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What is the recommended way to increment date in JAVA?

I am using the Calendar class to increment a date. However, all I see for any month is that it is incrementing until the 31st day of that month, regardless of the month being February or not.
Below is the code I am using now:
long curDayDate = 1524787200; // April, 27th, 2018
Instant instant = Instant.ofEpochMilli(curDayDate*1000);
LocalDateTime ldt = instant.atZone(ZoneId.of("GMT")).toLocalDateTime();
int gYear = ldt.getYear();
int gMonth = ldt.getMonthValue();
int gDay = ldt.getDayOfMonth();
Calendar Cal = Calendar.getInstance();
Cal.set(gYear, gMonth, gDay);
for(int i = 0; i < 7; i++) {
// Next day
Cal.add(Calendar.DATE, 1);
System.out.println("Next Year = " + Cal.get(Calendar.YEAR) + ", Next Month = " + Cal.get(Calendar.MONTH) + ", Next Date = " + Cal.get(Calendar.DATE));
}
The above code goes until the 31st of April, even though there is no 31st day for the month of April.

Don't use Calendar. It is part of a raft of poorly-designed date/time APIs that were introduced in early versions of Java (Calendar was introduced in JDK 1.1), and supplanted by the java.time package introduced in Java 8.
If you want to add a day to a LocalDateTime, use plusDays.

Get the number of weeks between two Dates.

Im working in a project and I got two types in Date. I want to calculate the number of weeks between these two dates. The dates can be in diffrent years. Is there any good solution for this?
I have tried to implemenent this with Joda-time which was suggested in other topics..
Im not familar with this library, but I tried to do something like this:
public static int getNumberOfWeeks(Date f, Date l){
Calendar c1 = Calendar.getInstance();
Calendar c2 = Calendar.getInstance();
c1.setTime(f);
c2.setTime(l);
DateTime start = new DateTime(c1.YEAR, c1.MONTH, c1.DAY_OF_MONTH, 0, 0, 0, 0);
DateTime end = new DateTime(c2.YEAR, c2.MONTH, c2.DAY_OF_MONTH, 0, 0, 0, 0);
Interval interval = new Interval(start, end);
Period p = interval.toPeriod();
return p.getWeeks();
}
But this is completely wrong... any suggestions ?

Updating answer to account for Java 8
// TechTrip - ASSUMPTION d1 is earlier than d2
// leave that for exercise
public static long getFullWeeks(Calendar d1, Calendar d2){
Instant d1i = Instant.ofEpochMilli(d1.getTimeInMillis());
Instant d2i = Instant.ofEpochMilli(d2.getTimeInMillis());
LocalDateTime startDate = LocalDateTime.ofInstant(d1i, ZoneId.systemDefault());
LocalDateTime endDate = LocalDateTime.ofInstant(d2i, ZoneId.systemDefault());
return ChronoUnit.WEEKS.between(startDate, endDate);
}

It is pretty easy with joda time:
DateTime dateTime1 = new DateTime(date1);
DateTime dateTime2 = new DateTime(date2);
int weeks = Weeks.weeksBetween(dateTime1, dateTime2).getWeeks();

tl;dr
ChronoUnit
.WEEKS
.between(
myJavaUtilDate_Start.toInstant().atZone( ZoneId.of( "Asia/Tokyo" ) ) ,
myJavaUtilDate_Stop.toInstant().atZone( ZoneId.of( "Asia/Tokyo" ) )
)
7
java.time
The java.time framework is built into Java 8 and later. These new classes supplant the old date-time classes bundled with the earliest versions of Java.
The java.time classes also supplant the highly successful Joda-Time framework. Both java.time and Joda-Time are led by Stephen Colbourne.
Instant replaces java.util.Date
The modern class Instant replaces the legacy class java.util.Date. Both represent a moment in UTC, a specific point on the timeline. Both internally use a count since the same epoch reference of the first moment of 1970 in UTC, 1970-01-01T00:00Z. The old class uses a count of milliseconds, while Instant uses a finer count of nanoseconds.
To convert, call new methods added to the old classes.
Instant start = myJavaUtilDateStart.toInstant() ;
Instant stop = myJavaUtilDateStop.toInstant() ;
Let's make this concrete with some example values.
Instant start = OffsetDateTime.of( 2020 , 1 , 23 , 15 , 30 , 0 , 0 , ZoneOffset.UTC ).toInstant();
Instant stop = OffsetDateTime.of( 2020 , 1 , 23 , 15 , 30 , 0 , 0 , ZoneOffset.UTC ).plusWeeks(7 ).toInstant();
Moments versus dates
Both of our Instant objects represent a moment. The goal is a count of weeks. Weeks means days, and days mean certain dates on the calendar.
So we have a bit of a mismatch. For any given moment, the date varies around the globe by time zone. A few minutes after midnight in Paris France is a new date. Meanwhile in Montréal Québec, being several hours behind, that same moment is still “yesterday”, the date before on the calendar. So we cannot directly calculate weeks from a pair of moments.
You must first decide on the time zone by which you want to perceive a calendar for those moments.
Specify a proper time zone name in the format of Continent/Region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 2-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).
ZoneId z = ZoneId.of( "America/Montreal" ) ;
ZonedDateTime
Apply this ZoneId to our Instant objects to adjust into a time zone, yielding a pair of ZonedDateTime objects.
ZonedDateTime startZdt = start.atZone( z ) ;
ZonedDateTime stopZdt = stop.atZone( z ) ;
ChronoUnit.WEEKS
Now we can use the ChronoUnit enum to calculate elapsed weeks.
long weeks = ChronoUnit.WEEKS.between( startZdt , stopZdt );
Dump to console.
System.out.println( "start.toString() = " + start );
System.out.println( "stop.toString() = " + stop );
System.out.println( "startZdt.toString() = " + startZdt );
System.out.println( "stopZdt.toString() = " + stopZdt );
System.out.println( "weeksCount: " + weeksCount );
See this code run live at IdeOne.com.
start.toString() = 2020-01-23T15:30:00Z
stop.toString() = 2020-03-12T15:30:00Z
startZdt.toString() = 2020-01-23T10:30-05:00[America/Montreal]
stopZdt.toString() = 2020-03-12T11:30-04:00[America/Montreal]
weeksCount: 7
ThreeTen-Extra
The ThreeTen-Extra project adds functionality to the java.time framework built into Java 8 and later.
Weeks class
That project includes a Weeks class to represent a number of weeks. Not only can it calculate, it is also meant to be used in your code as a type-safe object. Such use also helps to make your code self-documenting.
You can instantiate by providing a pair of points in time with the Weeks.between method. Those points in time can be anything implementing java.time.temporal.Temporal including Instant, LocalDate, OffsetDateTime, ZonedDateTime, Year, YearMonth, and more.
Your java.util.Date objects can be easily converted to Instant objects, moments on the timeline in UTC with a resolution in nanoseconds. Look at new methods added to the old date-time classes. For going from Date to Instant, call java.util.Date::toInstant.
Weeks weeks = Weeks.between( startZdt , stopZdt );
You can ask for the number of weeks.
int weeksNumber = weeks.getAmount(); // The number of weeks in this Weeks object.
You can also do much more.
Generate a string in standard ISO 8601 format. The P marks the beginning. The W indicates a number of weeks.
PW7
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.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.
Where to obtain the java.time classes?
Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later - Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
Later versions of Android bundle implementations of the java.time classes.
For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….
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.

Using the date arithmetic in java.util.Calendar:
public static int getWeeksBetween (Date a, Date b) {
if (b.before(a)) {
return -getWeeksBetween(b, a);
}
a = resetTime(a);
b = resetTime(b);
Calendar cal = new GregorianCalendar();
cal.setTime(a);
int weeks = 0;
while (cal.getTime().before(b)) {
// add another week
cal.add(Calendar.WEEK_OF_YEAR, 1);
weeks++;
}
return weeks;
}
public static Date resetTime (Date d) {
Calendar cal = new GregorianCalendar();
cal.setTime(d);
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
return cal.getTime();
}

If your requirement is like the start date is 03-Apr-2020 and end date is 07-Apr-2020. the difference between the two dates is 4 days. Now the number of weeks between two dates as 1 for this you can use below snippet.
ChronoUnit.WEEKS.between(LocalDate startDate, LocalDate endDate);
But If your requirement is like 03-Apr-2020 is in one week and 07-Apr-2020 is in another week so you want the number of weeks between two dates as 2 you can use the below snippet.
LocalDate actualStartDate=...
LocalDate actualEndDate=...
LocalDate startDate = actualStartDate.with(TemporalAdjusters.previousOrSame(DayOfWeek.SUNDAY))
LocalDate endDate = actualEndDate.with(TemporalAdjusters.previousOrSame(DayOfWeek.SATURDAY))
long daysBetweenTwoDates = ChronoUnit.DAYS.between(startDate, endDate);
int numberOfWeeks = (int)Math.ceil(daysBetweenTwoDates/7.0);
Tested in java 1.8

Calendar a = new GregorianCalendar(2002,1,22);
Calendar b = new GregorianCalendar(2002,1,28);
System.out.println(a.get(Calendar.WEEK_OF_YEAR));
System.out.println(b.get(Calendar.WEEK_OF_YEAR));
int weeks = b.get(Calendar.WEEK_OF_YEAR)-a.get(Calendar.WEEK_OF_YEAR);
System.out.println(weeks);
try this must work
Calendar calendar1 = Calendar.getInstance();
Calendar calendar2 = Calendar.getInstance();
calendar1.set(2007, 01, 10);
calendar2.set(2007, 07, 01);
long milliseconds1 = calendar1.getTimeInMillis();
long milliseconds2 = calendar2.getTimeInMillis();
long diff = milliseconds2 - milliseconds1;
int diffWeeks = (int)diff / (7*24 * 60 * 60 * 1000);

Here are 2 methods I wrote that not based on an external library.
The first method is when Monday is the first day of the week.
The second method is when Sunday is the first day of the week.
Please read the comments inside the code, there is an option to return the number of the full weeks between 2 dates, and also with the fraction of the remaining days before and after the 2 dates.
public static int getNumberOfFullWeeks(LocalDate startDate,LocalDate endDate)
{
int dayBeforeStartOfWeek = 0;
int daysAfterLastFullWeek = 0;
if(startDate.getDayOfWeek() != DayOfWeek.MONDAY)
{
// get the partial value before loop starting
dayBeforeStartOfWeek = 7-startDate.getDayOfWeek().getValue() + 1;
}
if(endDate.getDayOfWeek() != DayOfWeek.SUNDAY)
{
// get the partial value after loop ending
daysAfterLastFullWeek = endDate.getDayOfWeek().getValue();
}
LocalDate d1 = startDate.plusDays(dayBeforeStartOfWeek); // now it is the first day of week;
LocalDate d2 = endDate.minusDays(daysAfterLastFullWeek); // now it end in the last full week
// Count how many days there are of full weeks that start on Mon and end in Sun
// if the startDate and endDate are less than a full week the while loop
// will not iterate at all because d1 and d2 will be the same date
LocalDate looper = d1;
int counter = 1;
while (looper.isBefore(d2))
{
counter++;
looper = looper.plusDays(1);
}
// Counter / 7 will always be an integer that will represents full week
// because we started to count at Mon and stop counting in Sun
int fullWeeks = counter / 7;
System.out.println("Full weeks between dates: "
+ fullWeeks + " Days before the first monday: "
+ dayBeforeStartOfWeek + " "
+ " Days after the last sunday: " + daysAfterLastFullWeek);
System.out.println(startDate.toString() + " - " + endDate.toString());
// You can also get a decimal value of the full weeks plus the fraction if the days before
// and after the full weeks
float full_weeks_decimal = (float)fullWeeks;
float fraction = ((float)dayBeforeStartOfWeek + (float)daysAfterLastFullWeek) / 7.0F;
System.out.println("Full weeks with fraction: " + String.valueOf(fraction + full_weeks_decimal));
return fullWeeks;
}
public static int getNumberOfFullWeeks_WeekStartAtSunday(LocalDate startDate,LocalDate endDate)
{
int dayBeforeStartOfWeek = 0;
int daysAfterLastFullWeek = 0;
if(startDate.getDayOfWeek() != DayOfWeek.SUNDAY)
{
// get the partial value before loop starting
dayBeforeStartOfWeek = 7-getDayOfWeekBySundayIs0(startDate.getDayOfWeek()) + 1;
}
if(endDate.getDayOfWeek() != DayOfWeek.SATURDAY)
{
// get the partial value after loop ending
daysAfterLastFullWeek = 1+getDayOfWeekBySundayIs0(endDate.getDayOfWeek());
}
LocalDate d1 = startDate.plusDays(dayBeforeStartOfWeek); // now it is the first day of week;
LocalDate d2 = endDate.minusDays(daysAfterLastFullWeek); // now it end in the last full week
// Count how many days there are of full weeks that start on Sun and end in Sat
// if the startDate and endDate are less than a full week the while loop
// will not iterate at all because d1 and d2 will be the same date
LocalDate looper = d1;
int counter = 1;
while (looper.isBefore(d2))
{
counter++;
looper = looper.plusDays(1);
}
// Counter / 7 will always be an integer that will represents full week
// because we started to count at Sun and stop counting in Sat
int fullWeeks = counter / 7;
System.out.println("Full weeks between dates: "
+ fullWeeks + " Days before the first sunday: "
+ dayBeforeStartOfWeek + " "
+ " Days after the last saturday: " + daysAfterLastFullWeek);
System.out.println(startDate.toString() + " - " + endDate.toString());
// You can also get a decimal value of the full weeks plus the fraction if the days before
// and after the full weeks
float full_weeks_decimal = (float)fullWeeks;
float fraction = ((float)dayBeforeStartOfWeek + (float)daysAfterLastFullWeek) / 7.0F;
System.out.println("Full weeks with fraction: " + String.valueOf(fraction + full_weeks_decimal));
return fullWeeks;
}
public static int getDayOfWeekBySundayIs0(DayOfWeek day)
{
if(day == DayOfWeek.SUNDAY)
{
return 0;
}
else
{
// NOTE: getValue() is starting to count from 1 and not from 0
return day.getValue();
}
}

If you want exact number of full weeks use below method, where end date is exclusive:
public static long weeksBetween(Date date1, Date date2) {
return WEEKS.between(date1.toInstant().atZone(ZoneId.systemDefault()).toLocalDate(),
date2.toInstant().atZone(ZoneId.systemDefault()).toLocalDate());
}
If you want a ceil version of this, use below:
public static long weeksBetween(Date date1, Date date2) {
long daysBetween = DAYS.between(date1.toInstant().atZone(ZoneId.systemDefault()).toLocalDate(),
date2.toInstant().atZone(ZoneId.systemDefault()).toLocalDate()) + 1;
return daysBetween / 7 + (daysBetween % 7 == 0 ? 0 : 1);
}

You may do it the following way:
// method header not shown
// example dates:
f = new GregorianCalendar(2009,Calendar.AUGUST,1);
l = new GregorianCalendar(2010,Calendar.SEPTEMBER,1);
DateTime start = new DateTime(f);
DateTime end = new DateTime(l);
// Alternative to above - example dates with joda:
// DateTime start = new DateTime(2009,8,1,0,0,0,0);
// DateTime end = new DateTime(2010,9,1,0,0,0,0);
Interval interval = new Interval(start,end);
int weeksBetween = interval.toPeriod(PeriodType.weeks()).getWeeks();
// return weeksBetween;
This should give you an int representing the number of weeks between the two dates.

Joda Time computes weeks with durations of two dates which may not meet our requirements in some cases. I have a method with Joda Time to compute natural weeks between two dates. Hope it can help you. If you don't use Joda Time, you may modify the code with Calendar to do the same thing.
//Unlike Joda Time Weeks.weeksBetween() that returns whole weeks computed
//from duration, we return natural weeks between two dates based on week of year
public static int weeksBetween(ReadablePartial date1, ReadablePartial date2) {
int comp = date1.compareTo(date2);
if (comp == 0) {
return 0;
}
if (comp > 0) {
ReadablePartial mid = date2;
date2 = date1;
date1 = mid;
}
int year1 = date1.get(DateTimeFieldType.weekyear());
int year2 = date2.get(DateTimeFieldType.weekyear());
if (year1 == year2) {
return date2.get(DateTimeFieldType.weekOfWeekyear()) - date1.get(DateTimeFieldType.weekOfWeekyear());
}
int weeks1 = 0;
LocalDate lastDay1 = new LocalDate(date1.get(DateTimeFieldType.year()), 12, 31);
if (lastDay1.getWeekyear() > year1) {
lastDay1 = lastDay1.minusDays(7);
weeks1++;
}
weeks1 += lastDay1.getWeekOfWeekyear() - date1.get(DateTimeFieldType.weekOfWeekyear());
int midWeeks = 0;
for (int i = year1 + 1; i < year2; i++) {
LocalDate y1 = new LocalDate(i, 1, 1);
int yearY1 = y1.getWeekyear();
if (yearY1 < i) {
y1 = y1.plusDays(7);
midWeeks++;
}
LocalDate y2 = new LocalDate(i, 12, 31);
int yearY2 = y2.getWeekyear();
if (yearY2 > i) {
y2 = y2.minusDays(7);
midWeeks++;
}
midWeeks += y2.getWeekOfWeekyear() - y1.getWeekOfWeekyear();
}
int weeks2 = 0;
LocalDate firstDay2 = new LocalDate(date2.get(DateTimeFieldType.year()), 1, 1);
if (firstDay2.getWeekyear() < firstDay2.getYear()) {
firstDay2 = firstDay2.plusDays(7);
weeks2++;
}
weeks2 += date2.get(DateTimeFieldType.weekOfWeekyear()) - firstDay2.getWeekOfWeekyear();
return weeks1 + midWeeks + weeks2;
}

int startWeek = c1.get(Calendar.WEEK_OF_YEAR);
int endWeek = c2.get(Calendar.WEEK_OF_YEAR);
int diff = c2.get(Calendar.YEAR) - c1.get(Calendar.YEAR);
int deltaYears = 0;
for(int i = 0;i < diff;i++){
deltaYears += c1.getWeeksInWeekYear();
c1.add(Calendar.YEAR, 1);
}
diff = (endWeek + deltaYears) - startWeek;
Includes the year differences.
This worked for me :)

private int weeksBetween(Calendar startDate, Calendar endDate) {
startDate.set(Calendar.HOUR_OF_DAY, 0);
startDate.set(Calendar.MINUTE, 0);
startDate.set(Calendar.SECOND, 0);
int start = (int)TimeUnit.MILLISECONDS.toDays(
startDate.getTimeInMillis())
- startDate.get(Calendar.DAY_OF_WEEK);
int end = (int)TimeUnit.MILLISECONDS.toDays(
endDate.getTimeInMillis());
return (end - start) / 7;
}
if this method returns 0 they are in the same week
if this method return 1 endDate is the week after startDate
if this method returns -1 endDate is the week before startDate
you get the idea

Without using JodaTime, I was able to accurately calculate the number of weeks between 2 calendars (which accounts for leap years etc.)
private fun calculateNumberOfWeeks() {
val calendarFrom = Calendar.getInstance()
calendarFrom.set(Calendar.HOUR_OF_DAY, 0)
calendarFrom.set(Calendar.MINUTE, 0)
calendarFrom.set(Calendar.SECOND, 0)
calendarFrom.set(Calendar.MILLISECOND, 0)
val calendarTo = Calendar.getInstance()
calendarTo.add(Calendar.MONTH, months)
calendarTo.set(Calendar.HOUR_OF_DAY, 0)
calendarTo.set(Calendar.MINUTE, 0)
calendarTo.set(Calendar.SECOND, 0)
calendarTo.set(Calendar.MILLISECOND, 0)
var weeks = -1
while (calendarFrom.timeInMillis < calendarTo.timeInMillis) {
calendarFrom.add(Calendar.DATE, 7)
weeks++
Log.d(Constants.LOG_TAG, "weeks $weeks")
}
}

Easy way
Calendar cal1 = new GregorianCalendar();
Calendar cal2 = new GregorianCalendar();
cal1.set(2014, 3, 3);
cal2.set(2015, 3, 6);
weekscount.setText("weeks= "+ ( (cal2.getTime().getTime() - cal1.getTime().getTime()) / (1000 * 60 * 60 * 24))/7);

Here is a simple way to find the number of weeks between two dates.
SimpleDateFormat myFormat = new SimpleDateFormat("dd MM yyyy");
String classStartData = "31 01 2021";
String classEndData = "08 03 2021";
Date dateClassStart = myFormat.parse(classStartData);
Date dateClassEnd = myFormat.parse(classEndData);
long differenceWeek = dateClassEnd.getTime() - dateClassStart.getTime();
int programLength = (int)(TimeUnit.DAYS.convert(differenceWeek, TimeUnit.MILLISECONDS)/7);
System.out.println("Class length in weeks: " +programLength);

After referring many solution, this worked for me.
{Provided I did not want to use external Libraries}
public static int getNumberOfWeeks(Date date1, Date date2) {
if (date1.after(date2)) {
return getNumberOfWeeks(date2, date1);
}
Date date = date1;
int days = 0;
while (date.before(date2)) {
days++;
date = addDays(date, 1);
}
return days/7;
}
To add days to a date :
Date addDays(Date date, int days) {
if (days == 0) {
return date;
} else {
Date shiftedDate = new Date(date.getTime() + (long)days * 86400000L);
return shiftedDate;
}
}

Take a look at the following article: Java - calculate the difference between two dates
The daysBetween method will allow you to get the number of days between dates. Then you can simply divide by 7 to get the number of full weeks.

Calendar date1 = Calendar.getInstance();
Calendar date2 = Calendar.getInstance();
date1.clear();
date1.set(datePicker1.getYear(), datePicker1.getMonth(),
datePicker1.getDayOfMonth());
date2.clear();
date2.set(datePicker2.getYear(), datePicker2.getMonth(),
datePicker2.getDayOfMonth());
long diff = date2.getTimeInMillis() - date1.getTimeInMillis();
float dayCount = (float) diff / (24 * 60 * 60 * 1000);
int week = (dayCount / 7) ;
Hope this might Help you

public int diffInWeeks(Date start, Date end) {
long diffSeconds = (end.getTime() - start.getTime())/1000;
return (int)diffSeconds/(60 * 60 * 24 * 7);
}

unable to get difference of days between two dates in java

I want to calculate the difference of days between two dates. My code works fine when the year of the date does not change, but when I calculate the difference between two dates like so: (13/01/2012 to 13/12/2011), it gives a negative value. It also gives wrong values of difference when I calculate the difference between today's date and a future date. Please help me. Thank you in advance. Here is my code:
//getting values from text box
String fromtext = from.getText().toString();
String totext = to.getText().toString();
//sdf if a simple date formatter
SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
Date fromdate = (Date) sdf.parse(fromtext);
Date todate = (Date) sdf.parse(totext);
Calendar fromcal = Calendar.getInstance();
Calendar tocal = Calendar.getInstance();
fromcal.setTime(fromdate);
tocal.setTime(todate);// setting to date
int reportDays=(int)(todate.getTime()-fromdate.getTime())/(3600*24*1000);
please tell me what is the best way to calculate the difference in days.

Dates input : 13/01/2012, 13/12/2011
format seems dd/MM/yyyy and you are using wrong one (i.e. MM/dd/yyyy)

tl;dr
ChronoUnit.DAYS.between(
LocalDate.parse( "13/01/2012" , DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) ) ,
LocalDate.parse( "13/12/2011" , DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) )
)
Using java.time
Much easier with the modern java.time classes that supplant the troublesome old legacy date-time classes such as Date & Calendar.
(13/01/2012 to 13/12/2011),
The LocalDate class represents a date-only value without time-of-day and without time zone.
DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd/MM/uuuu" );
LocalDate start = LocalDate.parse( "13/01/2012" , f );
LocalDate stop = LocalDate.parse( "13/12/2011" , f );
Use ChronoUnit to calculate elapsed days.
long days = ChronoUnit.DAYS.between( start , stop );
Of course the number of days is negative when going back in time. Notice how your stop date is earlier than your start date.
A time zone is crucial in determining a date. For any given moment, the date varies around the globe by zone. For example, a few minutes after midnight in Paris France is a new day while still “yesterday” in Montréal Québec.
Specify a proper time zone name in the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).
ZoneId z = ZoneId.of( "America/Montreal" );
LocalDate today = LocalDate.now( z );
You can use ChronoUnit again to count days into the future.
long days = ChronoUnit.DAYS.between( today , today.plusMonths( 7 ) );
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 the java.time classes.
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 ThreeTenABP….
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.

In addition to the format issue already mentionned, you are likely to have an overflow.
Try this:
int reportDays=(int)((todate.getTime()-fromdate.getTime())/(3600*24*1000));

I think you should try better googling....
http://www.java2s.com/Code/Java/Development-Class/DateDiffcomputethedifferencebetweentwodates.htm

Using joda time would be the simplest way.

check this code:
import java.util.Calendar;
public class DateDifferent{
public static void main(String[] args){
Calendar calendar1 = Calendar.getInstance();
Calendar calendar2 = Calendar.getInstance();
calendar1.set(2007, 01, 10);
calendar2.set(2007, 07, 01);
long milliseconds1 = calendar1.getTimeInMillis();
long milliseconds2 = calendar2.getTimeInMillis();
long diff = milliseconds2 - milliseconds1;
long diffSeconds = diff / 1000;
long diffMinutes = diff / (60 * 1000);
long diffHours = diff / (60 * 60 * 1000);
long diffDays = diff / (24 * 60 * 60 * 1000);
System.out.println("\nThe Date Different Example");
System.out.println("Time in milliseconds: " + diff + " milliseconds.");
System.out.println("Time in seconds: " + diffSeconds + " seconds.");
System.out.println("Time in minutes: " + diffMinutes + " minutes.");
System.out.println("Time in hours: " + diffHours + " hours.");
System.out.println("Time in days: " + diffDays + " days.");
}
}

Here's a simple little class I wrote for this purpose:
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class DifferenceInDays
{
public int dateOffset(String incomingDate) throws ParseException
{
// parse dates
DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
Date date = (Date) formatter.parse(incomingDate);
// convert to milliseconds
long millisecs = date.getTime();
// convert to days
int offsetInDays = (int) Math.abs(millisecs / (1000 * 60 * 60 * 24));
return offsetInDays;
}
}
It takes care of negative offsets using the absolute value method.

If you try this with a locale that has daylight saving, and the from and to dates are before and after a daylight saving change the result may be different by 1 day. This is because Date and Calendar use timezones.
If you are only going to be dealing with dates between the years 1900 and 2100, there is a simple calculation which will give you the number of days since 1900:
public static int daysSince1900(Date date) {
Calendar c = new GregorianCalendar();
c.setTime(date);
int year = c.get(Calendar.YEAR);
if (year < 1900 || year > 2099) {
throw new IllegalArgumentException("daysSince1900 - Date must be between 1900 and 2099");
}
year -= 1900;
int month = c.get(Calendar.MONTH) + 1;
int days = c.get(Calendar.DAY_OF_MONTH);
if (month < 3) {
month += 12;
year--;
}
int yearDays = (int) (year * 365.25);
int monthDays = (int) ((month + 1) * 30.61);
return (yearDays + monthDays + days - 63);
}
Thus, to get the difference in days between two dates, you calculate their days since 1900 and calc the difference. Our daysBetween method looks like this:
public static Integer getDaysBetween(Date date1, Date date2) {
if (date1 == null || date2 == null) {
return null;
}
int days1 = daysSince1900(date1);
int days2 = daysSince1900(date2);
if (days1 < days2) {
return days2 - days1;
} else {
return days1 - days2;
}
}
And don't ask me where this calculation came from because we've used it since the early '90s.

I would do it like this!
package javaapplication2;
//#author Ibrahim Yesilay
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Scanner;
public class JavaApplication2 {
public static void main(String[] args) throws ParseException {
Scanner scan = new Scanner(System.in);
System.out.println("First dates Day :");
int d = scan.nextInt();
System.out.println("First dates Mounth :");
int m = scan.nextInt();
System.out.println("First dates Year :");
int y = scan.nextInt();
String date;
date = Integer.toString(d) + "/" + Integer.toString(m) + "/" + Integer.toString(y);
SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy");
Date firstdate = null;
firstdate = dateFormat.parse(date);
System.out.println(dateFormat.format(firstdate));
System.out.println("Second dates Day :");
d = scan.nextInt();
System.out.println("Second dates Month :");
m = scan.nextInt();
System.out.println("Second dates Year :");
y = scan.nextInt();
date = Integer.toString(d) + "/" + Integer.toString(m) + "/" + Integer.toString(y);
Date seconddate = null;
seconddate = dateFormat.parse(date);
System.out.println(dateFormat.format(seconddate));
if (seconddate.getTime() > firstdate.getTime()) {
long sonuc = (long)(seconddate.getTime()- firstdate.getTime())/(3600*24*1000);
System.out.println("" + sonuc);
} else if (firstdate.getTime() > seconddate.getTime()) {
long sonuc = (long)(firstdate.getTime()- seconddate.getTime())/(3600*24*1000);
System.out.println("" + sonuc);
} else {
System.out.println("The dates are equal!");
}
}
}

Changing Java Date one hour back

I have a Java date object:
Date currentDate = new Date();
This will give the current date and time. Example:
Thu Jan 12 10:17:47 GMT 2012
Instead, I want to get the date, changing it to one hour back so it should give me:
Thu Jan 12 09:17:47 GMT 2012
What would be the best way to do it?

java.util.Calendar
Calendar cal = Calendar.getInstance();
// remove next line if you're always using the current time.
cal.setTime(currentDate);
cal.add(Calendar.HOUR, -1);
Date oneHourBack = cal.getTime();
java.util.Date
new Date(System.currentTimeMillis() - 3600 * 1000);
org.joda.time.LocalDateTime
new LocalDateTime().minusHours(1)
Java 8: java.time.LocalDateTime
LocalDateTime.now().minusHours(1)
Java 8 java.time.Instant
// always in UTC if not timezone set
Instant.now().minus(1, ChronoUnit.HOURS));
// with timezone, Europe/Berlin for example
Instant.now()
.atZone(ZoneId.of("Europe/Berlin"))
.minusHours(1));

Similar to #Sumit Jain's solution
Date currentDate = new Date(System.currentTimeMillis() - 3600 * 1000);
or
Date currentDate = new Date(System.currentTimeMillis() - TimeUnit.HOURS.toMillis(1));

tl;dr
In UTC:
Instant.now().minus( 1 , ChronoUnit.HOURS )
Or, zoned:
Instant.now()
.atZone( ZoneId.of ( "America/Montreal" ) )
.minusHours( 1 )
Using java.time
Java 8 and later has the new java.time framework built-in.
Instant
If you only care about UTC (GMT), then use the Instant class.
Instant instant = Instant.now ();
Instant instantHourEarlier = instant.minus ( 1 , ChronoUnit.HOURS );
Dump to console.
System.out.println ( "instant: " + instant + " | instantHourEarlier: " + instantHourEarlier );
instant: 2015-10-29T00:37:48.921Z | instantHourEarlier: 2015-10-28T23:37:48.921Z
Note how in this instant happened to skip back to yesterday’s date.
ZonedDateTime
If you care about a time zone, use the ZonedDateTime class. You can start with an Instant and the assign a time zone, a ZoneId object. This class handles the necessary adjustments for anomalies such as Daylight Saving Time (DST).
Instant instant = Instant.now ();
ZoneId zoneId = ZoneId.of ( "America/Montreal" );
ZonedDateTime zdt = ZonedDateTime.ofInstant ( instant , zoneId );
ZonedDateTime zdtHourEarlier = zdt.minus ( 1 , ChronoUnit.HOURS );
Dump to console.
System.out.println ( "instant: " + instant + "\nzdt: " + zdt + "\nzdtHourEarlier: " + zdtHourEarlier );
instant: 2015-10-29T00:50:30.778Z
zdt: 2015-10-28T20:50:30.778-04:00[America/Montreal]
zdtHourEarlier: 2015-10-28T19:50:30.778-04:00[America/Montreal]
Conversion
The old java.util.Date/.Calendar classes are now outmoded. Avoid them. They are notoriously troublesome and confusing.
When you must use the old classes for operating with old code not yet updated for the java.time types, call the conversion methods. Here is example code going from an Instant or a ZonedDateTime to a java.util.Date.
java.util.Date date = java.util.Date.from( instant );
…or…
java.util.Date date = java.util.Date.from( zdt.toInstant() );
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 the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.
Where to obtain the java.time classes?
Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later - Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
Later versions of Android bundle implementations of the java.time classes.
For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….
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.

Use Calendar.
Calendar cal = Calendar.getInstance();
cal.setTime(new Date());
cal.set(Calendar.HOUR, cal.get(Calendar.HOUR) - 1);

Or using the famous Joda Time library:
DateTime dateTime = new DateTime();
dateTime = dateTime.minusHours(1);
Date modifiedDate = dateTime.toDate();

Just subtract the number of milliseconds in an hour from the date.
currentDate.setTime(currentDate.getTime() - 3600 * 1000));

You can use from bellow code for date and time :
DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
//get current date time with Calendar()
Calendar cal = Calendar.getInstance();
System.out.println("Current Date Time : " + dateFormat.format(cal.getTime()));
cal.add(Calendar.DATE, 1);
System.out.println("Add one day to current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.MONTH, 1);
System.out.println("Add one month to current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.YEAR, 1);
System.out.println("Add one year to current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.HOUR, 1);
System.out.println("Add one hour to current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.MINUTE, 1);
System.out.println("Add one minute to current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.SECOND, 1);
System.out.println("Add one second to current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.DATE, -1);
System.out.println("Subtract one day from current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.MONTH, -1);
System.out.println("Subtract one month from current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.YEAR, -1);
System.out.println("Subtract one year from current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.HOUR, -1);
System.out.println("Subtract one hour from current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.MINUTE, -1);
System.out.println("Subtract one minute from current date : " + dateFormat.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.SECOND, -1);
System.out.println("Subtract one second from current date : " + dateFormat.format(cal.getTime()));
Output :
Current Date Time : 2008/12/28 10:24:53
Add one day to current date : 2008/12/29 10:24:53
Add one month to current date : 2009/01/28 10:24:53
Add one year to current date : 2009/12/28 10:24:53
Add one hour to current date : 2008/12/28 11:24:53
Add one minute to current date : 2008/12/28 10:25:53
Add one second to current date : 2008/12/28 10:24:54
Subtract one day from current date : 2008/12/27 10:24:53
Subtract one month from current date : 2008/11/28 10:24:53
Subtract one year from current date : 2007/12/28 10:24:53
Subtract one hour from current date : 2008/12/28 09:24:53
Subtract one minute from current date : 2008/12/28 10:23:53
Subtract one second from current date : 2008/12/28 10:24:52
This link is good : See here
And see : See too
And : Here
And : Here
And : Here
If you need just time :
DateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");

This can be achieved using java.util.Date. The following code will subtract 1 hour from your date.
Date date = new Date(yourdate in date format);
Date newDate = DateUtils.addHours(date, -1)
Similarly for subtracting 20 seconds from your date
newDate = DateUtils.addSeconds(date, -20)

To subtract hours, you need to use the HOUR_OF_DAY constant. Within that, include the number with the negative sign. This would be the hours you want to reduce. All this is done under the Calendar add() method.
The following is an example:
import java.util.Calendar;
public class Example {
public static void main(String[] args) {
Calendar c = Calendar.getInstance();
System.out.println("Date : " + c.getTime());
// 2 hours subtracted
c.add(Calendar.HOUR_OF_DAY, -2);
System.out.println("After subtracting 2 hrs : " + c.getTime());
}
}
Here is the output:
Date : Sun Dec 16 16:28:53 UTC 2018
After subtracting 2 hrs : Sun Dec 16 14:28:53 UTC 2018

Get the time in milliseconds, minus your minutes in milliseconds and convert it to Date. Here you need to objectify one!!!
int minutes = 60;
long currentDateTime = System.currentTimeMillis();
Date currentDate = new Date(currentDateTime - minutes*60*1000);
System.out.println(currentDate);

It worked for me instead using format .To work with time just use parse and toString() methods
String localTime="6:11";
LocalTime localTime = LocalTime.parse(localtime)
LocalTime lt = 6:11;
localTime = lt.toString()

How to get all dates of sundays in a particular year in Java?

I am seriously looking for this code...I am new programmer.
Actually I want to make all dates with flag, which all are sunday in a particular year.
Please, I am eagerly waiting for your response....

Create a new calendar. Set the time to 1/1/yyyy and some time. Check if the current date is a Sunday and roll forward one day until it is. That's the first Sunday of the year. Roll forward 7 days until the year no longer matches, marking as you go.

Study the the docs of java.util.Calendar carefully.

If i was doing it I would use Joda Time to find the first Sunday in the year using LocalDate. Create 1st of Jan and then add 1 day until it is a Sunday, then add 7 days until your run out of year.
LocalDate date = new LocalDate(YEAR, 1, 1);
while ( date.dayOfWeek() != 7 )
{
date = date.addDays(1);
}
while ( date.year() == YEAR )
{
date = date.addDays(7);
}
Or something like that.

Something like this should work.
int year = 2009;
Calendar cal = new GregorianCalendar(year, Calendar.JANUARY, 1);
for (int i = 0, inc = 1; i < 366 && cal.get(Calendar.YEAR) == year; i+=inc) {
if (cal.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY) {
// this is a sunday
cal.add(Calendar.DAY_OF_MONTH, 7);
inc = 7;
} else {
cal.add(Calendar.DAY_OF_MONTH, 1);
}
}

This is an example code using java.util.Calendar and java.util.GregorianCalendar that prints out each Sunday of the year 2009.
A lot of optimizing can be done in formatting the date, but i'll leave that as an exercise for you.
import java.util.Calendar;
import java.util.GregorianCalendar;
public class Test
{
public static void main(String[] args)
{
int year =2009;
int dayOfWeek = Calendar.SUNDAY;
String dayOfWeekString = "Sunday";
// instantiate Calender and set to first Sunday of 2009
Calendar cal = new GregorianCalendar();
cal.set(2009, 0, 1, 0, 0); cal.getTime();
cal.set(Calendar.DAY_OF_WEEK, dayOfWeek); cal.getTime();
int i = 1;
while (cal.get(Calendar.YEAR) == 2009)
{
System.out.println(dayOfWeekString + " " + i + ": " + cal);
cal.add(Calendar.DAY_OF_MONTH, 7);
i++;
}
}
}
As you can see, TiGz's way of using Joda Time is a lot simpler.

List arrList = new ArrayList();
SimpleDateFormat format1 = new SimpleDateFormat("dd-M-yyyy");
Date date = null;
Calendar cal = Calendar.getInstance();
for (int i = 0; i <= 51; i++)
{
try
{
cal.add(Calendar.WEEK_OF_YEAR, +1);
cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
String formatted = format1.format(cal.getTime());
date = format1.parse(formatted);
arrList.add(date);
} catch (Exception e) {
e.printStackTrace();
}
}

java.time
Java 8 and later comes with the new java.time package. Inspired by Joda-Time, defined by JSR 310, extended by the ThreeTen-Extra project. These new classes supplant the notoriously troublesome java.util.Date/.Calendar & java.text.SimpleDateFormat and such.
Note that we specify a time zone, crucial for determining a date. For example, a new day dawns earlier in Paris than in Montréal.
ZoneId zoneId = ZoneId.of( "America/Montreal" ); // Time zone is crucial in determining the date. A new day dawns earlier in Paris than In Montréal, for example.
You would write this code to use only LocalDate without any time-of-day. But in business, the full date-time is often more useful. So my example here uses ZonedDateTime.
To be neat, I want the time-of-day set to first moment of the day. You might assume that means 00:00:00.0 but not always because of anomalies such as Daylight Saving Time. To soft-code this first-moment, we want to call the atStartOfDay method found on LocalDate. So we start with LocalDate, then use that method to get a ZonedDateTime object.
Again, note that we specify a time zone when getting today’s date. A very common mistake is to omit time zone. When omitted, the JVM’s current default time zone will be implicitly applied. That means your results can vary by machine or by admin’s settings. Even worse, any code in any thread of any app within this JVM can make a call to change that default time zone at any moment during runtime while your app executes! So always specify rather than rely implicitly on current default.
LocalDate today = LocalDate.now( zoneId ); // We want a ZonedDateTime, but starting with a LocalDate in order to get first moment of the day (see next line).
ZonedDateTime todayStart = today.atStartOfDay( zoneId ); // Set time-of-day to first moment of this date, just to be neat. Usually that time is '00:00:00.0' but not always.
The java.time framework includes some handy TemporalAdjustors to get first day of year, and from there, the first Sunday of that month.
ZonedDateTime firstOfThisYear = todayStart.with( TemporalAdjusters.firstDayOfYear( ) );
ZonedDateTime zdtFirstOfNextYear = firstOfThisYear.with( TemporalAdjusters.firstDayOfNextYear( ) );
ZonedDateTime firstSundayOfThisYear = firstOfThisYear.with( TemporalAdjusters.dayOfWeekInMonth( 1, DayOfWeek.SUNDAY ) );
Now we are set to loop through all the weeks of the year. We increment a week at a time until we find ourselves in the next year. We collect each Sunday in a List.
ZonedDateTime zdt = firstSundayOfThisYear; // Var changing throughout loop.
List< ZonedDateTime > sundays = new ArrayList<>( 53 ); // Set initial capacity to maximum number of values.
while ( zdt.isBefore( zdtFirstOfNextYear ) ) {
// Handle this iteration.
sundays.add( zdt );
System.out.println( "Sunday # " + sundays.size( ) + " : " + zdt );
// Prepare next iteration.
zdt = zdt.plusWeeks( 1 );
}
When run.
Sunday # 1 : 2015-01-04T00:00-05:00[America/Montreal]
Sunday # 2 : 2015-01-11T00:00-05:00[America/Montreal]
…
Sunday # 51 : 2015-12-20T00:00-05:00[America/Montreal]
Sunday # 52 : 2015-12-27T00:00-05:00[America/Montreal]

A year has approximately 365 days, so the Big-O's n is pretty manageable. I'd say just iterate from the beginning of the year through to the last day of the year, and check if each day is a Sunday or not.
You need at least Calendar.get(), Calendar.DAY_OF_WEEK and Calendar.SUNDAY

I recently developed [Lamma Date] which is designed to serve this type of use cases.
Following code will print out all Sundays in 2014:
List<Date> sundays2014 = Dates.from(2014, 1, 1).to(2014, 12, 31).byWeek().on(DayOfWeek.SUNDAY).build();
for(Date date: sundays2014) {
System.out.println(date);
}

**this will give u all Sundays of the year **
invented By me and friend Hemant
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
public class Test {
public static void main(String[] args) {
SimpleDateFormat format =new SimpleDateFormat("dd-MMM-yyyy");
String DATE_FORMAT = "yyyy MM dd";
SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT);
Calendar c1 = Calendar.getInstance(); // today
String y=sdf.format(c1.getTime());
String years=y.substring(0,4);
int year=Integer.parseInt(years);
//Connection con=null;
Calendar cal = new GregorianCalendar(year, Calendar.JANUARY, 1);
for (int i = 0, inc = 1; i <366 && cal.get(Calendar.YEAR) == year; i+=inc) {
if (cal.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY) {
// this is a sunday
String frm="";
frm=format.format(cal.getTime());
//System.out.println("From :"+frm);
System.out.println("the value of the sunday is "+format.format(cal.getTime()));
cal.add(Calendar.DAY_OF_MONTH, 7);
} else {
cal.add(Calendar.DAY_OF_MONTH, 1);
}
}
}
}