.newArrayList();
LocalDate start = startDate;
while (start.isBefore(endDate)) {
list.add(start);
start = start.plus(1, ChronoUnit.DAYS);
}
long numberOfDays = list.stream().filter(d -> !weekend.contains(d.getDayOfWeek())).count();
return numberOfDays;
}
Description:
Define your off-days in an EnumSet (weekends in this case).
Create a list holding all the days between the startDate and endDate.
Reduce the outcome list by removing any occurrence of a day from the EnumSet.
Then finally count the size of this reduced list.
Note: this function can be optimized, but might be helpful as a starting point.

public long getNumberOfWeekDayBetweenDates(LocalDate startDate, LocalDate endDate, String dayOfWeek) {
long result = -1;
if (startDate != null && endDate != null && dayOfWeek != null && (startDate.isBefore(endDate) || startDate.isEqual(endDate))) {
java.time.DayOfWeek givenDayOfWeek = java.time.DayOfWeek.valueOf(dayOfWeek);
// find the first given day of week in the interval
LocalDate firstOccurrence = startDate.with(TemporalAdjusters.nextOrSame(givenDayOfWeek));
// similarly find last Monday
LocalDate lastOccurrence = endDate.with(TemporalAdjusters.previousOrSame(givenDayOfWeek));
if (firstOccurrence != null && lastOccurrence != null) {
// count the number of weeks between the first and last occurrence, then add 1 as end day is exclusive
result = ChronoUnit.WEEKS.between(firstOccurrence, lastOccurrence) + 1;
} else if (firstOccurrence == null && lastOccurrence == null) {
// no occurrence
result = 0;
} else {
result = 1;
}
}
return result;
}

Here is a set-based solution that completes in constant time for any given subset of weekdays, not just Monday-Friday. It splits the problem into counting full weeks and counting the days in the residual week. If you are interested, here's a detailed explanation and a formal proof that the algorithm is correct. Note that the intervals are inclusive, i.e. startDate and endDate are counted in. If startDate is after endDate, the result is zero rather than negative.
long countWeekDays(LocalDate startDate, LocalDate endDate, Set<DayOfWeek> daysOfWeek) {
long periodLength = Math.max(0, ChronoUnit.DAYS.between(startDate, endDate) + 1);
long fullWeeks = periodLength / 7;
long residualWeekLength = periodLength % 7;
Set<DayOfWeek> residualWeekDays = LongStream.range(0, residualWeekLength)
.mapToObj(offset -> startDate.plusDays(offset).getDayOfWeek())
.collect(Collectors.toSet());
residualWeekDays.retainAll(daysOfWeek);
return fullWeeks * daysOfWeek.size() + residualWeekDays.size();
}
For the original problem (Monday-Friday) it is called e.g. with:
countWeekDays(
LocalDate.of(2016, 2, 8),
LocalDate.of(2016, 2, 26),
new HashSet(Arrays.asList(
DayOfWeek.MONDAY,
DayOfWeek.TUESDAY,
DayOfWeek.WEDNESDAY,
DayOfWeek.THURSDAY,
DayOfWeek.FRIDAY
)
)
)
This assumes you are working with inclusive intervals. If you want to skip the first day of the interval, just add one day to the first parameter:
countWeekDays(
LocalDate.of(2016, 2, 8).plusDays(1),
LocalDate.of(2016, 2, 26),
new HashSet(Arrays.asList(
DayOfWeek.MONDAY,
DayOfWeek.TUESDAY,
DayOfWeek.WEDNESDAY,
DayOfWeek.THURSDAY,
DayOfWeek.FRIDAY
)
)
)
Likewise, if you want to skip the last day of the inclusive interval, subtract one day from the second parameter:
countWeekDays(
LocalDate.of(2016, 2, 8),
LocalDate.of(2016, 2, 26).minusDays(1),
new HashSet(Arrays.asList(
DayOfWeek.MONDAY,
DayOfWeek.TUESDAY,
DayOfWeek.WEDNESDAY,
DayOfWeek.THURSDAY,
DayOfWeek.FRIDAY
)
)
)
Finally, if you need to skip both interval-delimiting days, combine the two previous modifications:
countWeekDays(
LocalDate.of(2016, 2, 8).plusDays(1),
LocalDate.of(2016, 2, 26).minusDays(1),
new HashSet(Arrays.asList(
DayOfWeek.MONDAY,
DayOfWeek.TUESDAY,
DayOfWeek.WEDNESDAY,
DayOfWeek.THURSDAY,
DayOfWeek.FRIDAY
)
)
)

For LocalDate supported by latest java version you can try below function.
It provides support of functiongetDayOfWeek().
The getDayOfWeek() method of LocalDate class in Java gets the day-of-week field, which is an enum DayOfWeek.
public static int getWeekEndCount(LocalDate fromDate, LocalDate toDate) {
int saturday = 0;
int sunday = 0;
while (!fromDate.isAfter(toDate)) {
if (fromDate.getDayOfWeek().equals(DayOfWeek.SATURDAY))
saturday++;
else if (fromDate.getDayOfWeek().equals(DayOfWeek.SUNDAY))
sunday++;
fromDate = fromDate.plusDays(1);
}
System.out.println("Saturday count=="+saturday);
System.out.println("Sunday count=="+sunday);
return saturday+sunday;
}

How do I calculate someone's age in Java?

I want to return an age in years as an int in a Java method.
What I have now is the following where getBirthDate() returns a Date object (with the birth date ;-)):
public int getAge() {
long ageInMillis = new Date().getTime() - getBirthDate().getTime();
Date age = new Date(ageInMillis);
return age.getYear();
}
But since getYear() is deprecated I'm wondering if there is a better way to do this? I'm not even sure this works correctly, since I have no unit tests in place (yet).

JDK 8 makes this easy and elegant:
public class AgeCalculator {
public static int calculateAge(LocalDate birthDate, LocalDate currentDate) {
if ((birthDate != null) && (currentDate != null)) {
return Period.between(birthDate, currentDate).getYears();
} else {
return 0;
}
}
}
A JUnit test to demonstrate its use:
public class AgeCalculatorTest {
#Test
public void testCalculateAge_Success() {
// setup
LocalDate birthDate = LocalDate.of(1961, 5, 17);
// exercise
int actual = AgeCalculator.calculateAge(birthDate, LocalDate.of(2016, 7, 12));
// assert
Assert.assertEquals(55, actual);
}
}
Everyone should be using JDK 8 by now. All earlier versions have passed the end of their support lives.

Check out Joda, which simplifies date/time calculations (Joda is also the basis of the new standard Java date/time apis, so you'll be learning a soon-to-be-standard API).
e.g.
LocalDate birthdate = new LocalDate (1970, 1, 20);
LocalDate now = new LocalDate();
Years age = Years.yearsBetween(birthdate, now);
which is as simple as you could want. The pre-Java 8 stuff is (as you've identified) somewhat unintuitive.
EDIT: Java 8 has something very similar and is worth checking out.
EDIT: This answer pre-dates the Java 8 date/time classes and is not current any more.

Modern answer and overview
a) Java-8 (java.time-package)
LocalDate start = LocalDate.of(1996, 2, 29);
LocalDate end = LocalDate.of(2014, 2, 28); // use for age-calculation: LocalDate.now()
long years = ChronoUnit.YEARS.between(start, end);
System.out.println(years); // 17
Note that the expression LocalDate.now() is implicitly related to the system timezone (which is often overlooked by users). For clarity it is generally better to use the overloaded method now(ZoneId.of("Europe/Paris")) specifying an explicit timezone (here "Europe/Paris" as example). If the system timezone is requested then my personal preference is to write LocalDate.now(ZoneId.systemDefault()) to make the relation to the system timezone clearer. This is more writing effort but makes reading easier.
b) Joda-Time
Please note that the proposed and accepted Joda-Time-solution yields a different computation result for the dates shown above (a rare case), namely:
LocalDate birthdate = new LocalDate(1996, 2, 29);
LocalDate now = new LocalDate(2014, 2, 28); // test, in real world without args
Years age = Years.yearsBetween(birthdate, now);
System.out.println(age.getYears()); // 18
I consider this as a small bug but the Joda-team has a different view on this weird behaviour and does not want to fix it (weird because the day-of-month of end date is smaller than of start date so the year should be one less). See also this closed issue.
c) java.util.Calendar etc.
For comparison see the various other answers. I would not recommend using these outdated classes at all because the resulting code is still errorprone in some exotic cases and/or way too complex considering the fact that the original question sounds so simple. In year 2015 we have really better libraries.
d) About Date4J:
The proposed solution is simple but will sometimes fail in case of leap years. Just evaluating the day of year is not reliable.
e) My own library Time4J:
This works similar to Java-8-solution. Just replace LocalDate by PlainDate and ChronoUnit.YEARS by CalendarUnit.YEARS. However, getting "today" requires an explicit timezone reference.
PlainDate start = PlainDate.of(1996, 2, 29);
PlainDate end = PlainDate.of(2014, 2, 28);
// use for age-calculation (today):
// => end = SystemClock.inZonalView(EUROPE.PARIS).today();
// or in system timezone: end = SystemClock.inLocalView().today();
long years = CalendarUnit.YEARS.between(start, end);
System.out.println(years); // 17

Calendar now = Calendar.getInstance();
Calendar dob = Calendar.getInstance();
dob.setTime(...);
if (dob.after(now)) {
throw new IllegalArgumentException("Can't be born in the future");
}
int year1 = now.get(Calendar.YEAR);
int year2 = dob.get(Calendar.YEAR);
int age = year1 - year2;
int month1 = now.get(Calendar.MONTH);
int month2 = dob.get(Calendar.MONTH);
if (month2 > month1) {
age--;
} else if (month1 == month2) {
int day1 = now.get(Calendar.DAY_OF_MONTH);
int day2 = dob.get(Calendar.DAY_OF_MONTH);
if (day2 > day1) {
age--;
}
}
// age is now correct

/**
* This Method is unit tested properly for very different cases ,
* taking care of Leap Year days difference in a year,
* and date cases month and Year boundary cases (12/31/1980, 01/01/1980 etc)
**/
public static int getAge(Date dateOfBirth) {
Calendar today = Calendar.getInstance();
Calendar birthDate = Calendar.getInstance();
int age = 0;
birthDate.setTime(dateOfBirth);
if (birthDate.after(today)) {
throw new IllegalArgumentException("Can't be born in the future");
}
age = today.get(Calendar.YEAR) - birthDate.get(Calendar.YEAR);
// If birth date is greater than todays date (after 2 days adjustment of leap year) then decrement age one year
if ( (birthDate.get(Calendar.DAY_OF_YEAR) - today.get(Calendar.DAY_OF_YEAR) > 3) ||
(birthDate.get(Calendar.MONTH) > today.get(Calendar.MONTH ))){
age--;
// If birth date and todays date are of same month and birth day of month is greater than todays day of month then decrement age
}else if ((birthDate.get(Calendar.MONTH) == today.get(Calendar.MONTH )) &&
(birthDate.get(Calendar.DAY_OF_MONTH) > today.get(Calendar.DAY_OF_MONTH ))){
age--;
}
return age;
}

I simply use the milliseconds in a year constant value to my advantage:
Date now = new Date();
long timeBetween = now.getTime() - age.getTime();
double yearsBetween = timeBetween / 3.15576e+10;
int age = (int) Math.floor(yearsBetween);

If you are using GWT you will be limited to using java.util.Date, here is a method that takes the date as integers, but still uses java.util.Date:
public int getAge(int year, int month, int day) {
Date now = new Date();
int nowMonth = now.getMonth()+1;
int nowYear = now.getYear()+1900;
int result = nowYear - year;
if (month > nowMonth) {
result--;
}
else if (month == nowMonth) {
int nowDay = now.getDate();
if (day > nowDay) {
result--;
}
}
return result;
}

It's perhaps surprising to note that you don't need to know how many days or months there are in a year or how many days are in those months, likewise, you don't need to know about leap years, leap seconds, or any of that stuff using this simple, 100% accurate method:
public static int age(Date birthday, Date date) {
DateFormat formatter = new SimpleDateFormat("yyyyMMdd");
int d1 = Integer.parseInt(formatter.format(birthday));
int d2 = Integer.parseInt(formatter.format(date));
int age = (d2-d1)/10000;
return age;
}

With the date4j library :
int age = today.getYear() - birthdate.getYear();
if(today.getDayOfYear() < birthdate.getDayOfYear()){
age = age - 1;
}

This is an improved version of the one above... considering that you want age to be an 'int'. because sometimes you don't want to fill your program with a bunch of libraries.
public int getAge(Date dateOfBirth) {
int age = 0;
Calendar born = Calendar.getInstance();
Calendar now = Calendar.getInstance();
if(dateOfBirth!= null) {
now.setTime(new Date());
born.setTime(dateOfBirth);
if(born.after(now)) {
throw new IllegalArgumentException("Can't be born in the future");
}
age = now.get(Calendar.YEAR) - born.get(Calendar.YEAR);
if(now.get(Calendar.DAY_OF_YEAR) < born.get(Calendar.DAY_OF_YEAR)) {
age-=1;
}
}
return age;
}

The correct answer using JodaTime is:
public int getAge() {
Years years = Years.yearsBetween(new LocalDate(getBirthDate()), new LocalDate());
return years.getYears();
}
You could even shorten it into one line if you like. I copied the idea from BrianAgnew's answer, but I believe this is more correct as you see from the comments there (and it answers the question exactly).

Try to copy this one in your code, then use the method to get the age.
public static int getAge(Date birthday)
{
GregorianCalendar today = new GregorianCalendar();
GregorianCalendar bday = new GregorianCalendar();
GregorianCalendar bdayThisYear = new GregorianCalendar();
bday.setTime(birthday);
bdayThisYear.setTime(birthday);
bdayThisYear.set(Calendar.YEAR, today.get(Calendar.YEAR));
int age = today.get(Calendar.YEAR) - bday.get(Calendar.YEAR);
if(today.getTimeInMillis() < bdayThisYear.getTimeInMillis())
age--;
return age;
}

I use this piece of code for age calculation ,Hope this helps ..no libraries used
private static DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd", Locale.getDefault());
public static int calculateAge(String date) {
int age = 0;
try {
Date date1 = dateFormat.parse(date);
Calendar now = Calendar.getInstance();
Calendar dob = Calendar.getInstance();
dob.setTime(date1);
if (dob.after(now)) {
throw new IllegalArgumentException("Can't be born in the future");
}
int year1 = now.get(Calendar.YEAR);
int year2 = dob.get(Calendar.YEAR);
age = year1 - year2;
int month1 = now.get(Calendar.MONTH);
int month2 = dob.get(Calendar.MONTH);
if (month2 > month1) {
age--;
} else if (month1 == month2) {
int day1 = now.get(Calendar.DAY_OF_MONTH);
int day2 = dob.get(Calendar.DAY_OF_MONTH);
if (day2 > day1) {
age--;
}
}
} catch (ParseException e) {
e.printStackTrace();
}
return age ;
}

The fields birth and effect are both date fields:
Calendar bir = Calendar.getInstance();
bir.setTime(birth);
int birthNm = bir.get(Calendar.DAY_OF_YEAR);
int birthYear = bir.get(Calendar.YEAR);
Calendar eff = Calendar.getInstance();
eff.setTime(effect);
This basically a modification of John O's solution without using depreciated methods. I spent a fair amount of time trying to get his code to work in in my code. Maybe this will save others that time.

What about this one?
public Integer calculateAge(Date date) {
if (date == null) {
return null;
}
Calendar cal1 = Calendar.getInstance();
cal1.setTime(date);
Calendar cal2 = Calendar.getInstance();
int i = 0;
while (cal1.before(cal2)) {
cal1.add(Calendar.YEAR, 1);
i += 1;
}
return i;
}

String dateofbirth has the date of birth. and format is whatever (defined in the following line):
org.joda.time.format.DateTimeFormatter formatter = org.joda.time.format.DateTimeFormat.forPattern("mm/dd/yyyy");
Here is how to format:
org.joda.time.DateTime birthdateDate = formatter.parseDateTime(dateofbirth );
org.joda.time.DateMidnight birthdate = new org.joda.time.DateMidnight(birthdateDate.getYear(), birthdateDate.getMonthOfYear(), birthdateDate.getDayOfMonth() );
org.joda.time.DateTime now = new org.joda.time.DateTime();
org.joda.time.Years age = org.joda.time.Years.yearsBetween(birthdate, now);
java.lang.String ageStr = java.lang.String.valueOf (age.getYears());
Variable ageStr will have the years.

Elegant, seemingly correct, timestamp difference based variant of Yaron Ronen solution.
I am including a unit test to prove when and why it is not correct. It is impossible due (to possibly) different number of leap days (and seconds) in any timestamp difference. The discrepancy should be max +-1 day (and one second) for this algorithm, see test2(), whereas Yaron Ronen solution based on completely constant assumption of timeDiff / MILLI_SECONDS_YEAR can differ 10 days for a 40ty year old, nevertheless this variant is incorrect too.
It is tricky, because this improved variant, using formula diffAsCalendar.get(Calendar.YEAR) - 1970, returns correct results most of the time, as number of leap years in on average same between two dates.
/**
* Compute person's age based on timestamp difference between birth date and given date
* and prove it is INCORRECT approach.
*/
public class AgeUsingTimestamps {
public int getAge(Date today, Date dateOfBirth) {
long diffAsLong = today.getTime() - dateOfBirth.getTime();
Calendar diffAsCalendar = Calendar.getInstance();
diffAsCalendar.setTimeInMillis(diffAsLong);
return diffAsCalendar.get(Calendar.YEAR) - 1970; // base time where timestamp=0, precisely 1/1/1970 00:00:00
}
final static DateFormat df = new SimpleDateFormat("dd.MM.yyy HH:mm:ss");
#Test
public void test1() throws Exception {
Date dateOfBirth = df.parse("10.1.2000 00:00:00");
assertEquals(87, getAge(df.parse("08.1.2088 23:59:59"), dateOfBirth));
assertEquals(87, getAge(df.parse("09.1.2088 23:59:59"), dateOfBirth));
assertEquals(88, getAge(df.parse("10.1.2088 00:00:01"), dateOfBirth));
}
#Test
public void test2() throws Exception {
// between 2000 and 2021 was 6 leap days
// but between 1970 (base time) and 1991 there was only 5 leap days
// therefore age is switched one day earlier
// See http://www.onlineconversion.com/leapyear.htm
Date dateOfBirth = df.parse("10.1.2000 00:00:00");
assertEquals(20, getAge(df.parse("08.1.2021 23:59:59"), dateOfBirth));
assertEquals(20, getAge(df.parse("09.1.2021 23:59:59"), dateOfBirth)); // ERROR! returns incorrect age=21 here
assertEquals(21, getAge(df.parse("10.1.2021 00:00:01"), dateOfBirth));
}
}

public class CalculateAge {
private int age;
private void setAge(int age){
this.age=age;
}
public void calculateAge(Date date){
Calendar calendar=Calendar.getInstance();
Calendar calendarnow=Calendar.getInstance();
calendarnow.getTimeZone();
calendar.setTime(date);
int getmonth= calendar.get(calendar.MONTH);
int getyears= calendar.get(calendar.YEAR);
int currentmonth= calendarnow.get(calendarnow.MONTH);
int currentyear= calendarnow.get(calendarnow.YEAR);
int age = ((currentyear*12+currentmonth)-(getyears*12+getmonth))/12;
setAge(age);
}
public int getAge(){
return this.age;
}

/**
* Compute from string date in the format of yyyy-MM-dd HH:mm:ss the age of a person.
* #author Yaron Ronen
* #date 04/06/2012
*/
private int computeAge(String sDate)
{
// Initial variables.
Date dbDate = null;
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
// Parse sDate.
try
{
dbDate = (Date)dateFormat.parse(sDate);
}
catch(ParseException e)
{
Log.e("MyApplication","Can not compute age from date:"+sDate,e);
return ILLEGAL_DATE; // Const = -2
}
// Compute age.
long timeDiff = System.currentTimeMillis() - dbDate.getTime();
int age = (int)(timeDiff / MILLI_SECONDS_YEAR); // MILLI_SECONDS_YEAR = 31558464000L;
return age;
}

Here is the java code to calculate age in year, month and days.
public static AgeModel calculateAge(long birthDate) {
int years = 0;
int months = 0;
int days = 0;
if (birthDate != 0) {
//create calendar object for birth day
Calendar birthDay = Calendar.getInstance();
birthDay.setTimeInMillis(birthDate);
//create calendar object for current day
Calendar now = Calendar.getInstance();
Calendar current = Calendar.getInstance();
//Get difference between years
years = now.get(Calendar.YEAR) - birthDay.get(Calendar.YEAR);
//get months
int currMonth = now.get(Calendar.MONTH) + 1;
int birthMonth = birthDay.get(Calendar.MONTH) + 1;
//Get difference between months
months = currMonth - birthMonth;
//if month difference is in negative then reduce years by one and calculate the number of months.
if (months < 0) {
years--;
months = 12 - birthMonth + currMonth;
} else if (months == 0 && now.get(Calendar.DATE) < birthDay.get(Calendar.DATE)) {
years--;
months = 11;
}
//Calculate the days
if (now.get(Calendar.DATE) > birthDay.get(Calendar.DATE))
days = now.get(Calendar.DATE) - birthDay.get(Calendar.DATE);
else if (now.get(Calendar.DATE) < birthDay.get(Calendar.DATE)) {
int today = now.get(Calendar.DAY_OF_MONTH);
now.add(Calendar.MONTH, -1);
days = now.getActualMaximum(Calendar.DAY_OF_MONTH) - birthDay.get(Calendar.DAY_OF_MONTH) + today;
} else {
days = 0;
if (months == 12) {
years++;
months = 0;
}
}
}
//Create new Age object
return new AgeModel(days, months, years);
}

Easiest way without any libraries:
long today = new Date().getTime();
long diff = today - birth;
long age = diff / DateUtils.YEAR_IN_MILLIS;

With Java 8, we can calculate a person age with one line of code:
public int calCAge(int year, int month,int days){
return LocalDate.now().minus(Period.of(year, month, days)).getYear();
}

Simple solution in kotlin.
fun getAgeOfUser(date: String?) : Int {
if(date.isNullOrEmpty()) return 0
val calendar = Calendar.getInstance()
val cYear = calendar.get(Calendar.YEAR)
val cDay = calendar.get(Calendar.DAY_OF_YEAR)
val dob = Calendar.getInstance()
dob.timeInMillis = date.toLong()
val bYear = dob.get(Calendar.YEAR)
val bDay = dob.get(Calendar.DAY_OF_YEAR)
var age = cYear - bYear
if(cDay < bDay) age--
return age
}

public int getAge(Date dateOfBirth)
{
Calendar now = Calendar.getInstance();
Calendar dob = Calendar.getInstance();
dob.setTime(dateOfBirth);
if (dob.after(now))
{
throw new IllegalArgumentException("Can't be born in the future");
}
int age = now.get(Calendar.YEAR) - dob.get(Calendar.YEAR);
if (now.get(Calendar.DAY_OF_YEAR) < dob.get(Calendar.DAY_OF_YEAR))
{
age--;
}
return age;
}

import java.io.*;
class AgeCalculator
{
public static void main(String args[])
{
InputStreamReader ins=new InputStreamReader(System.in);
BufferedReader hey=new BufferedReader(ins);
try
{
System.out.println("Please enter your name: ");
String name=hey.readLine();
System.out.println("Please enter your birth date: ");
String date=hey.readLine();
System.out.println("please enter your birth month:");
String month=hey.readLine();
System.out.println("please enter your birth year:");
String year=hey.readLine();
System.out.println("please enter current year:");
String cYear=hey.readLine();
int bDate = Integer.parseInt(date);
int bMonth = Integer.parseInt(month);
int bYear = Integer.parseInt(year);
int ccYear=Integer.parseInt(cYear);
int age;
age = ccYear-bYear;
int totalMonth=12;
int yourMonth=totalMonth-bMonth;
System.out.println(" Hi " + name + " your are " + age + " years " + yourMonth + " months old ");
}
catch(IOException err)
{
System.out.println("");
}
}
}

public int getAge(String birthdate, String today){
// birthdate = "1986-02-22"
// today = "2014-09-16"
// String class has a split method for splitting a string
// split(<delimiter>)
// birth[0] = 1986 as string
// birth[1] = 02 as string
// birth[2] = 22 as string
// now[0] = 2014 as string
// now[1] = 09 as string
// now[2] = 16 as string
// **birth** and **now** arrays are automatically contains 3 elements
// split method here returns 3 elements because of yyyy-MM-dd value
String birth[] = birthdate.split("-");
String now[] = today.split("-");
int age = 0;
// let us convert string values into integer values
// with the use of Integer.parseInt(<string>)
int ybirth = Integer.parseInt(birth[0]);
int mbirth = Integer.parseInt(birth[1]);
int dbirth = Integer.parseInt(birth[2]);
int ynow = Integer.parseInt(now[0]);
int mnow = Integer.parseInt(now[1]);
int dnow = Integer.parseInt(now[2]);
if(ybirth < ynow){ // has age if birth year is lesser than current year
age = ynow - ybirth; // let us get the interval of birth year and current year
if(mbirth == mnow){ // when birth month comes, it's ok to have age = ynow - ybirth if
if(dbirth > dnow) // birth day is coming. need to subtract 1 from age. not yet a bday
age--;
}else if(mbirth > mnow){ age--; } // birth month is comming. need to subtract 1 from age
}
return age;
}

import java.time.LocalDate;
import java.time.ZoneId;
import java.time.Period;
public class AgeCalculator1 {
public static void main(String args[]) {
LocalDate start = LocalDate.of(1970, 2, 23);
LocalDate end = LocalDate.now(ZoneId.systemDefault());
Period p = Period.between(start, end);
//The output of the program is :
//45 years 6 months and 6 days.
System.out.print(p.getYears() + " year" + (p.getYears() > 1 ? "s " : " ") );
System.out.print(p.getMonths() + " month" + (p.getMonths() > 1 ? "s and " : " and ") );
System.out.print(p.getDays() + " day" + (p.getDays() > 1 ? "s.\n" : ".\n") );
}//method main ends here.
}

I appreciate all correct answers but this is the kotlin answer for the same question
I hope would be helpful to kotlin developers
fun calculateAge(birthDate: Date): Int {
val now = Date()
val timeBetween = now.getTime() - birthDate.getTime();
val yearsBetween = timeBetween / 3.15576e+10;
return Math.floor(yearsBetween).toInt()
}