How to obtain elapsed years from string

How to obtain elapsed years from string - java

I have the string date "3.9.1991". And I want to obtain how many years have passed since the date. For example 23. How can I achieve it using Calendar or Date?
EDIT:
I have been trying this:
private String parseVkBirthday(String birthdayString) {
// 3.9.1991
SimpleDateFormat formatter = new SimpleDateFormat("d.M.yyyy");
String formattedDate = null;
Calendar date = Calendar.getInstance();
int year = 0;
try {
Date currentDate = new Date();
Date birthdayDate = formatter.parse(birthdayString);
Log.d(LOG_TAG, "year1 = " + currentDate.getTime() + " year2 = " + birthdayDate.getTime());
long diff = currentDate.getTime() - birthdayDate.getTime();
birthdayDate.setTime(diff);
date.setTime(birthdayDate);
year = date.get(Calendar.YEAR);
} catch (ParseException e) {
e.printStackTrace();
}
return "" + year;
}
But it returns me 1993.
Answer:
There are while 3 ways for solving this problem:
1) As codeaholicguy answered, we can use Joda-Time library(what I prefer for Android).
2) As Basil Bourque answered, we can use ThreeTen-Backport library for using java.time classes from java 8.
3) And we can use java 8 and classes from java.time.
Thanks to everyone.

Use SimpleDateFormat and Period of Joda-Time library, example below:
String pattern = "dd.MM.yyyy";
SimpleDateFormat format = new SimpleDateFormat(pattern);
Date date = format.parse("3.9.1991");
System.out.println(date);
Period period = new Period(date.getTime(), (new Date()).getTime());
System.out.println(period.getYears());

String fullDate="3.9.1991";
String[] splitDate=fullDate.split(".");
int year=Integer.parseInt(splitDate[2]);
int currentYear = Calendar.getInstance().get(Calendar.YEAR);
int passedYears=currentYear-year;

Calendar.YEAR can be used to add or subtract year from current date in the same fashion we added days and month into date.
http://javarevisited.blogspot.in/2012/12/how-to-add-subtract-days-months-years-to-date-time-java.html
sample program:
import java.util.Calendar;
public class Years {
public static void main(String[] args) {
//create Calendar instance
Calendar now = Calendar.getInstance();
System.out.println("Current date : " + (now.get(Calendar.MONTH) + 1)
+ "-"
+ now.get(Calendar.DATE)
+ "-"
+ now.get(Calendar.YEAR));
//add year to current date using Calendar.add method
now.add(Calendar.YEAR,1);
System.out.println("date after one year : " + (now.get(Calendar.MONTH) + 1)
+ "-"
+ now.get(Calendar.DATE)
+ "-"
+ now.get(Calendar.YEAR));
//substract year from current date
now =Calendar.getInstance();
now.add(Calendar.YEAR,-100);
System.out.println("date before 100 years : " + (now.get(Calendar.MONTH) + 1)
+ "-"
+ now.get(Calendar.DATE)
+ "-"
+ now.get(Calendar.YEAR));
}
}
http://forgetcode.com/Java/1568-Adding-or-Subtracting-Years-to-Current-Date#

Based on example code by xrcwrn with the Joda-Time 2.8 library:
// get the current year with #xrcwm's code
Calendar mydate = new GregorianCalendar();
String mystring = "3.9.1991";
Date thedate = new SimpleDateFormat("d.m.yyyy", Locale.ENGLISH).parse(mystring);
DateTime myDateTime = new DateTime(thedate.getTime()); // joda DateTime object
// get he current date
DateTime currentDateTime = new DateTime();
// get the years value
long years = Years.between(currentDateTime, myDateTime).getYears()
The code above should give you the correct value. Mind you, this code may have some syntax errors.
As a side note, Java 8 has a time package which seems to provide more of the same functionality.

java.time
The new java.time package in Java 8 and later supplants the old java.util.Date/.Calendar & SimpleTextFormat classes.
First parse the string using new DateTimeFormatter class. Do not use SimpleTextFormat. And read the doc as there may be subtle differences in the symbol codes between the old and new classes.
Get today's date, to calculate elapsed years. Note that we need a time zone. Time zone is crucial in determining a date. A new day dawns earlier in Paris, for example, than it does in Montréal.
The Period class considers a span of time as a number of years, months and days not tied to any points on the timeline.
The between method uses the "Half-Open" approach common to date-time handling. The beginning is inclusive while the ending is exclusive.
The default formatting of java.time follows the ISO 8601 standard. Apply formatter if you wish a different string representation of your date-time values.
String input = "3.9.1991" ;
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("d.M.yyyy") ;
LocalDate then = LocalDate.parse( input, formatter ) ;
ZoneId zone = ZoneId.of( "America/Montreal" ) ;
LocalDate today = LocalDate.now( zone ) ; // Specify time zone to get your locality’s current date.
Period period = Period.between( then , today ) ;
int years = period.getYears() ;
System.out.println( "Between " + then + " and " + today + " is " + years + " years.");
Between 1991-09-03 and 2015-07-09 is 23 years.
Joda-Time
Android currently lacks Java 8 features. So you cannot use java.time. Unless perhaps the ThreeTen-Backport project (a) supports the classes used in the above example and (b) works on Android (I do not know about either).
Alternatively, you can use Joda-Time, the third-party library that inspired java.time. The Joda-Time code version of the above code example would be very similar. In this case, java.time and Joda-Time parallel one another with similar classes.

Calendar mydate = new GregorianCalendar();
String mystring = "3.9.1991";
Date thedate = new SimpleDateFormat("d.m.yyyy", Locale.ENGLISH).parse(mystring);
mydate.setTime(thedate);
//breakdown
System.out.println("year -> "+mydate.get(Calendar.YEAR));
Reference

Related

Date selector based on months in Java

I have code in Java for Selenium Webdriver TestNG. Is for comparing if the date on the website is same as today date.
Problem is that date on webpage dateOnWebpage for 11th April 2018 is in format
Today 4/11/2018
So I made selecter to compare date formats if months < 10 if(javaDateSelector < 10) than date to compare is in format M/dd/yyyy else is in format MM/dd/yyyy.
Is there better way to code it than I made it? Because I needed to parse date to string and than to int to compare it and code is quite long.
#Test(priority=3)
public void test3DateCheck() throws Exception
{
String dateOnWebpage = driver.findElement(By.xpath("//div[#id='homeCalendarSection']/div/div[2]/table/tbody/tr/td/div/ul/li")).getText();
System.out.println("Today Date on webpage is : " + dateOnWebpage);
//DateFormat dateFormat1 = new SimpleDateFormat("M/dd/yyyy");
DateFormat dateFormat1 = new SimpleDateFormat("MM");
Date date = new Date();
String javaDate1 = dateFormat1.format(date);
int javaDateSelector = Integer.parseInt(javaDate1);
if(javaDateSelector < 10)
{
DateFormat dateFormat2 = new SimpleDateFormat("M/dd/yyyy");
String javaDate2 = dateFormat2.format(date);
System.out.println("Today Date from Java is : " + javaDate2);
Assert.assertEquals(dateOnWebpage, "Today " + javaDate2);
}
else
{
DateFormat dateFormat3 = new SimpleDateFormat("MM/dd/yyyy");
String javaDate3 = dateFormat3.format(date);
System.out.println("Today Date from Java is : " + javaDate3);
Assert.assertEquals(dateOnWebpage, "Today " + javaDate3);
}
}

If you don’t care whether the date on the web page is written with leading zero for month and day of month or not and just want to test whether the date is correct:
DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("'Today' M/d/uuuu");
LocalDate today = LocalDate.now(ZoneId.of("Pacific/Norfolk"));
System.out.println("Today is " + today);
LocalDate observedDate = LocalDate.parse(dateOnWebpage, dateFormatter);
Assert.assertEquals(today, observedDate);
Rather than testing the string I am parsing the date and testing it. Even though the pattern has one M and one d in it, parsing two-digit months and two-digits day of month poses no problem.
If on the other hand you also want to test that the date on the web page is written without any leading zeroes, it’s best to test the string, like you already did:
DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("M/d/uuuu");
LocalDate today = LocalDate.now(ZoneId.of("Pacific/Norfolk"));
String todayString = today.format(dateFormatter);
System.out.println("Today is " + todayString);
Assert.assertEquals("Today " + todayString, dateOnWebpage);
Again, even though the pattern has one M and one d in it, two digits will be printed if the month or the day of month is greater than 9. What else could the format method do? If you require two-digit day of month always, put dd in the format pattern string.
In both snippets please fill in your desired time zone where I put Pacific/Norfolk since it is never the same date everywhere on the globe.
I am using and recommending java.time, the modern Java date and time API. DateFormat and SimpleDateFormat are not only long outdated, they are also notoriously troublesome. Date is just as outdated. I would avoid those classes completely. The modern API is generally so much nicer to work with.
Link: Oracle tutorial: Date Time explaining how to use java.time.

Java year display coming out in 3 digits

I'm trying to do a simple console display in Eclipse and my time and date are coming directly from the computer. For some reason, the year display is only coming out in 3 characters instead of 4, and I have no idea why. Any help would be amazing. Here's the code:
public class InClass3 implements ActionListener
{
static int month, day, year, hour, minute;
public static void Display()
{
int i;
String []Date = new String[3];
String []Hello = new String[3];
String []Time = new String[3];
Date();
Time();
for (i = 0; i < 3; i ++)
{
switch (i)
{
case 0:
Hello[0] = "HELLO WORLD";
Date[0] = month + "/" + day + "/" + year;
Time[0] = hour + ":" + minute;
break;
case 1:
Hello[1] = "hello world";
Date[1] = year + "." + month + "." + day;
if (hour > 12)
{
hour = hour - 12;
Time[1] = hour + ":" + minute + "pm";
}
else
{
Time[1] = hour + ":" + minute + "am";
}
break;
case 2:
Hello[2] = "Hello World";
Date[2] = day + " " + month + " " + year;
Time[2] = hour + ":" + minute;
break;
default: System.out.println("Fatal error occured. Please relaunch this application.");
}
System.out.println(Hello[i] + "\n" + Date[i] + "\n" + Time[i]);
}
}
#SuppressWarnings("deprecation")
public static void Time()
{
Date t = new Date();
hour = t.getHours();
minute = t.getMinutes();
}
#SuppressWarnings("deprecation")
public static void Date()
{
Date d = new Date();
year = d.getYear();
month = d.getMonth();
day = d.getDay();
}
public static void main(String[] args)
{
Display();
}
#Override
public void actionPerformed(ActionEvent arg0)
{
// TODO Auto-generated method stub
}
}
And this is what it's outputting:
HELLO WORLD
3/5/115
14:47
hello world
115.3.5
2:47pm
Hello World
5 3 115
2:47
I would obviously like it to display the 2015 - not the 115. Thanks for any insight.

year = d.getYear() + 1900;
That's because the year is stored as the number of years since 1900.
However, there are some good reasons why Date is deprecated. You should use Calendar instead.

Do not rely on Date's get-like methods. They are deprecated.
The getYear() method returns the date "minus 1900", so that 1999 is 99, 2000 is 100, etc. You have a Y2K bug!
Returns:
the year represented by this date, minus 1900.
Instead, use a SimpleDateFormat object to control your formatting.
SimpleDateFormat sdf = new SimpleDateFormat("M/d/yyyy");
System.out.println(sdf.format(new Date()));

https://docs.oracle.com/javase/8/docs/api/java/util/Date.html#getYear--
getYear
#Deprecated !!!
public int getYear()
Deprecated. As of JDK version 1.1,
replaced by Calendar.get(Calendar.YEAR) - 1900.
Returns a value that is the result of subtracting 1900 from the year that contains or begins with the instant in time represented by this Date object, as interpreted in the local time zone.
Returns:
the year represented by this date, minus 1900.
You could consider newer options from Java 8
https://docs.oracle.com/javase/8/docs/api/java/time/Year.html#now--

tl;dr
Year.now( ZoneID.of( "America/Montreal" ) )
.getValue()
Details
You are using troublesome old date-time classes now supplanted by the java.time classes.
LocalDate
The LocalDate class represents a date-only value without time-of-day and without time zone.
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.
ZoneId z = ZoneId.of( “America/Montreal” );
LocalDate today = LocalDate.now( z );
Interrogate the LocalDate for its year number.
int year = today.getYear() ;
Alternatively, use Year class.
int yearNumber = Year.now( ZoneId.of( "Pacific/Auckland" ) ).getValue() ;
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old date-time classes such as java.util.Date, .Calendar, & java.text.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.
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport and further adapted to Android in ThreeTenABP (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.

java.util.Date and getYear()

I am having the following problem in Java (I see some people are having
a similar problem in JavaScript but I'm using Java)
System.out.println(new Date().getYear());
System.out.println(new GregorianCalendar().getTime().getYear());
System.out.println(this.sale.getSaleDate().getYear());
System.out.println(this.sale.getSaleDate().getMonth());
System.out.println(this.sale.getSaleDate().getDate());
returns
I/System.out( 4274): 112
I/System.out( 4274): 112
I/System.out( 4274): 112
I/System.out( 4274): 1
I/System.out( 4274): 11
I don't understand the 112 bit which I thought would have been 2012.
What's going on? Is the
java.util.Date class unusable? I am storing this as a field in several
of my classes to store a date and time. What should I do?

In addition to all the comments, I thought I might add some code on how to use java.util.Date, java.util.Calendar and java.util.GregorianCalendar according to the javadoc.
//Initialize your Date however you like it.
Date date = new Date();
Calendar calendar = new GregorianCalendar();
calendar.setTime(date);
int year = calendar.get(Calendar.YEAR);
//Add one to month {0 - 11}
int month = calendar.get(Calendar.MONTH) + 1;
int day = calendar.get(Calendar.DAY_OF_MONTH);

According to javadocs:
#Deprecated
public int getYear()
Deprecated. As of JDK version 1.1, replaced by Calendar.get(Calendar.YEAR) - 1900.
Returns a value that is the result of subtracting 1900 from the year that contains or begins with the instant in time represented by this Date object, as interpreted in the local time zone.
Returns:
the year represented by this date, minus 1900.
See Also:
Calendar
So 112 is the correct output. I would follow the advice in the Javadoc or use JodaTime instead.

Use date format
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date date = format.parse(datetime);
SimpleDateFormat df = new SimpleDateFormat("yyyy");
year = df.format(date);

Don't use Date, use Calendar:
// Beware: months are zero-based and no out of range errors are reported
Calendar date = new GregorianCalendar(2012, 9, 5);
int year = date.get(Calendar.YEAR); // 2012
int month = date.get(Calendar.MONTH); // 9 - October!!!
int day = date.get(Calendar.DAY_OF_MONTH); // 5
It supports time as well:
Calendar dateTime = new GregorianCalendar(2012, 3, 4, 15, 16, 17);
int hour = dateTime.get(Calendar.HOUR_OF_DAY); // 15
int minute = dateTime.get(Calendar.MINUTE); // 16
int second = dateTime.get(Calendar.SECOND); // 17

The java documentation suggests to make use of Calendar class instead of this deprecated way
Here is the sample code to set up the calendar object
Calendar calendar = Calendar.getInstance();
calendar.setTime(new Date());
Here is the sample code to get the year, month, etc.
System.out.println(calendar.get(Calendar.YEAR));
System.out.println(calendar.get(Calendar.MONTH));
Calendar also has support for many other useful information like, TIME, DAY_OF_MONTH, etc. Here the documentation listing all of them
Please note that the month are 0 based. January is 0th month.

tl;dr
LocalDate.now() // Capture the date-only value current in the JVM’s current default time zone.
.getYear() // Extract the year number from that date.
2018
java.time
Both the java.util.Date and java.util.Calendar classes are legacy, now supplanted by the java.time framework built into Java 8 and later.
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.
If no time zone is specified, the JVM implicitly applies its current default time zone. That default may change at any moment, so your results may vary. Better to specify your desired/expected time zone explicitly as an argument.
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( "Africa/Tunis" ) ;
If you want only the date without time-of-day, use LocalDate. This class lacks time zone info but you can specify a time zone to determine the current date.
ZoneId zoneId = ZoneId.of( "America/Montreal" );
LocalDate localDate = LocalDate.now( zoneId );
You can get the various pieces of information with getYear, getMonth, and getDayOfMonth. You will actually get the year number with java.time!
int year = localDate.getYear();
2016
If you want a date-time instead of just a date, use ZonedDateTime class.
ZonedDateTime zdt = ZonedDateTime.now( zoneId ) ;
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old date-time classes such as java.util.Date, .Calendar, & java.text.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.
Much of the java.time functionality is back-ported to Java 6 & Java 7 in ThreeTen-Backport and further adapted to Android in ThreeTenABP (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.

Yup, this is in fact what's happening. See also the Javadoc:
Returns:
the year represented by this date, minus 1900.
The getYear method is deprecated for this reason. So, don't use it.
Note also that getMonth returns a number between 0 and 11. Therefore, this.sale.getSaleDate().getMonth() returns 1 for February, instead of 2. While java.util.Calendar doesn't add 1900 to all years, it does suffer from the off-by-one-month problem.
You're much better off using JodaTime.

Java 8 LocalDate class is another option to get the year from a java.util.Date,
int year = LocalDate.parse(new SimpleDateFormat("yyyy-MM-dd").format(date)).getYear();
Another option is,
int year = Integer.parseInt(new SimpleDateFormat("yyyy").format(date));

There are may ways of getting day, month and year in java.
You may use any-
Date date1 = new Date();
String mmddyyyy1 = new SimpleDateFormat("MM-dd-yyyy").format(date1);
System.out.println("Formatted Date 1: " + mmddyyyy1);
Date date2 = new Date();
Calendar calendar1 = new GregorianCalendar();
calendar1.setTime(date2);
int day1 = calendar1.get(Calendar.DAY_OF_MONTH);
int month1 = calendar1.get(Calendar.MONTH) + 1; // {0 - 11}
int year1 = calendar1.get(Calendar.YEAR);
String mmddyyyy2 = ((month1<10)?"0"+month1:month1) + "-" + ((day1<10)?"0"+day1:day1) + "-" + (year1);
System.out.println("Formatted Date 2: " + mmddyyyy2);
LocalDateTime ldt1 = LocalDateTime.now();
DateTimeFormatter format1 = DateTimeFormatter.ofPattern("MM-dd-yyyy");
String mmddyyyy3 = ldt1.format(format1);
System.out.println("Formatted Date 3: " + mmddyyyy3);
LocalDateTime ldt2 = LocalDateTime.now();
int day2 = ldt2.getDayOfMonth();
int mont2= ldt2.getMonthValue();
int year2= ldt2.getYear();
String mmddyyyy4 = ((mont2<10)?"0"+mont2:mont2) + "-" + ((day2<10)?"0"+day2:day2) + "-" + (year2);
System.out.println("Formatted Date 4: " + mmddyyyy4);
LocalDateTime ldt3 = LocalDateTime.of(2020, 6, 11, 14, 30); // int year, int month, int dayOfMonth, int hour, int minute
DateTimeFormatter format2 = DateTimeFormatter.ofPattern("MM-dd-yyyy");
String mmddyyyy5 = ldt3.format(format2);
System.out.println("Formatted Date 5: " + mmddyyyy5);
Calendar calendar2 = Calendar.getInstance();
calendar2.setTime(new Date());
int day3 = calendar2.get(Calendar.DAY_OF_MONTH); // OR Calendar.DATE
int month3= calendar2.get(Calendar.MONTH) + 1;
int year3 = calendar2.get(Calendar.YEAR);
String mmddyyyy6 = ((month3<10)?"0"+month3:month3) + "-" + ((day3<10)?"0"+day3:day3) + "-" + (year3);
System.out.println("Formatted Date 6: " + mmddyyyy6);
Date date3 = new Date();
LocalDate ld1 = LocalDate.parse(new SimpleDateFormat("yyyy-MM-dd").format(date3)); // Accepts only yyyy-MM-dd
int day4 = ld1.getDayOfMonth();
int month4= ld1.getMonthValue();
int year4 = ld1.getYear();
String mmddyyyy7 = ((month4<10)?"0"+month4:month4) + "-" + ((day4<10)?"0"+day4:day4) + "-" + (year4);
System.out.println("Formatted Date 7: " + mmddyyyy7);
Date date4 = new Date();
int day5 = LocalDate.parse(new SimpleDateFormat("yyyy-MM-dd").format(date4)).getDayOfMonth();
int month5 = LocalDate.parse(new SimpleDateFormat("yyyy-MM-dd").format(date4)).getMonthValue();
int year5 = LocalDate.parse(new SimpleDateFormat("yyyy-MM-dd").format(date4)).getYear();
String mmddyyyy8 = ((month5<10)?"0"+month5:month5) + "-" + ((day5<10)?"0"+day5:day5) + "-" + (year5);
System.out.println("Formatted Date 8: " + mmddyyyy8);
Date date5 = new Date();
int day6 = Integer.parseInt(new SimpleDateFormat("dd").format(date5));
int month6 = Integer.parseInt(new SimpleDateFormat("MM").format(date5));
int year6 = Integer.parseInt(new SimpleDateFormat("yyyy").format(date5));
String mmddyyyy9 = ((month6<10)?"0"+month6:month6) + "-" + ((day6<10)?"0"+day6:day6) + "-" + (year6);
System.out.println("Formatted Date 9: " + mmddyyyy9);

Year.now()
There's an easier way to use the java.time library in Java 8+. The expression:
java.time.Year.now().getValue()
returns the current year as a four-digit int, using your default time zone. There are lots of options for different time ZoneIds, Calendars and Clocks, but I think this is what you will want most of the time. If you want the code to look cleaner (and don't need any other java.time.*.now() functions), put:
import static java.time.Year.now;
at the top of your file, and call:
now().getValue()
as needed.

This behavior is documented in the java.util.Date -class documentation:
Returns a value that is the result of subtracting 1900 from the year
that contains or begins with the instant in time represented by this
Date object, as interpreted in the local time zone.
It is also marked as deprecated. Use java.util.Calendar instead.

try{
int year = Integer.parseInt(new Date().toString().split("-")[0]);
}
catch(NumberFormatException e){
}
Much of Date is deprecated.

How to get the current date/time in Java [duplicate]

This question already has answers here:
How to get the current date and time
(10 answers)
Closed 2 years ago.
What's the best way to get the current date/time in Java?

It depends on what form of date / time you want:
If you want the date / time as a single numeric value, then System.currentTimeMillis() gives you that, expressed as the number of milliseconds after the UNIX epoch (as a Java long). This value is a delta from a UTC time-point, and is independent of the local time-zone1.
If you want the date / time in a form that allows you to access the components (year, month, etc) numerically, you could use one of the following:
new Date() gives you a Date object initialized with the current date / time. The problem is that the Date API methods are mostly flawed ... and deprecated.
Calendar.getInstance() gives you a Calendar object initialized with the current date / time, using the default Locale and TimeZone. Other overloads allow you to use a specific Locale and/or TimeZone. Calendar works ... but the APIs are still cumbersome.
new org.joda.time.DateTime() gives you a Joda-time object initialized with the current date / time, using the default time zone and chronology. There are lots of other Joda alternatives ... too many to describe here. (But note that some people report that Joda time has performance issues.; e.g. https://stackoverflow.com/questions/6280829.)
in Java 8, calling java.time.LocalDateTime.now() and java.time.ZonedDateTime.now() will give you representations2 for the current date / time.
Prior to Java 8, most people who know about these things recommended Joda-time as having (by far) the best Java APIs for doing things involving time point and duration calculations.
With Java 8 and later, the standard java.time package is recommended. Joda time is now considered "obsolete", and the Joda maintainers are recommending that people migrate.3.
1 - System.currentTimeMillis() gives the "system" time. While it is normal practice for the system clock to be set to (nominal) UTC, there will be a difference (a delta) between the local UTC clock and true UTC. The size of the delta depends on how well (and how often) the system's clock is synced with UTC.
2 - Note that LocalDateTime doesn't include a time zone. As the javadoc says: "It cannot represent an instant on the time-line without additional information such as an offset or time-zone."
3 - Note: your Java 8 code won't break if you don't migrate, but the Joda codebase may eventually stop getting bug fixes and other patches. As of 2020-02, an official "end of life" for Joda has not been announced, and the Joda APIs have not been marked as Deprecated.

(Attention: only for use with Java versions <8. For Java 8+ check other replies.)
If you just need to output a time stamp in format YYYY.MM.DD-HH.MM.SS (very frequent case) then here's the way to do it:
String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(Calendar.getInstance().getTime());

If you want the current date as String, try this:
DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Date date = new Date();
System.out.println(dateFormat.format(date));
or
DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Calendar cal = Calendar.getInstance();
System.out.println(dateFormat.format(cal.getTime()));
http://www.mkyong.com/java/java-how-to-get-current-date-time-date-and-calender/

tl;dr
Instant.now() // Capture the current moment in UTC, with a resolution of nanoseconds. Returns a `Instant` object.
… or …
ZonedDateTime.now( // Capture the current moment as seen in…
ZoneId.of( "America/Montreal" ) // … the wall-clock time used by the people of a particular region (a time zone).
) // Returns a `ZonedDateTime` object.
java.time
A few of the Answers mention that java.time classes are the modern replacement for the troublesome old legacy date-time classes bundled with the earliest versions of Java. Below is a bit more information.
Time zone
The other Answers fail to explain how a time zone is crucial in determining the current date and time. For any given moment, the date and the time vary around the globe by zone. For example, a few minutes after midnight is a new day in Paris France while still being “yesterday” in Montréal Québec.
Instant
Much of your business logic and data storage/exchange should be done in UTC, as a best practice.
To get the current moment in UTC with a resolution in nanoseconds, use Instant class. Conventional computer hardware clocks are limited in their accuracy, so the current moment may be captured in milliseconds or microseconds rather than nanoseconds.
Instant instant = Instant.now();
ZonedDateTime
You can adjust that Instant into other time zones. Apply a ZoneId object to get a ZonedDateTime.
ZoneId z = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = instant.atZone( z );
We can skip the Instant and get the current ZonedDateTime directly.
ZonedDateTime zdt = ZonedDateTime.now( z );
Always pass that optional time zone argument. If omitted, your JVM’s current default time zone is applied. The default can change at any moment, even during runtime. Do not subject your app to an externality out of your control. Always specify the desired/expected time zone.
ZonedDateTime do_Not_Do_This = ZonedDateTime.now(); // BAD - Never rely implicitly on the current default time zone.
You can later extract an Instant from the ZonedDateTime.
Instant instant = zdt.toInstant();
Always use an Instant or ZonedDateTime rather than a LocalDateTime when you want an actual moment on the timeline. The Local… types purposely have no concept of time zone so they represent only a rough idea of a possible moment. To get an actual moment you must assign a time zone to transform the Local… types into a ZonedDateTime and thereby make it meaningful.
LocalDate
The LocalDate class represents a date-only value without time-of-day and without time zone.
ZoneId z = ZoneId.of( "America/Montreal" );
LocalDate today = LocalDate.now( z ); // Always pass a time zone.
Strings
To generate a String representing the date-time value, simply call toString on the java.time classes for the standard ISO 8601 formats.
String output = myLocalDate.toString(); // 2016-09-23
… or …
String output = zdt.toString(); // 2016-09-23T12:34:56.789+03:00[America/Montreal]
The ZonedDateTime class extends the standard format by wisely appending the name of the time zone in square brackets.
For other formats, search Stack Overflow for many Questions and Answers on the DateTimeFormatter class.
Avoid LocalDateTime
Contrary to the comment on the Question by RamanSB, you should not use LocalDateTime class for the current date-time.
The LocalDateTime purposely lacks any time zone or offset-from-UTC information. So, this is not appropriate when you are tracking a specific moment on the timeline. Certainly not appropriate for capturing the current moment.
A LocalDateTime has only a date and a time-of-day such as "noon on 23rd of January 2020", but we have no idea if that is noon in Tokyo Japan or noon in Toledo Ohio US, two different moments many hours apart.
The “Local” wording is counter-intuitive. It means any locality rather than any one specific locality. For example Christmas this year starts at midnight on the 25th of December: 2017-12-25T00:00:00, to be represented as a LocalDateTime. But this means midnight at various points around the globe at different times. Midnight happens first in Kiribati, later in New Zealand, hours more later in India, and so on, with several more hours passing before Christmas begins in France when the kids in Canada are still awaiting that day. Each one of these Christmas-start points would be represented as a separate ZonedDateTime.
From outside your system
If you cannot trust your system clock, see Java: Get current Date and Time from Server not System clock and my Answer.
java.time.Clock
To harness an alternate supplier of the current moment, write a subclass of the abstract java.time.Clock class.
You can pass your Clock implementation as an argument to the various java.time methods. For example, Instant.now( clock ).
Instant instant = Instant.now( yourClockGoesHere ) ;
For testing purposes, note the alternate implementations of Clock available statically from Clock itself: fixed, offset, tick, and more.
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.

In Java 8 it is:
LocalDateTime.now()
and in case you need time zone info:
ZonedDateTime.now()
and in case you want to print fancy formatted string:
System.out.println(ZonedDateTime.now().format(DateTimeFormatter.RFC_1123_DATE_TIME))

Just create a Date object...
import java.util.Date;
Date date = new Date();

// 2015/09/27 15:07:53
System.out.println( new SimpleDateFormat("yyyy/MM/dd HH:mm:ss").format(Calendar.getInstance().getTime()) );
// 15:07:53
System.out.println( new SimpleDateFormat("HH:mm:ss").format(Calendar.getInstance().getTime()) );
// 09/28/2015
System.out.println(new SimpleDateFormat("MM/dd/yyyy").format(Calendar.getInstance().getTime()));
// 20150928_161823
System.out.println( new SimpleDateFormat("yyyyMMdd_HHmmss").format(Calendar.getInstance().getTime()) );
// Mon Sep 28 16:24:28 CEST 2015
System.out.println( Calendar.getInstance().getTime() );
// Mon Sep 28 16:24:51 CEST 2015
System.out.println( new Date(System.currentTimeMillis()) );
// Mon Sep 28
System.out.println( new Date().toString().substring(0, 10) );
// 2015-09-28
System.out.println( new java.sql.Date(System.currentTimeMillis()) );
// 14:32:26
Date d = new Date();
System.out.println( (d.getTime() / 1000 / 60 / 60) % 24 + ":" + (d.getTime() / 1000 / 60) % 60 + ":" + (d.getTime() / 1000) % 60 );
// 2015-09-28 17:12:35.584
System.out.println( new Timestamp(System.currentTimeMillis()) );
// Java 8
// 2015-09-28T16:16:23.308+02:00[Europe/Belgrade]
System.out.println( ZonedDateTime.now() );
// Mon, 28 Sep 2015 16:16:23 +0200
System.out.println( ZonedDateTime.now().format(DateTimeFormatter.RFC_1123_DATE_TIME) );
// 2015-09-28
System.out.println( LocalDate.now(ZoneId.of("Europe/Paris")) ); // rest zones id in ZoneId class
// 16
System.out.println( LocalTime.now().getHour() );
// 2015-09-28T16:16:23.315
System.out.println( LocalDateTime.now() );

Use:
String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(Calendar.getInstance().getTime());
System.out.println(timeStamp );
(It's working.)

There are many different methods:
System.currentTimeMillis()
Date
Calendar

Create object of date and simply print it down.
Date d = new Date(System.currentTimeMillis());
System.out.print(d);

java.util.Date date = new java.util.Date();
It's automatically populated with the time it's instantiated.

Similar to above solutions. But I always find myself looking for this chunk of code:
Date date=Calendar.getInstance().getTime();
System.out.println(date);

For java.util.Date, just create a new Date()
DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Date date = new Date();
System.out.println(dateFormat.format(date)); //2016/11/16 12:08:43
For java.util.Calendar, uses Calendar.getInstance()
DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Calendar cal = Calendar.getInstance();
System.out.println(dateFormat.format(cal)); //2016/11/16 12:08:43
For java.time.LocalDateTime, uses LocalDateTime.now()
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
LocalDateTime now = LocalDateTime.now();
System.out.println(dtf.format(now)); //2016/11/16 12:08:43
For java.time.LocalDate, uses LocalDate.now()
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy/MM/dd");
LocalDate localDate = LocalDate.now();
System.out.println(dtf.format(localDate)); //2016/11/16
Reference: https://www.mkyong.com/java/java-how-to-get-current-date-time-date-and-calender/

1st Understand the java.util.Date class
1.1 How to obtain current Date
import java.util.Date;
class Demostration{
public static void main(String[]args){
Date date = new Date(); // date object
System.out.println(date); // Try to print the date object
}
}
1.2 How to use getTime() method
import java.util.Date;
public class Main {
public static void main(String[]args){
Date date = new Date();
long timeInMilliSeconds = date.getTime();
System.out.println(timeInMilliSeconds);
}
}
This will return the number of milliseconds since January 1, 1970, 00:00:00 GMT for time comparison purposes.
1.3 How to format time using SimpleDateFormat class
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
class Demostration{
public static void main(String[]args){
Date date=new Date();
DateFormat dateFormat=new SimpleDateFormat("yyyy-MM-dd");
String formattedDate=dateFormat.format(date);
System.out.println(formattedDate);
}
}
Also try using different format patterns like "yyyy-MM-dd hh:mm:ss" and select desired pattern. http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html
2nd Understand the java.util.Calendar class
2.1 Using Calendar Class to obtain current time stamp
import java.util.Calendar;
class Demostration{
public static void main(String[]args){
Calendar calendar=Calendar.getInstance();
System.out.println(calendar.getTime());
}
}
2.2 Try using setTime and other set methods for set calendar to different date.
Source: http://javau91.blogspot.com/

Have you looked at java.util.Date? It is exactly what you want.

Java 8 or above
LocalDateTime.now() and ZonedDateTime.now()

I find this to be the best way:
DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Calendar cal = Calendar.getInstance();
System.out.println(dateFormat.format(cal.getTime())); // 2014/08/06 16:00:22

Have a look at the Date class. There's also the newer Calendar class which is the preferred method of doing many date / time operations (a lot of the methods on Date have been deprecated.)
If you just want the current date, then either create a new Date object or call Calendar.getInstance();.

As mentioned the basic Date() can do what you need in terms of getting the current time. In my recent experience working heavily with Java dates there are a lot of oddities with the built in classes (as well as deprecation of many of the Date class methods). One oddity that stood out to me was that months are 0 index based which from a technical standpoint makes sense, but in real terms can be very confusing.
If you are only concerned with the current date that should suffice - however if you intend to do a lot of manipulating/calculations with dates it could be very beneficial to use a third party library (so many exist because many Java developers have been unsatisfied with the built in functionality).
I second Stephen C's recommendation as I have found Joda-time to be very useful in simplifying my work with dates, it is also very well documented and you can find many useful examples throughout the web. I even ended up writing a static wrapper class (as DateUtils) which I use to consolidate and simplify all of my common date manipulation.

Use:
SimpleDateFormat sdf = new SimpleDateFormat("yyyy:MM:dd::HH:mm:ss");
System.out.println(sdf.format(System.currentTimeMillis()));
The print statement will print the time when it is called and not when the SimpleDateFormat was created. So it can be called repeatedly without creating any new objects.

System.out.println( new SimpleDateFormat("yyyy:MM:dd - hh:mm:ss a").format(Calendar.getInstance().getTime()) );
//2018:02:10 - 05:04:20 PM
date/time with AM/PM

New Data-Time API is introduced with the dawn of Java 8. This is due
to following issues that were caused in the old data-time API.
Difficult to handle time zone : need to write lot of code to deal with
time zones.
Not Thread Safe : java.util.Date is not thread safe.
So have a look around with Java 8
import java.time.LocalDate;
import java.time.LocalTime;
import java.time.LocalDateTime;
import java.time.Month;
public class DataTimeChecker {
public static void main(String args[]) {
DataTimeChecker dateTimeChecker = new DataTimeChecker();
dateTimeChecker.DateTime();
}
public void DateTime() {
// Get the current date and time
LocalDateTime currentTime = LocalDateTime.now();
System.out.println("Current DateTime: " + currentTime);
LocalDate date1 = currentTime.toLocalDate();
System.out.println("Date : " + date1);
Month month = currentTime.getMonth();
int day = currentTime.getDayOfMonth();
int seconds = currentTime.getSecond();
System.out.println("Month : " + month);
System.out.println("Day : " + day);
System.out.println("Seconds : " + seconds);
LocalDateTime date2 = currentTime.withDayOfMonth(17).withYear(2018);
System.out.println("Date : " + date2);
//Prints 17 May 2018
LocalDate date3 = LocalDate.of(2018, Month.MAY, 17);
System.out.println("Date : " + date3);
//Prints 04 hour 45 minutes
LocalTime date4 = LocalTime.of(4, 45);
System.out.println("Date : " + date4);
// Convert to a String
LocalTime date5 = LocalTime.parse("20:15:30");
System.out.println("Date : " + date5);
}
}
Output of the coding above :
Current DateTime: 2018-05-17T04:40:34.603
Date : 2018-05-17
Month : MAY
Day : 17
Seconds : 34
Date : 2018-05-17T04:40:34.603
Date : 2018-05-17
Date : 04:45
Date : 20:15:30

I created this methods, it works for me...
public String GetDay() {
return String.valueOf(LocalDateTime.now().format(DateTimeFormatter.ofPattern("dd")));
}
public String GetNameOfTheDay() {
return String.valueOf(LocalDateTime.now().getDayOfWeek());
}
public String GetMonth() {
return String.valueOf(LocalDateTime.now().format(DateTimeFormatter.ofPattern("MM")));
}
public String GetNameOfTheMonth() {
return String.valueOf(LocalDateTime.now().getMonth());
}
public String GetYear() {
return String.valueOf(LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy")));
}
public boolean isLeapYear(long year) {
return Year.isLeap(year);
}
public String GetDate() {
return GetDay() + "/" + GetMonth() + "/" + GetYear();
}
public String Get12HHour() {
return String.valueOf(LocalDateTime.now().format(DateTimeFormatter.ofPattern("hh")));
}
public String Get24HHour() {
return String.valueOf(LocalDateTime.now().getHour());
}
public String GetMinutes() {
return String.valueOf(LocalDateTime.now().format(DateTimeFormatter.ofPattern("mm")));
}
public String GetSeconds() {
return String.valueOf(LocalDateTime.now().format(DateTimeFormatter.ofPattern("ss")));
}
public String Get24HTime() {
return Get24HHour() + ":" + GetMinutes();
}
public String Get24HFullTime() {
return Get24HHour() + ":" + GetMinutes() + ":" + GetSeconds();
}
public String Get12HTime() {
return Get12HHour() + ":" + GetMinutes();
}
public String Get12HFullTime() {
return Get12HHour() + ":" + GetMinutes() + ":" + GetSeconds();
}

import java.util.*;
import java.text.*;
public class DateDemo {
public static void main(String args[]) {
Date dNow = new Date( );
SimpleDateFormat ft =
new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");
System.out.println("Current Date: " + ft.format(dNow));
}
}
you can use date for fet current data. so using SimpleDateFormat get format

just try this code:
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class CurrentTimeDateCalendar {
public static void getCurrentTimeUsingDate() {
Date date = new Date();
String strDateFormat = "hh:mm:ss a";
DateFormat dateFormat = new SimpleDateFormat(strDateFormat);
String formattedDate= dateFormat.format(date);
System.out.println("Current time of the day using Date - 12 hour format: " + formattedDate);
}
public static void getCurrentTimeUsingCalendar() {
Calendar cal = Calendar.getInstance();
Date date=cal.getTime();
DateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
String formattedDate=dateFormat.format(date);
System.out.println("Current time of the day using Calendar - 24 hour format: "+ formattedDate);
}
}
which the sample output is:
Current time of the day using Date - 12 hour format: 11:13:01 PM
Current time of the day using Calendar - 24 hour format: 23:13:01
more information on:
Getting Current Date Time in Java

Current Date using java 8:
First, let's use java.time.LocalDate to get the current system date:
LocalDate localDate = LocalDate.now();
To get the date in any other timezone we can use LocalDate.now(ZoneId):
LocalDate localDate = LocalDate.now(ZoneId.of("GMT+02:30"));
We can also use java.time.LocalDateTime to get an instance of LocalDate:
LocalDateTime localDateTime = LocalDateTime.now();
LocalDate localDate = localDateTime.toLocalDate();

You can use Date object and format by yourself. It is hard to format and need more codes, as a example,
Date dateInstance = new Date();
int year = dateInstance.getYear()+1900;//Returns:the year represented by this date, minus 1900.
int date = dateInstance.getDate();
int month = dateInstance.getMonth();
int day = dateInstance.getDay();
int hours = dateInstance.getHours();
int min = dateInstance.getMinutes();
int sec = dateInstance.getSeconds();
String dayOfWeek = "";
switch(day){
case 0:
dayOfWeek = "Sunday";
break;
case 1:
dayOfWeek = "Monday";
break;
case 2:
dayOfWeek = "Tuesday";
break;
case 3:
dayOfWeek = "Wednesday";
break;
case 4:
dayOfWeek = "Thursday";
break;
case 5:
dayOfWeek = "Friday";
break;
case 6:
dayOfWeek = "Saturday";
break;
}
System.out.println("Date: " + year +"-"+ month + "-" + date + " "+ dayOfWeek);
System.out.println("Time: " + hours +":"+ min + ":" + sec);
output:
Date: 2017-6-23 Sunday
Time: 14:6:20
As you can see this is the worst way you can do it and according to oracle documentation it is deprecated.
Oracle doc:
The class Date represents a specific instant in time, with millisecond
precision.
Prior to JDK 1.1, the class Date had two additional functions. It
allowed the interpretation of dates as year, month, day, hour, minute,
and second values. It also allowed the formatting and parsing of date
strings. Unfortunately, the API for these functions was not amenable
to internationalization. As of JDK 1.1, the Calendar class should be
used to convert between dates and time fields and the DateFormat class
should be used to format and parse date strings. The corresponding
methods in Date are deprecated.
So alternatively, you can use Calendar class,
Calendar.YEAR;
//and lot more
To get current time, you can use:
Calendar rightNow = Calendar.getInstance();
Doc:
Like other locale-sensitive classes, Calendar provides a class method,
getInstance, for getting a generally useful object of this type.
Calendar's getInstance method returns a Calendar object whose calendar
fields have been initialized with the current date and time
Below code for to get only date
Date rightNow = Calendar.getInstance().getTime();
System.out.println(rightNow);
Also, Calendar class have Subclasses. GregorianCalendar is a one of them and concrete subclass of Calendar and provides the standard calendar system used by most of the world.
Example using GregorianCalendar:
Calendar cal = new GregorianCalendar();
int hours = cal.get(Calendar.HOUR);
int minute = cal.get(Calendar.MINUTE);
int second = cal.get(Calendar.SECOND);
int ap = cal.get(Calendar.AM_PM);
String amVSpm;
if(ap == 0){
amVSpm = "AM";
}else{
amVSpm = "PM";
}
String timer = hours + "-" + minute + "-" + second + " " +amVSpm;
System.out.println(timer);
You can use SimpleDateFormat, simple and quick way to format date:
String pattern = "yyyy-MM-dd";
SimpleDateFormat simpleDateFormat = new SimpleDateFormat(pattern);
String date = simpleDateFormat.format(new Date());
System.out.println(date);
Read this Jakob Jenkov tutorial: Java SimpleDateFormat.
As others mentioned, when we need to do manipulation from dates, we didn't had simple and best way or we couldn't satisfied built in classes, APIs.
As a example, When we need to get different between two dates, when we need to compare two dates(there is in-built method also for this) and many more. We had to use third party libraries. One of the good and popular one is Joda Time.
Also read:
How to get properly current date and time in Joda-Time?
JodaTime - how to get current time in UTC
Examples for JodaTime.
Download Joda
.
The happiest thing is now(in java 8), no one need to download and use libraries for any reasons. A simple example to get current date & time in Java 8,
LocalTime localTime = LocalTime.now();
System.out.println(localTime);
//with time zone
LocalTime localTimeWtZone = LocalTime.now(ZoneId.of("GMT+02:30"));
System.out.println(localTimeWtZone);
One of the good blog post to read about Java 8 date.
And keep remeber to find out more about Java date and time because there is lot more ways and/or useful ways that you can get/use.
Oracle tutorials for date & time.
Oracle tutorials for formatter.
Lesson: Standard Calendar.
EDIT:
According to #BasilBourque comment, the troublesome old date-time classes such as java.util.Date, java.util.Calendar, and java.text.SimpleTextFormat are now legacy, supplanted by the java.time classes.

I'll go ahead and throw this answer in because it is all I needed when I had the same question:
Date currentDate = new Date(System.currentTimeMillis());
currentDate is now your current date in a Java Date object.

How to get the first day of the current week and month?

I have the date of several events expressed in milliseconds[1], and I want to know which events are inside the current week and the current month, but I can't figure out how to obtain the first day (day/month/year) of the running week and convert it to milliseconds, the same for the first day of the month.
[1]Since January 1, 1970, 00:00:00 GMT

This week in milliseconds:
// get today and clear time of day
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY, 0); // ! clear would not reset the hour of day !
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
// get start of this week in milliseconds
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
System.out.println("Start of this week: " + cal.getTime());
System.out.println("... in milliseconds: " + cal.getTimeInMillis());
// start of the next week
cal.add(Calendar.WEEK_OF_YEAR, 1);
System.out.println("Start of the next week: " + cal.getTime());
System.out.println("... in milliseconds: " + cal.getTimeInMillis());
This month in milliseconds:
// get today and clear time of day
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY, 0); // ! clear would not reset the hour of day !
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
// get start of the month
cal.set(Calendar.DAY_OF_MONTH, 1);
System.out.println("Start of the month: " + cal.getTime());
System.out.println("... in milliseconds: " + cal.getTimeInMillis());
// get start of the next month
cal.add(Calendar.MONTH, 1);
System.out.println("Start of the next month: " + cal.getTime());
System.out.println("... in milliseconds: " + cal.getTimeInMillis());

The first day of week can be determined with help of java.util.Calendar as follows:
Calendar calendar = Calendar.getInstance();
calendar.clear();
calendar.setTimeInMillis(timestamp);
while (calendar.get(Calendar.DAY_OF_WEEK) > calendar.getFirstDayOfWeek()) {
calendar.add(Calendar.DATE, -1); // Substract 1 day until first day of week.
}
long firstDayOfWeekTimestamp = calendar.getTimeInMillis();
The first day of month can be determined as follows:
Calendar calendar = Calendar.getInstance();
calendar.clear();
calendar.setTimeInMillis(timestamp);
while (calendar.get(Calendar.DATE) > 1) {
calendar.add(Calendar.DATE, -1); // Substract 1 day until first day of month.
}
long firstDayOfMonthTimestamp = calendar.getTimeInMillis();
Pretty verbose, yes.
Java 7 will come with a much improved Date and Time API (JSR-310). If you can't switch yet, then you can as far use JodaTime which makes it all less complicated:
DateTime dateTime = new DateTime(timestamp);
long firstDayOfWeekTimestamp = dateTime.withDayOfWeek(1).getMillis();
and
DateTime dateTime = new DateTime(timestamp);
long firstDayOfMonthTimestamp = dateTime.withDayOfMonth(1).getMillis();

java.time
The java.time framework in Java 8 and later supplants the old java.util.Date/.Calendar classes. The old classes have proven to be troublesome, confusing, and flawed. Avoid them.
The java.time framework is inspired by the highly-successful Joda-Time library, defined by JSR 310, extended by the ThreeTen-Extra project, and explained in the Tutorial.
Instant
The Instant class represents a moment on the timeline in UTC.
The java.time framework has a resolution of nanoseconds, or 9 digits of a fractional second. Milliseconds is only 3 digits of a fractional second. Because millisecond resolution is common, java.time includes a handy factory method.
long millisecondsSinceEpoch = 1446959825213L;
Instant instant = Instant.ofEpochMilli ( millisecondsSinceEpoch );
millisecondsSinceEpoch: 1446959825213 is instant: 2015-11-08T05:17:05.213Z
ZonedDateTime
To consider current week and current month, we need to apply a particular time zone.
ZoneId zoneId = ZoneId.of ( "America/Montreal" );
ZonedDateTime zdt = ZonedDateTime.ofInstant ( instant , zoneId );
In zoneId: America/Montreal that is: 2015-11-08T00:17:05.213-05:00[America/Montreal]
Half-Open
In date-time work, we commonly use the Half-Open approach to defining a span of time. The beginning is inclusive while the ending in exclusive. Rather than try to determine the last split-second of the end of the week (or month), we get the first moment of the following week (or month). So a week runs from the first moment of Monday and goes up to but not including the first moment of the following Monday.
Let's the first day of the week, and last. The java.time framework includes a tool for that, the with method and the ChronoField enum.
By default, java.time uses the ISO 8601 standard. So Monday is the first day of the week (1) and Sunday is last (7).
ZonedDateTime firstOfWeek = zdt.with ( ChronoField.DAY_OF_WEEK , 1 ); // ISO 8601, Monday is first day of week.
ZonedDateTime firstOfNextWeek = firstOfWeek.plusWeeks ( 1 );
That week runs from: 2015-11-02T00:17:05.213-05:00[America/Montreal] to 2015-11-09T00:17:05.213-05:00[America/Montreal]
Oops! Look at the time-of-day on those values. We want the first moment of the day. The first moment of the day is not always 00:00:00.000 because of Daylight Saving Time (DST) or other anomalies. So we should let java.time make the adjustment on our behalf. To do that, we must go through the LocalDate class.
ZonedDateTime firstOfWeek = zdt.with ( ChronoField.DAY_OF_WEEK , 1 ); // ISO 8601, Monday is first day of week.
firstOfWeek = firstOfWeek.toLocalDate ().atStartOfDay ( zoneId );
ZonedDateTime firstOfNextWeek = firstOfWeek.plusWeeks ( 1 );
That week runs from: 2015-11-02T00:00-05:00[America/Montreal] to 2015-11-09T00:00-05:00[America/Montreal]
And same for the month.
ZonedDateTime firstOfMonth = zdt.with ( ChronoField.DAY_OF_MONTH , 1 );
firstOfMonth = firstOfMonth.toLocalDate ().atStartOfDay ( zoneId );
ZonedDateTime firstOfNextMonth = firstOfMonth.plusMonths ( 1 );
That month runs from: 2015-11-01T00:00-04:00[America/Montreal] to 2015-12-01T00:00-05:00[America/Montreal]
YearMonth
Another way to see if a pair of moments are in the same month is to check for the same YearMonth value.
For example, assuming thisZdt and thatZdt are both ZonedDateTime objects:
boolean inSameMonth = YearMonth.from( thisZdt ).equals( YearMonth.from( thatZdt ) ) ;
Milliseconds
I strongly recommend against doing your date-time work in milliseconds-from-epoch. That is indeed the way date-time classes tend to work internally, but we have the classes for a reason. Handling a count-from-epoch is clumsy as the values are not intelligible by humans so debugging and logging is difficult and error-prone. And, as we've already seen, different resolutions may be in play; old Java classes and Joda-Time library use milliseconds, while databases like Postgres use microseconds, and now java.time uses nanoseconds.
Would you handle text as bits, or do you let classes such as String, StringBuffer, and StringBuilder handle such details?
But if you insist, from a ZonedDateTime get an Instant, and from that get a milliseconds-count-from-epoch. But keep in mind this call can mean loss of data. Any microseconds or nanoseconds that you might have in your ZonedDateTime/Instant will be truncated (lost).
long millis = firstOfWeek.toInstant().toEpochMilli(); // Possible data loss.
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….

Attention!
while (calendar.get(Calendar.DAY_OF_WEEK) > calendar.getFirstDayOfWeek()) {
calendar.add(Calendar.DATE, -1); // Substract 1 day until first day of week.
}
is good idea, but there is some issue:
For example, i'm from Ukraine and calendar.getFirstDayOfWeek() in my country is 2 (Monday).
And today is 1 (Sunday). In this case calendar.add not called.
So, correct way is change ">" to "!=":
while (calendar.get(Calendar.DAY_OF_WEEK) != calendar.getFirstDayOfWeek()) {...

You can use the java.time package (since Java8 and late) to get start/end of day/week/month.
The util class example below:
import org.junit.Test;
import java.time.DayOfWeek;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAdjusters;
import java.util.Date;
public class DateUtil {
private static final ZoneId DEFAULT_ZONE_ID = ZoneId.of("UTC");
public static LocalDateTime startOfDay() {
return LocalDateTime.now(DEFAULT_ZONE_ID).with(LocalTime.MIN);
}
public static LocalDateTime endOfDay() {
return LocalDateTime.now(DEFAULT_ZONE_ID).with(LocalTime.MAX);
}
public static boolean belongsToCurrentDay(final LocalDateTime localDateTime) {
return localDateTime.isAfter(startOfDay()) && localDateTime.isBefore(endOfDay());
}
//note that week starts with Monday
public static LocalDateTime startOfWeek() {
return LocalDateTime.now(DEFAULT_ZONE_ID)
.with(LocalTime.MIN)
.with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY));
}
//note that week ends with Sunday
public static LocalDateTime endOfWeek() {
return LocalDateTime.now(DEFAULT_ZONE_ID)
.with(LocalTime.MAX)
.with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY));
}
public static boolean belongsToCurrentWeek(final LocalDateTime localDateTime) {
return localDateTime.isAfter(startOfWeek()) && localDateTime.isBefore(endOfWeek());
}
public static LocalDateTime startOfMonth() {
return LocalDateTime.now(DEFAULT_ZONE_ID)
.with(LocalTime.MIN)
.with(TemporalAdjusters.firstDayOfMonth());
}
public static LocalDateTime endOfMonth() {
return LocalDateTime.now(DEFAULT_ZONE_ID)
.with(LocalTime.MAX)
.with(TemporalAdjusters.lastDayOfMonth());
}
public static boolean belongsToCurrentMonth(final LocalDateTime localDateTime) {
return localDateTime.isAfter(startOfMonth()) && localDateTime.isBefore(endOfMonth());
}
public static long toMills(final LocalDateTime localDateTime) {
return localDateTime.atZone(DEFAULT_ZONE_ID).toInstant().toEpochMilli();
}
public static Date toDate(final LocalDateTime localDateTime) {
return Date.from(localDateTime.atZone(DEFAULT_ZONE_ID).toInstant());
}
public static String toString(final LocalDateTime localDateTime) {
return localDateTime.format(DateTimeFormatter.ISO_DATE_TIME);
}
#Test
public void test() {
//day
final LocalDateTime now = LocalDateTime.now();
System.out.println("Now: " + toString(now) + ", in mills: " + toMills(now));
System.out.println("Start of day: " + toString(startOfDay()));
System.out.println("End of day: " + toString(endOfDay()));
System.out.println("Does '" + toString(now) + "' belong to the current day? > " + belongsToCurrentDay(now));
final LocalDateTime yesterday = now.minusDays(1);
System.out.println("Does '" + toString(yesterday) + "' belong to the current day? > " + belongsToCurrentDay(yesterday));
final LocalDateTime tomorrow = now.plusDays(1);
System.out.println("Does '" + toString(tomorrow) + "' belong to the current day? > " + belongsToCurrentDay(tomorrow));
//week
System.out.println("Start of week: " + toString(startOfWeek()));
System.out.println("End of week: " + toString(endOfWeek()));
System.out.println("Does '" + toString(now) + "' belong to the current week? > " + belongsToCurrentWeek(now));
final LocalDateTime previousWeek = now.minusWeeks(1);
System.out.println("Does '" + toString(previousWeek) + "' belong to the current week? > " + belongsToCurrentWeek(previousWeek));
final LocalDateTime nextWeek = now.plusWeeks(1);
System.out.println("Does '" + toString(nextWeek) + "' belong to the current week? > " + belongsToCurrentWeek(nextWeek));
//month
System.out.println("Start of month: " + toString(startOfMonth()));
System.out.println("End of month: " + toString(endOfMonth()));
System.out.println("Does '" + toString(now) + "' belong to the current month? > " + belongsToCurrentMonth(now));
final LocalDateTime previousMonth = now.minusMonths(1);
System.out.println("Does '" + toString(previousMonth) + "' belong to the current month? > " + belongsToCurrentMonth(previousMonth));
final LocalDateTime nextMonth = now.plusMonths(1);
System.out.println("Does '" + toString(nextMonth) + "' belong to the current month? > " + belongsToCurrentMonth(nextMonth));
}
}
Test output:
Now: 2020-02-16T22:12:49.957, in mills: 1581891169957
Start of day: 2020-02-16T00:00:00
End of day: 2020-02-16T23:59:59.999999999
Does '2020-02-16T22:12:49.957' belong to the current day? > true
Does '2020-02-15T22:12:49.957' belong to the current day? > false
Does '2020-02-17T22:12:49.957' belong to the current day? > false
Start of week: 2020-02-10T00:00:00
End of week: 2020-02-16T23:59:59.999999999
Does '2020-02-16T22:12:49.957' belong to the current week? > true
Does '2020-02-09T22:12:49.957' belong to the current week? > false
Does '2020-02-23T22:12:49.957' belong to the current week? > false
Start of month: 2020-02-01T00:00:00
End of month: 2020-02-29T23:59:59.999999999
Does '2020-02-16T22:12:49.957' belong to the current month? > true
Does '2020-01-16T22:12:49.957' belong to the current month? > false
Does '2020-03-16T22:12:49.957' belong to the current month? > false

I have created some methods for this:
public static String catchLastDayOfCurrentWeek(String pattern) {
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
return calendarToString(cal, pattern);
}
public static String catchLastDayOfCurrentWeek(String pattern) {
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
cal.add(Calendar.WEEK_OF_YEAR, 1);
cal.add(Calendar.MILLISECOND, -1);
return calendarToString(cal, pattern);
}
public static String catchTheFirstDayOfThemonth(Integer month, pattern padrao) {
Calendar cal = GregorianCalendar.getInstance();
cal.setTime(new Date());
cal.set(Calendar.MONTH, month);
cal.set(Calendar.DAY_OF_MONTH, 1);
return calendarToString(cal, pattern);
}
public static String catchTheLastDayOfThemonth(Integer month, String pattern) {
Calendar cal = GregorianCalendar.getInstance();
cal.setTime(new Date());
cal.set(cal.get(Calendar.YEAR), month, cal.getActualMaximum(Calendar.DAY_OF_MONTH));
return calendarToString(cal, pattern);
}
public static String calendarToString(Calendar calendar, String pattern) {
if (calendar == null) {
return "";
}
SimpleDateFormat format = new SimpleDateFormat(pattern, LocaleUtils.DEFAULT_LOCALE);
return format.format(calendar.getTime());
}
You can see more here.

To get the first day of the month, simply get a Date and set the current day to day 1 of the month. Clear hour, minute, second and milliseconds if you need it.
private static Date firstDayOfMonth(Date date) {
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.set(Calendar.DATE, 1);
return calendar.getTime();
}
First day of the week is the same thing, but using Calendar.DAY_OF_WEEK instead
private static Date firstDayOfWeek(Date date) {
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.set(Calendar.DAY_OF_WEEK, 1);
return calendar.getTime();
}

In this case:
// get today and clear time of day
Calendar cal = Calendar.getInstance();
cal.clear(Calendar.HOUR_OF_DAY); <---- is the current hour not 0 hour
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
So the Calendar.HOUR_OF_DAY returns 8, 9, 12, 15, 18 as the current running hour.
I think will be better change such line by:
c.set(Calendar.HOUR_OF_DAY,0);
this way the day always begin at 0 hour

Get First date of next month:-
SimpleDateFormat df = new SimpleDateFormat("MM-dd-yyyy");
String selectedDate="MM-dd-yyyy like 07-02-2018";
Date dt = df.parse(selectedDate);`enter code here`
calendar = Calendar.getInstance();
calendar.setTime(dt);
calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH) + 1);
String firstDate = df.format(calendar.getTime());
System.out.println("firstDateof next month ==>" + firstDate);

A one-line solution using Java 8 features
In Java
LocalDateTime firstOfWeek = LocalDateTime.now().with(ChronoField.DAY_OF_WEEK, 1).toLocalDate().atStartOfDay(); // 2020-06-08 00:00 MONDAY
LocalDateTime firstOfMonth = LocalDateTime.now().with(ChronoField.DAY_OF_MONTH , 1).toLocalDate().atStartOfDay(); // 2020-06-01 00:00
// Convert to milliseconds:
firstOfWeek.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
In Kotlin
val firstOfWeek = LocalDateTime.now().with(ChronoField.DAY_OF_WEEK, 1).toLocalDate().atStartOfDay() // 2020-06-08 00:00 MONDAY
val firstOfMonth = LocalDateTime.now().with(ChronoField.DAY_OF_MONTH , 1).toLocalDate().atStartOfDay() // 2020-06-01 00:00
// Convert to milliseconds:
firstOfWeek.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli()

You should be able to convert your number to a Java Calendar, e.g.:
Calendar.getInstance().setTimeInMillis(myDate);
From there, the comparison shouldn't be too hard.

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Scanner;
/**
This Program will display day for, 1st and last days in a given month and year
#author Manoj Kumar Dunna
Mail Id : manojdunna#gmail.com
*/
public class DayOfWeek {
public static void main(String[] args) {
String strDate = null;
int year = 0, month = 0;
Scanner sc = new Scanner(System.in);
System.out.print("Enter YYYY/MM: ");
strDate = sc.next();
Calendar cal = new GregorianCalendar();
String [] date = strDate.split("/");
year = Integer.parseInt(date[0]);
month = Integer.parseInt(date[1]);
cal.set(year, month-1, 1);
System.out.println(new SimpleDateFormat("EEEE").format(cal.getTime()));
cal.add(Calendar.MONTH, 1);
cal.add(Calendar.DAY_OF_YEAR, -1);
System.out.println(new SimpleDateFormat("EEEE").format(cal.getTime()));
}
}

Simple Solution:
package com.util.calendarutil;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
public class CalUtil {
public static void main(String args[]){
DateFormat df = new SimpleDateFormat("dd/mm/yyyy");
Date dt = null;
try {
dt = df.parse("23/01/2016");
} catch (ParseException e) {
System.out.println("Error");
}
Calendar cal = Calendar.getInstance();
cal.setTime(dt);
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
Date startDate = cal.getTime();
cal.add(Calendar.DATE, 6);
Date endDate = cal.getTime();
System.out.println("Start Date:"+startDate+"End Date:"+endDate);
}
}

i use this trick to get the first day of the current month
note the order is
1 for Sunday
2 for Monday
3 for Tuesday
.... and so on
Calendar cal = new GregorianCalendar();
int startDay = cal.get(Calendar.DAY_OF_YEAR) % 7 + 1;
System.out.println(startDay);

public static void main(String[] args) {
System.out.println(getMonthlyEpochList(1498867199L,12,"Monthly"));
}
public static Map<String,String> getMonthlyEpochList(Long currentEpoch, int noOfTerms, String timeMode) {
Map<String,String> map = new LinkedHashMap<String,String>();
int month = 0;
while(noOfTerms != 0) {
Calendar calendar = Calendar.getInstance();
calendar.add(Calendar.MONTH, month);
calendar.set(Calendar.DATE, calendar.getActualMinimum(Calendar.DAY_OF_MONTH));
Date monthFirstDay = calendar.getTime();
calendar.set(Calendar.DATE, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
Date monthLastDay = calendar.getTime();
map.put(getMMYY(monthFirstDay.getTime()), monthFirstDay + ":" +monthLastDay);
month--;
noOfTerms--;
}
return map;
}

Develop Reference

Java is a programming language and computing platform first released by Sun Microsystems in 1995.