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Java: check if a given date is within current month

I need to check if a given date falls in the current month, and I wrote the following code, but the IDE reminded me that the getMonth() and getYear() methods are obsolete. I was wondering how to do the same thing in newer Java 7 or Java 8.
private boolean inCurrentMonth(Date givenDate) {
Date today = new Date();
return givenDate.getMonth() == today.getMonth() && givenDate.getYear() == today.getYear();
}

//Create 2 instances of Calendar
Calendar cal1 = Calendar.getInstance();
Calendar cal2 = Calendar.getInstance();
//set the given date in one of the instance and current date in the other
cal1.setTime(givenDate);
cal2.setTime(new Date());
//now compare the dates using methods on Calendar
if(cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR)) {
if(cal1.get(Calendar.MONTH) == cal2.get(Calendar.MONTH)) {
// the date falls in current month
}
}

java.time (Java 8)
There are several ways to do it with the new java.time API (tutorial). You can do it using .get(ChronoField.XY), but I think this is prettier:
Instant given = givenDate.toInstant();
Instant ref = Instant.now();
return Month.from(given) == Month.from(ref) && Year.from(given).equals(Year.from(ref));
For better re-usability you can also refactor this code to "temporal query":
public class TemporalQueries {
//TemporalQuery<R> { R queryFrom(TemporalAccessor temporal) }
public static Boolean isCurrentMonth(TemporalAccessor temporal) {
Instant ref = Instant.now();
return Month.from(temporal) == Month.from(ref) && Year.from(temporal).equals(Year.from(ref));
}
}
Boolean result = givenDate.toInstant().query(TemporalQueries::isCurrentMonth); //Lambda using method reference

Time Zone
The other answers ignore the crucial issue of time zone. A new day dawns earlier in Paris than in Montréal. So at the same simultaneous moment, the dates are different, "tomorrow" in Paris while "yesterday" in Montréal.
Joda-Time
The java.util.Date and .Calendar classes bundled with Java are notoriously troublesome, confusing, and flawed. Avoid them.
Instead use either Joda-Time library or the java.time package in Java 8 (inspired by Joda-Time).
Here is example code in Joda-Time 2.5.
DateTimeZone zone = DateTimeZone.forID( "America/Montreal" );
DateTime dateTime = new DateTime( yourJUDate, zone ); // Convert java.util.Date to Joda-Time, and assign time zone to adjust.
DateTime now = DateTime.now( zone );
// Now see if the month and year match.
if ( ( dateTime.getMonthOfYear() == now.getMonthOfYear() ) && ( dateTime.getYear() == now.getYear() ) ) {
// You have a hit.
}
For a more general solution to see if a moment falls within any span of time (not just a month), search StackOverflow for "joda" and "interval" and "contain".

java.time (Java 8)
Java 8 provides the YearMonth class which represents a given month within a given year (e.g. January 2018). This can be used to compare against the YearMonth of the given date.
private boolean inCurrentMonth(Date givenDate) {
ZoneId timeZone = ZoneOffset.UTC; // Use whichever time zone makes sense for your use case
LocalDateTime givenLocalDateTime = LocalDateTime.ofInstant(givenDate.toInstant(), timeZone);
YearMonth currentMonth = YearMonth.now(timeZone);
return currentMonth.equals(YearMonth.from(givenLocalDateTime));
}
Note that this approach will work for any of the Java 8 time classes that have both a month and a date part (LocalDate, ZonedDateTime, etc.) and not just LocalDateTime.

As far as I know the Calendar class and all derived from it return the date using the get(). See the documentation for this class. Also here is an example taken from here:
SimpleDateFormat sdf = new SimpleDateFormat("yyyy MMM dd HH:mm:ss");
Calendar calendar = new GregorianCalendar(2013,1,28,13,24,56);
int year = calendar.get(Calendar.YEAR);
int month = calendar.get(Calendar.MONTH); // Jan = 0, dec = 11
int dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);
int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
int weekOfYear = calendar.get(Calendar.WEEK_OF_YEAR);
int weekOfMonth= calendar.get(Calendar.WEEK_OF_MONTH);
int hour = calendar.get(Calendar.HOUR); // 12 hour clock
int hourOfDay = calendar.get(Calendar.HOUR_OF_DAY); // 24 hour clock
int minute = calendar.get(Calendar.MINUTE);
int second = calendar.get(Calendar.SECOND);
int millisecond= calendar.get(Calendar.MILLISECOND);
System.out.println(sdf.format(calendar.getTime()));
System.out.println("year \t\t: " + year);
System.out.println("month \t\t: " + month);
System.out.println("dayOfMonth \t: " + dayOfMonth);
System.out.println("dayOfWeek \t: " + dayOfWeek);
System.out.println("weekOfYear \t: " + weekOfYear);
System.out.println("weekOfMonth \t: " + weekOfMonth);
System.out.println("hour \t\t: " + hour);
System.out.println("hourOfDay \t: " + hourOfDay);
System.out.println("minute \t\t: " + minute);
System.out.println("second \t\t: " + second);
System.out.println("millisecond \t: " + millisecond);
which outputs
2013 Feb 28 13:24:56
year : 2013
month : 1
dayOfMonth : 28
dayOfWeek : 5
weekOfYear : 9
weekOfMonth : 5
hour : 1
hourOfDay : 13
minute : 24
second : 56
millisecond : 0
I think it was replaced because the new way offers a much simpler handling using a single function, which is much easier to remember.

Calculate difference between two times android

I am developing and android app, where I need to calculate the difference between two times.I need to calculate the time difference for 24 hrs, and also the difference between times on two days(Eg. 5pm today to 9 am tomorrow).
I have tried the below code, to calculate the difference which works only for 24 hrs,
String dateStart = "08:00:00";
String dateStop = "13:00:00";
//HH converts hour in 24 hours format (0-23), day calculation
SimpleDateFormat format = new SimpleDateFormat("HH:mm:ss");
Date d1 = null;
Date d2 = null;
try
{
d1 = format.parse(dateStart);
d2 = format.parse(dateStop);
//in milliseconds
long diff = d2.getTime() - d1.getTime();
long diffHours = diff / (60 * 60 * 1000) % 24;
Log.e("test",diffHours + " hours, ");
}
catch (Exception e)
{
// TODO: handle exception
}

Sir, you can make it easily in using java feature. long difference = date2.getTime() - date1.getTime(); Take a look in this link this will help you.

Correct way to find proper time difference:
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("HH:mm:ss");
Date startDate = simpleDateFormat.parse("22:00:59");
Date endDate = simpleDateFormat.parse("23:00:10");
long difference = endDate.getTime() - startDate.getTime();
if(difference<0)
{
Date dateMax = simpleDateFormat.parse("24:00:00");
Date dateMin = simpleDateFormat.parse("00:00:00");
difference=(dateMax.getTime() -startDate.getTime() )+(endDate.getTime()-dateMin.getTime());
}
int days = (int) (difference / (1000*60*60*24));
int hours = (int) ((difference - (1000*60*60*24*days)) / (1000*60*60));
int min = (int) (difference - (1000*60*60*24*days) - (1000*60*60*hours)) / (1000*60);
int sec = (int) (difference - (1000*60*60*24*days) - (1000*60*60*hours) - (1000*60*min)) / (1000);
Log.i("log_tag","Hours: "+hours+", Mins: "+min+", Secs: "+sec);
Result will be: Hours: 0, Mins: 59, Secs: 11

tl;dr
ChronoUnit.HOURS.between(
LocalTime.parse( "08:00:00" ) ,
LocalTime.parse( "13:00:00" )
)
5
…or…
ChronoUnit.HOURS.between(
ZonedDateTime.of(
LocalDate.of( 2017 , Month.JANUARY , 23 ) ,
LocalTime.parse( "08:00:00" ) ,
ZoneId.of( "America/Montreal" )
) ,
ZonedDateTime.of(
LocalDate.of( 2017 , Month.JANUARY , 25 ) ,
LocalTime.parse( "13:00:00" ) ,
ZoneId.of( "America/Montreal" )
)
)
53
java.time
Modern approach uses the java.time classes.
LocalTime
The LocalTime class represents a time-of-day without a date and without a time zone.
LocalTime start = LocalTime.parse( "08:00:00" ) ;
LocalTime stop = LocalTime.parse( "13:00:00" ) ;
Duration
Get a Duration object to represent the span-of-time.
Duration d = Duration.between( start , stop ) ;
ChronoUnit
For number of hours, use ChronoUnit.
long hours = ChronoUnit.HOURS.between( start , stop ) ;
Android
For Android, see the ThreeTen-Backport and ThreeTenABP projects. See last bullets below.
ZonedDateTime
If you want to cross days, going past midnight, you must assign dates and time zones.
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" ) ;
ZonedDateTime start = ZonedDateTime.of(
LocalDate.of( 2017 , Month.JANUARY , 23 ) ,
LocalTime.parse( "08:00:00" ) ,
z
) ;
ZonedDateTime stop = ZonedDateTime.of(
LocalDate.of( 2017 , Month.JANUARY , 25 ) ,
LocalTime.parse( "13:00:00" ) ,
z
) ;
long hours = ChronoUnit.HOURS.between( start , stop ) ;
See this code run live at IdeOne.com.
53
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, Java 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 Java 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….

You can try something like this also if you are sure the 9 am is next day you can add one day and calculate the difference:
String string1 = "05:00:00 PM";
Date time1 = new SimpleDateFormat("HH:mm:ss aa").parse(string1);
Calendar calendar1 = Calendar.getInstance();
calendar1.setTime(time1);
String string2 = "09:00:00 AM";
Date time2 = new SimpleDateFormat("HH:mm:ss aa").parse(string2);
Calendar calendar2 = Calendar.getInstance();
calendar2.setTime(time2);
calendar2.add(Calendar.DATE, 1);
Date x = calendar1.getTime();
Date xy = calendar2.getTime();
long diff = x.getTime() - xy.getTime();
diffMinutes = diff / (60 * 1000);
float diffHours = diffMinutes / 60;
System.out.println("diff hours" + diffHours);

Try simple piece of code using For 24 hour time
StartTime = "10:00";
EndTime = "13:00";
here starthour=10 and end hour=13
if(TextUtils.isEmpty(txtDate.getText().toString())||TextUtils.isEmpty(txtDate1.getText().toString())||TextUtils.isEmpty(txtTime.getText().toString())||TextUtils.isEmpty(txtTime1.getText().toString()))
{
Toast.makeText(getApplicationContext(), "Date/Time fields cannot be blank", Toast.LENGTH_SHORT).show();
}
else {
if (starthour > endhour) {
Toast.makeText(getApplicationContext(), "Start Time Should Be Less Than End Time", Toast.LENGTH_SHORT).show();
} else if (starthour == endhour) {
if (startmin > endmin) {
Toast.makeText(getApplicationContext(), "Start Time Should Be Less Than End Time", Toast.LENGTH_SHORT).show();
}
else{
tvalid = "True";
}
} else {
// Toast.makeText(getApplicationContext(),"Sucess"+(endhour-starthour)+(endmin-startmin),Toast.LENGTH_SHORT).show();
tvalid = "True";
}
}
same for date also

I worked it out this way:
Date time1 = new SimpleDateFormat("HH:mm:ss aa").parse(string1);
Calendar calendar1 = Calendar.getInstance();
calendar1.setTime(time1);
Date time2 = new SimpleDateFormat("HH:mm:ss aa").parse(string2);
Calendar calendar2 = Calendar.getInstance();
calendar2.setTime(time2);
if(calendar2.get(Calendar.AM_PM) == 1 && calendar1.get(Calendar.AM_PM) == 0) {
calendar2.add(Calendar.DATE, 1);
}
long diff = calendar1.getTimeInMillis() - calendar2.getTimeInMillis()
This will help to find the difference in time round the clock.

Java Time calculation

So my method receives a time in 24 hour format ("HH:MM:SS") and returns a string the difference time. If it's 2:00PM local time I should be able to send it "16:30:00"(4:30PM) and get the output "2 hours, 30 mins". But the code has some problem, and I am just a beginner and I need help to fix it.
The problem is if the time is 4:40PM, and I sent it "17:00:00"(5:00PM) it returns the message:
12 hours, 20 minutes instead of 0 hours, 20 minutes.
The other problem is if I sent it the current time, it would return "12 hours" away, and not 24 like it should.
Please keep in mind I am only a beginner at java and math really isn't my thing, so any help is highly appreciated. Thanks.
private static String timeUntil(String distanceTime) {
String returnMsg = null;
try {
SimpleDateFormat sdfDate = new SimpleDateFormat("hh:mm:ss");
Date now = new Date();
java.text.DateFormat df = new java.text.SimpleDateFormat("hh:mm:ss");
Date date1 = df.parse(sdfDate.format(now));
Date date2 = df.parse(distanceTime);
long diff = date2.getTime() - date1.getTime();
int timeInSeconds = (int) (diff / 1000);
int hours, minutes;
hours = timeInSeconds / 3600;
timeInSeconds = timeInSeconds - (hours * 3600);
minutes = timeInSeconds / 60;
if (hours >= 0) {
returnMsg = hours + " hours" +
"\n" + minutes + " mins";
} else {
returnMsg = minutes + " mins";
}
} catch (Exception e) {
e.printStackTrace();
}
return returnMsg;
}

In your date format, hh is used for 12-hour time. Use HH for 24-hour time:
new SimpleDateFormat("HH:mm:ss");

Code review comments...
Most of the Date class' methods are deprecated. You should consider using Calendar (GregorianCalendar) instead of Date.
Your variable names often lack meaning - you have to know the purpose of the variable to know its meaning. Your code will be more maintainable if you use better variable names. df could be renamed "format" or "dateFormat".
You create a Date object 'now', then you pass it through your df DateFormat instance, hten through your sdfDate instance, to convert it back to a Date. This is unnecessary. Replace this with Date date1 = new Date(); and remove Date now = new Date();. Simiilarly, I've seen very difficult to diagnose errors when converting between units, so you should change diff to indicate that it's milliseconds, like diff_ms. And you should keep names consistent - you change from "different" (diff) to "timeInSeconds". They should both be "timeInXxx" or "diff_xx". the distanceTime parameter should be renamed something like futureTime
You do a bunch of math to determine the difference between two times, but there are libraries that will do this for you. Google for "java difference between two dates" and find many answers.
Your code always assumes that the second time occurs after "now". This should be included in a comment at the top of your method.
When you instantiate date1 and date2, they're both probably for the same day. Try debugging or at least printing the objects to stdout immediately after they're created to see if this is the case. Is this what you really want?
Your code doesn't handle leap year.
Instead of handling all of the time conversions yourself, why don't you look for a library that does it for you?

This is your fixed code. I have changed the date format to HH:mm:ss and also your calculation logic. Try it and let us know
private static String timeUntil(String distanceTime) {
String returnMsg = null;
try {
SimpleDateFormat sdfDate = new SimpleDateFormat("HH:mm:ss");
Date now = new Date();
java.text.DateFormat df = new java.text.SimpleDateFormat("HH:mm:ss");
Date date1 = df.parse(sdfDate.format(now));
Date date2 = df.parse(distanceTime);
long diff = date2.getTime() - date1.getTime();
int timeInSeconds = (int) (diff / 1000);
int hours, minutes;
hours = timeInSeconds / 3600;
timeInSeconds = timeInSeconds - (hours * 3600);
minutes = timeInSeconds / 60;
if (hours != 0) {
returnMsg = hours + " hours" +
"\n" + minutes + " mins";
} else {
returnMsg = minutes + " mins";
}
} catch (Exception e) {
e.printStackTrace();
}
return returnMsg;
}

Here is an example which is more robust and uses Java more modern date functions. I could go point by point and point at all the thing you could have done better in your example, but sometimes its easier to give you a good example and let you glean what you can from other people code as far as good style.
import java.util.Calendar;
public class testSpace {
public static void main (String ... args){
System.out.println(timeUntil("00:12:12"));
}
private static String timeUntil(String distanceTime){
String[] times = distanceTime.split(":");
Calendar now = Calendar.getInstance();
Calendar then = Calendar.getInstance();
then.set(Calendar.SECOND, Integer.parseInt(times[2]));
then.set(Calendar.MINUTE, Integer.parseInt(times[1]));
then.set(Calendar.HOUR, Integer.parseInt(times[0]) % 12);
then.set(Calendar.AM_PM, (Integer.parseInt(times[0]) >= 12 ) ? Calendar.PM : Calendar.AM);
boolean isFuture = (then.getTimeInMillis() > now.getTimeInMillis());
long interval = (isFuture)
? then.getTimeInMillis() - now.getTimeInMillis()
: now.getTimeInMillis() - then.getTimeInMillis();
return ((isFuture) ? "" : "-") + millToTime(interval);
}
public static long MILLISECOND_PER_HOUR = 1000*60*60;
public static long MILLISECOND_PER_MIN = 1000*60;
public static long MILLISECOND_PER_SECOND = 1000;
public static String millToTime(long mill){
long hours = mill / MILLISECOND_PER_HOUR;
long mins = (mill % MILLISECOND_PER_HOUR) / MILLISECOND_PER_MIN;
long sec = ((mill % MILLISECOND_PER_HOUR) % MILLISECOND_PER_MIN) / MILLISECOND_PER_SECOND;
return String.format("%d:%d:%d", hours, mins, sec);
}
}

tl;dr
For time-of-day only, without a date or time zone.
LocalTime start = LocalTime.of( "16:40" ) ;
LocalTime stop = LocalTime.of( "17:00" ) ;
Duration d = Duration.between( start , stop ) ;
PT20M
Or, for date-time in a zone.
ZoneId z = ZoneId.of( "America/Montreal" )
ZonedDateTime zdtNow = ZonedDateTime.now( z );
ZonedDateTime zdtThen =
ZonedDateTime.of( // Pass a LocalDate, LocalTime, ZoneId.
zdtNow.toLocalDate() , // Same date…
LocalTime.parse( "16:30:00" ) , // … but different time-of-day.
z
)
Duration d = Duration.between( zdtNow , zdtThen ) ;
PT2H30M
Details
You are using old date-time classes, now legacy, supplanted by the java.time classes.
LocalTime
You are incorrectly using a date-time class for a time-of-day-only value. Instead use the LocalTime class. And use a span-of-time class when calculating elapsed time.
String input = "16:30:00" ;
LocalTime lt = LocalTime.parse( input );
Instant
The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).
Instant instant = Instant.now();
ZonedDateTime
Determining a wall-clock time requires a time zone. 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" );
ZonedDateTime zdtNow = instant.atZone( z ); // Adjusted into your time zone.
Now construct a ZonedDateTime for your given input time-of-day.
ZonedDateTime zdtTarget = ZonedDateTime.of( zdtNow.toLocalDate() , lt , z );
Duration
Use Duration to represent elapsed time not attached to the timeline.
Duration d = Duration.between( zdtNow , zdtTarget );
Note that the duration will be a negative amount if the specified time-of-day is earlier than the current time-of-day.
ISO 8601 string for duration
To get a String describing the hours, minutes, etc. of that span of time, simply call toString to generate a String in standard ISO 8601 format of PnYnMnDTnHnMnS where P marks the beginning and T separates the years-month-days from hours-minutes-seconds.
If the current time were 14:00:00 in the same zone, the output would be:
PT2H30M
Getter methods
Oddly, in Java 8 this class Duration lacks any getter methods for the parts such as 2 for hours and 30 for minutes. Remedied in Java 9 with methods such as toHoursPart and toMinutesPart.
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.

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!");
}
}
}