We Keep Coding

"is this date the third thursday of the month?" - Java Library?

I've got a few dozen backlog requests in the pipeline like
'I need this functionality to run on the third Thursday of every month, and the first Wednesday of every other month...'
I've already got a function that runs every day, i just need the: isThirdSundayOfMonth(date) bit to append onto then end.
The less time I spend considering the nuances of the Gregorian calendar and timezones, the better my life is.
Anyone know a Java library that simplifies this sort of calculation? No xml config or frameworks or anything. Just a .Jar and a documented, readable API would be perfect.
Any help would be much appreciated.

Complete overview:
In Java-8 (new standard):
LocalDate input = LocalDate.now(); // using system timezone
int ordinal = 3;
DayOfWeek weekday = DayOfWeek.SUNDAY;
LocalDate adjusted =
input.with(TemporalAdjusters.dayOfWeekInMonth(ordinal, weekday));
boolean isThirdSundayInMonth = input.equals(adjusted);
In Joda-Time (popular 3rd-party-library):
LocalDate input = new LocalDate(); // using system timezone
int ordinal = 3;
int weekday = DateTimeConstants.SUNDAY;
LocalDate start = new LocalDate(input.getYear(), input.getMonthOfYear(), 1);
LocalDate date = start.withDayOfWeek(weekday);
LocalDate adjusted = (
date.isBefore(start))
? date.plusWeeks(ordinal)
: date.plusWeeks(ordinal - 1);
boolean isThirdSundayInMonth = input.equals(adjusted);
Using java.util.GregorianCalendar (old standard):
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
GregorianCalendar input = new GregorianCalendar();
int ordinal = 3;
int weekday = Calendar.SUNDAY;
GregorianCalendar start =
new GregorianCalendar(input.get(Calendar.YEAR), input.get(Calendar.MONTH), 1);
int dow = start.get(Calendar.DAY_OF_WEEK); // Sun=1, Mon=2, ...
int delta = (weekday - dow);
if (delta < 0) {
delta += 7;
}
start.add(Calendar.DAY_OF_MONTH, delta + (ordinal - 1) * 7);
String comp1 = sdf.format(input.getTime());
String comp2 = sdf.format(start.getTime());
boolean isThirdSundayInMonth = comp1.equals(comp2);
Even with the ugliest library a solution is possible ;-) I have used a string comparison in order to get rid of any timezone effects or time-of-day-parts including milliseconds. A field-wise comparison based only on year, month and day-of-month is also a good idea.
Using Time4J (my own 3rd-party-library):
PlainDate input =
SystemClock.inLocalView().today(); // using system timezone
Weekday weekday = Weekday.SUNDAY;
PlainDate adjusted =
input.with(PlainDate.WEEKDAY_IN_MONTH.setToThird(weekday));
boolean isThirdSundayInMonth = input.equals(adjusted);

The canonical library for all things date and time related is Joda Time. Adopt that and purge all the standard java classes like Date, Calendar, etc.
It will make your life much better.
As for "How do I use joda-time to find the third Thursday of the month", there's a stackoverflow answer for that already. I'd suggest using the code that the question asker posted and then the question "is it now the third Thursday of the month" is answered by:
LocalDate today = new LocalDate();
if (today.equals(calcDayOfWeekOfMonth(DateTimeConstants.THURSDAY, 3, today))) {
// do special third-Thursday processing here
}

Fetching the first date of a week in java [duplicate]

This question already has answers here:
How to get the first day of the current week and month?
(15 answers)
Closed 6 years ago.
I would like to fetch the first date of a week.
My input is going to be a String type like 07/26/2014".
I need to get the first date of week in which the above date(07/26/2014) falls.
I need output date in MM/dd/YYYY format .
basically I need output as 07/21/2014.
Please give me the java program. I have done upto this
SimpleDateFormat formatter1 = new SimpleDateFormat("MM/dd/yy");
String date ="07/26/2014";
Date Currentdate = formatter1.parse(date);
int currentday=Currentdate.getDay();
Calendar calendar = Calendar.getInstance();
calendar.setTime(Currentdate);
int startDay=currentday-calendar.getFirstDayOfWeek();
Currentdate.setDate(contacteddate.getDate()-startDay);
System.out.println(contacteddate.getDate());
}
The above code only gives me the date.. I need date along with month and year in "MM/dd/YYYY"
Please help

I would do it this way
Calendar calendar = Calendar.getInstance();
calendar.setTime(Currentdate);
calendar.set(Calendar.DAY_OF_WEEK, calendar.getFirstDayOfWeek());

After setting time to Calendar
Calendar calendar = Calendar.getInstance();
calendar.setTime(Currentdate);
use
calendar.set(Calendar.DAY_OF_WEEK, 1)
and then
simpleFormat.format(calendar.getTime());

This will help you.
// Get calendar set to current date and time
Calendar c = Calendar.getInstance();
// Set the calendar to monday of the current week
c.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
// Print dates of the current week starting on Monday
DateFormat df = new SimpleDateFormat("EEE dd/MM/yyyy");
for (int i = 0; i < 1; i++) {
System.out.println(df.format(c.getTime()));
c.add(Calendar.DATE, 1);
}

The problem with all presented solutions so far is not to specify what exactly the week definition is. Week definitions are either technically specified like in ISO-8601-standard (Monday as first day of week and first calendar week of year containing at least four days), or they use localized rules (for example in US a week begins by Sunday!).
Due to the requirement that the OP wants "07/21/2014" as first day of week around "07/26/2014" it seems that ISO-8601 is what the OP really wants. But code like
Calendar calendar = Calendar.getInstance();
c.set(Calendar.DAY_OF_WEEK, calendar.getFirstDayOfWeek());
...
will not work in a country like US or an application server located in US. Counter example:
// simulating a US-located application server where this code is running
GregorianCalendar calendar = new GregorianCalendar(Locale.US);
calendar.set(2014, Calendar.JULY, 26);
calendar.getTime(); // avoid ugly side effects in calendar date handling
calendar.set(Calendar.DAY_OF_WEEK, calendar.getFirstDayOfWeek());
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
System.out.println(sdf.format(calendar.getTime())); // output: 2014-07-20
If the OP changes the choosen locale to let's say Locale.FRANCE (applying ISO-rules) then the OP can achieve his goal using the traditional Java-date-and-time-library.
It should be noted however that week handling using the java.util.Calendar-stuff is often confusing and hard. For example: Without the strange getter-call (calendar.getTime()) which enforces update of internal calculation the result would be: 2014-07-06 (surely not what OP wants).
Therefore I recommend following other libraries to choose a generic approach compatible with different week definitions:
a) Java-8 (built-in library JSR-310 aka java.time):
LocalDate date = LocalDate.of(2014, 7, 26);
TemporalField dowField = WeekFields.ISO.dayOfWeek();
date = date.with(dowField, dowField.range().getMinimum());
System.out.println(date); // output: 2014-07-21
Note: Avoid code like date.with(DayOfWeek.MONDAY) because in that case the java.time-library cannot evaluate the underlying week rules which possibly deviate from ISO-8601 (here choosen: WeekFields.ISO, but it might also be WeekFields.SUNDAY_START).
b) my own library Time4J:
PlainDate date = PlainDate.of(2014, 7, 26);
date = date.with(Weekmodel.ISO.localDayOfWeek().minimized());
System.out.println(date); // output: 2014-07-21
c) If you know in advance that you only want ISO-8601-week-rules then you might also consider a simpler approach in Java-8 or instead its predecessor JodaTime:
// Java-8 applying ISO-8601-rules
LocalDate date = LocalDate.of(2014, 7, 26);
date = date.with(DayOfWeek.MONDAY);
// Joda-Time
LocalDate date = new LocalDate(2014, 7, 26);
date = date.dayOfWeek().withMinimumValue();

How should I properly compare two dates?

Having some trouble implementing this simple task.
Basically I want to compare two dates(some older date vs new date). I want to know if the older date is more than x months old and y days old.
int monthDiff = new Date().getMonth() - detail.getCdLastUpdate().getMonth();
int dayDiff = new Date().getDay() - detail.getCdLastUpdate().getMonth();
System.out.println("\tthe last update date and new date month diff is --> " + monthDiff);
System.out.println("\tthe last update date and new date day diff is --> " + dayDiff);
If older date is 2012-09-21 00:00:00.0, currently, it will return negative numbers. I need to find out if the older date is EXACTLY 6 months and 4 days before new Date(). I'm thinking of using absolute values of both but just can't brain today.
Edit: I know about joda but I cannot use it. I must use Java JDK.
Edit 2: I'll try out the methods listed, if all failed I'll use Joda.

JDK dates have before and after methods, returning boolean, to accomplish your task:
Date now = new Date();
Calendar compareTo = Calendar.getInstance();
compareTo.add(Calendar.MONTH, -6);
compareTo.add(Calendar.DATE, -4);
if (compareTo.getTime().before(now)) {
// after
} else {
// before or equal
}

The best way I can think of is to use Joda-Time library. Example from their site:
Days d = Days.daysBetween(startDate, endDate);
int days = d.getDays();
Or number of months:
Months m = Months.monthsBetween(startDate, endDate)
int months = m.getMonths();
where:
DateTime startDate = new DateTime(/*jdk Date*/);
DateTime endDate = new DateTime(/*jdk Date*/);

Sigh, it is up to me to add the inevitable "use JodaTime" answer.
JodaTime gives you specific data types for all significant time distances.
Date yourReferenceDate = // get date from somewhere
int months = Months.monthsBetween(
new DateTime(yourReferenceDate),
DateTime.now()
).getMonths();

Error while calculating java Date difference

Calculating the difference between two dates (java.util.Date) in terms of no. of days look like very simple and we can find different ways to do that. I used the following code to calculate the date difference:
public static long daysBetween(Calendar startDate, Calendar endDate) {
Calendar date = (Calendar) startDate.clone();
long daysBetween = 0;
while (date.before(endDate)) {
date.add(Calendar.DAY_OF_MONTH, 1);
daysBetween++;
}
return daysBetween;
}
In main(), I used the following two dates :
Calendar c1 = Calendar.getInstance();
c1.set(2011, 1, 1);
Calendar c2 = Calendar.getInstance();
c2.set(2011, 1, 31);
long difference = daysBetween(c1, c2); //
But the value of the variable difference is not consistent. It is sometimes 30 and sometimes 31. So, why that might have happened.
Is there any solution to use the method results a consistent output ?

You're setting the date part of the calendars, but not the time part.
Sometimes the clock will tick between the calls to getInstance() and sometimes it won't, hence the inconsistency.
Options:
Set the time as well as the date, e.g. to midnight
Use a better date/time library - Joda Time - which has a more suitable representation (LocalDate). An important moral here is that if you can find a type which represents the exact information you have, and nothing else, that's likely to be a good fit and cause fewer complications.
Using LocalDate, you wouldn't even have to do the loop as Joda Time has good support for computing the differences between two values anyway.
LocalDate date1 = new LocalDate(2011, 1, 1);
LocalDate date2 = new LocalDate(2011, 1, 31);
Days period = Days.daysBetween(days1, days2);
int days = period.getDays();

You are only setting the year, month and day. The hours, minutes, seconds and milli-seconds are the current time (and thus different every time you run it)
I suggest you use Joda Time's LocalDate instead as it appears to does exactly what you want.

How to compare two Dates without the time portion?

I would like to have a compareTo method that ignores the time portion of a java.util.Date. I guess there are a number of ways to solve this. What's the simplest way?

Update: while Joda Time was a fine recommendation at the time, use the java.time library from Java 8+ instead where possible.
My preference is to use Joda Time which makes this incredibly easy:
DateTime first = ...;
DateTime second = ...;
LocalDate firstDate = first.toLocalDate();
LocalDate secondDate = second.toLocalDate();
return firstDate.compareTo(secondDate);
EDIT: As noted in comments, if you use DateTimeComparator.getDateOnlyInstance() it's even simpler :)
// TODO: consider extracting the comparator to a field.
return DateTimeComparator.getDateOnlyInstance().compare(first, second);
("Use Joda Time" is the basis of almost all SO questions which ask about java.util.Date or java.util.Calendar. It's a thoroughly superior API. If you're doing anything significant with dates/times, you should really use it if you possibly can.)
If you're absolutely forced to use the built in API, you should create an instance of Calendar with the appropriate date and using the appropriate time zone. You could then set each field in each calendar out of hour, minute, second and millisecond to 0, and compare the resulting times. Definitely icky compared with the Joda solution though :)
The time zone part is important: java.util.Date is always based on UTC. In most cases where I've been interested in a date, that's been a date in a specific time zone. That on its own will force you to use Calendar or Joda Time (unless you want to account for the time zone yourself, which I don't recommend.)
Quick reference for android developers
//Add joda library dependency to your build.gradle file
dependencies {
...
implementation 'joda-time:joda-time:2.9.9'
}
Sample code (example)
DateTimeComparator dateTimeComparator = DateTimeComparator.getDateOnlyInstance();
Date myDateOne = ...;
Date myDateTwo = ...;
int retVal = dateTimeComparator.compare(myDateOne, myDateTwo);
if(retVal == 0)
//both dates are equal
else if(retVal < 0)
//myDateOne is before myDateTwo
else if(retVal > 0)
//myDateOne is after myDateTwo

Apache commons-lang is almost ubiquitous. So what about this?
if (DateUtils.isSameDay(date1, date2)) {
// it's same
} else if (date1.before(date2)) {
// it's before
} else {
// it's after
}

If you really want to use the java.util.Date, you would do something like this:
public class TimeIgnoringComparator implements Comparator<Date> {
public int compare(Date d1, Date d2) {
if (d1.getYear() != d2.getYear())
return d1.getYear() - d2.getYear();
if (d1.getMonth() != d2.getMonth())
return d1.getMonth() - d2.getMonth();
return d1.getDate() - d2.getDate();
}
}
or, using a Calendar instead (preferred, since getYear() and such are deprecated)
public class TimeIgnoringComparator implements Comparator<Calendar> {
public int compare(Calendar c1, Calendar c2) {
if (c1.get(Calendar.YEAR) != c2.get(Calendar.YEAR))
return c1.get(Calendar.YEAR) - c2.get(Calendar.YEAR);
if (c1.get(Calendar.MONTH) != c2.get(Calendar.MONTH))
return c1.get(Calendar.MONTH) - c2.get(Calendar.MONTH);
return c1.get(Calendar.DAY_OF_MONTH) - c2.get(Calendar.DAY_OF_MONTH);
}
}

My preference would be to use the Joda library insetad of java.util.Date directly, as Joda makes a distinction between date and time (see YearMonthDay and DateTime classes).
However, if you do wish to use java.util.Date I would suggest writing a utility method; e.g.
public static Date setTimeToMidnight(Date date) {
Calendar calendar = Calendar.getInstance();
calendar.setTime( date );
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
return calendar.getTime();
}

Any opinions on this alternative?
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
sdf.format(date1).equals(sdf.format(date2));

If you want to compare only the month, day and year of two dates, following code works for me:
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
sdf.format(date1).equals(sdf.format(date2));
Thanks Rob.

tl;dr
myJavaUtilDate1.toInstant()
.atZone( ZoneId.of( "America/Montreal" ) )
.toLocalDate()
.isEqual (
myJavaUtilDate2.toInstant()
.atZone( ZoneId.of( "America/Montreal" ) )
.toLocalDate()
)
Avoid legacy date-time classes
Avoid the troublesome old legacy date-time classes such as Date & Calendar, now supplanted by the java.time classes.
Using java.time
A java.util.Date represents a moment on the timeline in UTC. The equivalent in java.time is Instant. You may convert using new methods added to the legacy class.
Instant instant1 = myJavaUtilDate1.toInstant();
Instant instant2 = myJavaUtilDate2.toInstant();
You want to compare by 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" );
Apply the ZoneId to the Instant to get a ZonedDateTime.
ZonedDateTime zdt1 = instant1.atZone( z );
ZonedDateTime zdt2 = instant2.atZone( z );
The LocalDate class represents a date-only value without time-of-day and without time zone. We can extract a LocalDate from a ZonedDateTime, effectively eliminating the time-of-day portion.
LocalDate localDate1 = zdt1.toLocalDate();
LocalDate localDate2 = zdt2.toLocalDate();
Now compare, using methods such as isEqual, isBefore, and isAfter.
Boolean sameDate = localDate1.isEqual( localDate2 );
See this code run live at IdeOne.com.
instant1: 2017-03-25T04:13:10.971Z | instant2: 2017-03-24T22:13:10.972Z
zdt1: 2017-03-25T00:13:10.971-04:00[America/Montreal] | zdt2: 2017-03-24T18:13:10.972-04:00[America/Montreal]
localDate1: 2017-03-25 | localDate2: 2017-03-24
sameDate: false
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.

I too prefer Joda Time, but here's an alternative:
long oneDay = 24 * 60 * 60 * 1000
long d1 = first.getTime() / oneDay
long d2 = second.getTime() / oneDay
d1 == d2
EDIT
I put the UTC thingy below in case you need to compare dates for a specific timezone other than UTC. If you do have such a need, though, then I really advise going for Joda.
long oneDay = 24 * 60 * 60 * 1000
long hoursFromUTC = -4 * 60 * 60 * 1000 // EST with Daylight Time Savings
long d1 = (first.getTime() + hoursFromUTC) / oneDay
long d2 = (second.getTime() + hoursFromUTC) / oneDay
d1 == d2

Already mentioned apache commons-utils:
org.apache.commons.lang.time.DateUtils.truncate(date, Calendar.DAY_OF_MONTH)
gives you Date object containing only date, without time, and you can compare it with Date.compareTo

If you're using Java 8, you should use the java.time.* classes to compare dates - it's preferred to the various java.util.* classes
eg; https://docs.oracle.com/javase/8/docs/api/java/time/LocalDate.html
LocalDate date1 = LocalDate.of(2016, 2, 14);
LocalDate date2 = LocalDate.of(2015, 5, 23);
date1.isAfter(date2);

I am afraid there is no method of comparing two dates that could be called "easy" or "simple".
When comparing two time instances with any sort of reduced precision (e.g. just comparing dates), you must always take into account how time zone affects the comparison.
If date1 is specifying an event that occurred in +2 timezone and date2 is specifying an event that occurred in EST, for example, you must take care to properly understand the implications of the comparison.
Is your purpose to figure out if the two events occurred in the same calendar date in their own respective time zones? Or do You need to know if the two dates fall into the same calendar date in a specific time zone (UTC or your local TZ, for example).
Once you figure out what it is actually that You are trying to compare, it is just a matter of getting the year-month-date triple in an appropriate time zone and do the comparison.
Joda time might make the actual comparison operation look much cleaner, but the semantics of the comparison are still something You need to figure out yourself.

Simply Check DAY_OF_YEAR in combination with YEAR property
boolean isSameDay =
firstCal.get(Calendar.YEAR) == secondCal.get(Calendar.YEAR) &&
firstCal.get(Calendar.DAY_OF_YEAR) == secondCal.get(Calendar.DAY_OF_YEAR)
EDIT:
Now we can use the power of Kotlin extension functions
fun Calendar.isSameDay(second: Calendar): Boolean {
return this[Calendar.YEAR] == second[Calendar.YEAR] && this[Calendar.DAY_OF_YEAR] == second[Calendar.DAY_OF_YEAR]
}
fun Calendar.compareDatesOnly(other: Calendar): Int {
return when {
isSameDay(other) -> 0
before(other) -> -1
else -> 1
}
}

If you just want to compare only two dates without time, then following code might help you:
final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
Date dLastUpdateDate = dateFormat.parse(20111116);
Date dCurrentDate = dateFormat.parse(dateFormat.format(new Date()));
if (dCurrentDate.after(dLastUpdateDate))
{
add your logic
}

I don't know it is new think or else, but i show you as i done
SimpleDateFormat dtf = new SimpleDateFormat("dd/MM/yyyy");
Date td_date = new Date();
String first_date = dtf.format(td_date); //First seted in String
String second_date = "30/11/2020"; //Second date you can set hear in String
String result = (first_date.equals(second_date)) ? "Yes, Its Equals":"No, It is not Equals";
System.out.println(result);

Here is a solution from this blog: http://brigitzblog.blogspot.com/2011/10/java-compare-dates.html
long milliseconds1 = calendar1.getTimeInMillis();
long milliseconds2 = calendar2.getTimeInMillis();
long diff = milliseconds2 - milliseconds1;
long diffDays = diff / (24 * 60 * 60 * 1000);
System.out.println("Time in days: " + diffDays + " days.");
i.e. you can see if the time difference in milliseconds is less than the length of one day.

`
SimpleDateFormat sdf= new SimpleDateFormat("MM/dd/yyyy")
Date date1=sdf.parse("03/25/2015");
Date currentDate= sdf.parse(sdf.format(new Date()));
return date1.compareTo(currentDate);
`

Using http://mvnrepository.com/artifact/commons-lang/commons-lang
Date date1 = new Date();
Date date2 = new Date();
if (DateUtils.truncatedCompareTo(date1, date2, Calendar.DAY_OF_MONTH) == 0)
// TRUE
else
// FALSE

In Java 8 you can use LocalDate which is very similar to the one from Joda Time.

public Date saveDateWithoutTime(Date date) {
Calendar calendar = Calendar.getInstance();
calendar.setTime( date );
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.HOUR, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
return calendar.getTime();
}
This will help you to compare dates without considering the time.

Using the getDateInstance of SimpleDateFormat, we can compare only two date object without time. Execute the below code.
public static void main(String[] args) {
Date date1 = new Date();
Date date2 = new Date();
DateFormat dfg = SimpleDateFormat.getDateInstance(DateFormat.DATE_FIELD);
String dateDtr1 = dfg.format(date1);
String dateDtr2 = dfg.format(date2);
System.out.println(dateDtr1+" : "+dateDtr2);
System.out.println(dateDtr1.equals(dateDtr2));
}

Another Simple compare method based on the answers here and my mentor guidance
public static int compare(Date d1, Date d2) {
Calendar c1 = Calendar.getInstance();
Calendar c2 = Calendar.getInstance();
c1.setTime(d1);
c1.set(Calendar.MILLISECOND, 0);
c1.set(Calendar.SECOND, 0);
c1.set(Calendar.MINUTE, 0);
c1.set(Calendar.HOUR_OF_DAY, 0);
c2.setTime(d2);
c2.set(Calendar.MILLISECOND, 0);
c2.set(Calendar.SECOND, 0);
c2.set(Calendar.MINUTE, 0);
c2.set(Calendar.HOUR_OF_DAY, 0);
return c1.getTime().compareTo(c2.getTime());
}
EDIT:
According to #Jonathan Drapeau, the code above fail some cases (I would like to see those cases, please) and he suggested the following as I understand:
public static int compare2(Date d1, Date d2) {
Calendar c1 = Calendar.getInstance();
Calendar c2 = Calendar.getInstance();
c1.clear();
c2.clear();
c1.set(Calendar.YEAR, d1.getYear());
c1.set(Calendar.MONTH, d1.getMonth());
c1.set(Calendar.DAY_OF_MONTH, d1.getDay());
c2.set(Calendar.YEAR, d2.getYear());
c2.set(Calendar.MONTH, d2.getMonth());
c2.set(Calendar.DAY_OF_MONTH, d2.getDay());
return c1.getTime().compareTo(c2.getTime());
}
Please notice that, the Date class is deprecated cause it was not amenable to internationalization. The Calendar class is used instead!

First, be aware that this operation depends on the time zone. So choose whether you want to do it in UTC, in the computer’s time zone, in your own favourite time zone or where. If you are not yet convinced it matters, see my example at the bottom of this answer.
Since your question isn’t quite clear about this, I am assuming that you have a class with an instance field representing a point in time and implementing Comparable, and you want the natural ordering of your objects to be by the date, but not the time, of that field. For example:
public class ArnesClass implements Comparable<ArnesClass> {
private static final ZoneId arnesTimeZone = ZoneId.systemDefault();
private Instant when;
#Override
public int compareTo(ArnesClass o) {
// question is what to put here
}
}
Java 8 java.time classes
I have taken the freedom of changing the type of your instance field from Date to Instant, the corresponding class in Java 8. I promise to return to the treatment of Date below. I have also added a time zone constant. You may set it to ZoneOffset.UTC or ZoneId.of("Europe/Stockholm") or what you find appropriate (setting it to a ZoneOffset works because ZoneOffset is a subclass of ZoneId).
I have chosen to show the solution using the Java 8 classes. You asked for the simplest way, right? :-) Here’s the compareTo method you asked for:
public int compareTo(ArnesClass o) {
LocalDate dateWithoutTime = when.atZone(arnesTimeZone).toLocalDate();
LocalDate otherDateWithoutTime = o.when.atZone(arnesTimeZone).toLocalDate();
return dateWithoutTime.compareTo(otherDateWithoutTime);
}
If you never need the time part of when, it is of course easier to declare when a LocalDate and skip all conversions. Then we don’t have to worry about the time zone anymore either.
Now suppose that for some reason you cannot declare your when field an Instant or you want to keep it an old-fashioned Date. If you can still use Java 8, just convert it to Instant, then do as before:
LocalDate dateWithoutTime = when.toInstant().atZone(arnesTimeZone).toLocalDate();
Similarly for o.when.
No Java 8?
If you cannot use java 8, there are two options:
Solve it using one of the old classes, either Calendar or SimpleDateFormat.
Use the backport of the Java 8 date and time classes to Java 6 and 7, then just do as above. I include a link at the bottom. Do not use JodaTime. JodaTime was probably a good suggestion when the answers recommending it were written; but JodaTime is now in maintenance mode, so the ThreeTen backport is a better and more futureproof option.
The old-fashioned ways
Adamski’s answer shows you how to strip the time part off a Date using the Calendar class. I suggest you use getInstance(TimeZone) to obtain the Calendar instance for the time zone you want. As an alternative you may use the idea from the second half of Jorn’s answer.
Using SimpleDateFormat is really an indirect way of using Calendar since a SimpleDateFormat contains a Calendar object. However, you may find it less troublesome than using Calendar directly:
private static final TimeZone arnesTimeZone = TimeZone.getTimeZone("Europe/Stockholm");
private static final DateFormat formatter = new SimpleDateFormat("yyyyMMdd");
static {
formatter.setTimeZone(arnesTimeZone);
}
private Date when;
#Override
public int compareTo(ArnesClass o) {
return formatter.format(when).compareTo(formatter.format(o.when));
}
This was inspired by Rob’s answer.
Time zone dependency
Why do we have to pick a specific time zone? Say that we want to compare two times that in UTC are March 24 0:00 (midnight) and 12:00 (noon). If you do that in CET (say, Europe/Paris), they are 1 am and 1 pm on March 24, that is, the same date. In New York (Eastern Daylight Time), they are 20:00 on March 23 and 8:00 on March 24, that is, not the same date. So it makes a difference which time zone you pick. If you just rely on the computer’s default, you may be in for surprises when someone tries to run your code on a computer in another place in this globalized world.
Link
Link to ThreeTen Backport, the backport of the Java 8 date and time classes to Java 6 and 7: http://www.threeten.org/threetenbp/.

My proposition:
Calendar cal = Calendar.getInstance();
cal.set(1999,10,01); // nov 1st, 1999
cal.set(Calendar.AM_PM,Calendar.AM);
cal.set(Calendar.HOUR,0);
cal.set(Calendar.MINUTE,0);
cal.set(Calendar.SECOND,0);
cal.set(Calendar.MILLISECOND,0);
// date column in the Thought table is of type sql date
Thought thought = thoughtDao.getThought(date, language);
Assert.assertEquals(cal.getTime(), thought.getDate());

Using Apache commons you can do:
import org.apache.commons.lang3.time.DateUtils
DateUtils.truncatedEquals(first, second, Calendar.DAY_OF_MONTH)

public static Date getZeroTimeDate(Date fecha) {
Date res = fecha;
Calendar calendar = Calendar.getInstance();
calendar.setTime( fecha );
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
res = calendar.getTime();
return res;
}
Date currentDate = getZeroTimeDate(new Date());// get current date
this is the simplest way to solve this problem.

I solved this by comparing by timestamp:
Calendar last = Calendar.getInstance();
last.setTimeInMillis(firstTimeInMillis);
Calendar current = Calendar.getInstance();
if (last.get(Calendar.DAY_OF_MONTH) != current.get(Calendar.DAY_OF_MONTH)) {
//not the same day
}
I avoid to use Joda Time because on Android uses a huge space. Size matters. ;)

Another solution using Java 8 and Instant, is using the truncatedTo method
Returns a copy of this Instant truncated to the specified unit.
Example:
#Test
public void dateTruncate() throws InterruptedException {
Instant now = Instant.now();
Thread.sleep(1000*5);
Instant later = Instant.now();
assertThat(now, not(equalTo(later)));
assertThat(now.truncatedTo(ChronoUnit.DAYS), equalTo(later.truncatedTo(ChronoUnit.DAYS)));
}

// Create one day 00:00:00 calendar
int oneDayTimeStamp = 1523017440;
Calendar oneDayCal = Calendar.getInstance();
oneDayCal.setTimeInMillis(oneDayTimeStamp * 1000L);
oneDayCal.set(Calendar.HOUR_OF_DAY, 0);
oneDayCal.set(Calendar.MINUTE, 0);
oneDayCal.set(Calendar.SECOND, 0);
oneDayCal.set(Calendar.MILLISECOND, 0);
// Create current day 00:00:00 calendar
Calendar currentCal = Calendar.getInstance();
currentCal.set(Calendar.HOUR_OF_DAY, 0);
currentCal.set(Calendar.MINUTE, 0);
currentCal.set(Calendar.SECOND, 0);
currentCal.set(Calendar.MILLISECOND, 0);
if (oneDayCal.compareTo(currentCal) == 0) {
// Same day (excluding time)
}

If you strictly want to use Date ( java.util.Date ), or without any use of external Library. Use this :
public Boolean compareDateWithoutTime(Date d1, Date d2) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
return sdf.format(d1).equals(sdf.format(d2));
}

Date today = new Date();
Date endDate = new Date();//this
endDate.setTime(endDate.getTime() - ((endDate.getHours()*60*60*1000) + (endDate.getMinutes()*60*1000) + (endDate.getSeconds()*1000)));
today.setTime(today.getTime() - ((today.getHours()*60*60*1000) + (today.getMinutes()*60*1000) + (today.getSeconds()*1000)));
System.out.println(endDate.compareTo(today) <= 0);
I am simply setting hours/minutes/second to 0 so no issue with the time as time will be same now for both dates. now you simply use compareTo. This method helped to find "if dueDate is today" where true means Yes.