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How to compare date in firestore [duplicate]

I'm working with a date in this format: yyyy-mm-dd.
How can I increment this date by one day?

Something like this should do the trick:
String dt = "2008-01-01"; // Start date
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar c = Calendar.getInstance();
c.setTime(sdf.parse(dt));
c.add(Calendar.DATE, 1); // number of days to add
dt = sdf.format(c.getTime()); // dt is now the new date

UPDATE (May 2021): This is a really outdated answer for old, old Java. For Java 8 and above, see https://stackoverflow.com/a/20906602/314283
Java does appear to be well behind the eight-ball compared to C#. This utility method shows the way to do in Java SE 6 using the Calendar.add method (presumably the only easy way).
public class DateUtil
{
public static Date addDays(Date date, int days)
{
Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.add(Calendar.DATE, days); //minus number would decrement the days
return cal.getTime();
}
}
To add one day, per the question asked, call it as follows:
String sourceDate = "2012-02-29";
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
Date myDate = format.parse(sourceDate);
myDate = DateUtil.addDays(myDate, 1);

java.time
On Java 8 and later, the java.time package makes this pretty much automatic. (Tutorial)
Assuming String input and output:
import java.time.LocalDate;
public class DateIncrementer {
static public String addOneDay(String date) {
return LocalDate.parse(date).plusDays(1).toString();
}
}

I prefer to use DateUtils from Apache. Check this http://commons.apache.org/proper/commons-lang/javadocs/api-2.6/org/apache/commons/lang/time/DateUtils.html. It is handy especially when you have to use it multiple places in your project and would not want to write your one liner method for this.
The API says:
addDays(Date date, int amount) : Adds a number of days to a date returning a new object.
Note that it returns a new Date object and does not make changes to the previous one itself.

SimpleDateFormat dateFormat = new SimpleDateFormat( "yyyy-MM-dd" );
Calendar cal = Calendar.getInstance();
cal.setTime( dateFormat.parse( inputString ) );
cal.add( Calendar.DATE, 1 );

Construct a Calendar object and call add(Calendar.DATE, 1);

Java 8 added a new API for working with dates and times.
With Java 8 you can use the following lines of code:
// parse date from yyyy-mm-dd pattern
LocalDate januaryFirst = LocalDate.parse("2014-01-01");
// add one day
LocalDate januarySecond = januaryFirst.plusDays(1);

Take a look at Joda-Time (https://www.joda.org/joda-time/).
DateTimeFormatter parser = ISODateTimeFormat.date();
DateTime date = parser.parseDateTime(dateString);
String nextDay = parser.print(date.plusDays(1));

Please note that this line adds 24 hours:
d1.getTime() + 1 * 24 * 60 * 60 * 1000
but this line adds one day
cal.add( Calendar.DATE, 1 );
On days with a daylight savings time change (25 or 23 hours) you will get different results!

you can use Simple java.util lib
Calendar cal = Calendar.getInstance();
cal.setTime(yourDate);
cal.add(Calendar.DATE, 1);
yourDate = cal.getTime();

Date today = new Date();
SimpleDateFormat formattedDate = new SimpleDateFormat("yyyyMMdd");
Calendar c = Calendar.getInstance();
c.add(Calendar.DATE, 1); // number of days to add
String tomorrow = (String)(formattedDate.format(c.getTime()));
System.out.println("Tomorrows date is " + tomorrow);
This will give tomorrow's date. c.add(...) parameters could be changed from 1 to another number for appropriate increment.

If you are using Java 8, then do it like this.
LocalDate sourceDate = LocalDate.of(2017, Month.MAY, 27); // Source Date
LocalDate destDate = sourceDate.plusDays(1); // Adding a day to source date.
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd"); // Setting date format
String destDate = destDate.format(formatter)); // End date
If you want to use SimpleDateFormat, then do it like this.
String sourceDate = "2017-05-27"; // Start date
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar calendar = Calendar.getInstance();
calendar.setTime(sdf.parse(sourceDate)); // parsed date and setting to calendar
calendar.add(Calendar.DATE, 1); // number of days to add
String destDate = sdf.format(calendar.getTime()); // End date

Since Java 1.5 TimeUnit.DAYS.toMillis(1) looks more clean to me.
SimpleDateFormat dateFormat = new SimpleDateFormat( "yyyy-MM-dd" );
Date day = dateFormat.parse(string);
// add the day
Date dayAfter = new Date(day.getTime() + TimeUnit.DAYS.toMillis(1));

long timeadj = 24*60*60*1000;
Date newDate = new Date (oldDate.getTime ()+timeadj);
This takes the number of milliseconds since epoch from oldDate and adds 1 day worth of milliseconds then uses the Date() public constructor to create a date using the new value. This method allows you to add 1 day, or any number of hours/minutes, not only whole days.

In Java 8 simple way to do is:
Date.from(Instant.now().plusSeconds(SECONDS_PER_DAY))

It's very simple, trying to explain in a simple word.
get the today's date as below
Calendar calendar = Calendar.getInstance();
System.out.println(calendar.getTime());// print today's date
calendar.add(Calendar.DATE, 1);
Now set one day ahead with this date by calendar.add method which takes (constant, value). Here constant could be DATE, hours, min, sec etc. and value is the value of constant. Like for one day, ahead constant is Calendar.DATE and its value are 1 because we want one day ahead value.
System.out.println(calendar.getTime());// print modified date which is tomorrow's date
Thanks

startCalendar.add(Calendar.DATE, 1); //Add 1 Day to the current Calender

In java 8 you can use java.time.LocalDate
LocalDate parsedDate = LocalDate.parse("2015-10-30"); //Parse date from String
LocalDate addedDate = parsedDate.plusDays(1); //Add one to the day field
You can convert in into java.util.Date object as follows.
Date date = Date.from(addedDate.atStartOfDay(ZoneId.systemDefault()).toInstant());
You can formate LocalDate into a String as follows.
String str = addedDate.format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));

With Java SE 8 or higher you should use the new Date/Time API
int days = 7;
LocalDate dateRedeemed = LocalDate.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/YYYY");
String newDate = dateRedeemed.plusDays(days).format(formatter);
System.out.println(newDate);
If you need to convert from java.util.Date to java.time.LocalDate, you may use this method.
public LocalDate asLocalDate(Date date) {
Instant instant = date.toInstant();
ZonedDateTime zdt = instant.atZone(ZoneId.systemDefault());
return zdt.toLocalDate();
}
With a version prior to Java SE 8 you may use Joda-Time
Joda-Time provides a quality replacement for the Java date and time
classes and is the de facto standard date and time library for Java
prior to Java SE 8
int days = 7;
DateTime dateRedeemed = DateTime.now();
DateTimeFormatter formatter = DateTimeFormat.forPattern("dd/MM/uuuu");
String newDate = dateRedeemed.plusDays(days).toString(formatter);
System.out.println(newDate);

Apache Commons already has this DateUtils.addDays(Date date, int amount) http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/time/DateUtils.html#addDays%28java.util.Date,%20int%29 which you use or you could go with the JodaTime to make it more cleaner.

Just pass date in String and number of next days
private String getNextDate(String givenDate,int noOfDays) {
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
Calendar cal = Calendar.getInstance();
String nextDaysDate = null;
try {
cal.setTime(dateFormat.parse(givenDate));
cal.add(Calendar.DATE, noOfDays);
nextDaysDate = dateFormat.format(cal.getTime());
} catch (ParseException ex) {
Logger.getLogger(GR_TravelRepublic.class.getName()).log(Level.SEVERE, null, ex);
}finally{
dateFormat = null;
cal = null;
}
return nextDaysDate;
}

If you want to add a single unit of time and you expect that other fields to be incremented as well, you can safely use add method. See example below:
SimpleDateFormat simpleDateFormat1 = new SimpleDateFormat("yyyy-MM-dd");
Calendar cal = Calendar.getInstance();
cal.set(1970,Calendar.DECEMBER,31);
System.out.println(simpleDateFormat1.format(cal.getTime()));
cal.add(Calendar.DATE, 1);
System.out.println(simpleDateFormat1.format(cal.getTime()));
cal.add(Calendar.DATE, -1);
System.out.println(simpleDateFormat1.format(cal.getTime()));
Will Print:
1970-12-31
1971-01-01
1970-12-31

Use the DateFormat API to convert the String into a Date object, then use the Calendar API to add one day. Let me know if you want specific code examples, and I can update my answer.

Try this method:
public static Date addDay(int day) {
Calendar calendar = Calendar.getInstance();
calendar.setTime(new Date());
calendar.add(Calendar.DATE, day);
return calendar.getTime();
}

It's simple actually.
One day contains 86400000 milliSeconds.
So first you get the current time in millis from The System by usingSystem.currentTimeMillis() then
add the 84000000 milliSeconds and use the Date Class to generate A date format for the milliseconds.
Example
String Today = new Date(System.currentTimeMillis()).toString();
String Today will be 2019-05-9
String Tommorow = new Date(System.currentTimeMillis() + 86400000).toString();
String Tommorow will be 2019-05-10
String DayAfterTommorow = new Date(System.currentTimeMillis() + (2 * 86400000)).toString();
String DayAfterTommorow will be 2019-05-11

You can use this package from "org.apache.commons.lang3.time":
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date myNewDate = DateUtils.addDays(myDate, 4);
Date yesterday = DateUtils.addDays(myDate, -1);
String formatedDate = sdf.format(myNewDate);

If you are using Java 8, java.time.LocalDate and java.time.format.DateTimeFormatter can make this work quite simple.
public String nextDate(String date){
LocalDate parsedDate = LocalDate.parse(date);
LocalDate addedDate = parsedDate.plusDays(1);
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-mm-dd");
return addedDate.format(formatter);
}

The highest voted answer uses legacy java.util date-time API which was the correct thing to do in 2009 when the question was asked. In March 2014, java.time API supplanted the error-prone legacy date-time API. Since then, it is strongly recommended to use this modern date-time API.
I'm working with a date in this format: yyyy-mm-dd
You have used the wrong letter for the month, irrespective of whether you are using the legacy parsing/formatting API or the modern one. The letter m is used for minute-of-hour and the correct letter for month-of-year is M.
yyyy-MM-dd is the default format of java.time.LocalDate
The java.time API is based on ISO 8601 standards and therefore it does not require specifying a DateTimeFormatter explicitly to parse a date-time string if it is already in ISO 8601 format. Similarly, the toString implementation of a java.time type returns a string in ISO 8601 format. Check LocalDate#parse and LocalDate#toString for more information.
Ways to increment a local date by one day
There are three options:
LocalDate#plusDays(long daysToAdd)
LocalDate#plus(long amountToAdd, TemporalUnit unit): It has got some additional capabilities e.g. you can use it to increment a local date by days, weeks, months, years etc.
LocalDate#plus(TemporalAmount amountToAdd): You can specify a Period (or any other type implementing the TemporalAmount) to add.
Demo:
import java.time.Instant;
import java.time.LocalDate;
import java.time.Period;
import java.time.temporal.ChronoUnit;
public class Main {
public static void main(String[] args) {
// Parsing
LocalDate ldt = LocalDate.parse("2020-10-20");
System.out.println(ldt);
// Incrementing by one day
LocalDate oneDayLater = ldt.plusDays(1);
System.out.println(oneDayLater);
// Alternatively
oneDayLater = ldt.plus(1, ChronoUnit.DAYS);
System.out.println(oneDayLater);
oneDayLater = ldt.plus(Period.ofDays(1));
System.out.println(oneDayLater);
String desiredString = oneDayLater.toString();
System.out.println(desiredString);
}
}
Output:
2020-10-20
2020-10-21
2020-10-21
2020-10-21
2020-10-21
How to switch from the legacy to the modern date-time API?
You can switch from the legacy to the modern date-time API using Date#toInstant on a java-util-date instance. Once you have an Instant, you can easily obtain other date-time types of java.time API. An Instant represents a moment in time and is independent of a time-zone i.e. it represents a date-time in UTC (often displayed as Z which stands for Zulu-time and has a ZoneOffset of +00:00).
Demo:
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;
import java.util.Date;
public class Main {
public static void main(String[] args) {
Date date = new Date();
Instant instant = date.toInstant();
System.out.println(instant);
ZonedDateTime zdt = instant.atZone(ZoneId.of("Asia/Kolkata"));
System.out.println(zdt);
OffsetDateTime odt = instant.atOffset(ZoneOffset.of("+05:30"));
System.out.println(odt);
// Alternatively, using time-zone
odt = instant.atZone(ZoneId.of("Asia/Kolkata")).toOffsetDateTime();
System.out.println(odt);
LocalDateTime ldt = LocalDateTime.ofInstant(instant, ZoneId.of("Asia/Kolkata"));
System.out.println(ldt);
// Alternatively,
ldt = instant.atZone(ZoneId.of("Asia/Kolkata")).toLocalDateTime();
System.out.println(ldt);
}
}
Output:
2022-11-12T12:52:18.016Z
2022-11-12T18:22:18.016+05:30[Asia/Kolkata]
2022-11-12T18:22:18.016+05:30
2022-11-12T18:22:18.016+05:30
2022-11-12T18:22:18.016
2022-11-12T18:22:18.016
Learn more about the modern Date-Time API from Trail: Date Time.

Let's clarify the use case: You want to do calendar arithmetic and start/end with a java.util.Date.
Some approaches:
Convert to string and back with SimpleDateFormat: This is an inefficient solution.
Convert to LocalDate: You would lose any time-of-day information.
Convert to LocalDateTime: This involves more steps and you need to worry about timezone.
Convert to epoch with Date.getTime(): This is efficient but you are calculating with milliseconds.
Consider using java.time.Instant:
Date _now = new Date();
Instant _instant = _now.toInstant().minus(5, ChronoUnit.DAYS);
Date _newDate = Date.from(_instant);

You can do this just in one line.
e.g to add 5 days
Date newDate = Date.from(Date().toInstant().plus(5, ChronoUnit.DAYS));
to subtract 5 days
Date newDate = Date.from(Date().toInstant().minus(5, ChronoUnit.DAYS));

How to get IST time zone in Android

I am new to android application development , I am developing an app that is going to run in india only, I want to get the time of asia/kolkata timezone without using "joda" library
I used the following code but i didn't get expected output
Calendar cal = Calendar.getInstance();
TimeZone tz = cal.getTimeZone();
Log.d("Time zone","="+tz.getDisplayName());
I want the time in hh:mm:ss format

import java.util.Calendar;
import java.util.TimeZone;
public class Main {
public static void main(String[] args) {
Calendar calender = Calendar.getInstance();
calender.setTimeZone(TimeZone.getTimeZone("Asia/Calcutta"));
System.out.println(calender.get(Calendar.HOUR_OF_DAY) + ":" + calender.get(Calendar.MINUTE) + ":" + calender.getActualMinimum(Calendar.SECOND));
}
}
This is a full program that gets the time from the timezone in Asia/Calcutta. It displays hours, minutes and seconds!

You do not speak english, so lets talk Java. ;-)
String format = "hh:mm:ss";
SimpleDateFormat sdf = new SimpleDateFormat(format);
sdf.setTimeZone(TimeZone.getTimeZone("IST"));
System.out.format("%s\n", sdf.format(new Date()));
IST is India Standard Time or UTC/GMT + 5:30 h. I took this from the android API-Documentation mentioned in a comment of Der Golem (+1) and from the following link: http://www.timeanddate.com/time/zone/india/kolkata

How to create the date explicitly in java?

I have tried this code. I got the output but not the right one...
//Iam getting my answer after the following changes below...
package patternsamp;
import java.io.*;
import java.util.*;
public class Mydate
{
static void test()
{
Date da = new Date(5,9,2014,07,00,00);
System.out.println(da.toGMTString());
}
public static void main(String[] args)
{
Mydate.test();
}
}
//I made the changes like this.....
Date da = new Date(114,8,5,12,30,0);
OUTPUT: 5 Sep 2014 07:00:00 GMT
This gives me right output... Thanks for your support friends.....

To get the sep 5 as output, shuold be given as 5-9,
Try using simpledateformat:
SimpleDateFormat sdf = new SimpleDateFormat("dd-M-yyyy hh:mm:ss");
String dateInString = "5-9-2014 07:00:00";
Date date = sdf.parse(dateInString);
System.out.println(date);

Quoting from Java Doc
Date(int year, int month, int date, int hrs, int min, int sec)
`Deprecated. As of JDK version 1.1, replaced by Calendar.set(year + 1900, month, date, hrs, min, sec) or GregorianCalendar(year + 1900, month, date, hrs, min, sec).`
Avoid using Date constructor (to set dates) at all, incase you insist maintain correct order of parameters, your code should look like this:-
package patternsamp;
import java.io.*;
import java.util.*;
public class Mydate
{
static void test()
{
Date da = new Date(114,9,5,07,00,00);
System.out.println(da.toGMTString());
}
public static void main(String[] args)
{
Mydate.test();
}
Note that I am using 114 in the year (and not 2014), since according to doc
A year y is represented by the integer y - 1900.
Hence to represent 2014 , you have to 2014-1900, which is 114.

if your project imported commons-lang.jar
you can get the Date object from String like this:
DateUtils.parseDate("2014-08-20",new String[]{"yyyy-MM-dd"})

Joda-Time
So much easier and sensible to use the Joda-Time library rather than the notoriously troublesome bundled java.util.Date and .Calendar classes. To specify a year, you specify a year (2014 rather than 114). To specify a month, you specify a month (9 means September rather than 8).
DateTime dateTime = new DateTime( 2014, 9, 5, 7, 0, 0, DateTimeZone.UTC );
If you must have a java.util.Date object, convert.
java.util.Date date = dateTime.toDate();

How to get dates of a week (I know week number)?

I know the week number of the year, a week is start from Sunday, then Monday, Tuesday...,Saturday.
Since I know the week number, what's the efficient way to get the dates of the specific week by using Java code??

If you don't want external library, just use calendar.
SimpleDateFormat sdf = new SimpleDateFormat("MM dd yyyy");
Calendar cal = Calendar.getInstance();
cal.set(Calendar.WEEK_OF_YEAR, 23);
cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
System.out.println(sdf.format(cal.getTime()));

Pure Java 8 / java.time solution
Based on this:
final long calendarWeek = 34;
LocalDate desiredDate = LocalDate.now()
.with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, calendarWeek)
.with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY));

You can use the joda time library
int weekNumber = 10;
DateTime weekStartDate = new DateTime().withWeekOfWeekyear(weekNumber);
DateTime weekEndDate = new DateTime().withWeekOfWeekyear(weekNumber + 1);

java.time
The java.util Date-Time API and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern Date-Time API*.
Also, quoted below is a notice from the home page of Joda-Time:
Note that from Java SE 8 onwards, users are asked to migrate to java.time (JSR-310) - a core part of the JDK which replaces this project.
Solution:
The first step is to find the first day of the week and as the second step, we just need to iterate all the seven days starting with this date.
Note that the first day of the week is Locale-dependent e.g. it is Monday in the UK while Sunday in the US. As per the ISO 8601 standards, it is Monday. For comparison, check the US calendar and the UK calendar.
Demo of the first step:
import java.time.LocalDate;
import java.time.Year;
import java.time.temporal.WeekFields;
import java.util.Locale;
public class Main {
public static void main(String[] args) {
// Test
int weekNumber = 34;
System.out.println(getFirstDayOfWeek(weekNumber, Locale.UK));
System.out.println(getFirstDayOfWeek(weekNumber, Locale.US));
}
static LocalDate getFirstDayOfWeek(int weekNumber, Locale locale) {
return LocalDate
.of(Year.now().getValue(), 2, 1)
.with(WeekFields.of(locale).getFirstDayOfWeek())
.with(WeekFields.of(locale).weekOfWeekBasedYear(), weekNumber);
}
}
Output:
2021-08-23
2021-08-15
ONLINE DEMO
Demo of the second step:
import java.time.LocalDate;
import java.time.Year;
import java.time.temporal.WeekFields;
import java.util.List;
import java.util.Locale;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
public class Main {
public static void main(String[] args) {
// Test
getAllDaysOfTheWeek(34, Locale.US).forEach(System.out::println);
}
static LocalDate getFirstDayOfWeek(int weekNumber, Locale locale) {
return LocalDate
.of(Year.now().getValue(), 2, 1)
.with(WeekFields.of(locale).getFirstDayOfWeek())
.with(WeekFields.of(locale).weekOfWeekBasedYear(), weekNumber);
}
static List<LocalDate> getAllDaysOfTheWeek(int weekNumber, Locale locale) {
LocalDate firstDayOfWeek = getFirstDayOfWeek(weekNumber, locale);
return IntStream
.rangeClosed(0, 6)
.mapToObj(i -> firstDayOfWeek.plusDays(i))
.collect(Collectors.toList());
}
}
Output:
2021-08-15
2021-08-16
2021-08-17
2021-08-18
2021-08-19
2021-08-20
2021-08-21
ONLINE DEMO
Learn more about the modern Date-Time API* from Trail: Date Time.
* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.

You did not mention what return type do you exactly need but this code should prove useful to you. sysouts and formatter are just to show you the result.
Calendar cal = Calendar.getInstance();
cal.setTime(new Date());
cal.set(Calendar.WEEK_OF_YEAR, 30);
SimpleDateFormat formatter = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
System.out.println(formatter.format(cal.getTime()));
cal.add(Calendar.DAY_OF_WEEK, 6);
System.out.println(formatter.format(cal.getTime()));

This answer is pretty much same as others. But, here it goes:
int year = 2018;
int week = 27;
int day = 1; //assuming week starts from sunday
Calendar calendar = Calendar.getInstance();
calendar.setWeekDate(year, week, day);
System.out.println(calendar.getTime());

for(int i=1; i<=7; i++) {
if(i <= 3) {
LocalDate desiredDate = LocalDate.now()
.with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, 26)
.with(TemporalAdjusters.previousOrSame(DayOfWeek.of(i)));
System.out.println(desiredDate.format(DateTimeFormatter.ofPattern("dd/MM/yyyy")));
} else {
LocalDate desiredDate = LocalDate.now()
.with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, 26)
.with(TemporalAdjusters.nextOrSame(DayOfWeek.of(i)));
System.out.println(desiredDate.format(DateTimeFormatter.ofPattern("dd/MM/yyyy")));
}
}
This snippet provides dates starting from monday to sunday based on the given week number
output:
28/06/2021
29/06/2021
30/06/2021
01/07/2021
02/07/2021
03/07/2021
04/07/2021
To verify check https://www.epochconverter.com/weeks/2021

How to get previous date in java

I have a String Object in format yyyyMMdd.Is there a simple way to get a String with previous date in the same format?
Thanks

I would rewrite these answers a bit.
You can use
DateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
// Get a Date object from the date string
Date myDate = dateFormat.parse(dateString);
// this calculation may skip a day (Standard-to-Daylight switch)...
//oneDayBefore = new Date(myDate.getTime() - (24 * 3600000));
// if the Date->time xform always places the time as YYYYMMDD 00:00:00
// this will be safer.
oneDayBefore = new Date(myDate.getTime() - 2);
String result = dateFormat.format(oneDayBefore);
To get the same results as those that are being computed by using Calendar.

Here is how to do it without Joda Time:
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class Main {
public static String previousDateString(String dateString)
throws ParseException {
// Create a date formatter using your format string
DateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
// Parse the given date string into a Date object.
// Note: This can throw a ParseException.
Date myDate = dateFormat.parse(dateString);
// Use the Calendar class to subtract one day
Calendar calendar = Calendar.getInstance();
calendar.setTime(myDate);
calendar.add(Calendar.DAY_OF_YEAR, -1);
// Use the date formatter to produce a formatted date string
Date previousDate = calendar.getTime();
String result = dateFormat.format(previousDate);
return result;
}
public static void main(String[] args) {
String dateString = "20100316";
try {
// This will print 20100315
System.out.println(previousDateString(dateString));
} catch (ParseException e) {
System.out.println("Invalid date string");
e.printStackTrace();
}
}
}

You can use:
Calendar cal = Calendar.getInstance();
//subtracting a day
cal.add(Calendar.DATE, -1);
SimpleDateFormat s = new SimpleDateFormat("yyyyMMdd");
String result = s.format(new Date(cal.getTimeInMillis()));

It's much harder than it should be in Java without library support.
You can parse the given String into a Date object using an instance of the SimpleDateFormat class.
Then you can use Calendar's add() to subtract one day.
Then you can use SimpleDateFormat's format() to get the formatted date as a String.
The Joda Time library a much easier API.

This is an old question, and most existing answers pre-date Java 8. Hence, adding this answer for Java 8+ users.
Java 8 introduced new APIs for Date and Time to replace poorly designed, and difficult to use java.util.Date and java.util.Calendar classes.
To deal with dates without time zones, LocalDate class can be used.
String dateString = "20200301";
// BASIC_ISO_DATE is "YYYYMMDD"
// See below link to docs for details
LocalDate date = LocalDate.parse(dateString, DateTimeFormatter.BASIC_ISO_DATE);
// get date for previous day
LocalDate previousDate = date.minusDays(1);
System.out.println(previousDate.format(DateTimeFormatter.BASIC_ISO_DATE));
// prints 20200229
Docs:
DateTimeFormatter.BASIC_ISO_DATE
LocalDate

use SimpleDateFormat to parse the String to Date, then subtract one day. after that convert the date to String again.

HI,
I want to get 20 days previous, to current date,
Calendar cal = Calendar.getInstance();
Calendar xdate = (Calendar)cal.clone();
xdate.set(Calendar.DAY_OF_YEAR, - 20);
System.out.println(" Current Time "+ cal.getTime().toString());
System.out.println(" X Time "+ xdate.getTime().toString());
I had some UN Expected result, When i tried on Jan 11th,
Current Time Tue Jan 11 12:32:16 IST 2011
X Time Sat Dec 11 12:32:16 IST 2010
Calendar cal = Calendar.getInstance();
Calendar xdate = (Calendar)cal.clone();
xdate.set(Calendar.DAY_OF_YEAR,cal.getTime().getDate() - 20 );
System.out.println(" Current Time "+ cal.getTime().toString());
System.out.println(" X Time "+ xdate.getTime().toString());
This code solved my Problem.

If you are willing to use the 3rd-party utility, Joda-Time, here is some example code using Joda-Time 2.3 on Java 7. Takes just two lines.
String dateAsString = "20130101";
org.joda.time.LocalDate someDay = org.joda.time.LocalDate.parse(dateAsString, org.joda.time.format.DateTimeFormat.forPattern("yyyymmdd"));
org.joda.time.LocalDate dayBefore = someDay.minusDays(1);
See the results:
System.out.println("someDay: " + someDay );
System.out.println("dayBefore: " + dayBefore );
When run:
someDay: 2013-01-01
dayBefore: 2012-12-31
This code assumes you have no time zone. Lacking a time zone is rarely a good thing, but if that's your case, that code may work for you. If you do have a time zone, use a DateTime object instead of LocalDate.
About that example code and about Joda-Time…
// © 2013 Basil Bourque. This source code may be used freely forever by anyone taking full responsibility for doing so.
// Joda-Time - The popular alternative to Sun/Oracle's notoriously bad date, time, and calendar classes bundled with Java 7 and earlier.
// http://www.joda.org/joda-time/
// Joda-Time will become outmoded by the JSR 310 Date and Time API introduced in Java 8.
// JSR 310 was inspired by Joda-Time but is not directly based on it.
// http://jcp.org/en/jsr/detail?id=310
// By default, Joda-Time produces strings in the standard ISO 8601 format.
// https://en.wikipedia.org/wiki/ISO_8601

you can create a generic method which takes
- Date (String) (current date or from date),
- Format (String) (your desired fromat) and
- Days (number of days before(-ve value) or after(+ve value))
as input and return your desired date in required format.
following method can resolve this problem.
public String getRequiredDate(String date , String format ,int days){
try{
final Calendar cal = Calendar.getInstance();
cal.setTime(new SimpleDateFormat(format).parse(date));
cal.add(Calendar.DATE, days);
SimpleDateFormat sdf = new SimpleDateFormat(format);
date = sdf.format(cal.getTime());
}
catch(Exception ex){
logger.error(ex.getMessage(), ex);
}
return date;
}
}

In Java 8 we can use directly for this purpose
LocalDate todayDate = LocalDate.now();
By default it provide the format of 2021-06-07, with the help of formater we can change this also
LocalDate previousDate = todayDate.minusDays(5);

Calendar cal2 = Calendar.getInstance();
cal2.add(Calendar.YEAR, -1);
Date dt2 = new Date(cal2.getTimeInMillis());
System.out.println(dt2);