Develop Reference

Subtract char of digits like normal integers

I have two strings which can be seen as time stamps:
String min="2017-04-15 13:27:31";
String max="2017-04-15 13:40:01";
Assume we want to find out the time passed from first time stamp to the second one. If there was only the time and no date included, I could get it using my following code:
String[] partsMin=min.split(":");
String[] partMax=max.split(":");
int diffZero=Integer.parseInt(partMax[0])-Integer.parseInt(partsMin[0]);
int diffOne=Integer.parseInt(partMax[1])-Integer.parseInt(partsMin[1]);
int diffOTwo=Integer.parseInt(partMax[2])-Integer.parseInt(partsMin[2]);
diffInSec=diffZero*3600+diffOne*60+diffOTwo;
So here is the question. How to get the job done while there is a date within the time stamp?

I would construct LocalDateTime instances from it.
Then i would get the milliseconds from it and substract startTime from EndTime.
What is remaining are the milliseconds passed between the two. A DateTimeFormatter is helpful as well for this purpose.
String strMin = "2017-04-15 13:27:31";
DateTimeFormatter formatterTime = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime dateTimeMin = LocalDateTime.parse(strMin, formatter);
String strMax = "2017-04-15 13:40:01";
LocalDateTime dateTimeMax = LocalDateTime.parse(strMax, formatter);
long minutes = ChronoUnit.MINUTES.between(dateMin, dateMaxto);
long hours = ChronoUnit.HOURS.between(dateMin, dateMax);
If you want to get the milliseconds:
long millisPassed = dateMax.toEpochMilli() - dateMax.toEpochMilli();

Use the java date time libraries (even the old Date class would be fine for this) to parse the string into a proper object.
Depending on the date time library you chose you can then look at the difference between them. The simplest would be something like:
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
Date date1 = sdf.parse(str1);
Date date2 = sdf.parse(str2);
long differenceInSeconds = (date2.getTime()-date1.getTime())/1000;
The new Java 8 time classes would also allow you to do this and would be better to learn going forwards. I can't remember the syntax for that off the top of my head though.

Did you try with replace all the other part of your String like this :
String[] partsMin = min.replaceAll("\\d+-\\d+-\\d+", "").trim().split(":");
String[] partMax = max.replaceAll("\\d+-\\d+-\\d+", "").trim().split(":");

Doing this in your code:
int diffZero=Integer.parseInt(partMax[0])
is the same as doing:
int diffZero=Integer.parseInt("2017-04-15")
that is generating an Exception(NumberFormatException)
you should better try to PARSE those strings min and max into a date
Edit:
you can inspect your code/ variables: and see that splitting to ":" is not giving you back the correct array since the element at index 0 is holding more information than you need...
but as I said before, you are going on the wrong path, dont re invent the wheel and look how practical will get using the APIs that java has for us:
String min = "2017-04-15 13:27:31";
String max = "2017-04-15 13:40:01";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime dateTimeMin = LocalDateTime.parse(min, formatter);
LocalDateTime dateTimeMax = LocalDateTime.parse(max, formatter);
long days = ChronoUnit.DAYS.between(dateTimeMin, dateTimeMax);
long minutes = ChronoUnit.MINUTES.between(dateTimeMin, dateTimeMax);
System.out.println(days);
System.out.println(minutes);

use SimpleDateFormat to parse the date string, and do operation on Date result, you will get right value. This works well for date between '2017-02-28 23:59:59' and '2017-03-01 00:00:01'
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date date1 = format.parse("2017-02-28 23:59:59");
Date date2 = format.parse("2017-03-01 00:00:01");
long time1 = date1.getTime();
long time2 = date2.getTime();
long diff = time2 - time2; // should be 2000

android getDate from milliseconds stored in String field

I have a date stored in a String field in SQLITE with the String value
"/Date(1411472160000+0100)/"
how can I convert this back into a date format , the code below doesn't work. I think I need to convert from the milliseconds first but I cant see how to even get the above text into a long format first ?
any suggestions ?
Date convertedDate = new Date();
SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy HH:mm",
java.util.Locale.getDefault());
convertedDate = dateFormat.parse(dateString);
return dateFormat.format(convertedDate);

Well, a substring from the indexOf("(") to the indexOf("+") and you should find the date in milli.
From there, I believe you can find the date ;)
String s = "/Date(1411472160000+0100)/";
s = s.substring(s.indexOf("(") + 1, s.indexOf("+"));
Date d = new Date(Long.parseLong(s));
With the same structure, you can find the timezone (+0100) (from "+" to ")") and work with a Calendar to find the right time for the right time area.

First you have to parse out the time value from String i.e. "1411472160000+0100" part.
Here in "1411472160000+0100" , "+0100" is the timezone info. If you don't want to consider the timezone, then you can take following approach.
Approach-1
long timestamp = 1245613885;
Calendar calendar = Calendar.getInstance();
calendar.setTimeZone(TimeZone.getDefault());
calendar.setTimeInMillis(timestamp * 1000);
int year = calendar.get(Calendar.YEAR);
int day = calendar.get(Calendar.DATE);
int hour = calendar.get(Calendar.HOUR_OF_DAY);
int minute = calendar.get(Calendar.MINUTE);
then to get the date in your specified format you can use-
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateString = sdf.format(calendar.getTime());
System.out.println(dateString); // 2009-06-21 15:51:25
Besides this approach, there is an excellent Java Date library called JodaTime.
If you want to incorporate the timezone info , you can refer to this constructor from JodaTime.
http://www.joda.org/joda-time/apidocs/org/joda/time/DateTime.html#DateTime-long-org.joda.time.DateTimeZone-

How do I format a java.sql.date into this format: "MM-dd-yyyy"?

I need to get a java.sql.date in the following format "MM-dd-yyyy", but I need it to stay a java.sql.date so I can put it into a table as date field. So, it cannot be a String after the formatting, it has to end up as a java.sql.date object.
This is what I have tried so far:
java.util.Date
today=new Date();
String date = formatter.format(today);
Date todaydate = formatter.parse(date);
java.sql.Date fromdate = new java.sql.Date(todaydate.getTime());
java.sql.Date todate=new java.sql.Date(todaydate.getTime());
String tempfromdate=formatter.format(fromdate);
String temptodate=formatter.format(todate);
java.sql.Date fromdate1=(java.sql.Date) formatter.parse(tempfromdate);
java.sql.Date todate1=(java.sql.Date) formatter.parse(temptodate);

You can do it the same way as a java.util.Date (since java.sql.Date is a sub-class of java.util.Date) with a SimpleDateFormat
SimpleDateFormat sdf = new SimpleDateFormat(
"MM-dd-yyyy");
int year = 2014;
int month = 10;
int day = 31;
Calendar cal = Calendar.getInstance();
cal.set(Calendar.YEAR, year);
cal.set(Calendar.MONTH, month - 1); // <-- months start
// at 0.
cal.set(Calendar.DAY_OF_MONTH, day);
java.sql.Date date = new java.sql.Date(cal.getTimeInMillis());
System.out.println(sdf.format(date));
Output is the expected
10-31-2014

Use below code i have convert today date. learn from it and try with your code
Date today = new Date();
//If you print Date, you will get un formatted output
System.out.println("Today is : " + today);
//formatting date in Java using SimpleDateFormat
SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("MM-dd-yyyy");
String date = DATE_FORMAT.format(today);
System.out.println("Today in MM-dd-yyyy format : " + date);
Date date1 = formatter.parse(date);
System.out.println(date1);
System.out.println(formatter.format(date1));

A simpler solution would be to just convert the date in the query to epoch before comparing.
SELECT date_column from YourTable where UNIX_TIMESTAMP(date_column) > ?;
Then, simply pass date.getTime() when binding value to ?.
NOTE: The UNIX_TIMESTAMP function is for MySQL. You'll find such functions for other databases too.

java.util.Date today=new Date();
java.sql.Date date=new java.sql.Date(today.getTime()); //your SQL date object
SimpleDateFormat simpDate = new SimpleDateFormat("MM-dd-yyyy");
System.out.println(simpDate.format(date)); //output String in MM-dd-yyyy
Note that it does not matter if your date is in format mm-dd-yyyy or any other format, when you compare date (java.sql.Date or java.util.Date) they will always be compared in form of the dates they represent. The format of date is just a way of setting or getting date in desired format.

The formatter.parse will only give you a java.util.Date not a java.sql.Date
once you have a java.util.Date you can convert it to a java.sql.Date by doing
java.sql.Date sqlDate = new java.sql.Date (normalDate.getTime ());
Also note that no dates have any built in format, it is in reality a class built on top of a number.

For anyone reading this in 2017 or later, the modern solution uses LocalDate from java.time, the modern Java date and time API, instead of java.sql.Date. The latter is long outdated.
Formatting your date
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MM-dd-uuuu", Locale.US);
LocalDate fromDate = LocalDate.now(ZoneId.of("Asia/Kolkata"));
String tempFromDate = fromDate.format(formatter);
System.out.println(tempFromDate);
This prints something like
11-25-2017
Don’t confuse your date value with its textual representation
Neither a LocalDate nor a java.sql.Date object has any inherent format. So please try — and try hard if necessary — to keep the two concepts apart, the date on one side and its presentation to a user on the other.
It’s like int and all other data types. An int can have a value of 4284. You may format this into 4,284 or 4 284, 004284 or even into hex representation. This does in no way alter the int itself. In the same way, formatting your date does not affect your date object. So use the string for presenting to the user, and use LocalDate for storing into your database (a modern JDBC driver or other modern means of database access wil be happy to do that, for example through PreparedStatement.setObject()).
Use explicit time zone
Getting today’s date is a time zone sensitive operation since it is not the same date in all time zones of the world. I strongly recommend you make this fact explicit in the code. In my snippet I have used Asia/Kolkata time zone, please substitute your desired time zone. You may use ZoneId.systemDefault() for your JVM’s time zone setting, but please be aware that this setting may be changed under our feet by other parts of your program or other programs running in the same JVM, so this is fragile.

Adding Years to a random date from Date class

Let's say I have this:
PrintStream out = System.out;
Scanner in = new Scanner(System.in);
out.print("Enter a number ... ");
int n = in.nextInt();
I have a random date, for example, 05/06/2015 (it is not a fixed date, it is random every time). If I want to take the 'year' of the this date, and add whatever 'n' is to this year, how do i do that?
None of the methods in the Date Class are 'int'.
And to add years from an int, 'years' has to be an int as well.

You need to convert the Date to a Calendar.
Calendar c = Calendar.getInstance();
c.setTime(randomDate);
c.add(Calendar.YEAR, n);
newDate = c.getTime();
You can manipulate the Year (or other fields) as a Calendar, then convert it back to a Date.

This question has long deserved a modern answer. And even more so after Add 10 years to current date in Java 8 has been deemed a duplicate of this question.
The other answers were fine answers in 2012. The years have moved on, today I believe that no one should use the now outdated classes Calendar and Date, not to mention SimpleDateFormat. The modern Java date and time API is so much nicer to work with.
Using the example from that duplicate question, first we need
private static final DateTimeFormatter formatter
= DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss");
With this we can do:
String currentDateString = "2017-09-12 00:00:00";
LocalDateTime dateTime = LocalDateTime.parse(currentDateString, formatter);
dateTime = dateTime.plusYears(10);
String tenYearsAfterString = dateTime.format(formatter);
System.out.println(tenYearsAfterString);
This prints:
2027-09-12 00:00:00
If you don’t need the time of day, I recommend the LocalDate class instead of LocalDateTime since it is exactly a date without time of day.
LocalDate date = dateTime.toLocalDate();
date = date.plusYears(10);
The result is a date of 2027-09-12.
Question: where can I learn to use the modern API?
You may start with the Oracle tutorial. There’s much more material on the net, go search.

Another package for doing this exists in org.apache.commons.lang3.time, DateUtils.
Date date = new Date();
date = DateUtils.addYears(date, int quantity = 1);

The Date class will not help you, but the Calendar class can:
Calendar cal = Calendar.getInstance();
Date f;
...
cal.setTime(f);
cal.add(Calendar.YEAR, n); // Where n is int
f = cal.getTime();
Notice that you still have to assign a value to the f variable. I frequently use SimpleDateFormat to convert strings to dates.
Hope this helps you.

Try java.util.Calendar type.
Calendar cal=Calendar.getInstance();
cal.setTime(yourDate.getTime());
cal.set(Calendar.YEAR,n);

This will add 3 years to the current date and print the year.
System.out.println(LocalDate.now().plusYears(3).getYear());

If you need add one year a any date use the object Calendar.
Calendar dateMoreOneYear = Calendar.getInstance();
dateMoreOneYear.setTime(dateOriginal);
dateMoreOneYear.add(Calendar.DAY_OF_MONTH, 365);

Try like this as well for a just month and year like (June 2019)
Calendar cal = Calendar.getInstance();
cal.add(Calendar.YEAR, n); //here n is no.of year you want to increase
SimpleDateFormat format1 = new SimpleDateFormat("MMM YYYY");
System.out.println(cal.getTime());
String formatted = format1.format(cal.getTime());
System.out.println(formatted);

Try this....
String s = new SimpleDateFormat("YYYY").format(new Date(random_date_in_long)); //
int i = Integer.parseInt(s)+n;

Removing time from a Date object?

I want to remove time from Date object.
DateFormat df;
String date;
df = new SimpleDateFormat("dd/MM/yyyy");
d = eventList.get(0).getStartDate(); // I'm getting the date using this method
date = df.format(d); // Converting date in "dd/MM/yyyy" format
But when I'm converting this date (which is in String format) it is appending time also.
I don't want time at all. What I want is simply "21/03/2012".

You can remove the time part from java.util.Date by setting the hour, minute, second and millisecond values to zero.
import java.util.Calendar;
import java.util.Date;
public class DateUtil {
public static Date removeTime(Date date) {
Calendar cal = Calendar.getInstance();
cal.setTime(date);
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();
}
}

The quick answer is :
No, you are not allowed to do that. Because that is what Date use for.
From javadoc of Date :
The class Date represents a specific instant in time, with millisecond precision.
However, since this class is simply a data object. It dose not care about how we describe it.
When we see a date 2012/01/01 12:05:10.321, we can say it is 2012/01/01, this is what you need.
There are many ways to do this.
Example 1 : by manipulating string
Input string : 2012/01/20 12:05:10.321
Desired output string : 2012/01/20
Since the yyyy/MM/dd are exactly what we need, we can simply manipulate the string to get the result.
String input = "2012/01/20 12:05:10.321";
String output = input.substring(0, 10); // Output : 2012/01/20
Example 2 : by SimpleDateFormat
Input string : 2012/01/20 12:05:10.321
Desired output string : 01/20/2012
In this case we want a different format.
String input = "2012/01/20 12:05:10.321";
DateFormat inputFormatter = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss.SSS");
Date date = inputFormatter.parse(input);
DateFormat outputFormatter = new SimpleDateFormat("MM/dd/yyyy");
String output = outputFormatter.format(date); // Output : 01/20/2012
For usage of SimpleDateFormat, check SimpleDateFormat JavaDoc.

Apache Commons DateUtils has a "truncate" method that I just used to do this and I think it will meet your needs. It's really easy to use:
DateUtils.truncate(dateYouWantToTruncate, Calendar.DAY_OF_MONTH);
DateUtils also has a host of other cool utilities like "isSameDay()" and the like. Check it out it! It might make things easier for you.

What about this:
Date today = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
today = sdf.parse(sdf.format(today));

What you want is impossible.
A Date object represents an "absolute" moment in time. You cannot "remove the time part" from it. When you print a Date object directly with System.out.println(date), it will always be formatted in a default format that includes the time. There is nothing you can do to change that.
Instead of somehow trying to use class Date for something that it was not designed for, you should look for another solution. For example, use SimpleDateFormat to format the date in whatever format you want.
The Java date and calendar APIs are unfortunately not the most well-designed classes of the standard Java API. There's a library called Joda-Time which has a much better and more powerful API.
Joda-Time has a number of special classes to support dates, times, periods, durations, etc. If you want to work with just a date without a time, then Joda-Time's LocalDate class would be what you'd use.
edit - note that my answer above is now more than 10 years old. If you are using a current version of Java (Java 8 or newer), then prefer to use the new standard date and time classes in package java.time. There are many classes available that represent just a date (day, month, year); a date and time; just a time; etc.

Date dateWithoutTime =
new Date(myDate.getYear(),myDate.getMonth(),myDate.getDate())
This is deprecated, but the fastest way to do it.

May be the below code may help people who are looking for zeroHour of the day :
Date todayDate = new Date();
GregorianCalendar todayDate_G = new GregorianCalendar();
gcd.setTime(currentDate);
int _Day = todayDate_GC.get(GregorianCalendar.DAY_OF_MONTH);
int _Month = todayDate_GC.get(GregorianCalendar.MONTH);
int _Year = todayDate_GC.get(GregorianCalendar.YEAR);
GregorianCalendar newDate = new GregorianCalendar(_Year,_Month,_Day,0,0,0);
zeroHourDate = newDate.getTime();
long zeroHourDateTime = newDate.getTimeInMillis();
Hope this will be helpful.

you could try something like this:
import java.text.*;
import java.util.*;
public class DtTime {
public static void main(String args[]) {
String s;
Format formatter;
Date date = new Date();
formatter = new SimpleDateFormat("dd/MM/yyyy");
s = formatter.format(date);
System.out.println(s);
}
}
This will give you output as21/03/2012
Or you could try this if you want the output as 21 Mar, 2012
import java.text.*;
import java.util.*;
public class DtTime {
public static void main(String args[]) {
Date date=new Date();
String df=DateFormat.getDateInstance().format(date);
System.out.println(df);
}
}

You can write that for example:
private Date TruncarFecha(Date fechaParametro) throws ParseException {
String fecha="";
DateFormat outputFormatter = new SimpleDateFormat("MM/dd/yyyy");
fecha =outputFormatter.format(fechaParametro);
return outputFormatter.parse(fecha);
}

The correct class to use for a date without time of day is LocalDate. LocalDate is a part of java.time, the modern Java date and time API.
So the best thing you can do is if you can modify the getStartDate method you are using to return a LocalDate:
DateTimeFormatter dateFormatter = DateTimeFormatter
.ofLocalizedDate(FormatStyle.SHORT)
.withLocale(Locale.forLanguageTag("en-IE"));
LocalDate d = eventList.get(0).getStartDate(); // We’re now getting a LocalDate using this method
String dateString = d.format(dateFormatter);
System.out.println(dateString);
Example output:
21/03/2012
If you cannot change the getStartDate, you may still be able to add a new method returning the type that we want. However, if you cannot afford to do that just now, convert the old-fashioned Date that you get (I assume java.util.Date):
d = eventList.get(0).getStartDate(); // I'm getting the old-fashioned Date using this method
LocalDate dateWithoutTime = d.toInstant()
.atZone(ZoneId.of("Asia/Kolkata"))
.toLocalDate();
Please insert the time zone that was assumed for the Date. You may use ZoneId.systemDefault() for the JVM’s time zone setting, only this setting can be changed at any time from other parts of your program or other programs running in the same JVM.
The java.util.Date class was what we were all using when this question was asked 6 years ago (no, not all; I was, and we were many). java.time came out a couple of years later and has replaced the old Date, Calendar, SimpleDateFormat and DateFormat. Recognizing that they were poorly designed. Furthermore, a Date despite its name cannot represent a date. It’s a point in time. What the other answers do is they round down the time to the start of the day (“midnight”) in the JVM’s default time zone. It doesn’t remove the time of day, only sets it, typically to 00:00. Change your default time zone — as I said, even another program running in the same JVM may do that at any time without notice — and everything will break (often).
Link: Oracle tutorial: Date Time explaining how to use java.time.

A bit of a fudge but you could use java.sql.Date. This only stored the date part and zero based time (midnight)
Calendar c = Calendar.getInstance();
c.set(Calendar.YEAR, 2011);
c.set(Calendar.MONTH, 11);
c.set(Calendar.DATE, 5);
java.sql.Date d = new java.sql.Date(c.getTimeInMillis());
System.out.println("date is " + d);
DateFormat df = new SimpleDateFormat("dd/MM/yyyy");
System.out.println("formatted date is " + df.format(d));
gives
date is 2011-12-05
formatted date is 05/12/2011
Or it might be worth creating your own date object which just contains dates and not times. This could wrap java.util.Date and ignore the time parts of it.

java.util.Date represents a date/time down to milliseconds. You don't have an option but to include a time with it. You could try zeroing out the time, but then timezones and daylight savings will come into play--and that can screw things up down the line (e.g. 21/03/2012 0:00 GMT is 20/03/2012 PDT).
What you might want is a java.sql.Date to represent only the date portion (though internally it still uses ms).

String substring(int startIndex, int endIndex)
In other words you know your string will be 10 characers long so you would do:
FinalDate = date.substring(0,9);

Another way to work out here is to use java.sql.Date as sql Date doesn't have time associated with it, whereas java.util.Date always have a timestamp.
Whats catching point here is java.sql.Date extends java.util.Date, therefore java.util.Date variable can be a reference to java.sql.Date(without time) and to java.util.Date of course(with timestamp).

In addtition to what #jseals has already said. I think the org.apache.commons.lang.time.DateUtils class is probably what you should be looking at.
It's method : truncate(Date date,int field) worked very well for me.
JavaDocs : https://commons.apache.org/proper/commons-lang/javadocs/api-2.6/org/apache/commons/lang/time/DateUtils.html#truncate(java.util.Date, int)
Since you needed to truncate all the time fields you can use :
DateUtils.truncate(new Date(),Calendar.DAY_OF_MONTH)

If you are using Java 8+, use java.time.LocalDate type instead.
LocalDate now = LocalDate.now();
System.out.println(now.toString());
The output:
2019-05-30
https://docs.oracle.com/javase/8/docs/api/java/time/LocalDate.html

You can also manually change the time part of date and format in "dd/mm/yyyy" pattern according to your requirement.
public static Date getZeroTimeDate(Date changeDate){
Date returnDate=new Date(changeDate.getTime()-(24*60*60*1000));
return returnDate;
}
If the return value is not working then check for the context parameter in web.xml.
eg.
<context-param>
<param-name>javax.faces.DATETIMECONVERTER_DEFAULT_TIMEZONE_IS_SYSTEM_TIMEZONE</param-name>
<param-value>true</param-value>
</context-param>

Don't try to make it hard just follow a simple way
date is a string where your date is saved
String s2=date.substring(0,date.length()-11);
now print the value of s2.
it will reduce your string length and you will get only date part.

Can't believe no one offered this shitty answer with all the rest of them. It's been deprecated for decades.
#SuppressWarnings("deprecation")
...
Date hitDate = new Date();
hitDate.setHours(0);
hitDate.setMinutes(0);
hitDate.setSeconds(0);