I'm struggling to find the error in my code here. paytotal is coming out 0 when it should have a number.
firstDayOfPaycheck is the date Oct. 23rd 2020.
lastDayOfPaycheck is the date Nov. 6 2020.
My Simple date format sdf is "MMM dd, yyyy".
string dateInQuestion passed into runPayroll is "Oct. 31, 2020" which came originally from the same sdf as above.
I'm new to java and haven't dealt with manipulating the calendar like this. It feels like the code below should work.
private void runPayroll(String dateInQuestion, long payForTask){
c.setTime(firstDayOfPaycheck);
//loop through days of paycheck. number from time.compareTo(time2) is negative while time is before time2
while(c.getTime().compareTo(lastDayOfPaycheck)<=0){
if(dateInQuestion != null) {
Date questionDate = sdf.parse(dateInQuestion, new ParsePosition(0));
if (c.getTime().compareTo(questionDate) == 0) {
payTotal += payForTask;
}
}
c.add(Calendar.DAY_OF_YEAR, 1);
}
} //ran inside the query to get the total pay
private void buildPayrollDash(){
String strPayrollAmt = "$" + payTotal;
String startDate = sdf.format(firstDayOfPaycheck);
String trimmedStart = startDate.split(",")[0]; //cuts out the year in the date
String endDate = sdf.format(lastDayOfPaycheck);
String trimmedEnd = endDate.split(",")[0];
int holdBack = sharedPreferences.getInt("payroll holdback", 7);
c.setTime(lastDayOfPaycheck);
c.add(Calendar.DAY_OF_YEAR, holdBack);
String payDate = sdf.format(c.getTime());
String trimmedPaydate = payDate.split(",")[0];
tvPayrollTimefame.setText("Pay from " + trimmedStart + " - " + trimmedEnd);
tvPayrollAmount.setText(strPayrollAmt + " due " + trimmedPaydate);
I'm struggling to find the error in my code here.
You are using terrible date-time classes that were supplanted years ago by the modern java.time classes. Never use Date, Calendar, GregorianCalendar, or their relatives.
firstDayOfPaycheck is the date Oct. 23rd 2020.
Use LocalDate to represent a date without time-of-day and without time zone.
LocalDate firstDayOfPayPeriod = LocalDate.of( 2020 , Month.OCTOBER , 23 ) ;
lastDayOfPaycheck is the date Nov. 6 2020.
You'll find date-time handling much easier if you define your spans-of-time using the Half-Open approach. The beginning is inclusive while the ending is exclusive. So instead of focusing on the last day of the pay period, focus on the first day of the following period.
LocalDate firstDayOfSuccessivePayPeriod = LocalDate.of( 2020 , 11 , 7 ) ;
Tip: You can represent the date range of the pay period as a LocalDateRange object if you add the ThreeTen-Extra library to your Java project.
My Simple date format sdf is "MMM dd, yyyy".
You should not be mixing business logic with localization code. Custom formatting of date-times should only be done for presentation to the user.
When exchanging date-time values textually as data, use the standard ISO 8601 formats. For a date-only value, the standard format is YYYY-MM-DD. The java.time use ISO 8601 formats by default, so no need to specify any formatting pattern.
string dateInQuestion passed into runPayroll is "Oct. 31, 2020" which came originally from the same sdf as above.
LocalDate dateInQuestion = LocalDate.parse( "2020-10-31" ) ;
If you must accommodate an input of formatted date string rather than standard ISO 8601 format, use DateTimeFormatter. This has been covered many many times already on Stack Overflow, so search for more info.
And rather than check for valid data later, check your inputs early in your code. “Fail fast” is the saying.
try
{
LocalDate dateInQuestion = LocalDate.parse( "2020-10-31" );
}
catch ( DateTimeParseException e )
{
// … Handle faulty input.
e.printStackTrace();
}
I'm new to java and haven't dealt with manipulating the calendar like this. It feels like the code below should work.
Your code will be much simpler when using java.time. For one thing, the java.time classes offer convenient isBefore, isAfter, and isEqual methods, so no need for clumsy compareTo calls.
LocalDate firstDayOfPayPeriod = LocalDate.of( 2020 , Month.OCTOBER , 23 );
LocalDate firstDayOfSuccessivePayPeriod = LocalDate.of( 2020 , 11 , 7 );
String input = "2020-10-31";
LocalDate dateInQuestion = null;
try
{
dateInQuestion = LocalDate.parse( input );
}
catch ( DateTimeParseException e )
{
// Handle faulty input.
e.printStackTrace();
}
// Validate dates.
Objects.requireNonNull( firstDayOfPayPeriod );
Objects.requireNonNull( firstDayOfSuccessivePayPeriod );
Objects.requireNonNull( dateInQuestion );
if ( ! firstDayOfPayPeriod.isBefore( firstDayOfSuccessivePayPeriod ) )
{
throw new IllegalStateException( "…" );
}
if ( dateInQuestion.isBefore( firstDayOfPayPeriod ) )
{
throw new IllegalStateException( "…" );
}
if ( ! dateInQuestion.isBefore( firstDayOfSuccessivePayPeriod ) )
{
throw new IllegalStateException( "…" );
}
long payPerDay = 100;
long partialPay = 0;
LocalDate localDate = firstDayOfPayPeriod;
while ( localDate.isBefore( firstDayOfSuccessivePayPeriod ) )
{
if ( localDate.isBefore( dateInQuestion ) )
{
partialPay = ( partialPay + payPerDay );
}
// Set up the next loop.
// Notice that java.time uses immutable objects. So we generate a new object based on another’s values rather than alter (mutate) the original.
localDate = localDate.plusDays( 1 ); // Increment to next date.
}
System.out.println( "Partial pay earned from firstDayOfPayPeriod " + firstDayOfPayPeriod + " to dateInQuestion " + dateInQuestion + " is " + partialPay );
See this code run live on IdeOne.com.
Partial pay earned from firstDayOfPayPeriod 2020-10-23 to dateInQuestion 2020-10-31 is 800
With more experience in programming Java, you may want to do this kind of work using streams. See LocalDate::datesUntil.
By the way, if you want to skip weekends, add something like this:
Set< DayOfWeek > weekend = EnumSet.of( DayOfWeek.SATURDAY , DayOfWeek.SUNDAY ) ;
…
if ( weekend.contains( localDate.getDayOfWeek() ) ) { … }
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. Hibernate 5 & JPA 2.2 support java.time.
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 brought 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 (26+) bundle implementations of the java.time classes.
For earlier Android (<26), a process known as API desugaring brings a subset of the java.time functionality not originally built into Android.
If the desugaring does not offer what you need, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above) to Android. See How to use ThreeTenABP….
Basically I have a date stored as text in this format: 16/09/2014 in SQLite Browser. I wonder is there any way to get the date after one day, one week, one month and one year of each records in the database using Java.
I retrieved and display the date retrieved from database in a listview:
viewHolder.txt_ddate.setText("Next Payment On: "
+ _recurlist.get(position).getRecurringStartDate().trim());
So I was thinking to use Java technique to get the dates I mentioned above. I have researched on this and found Documentation but I not sure how to implement it into my problem.
Any guides? Thanks in advance.
Use a Calendar object like in your example, which provides the add method.
String dateAsString = "16/09/2014";
DateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
Calendar c = Calendar.getInstance();
c.setTime(formatter.parse(dateAsString));
c.add(Calendar.DAY_OF_MONTH, 1);
System.out.println("After one day: " + formatter.format(c.getTimeInMillis()));
c.add(Calendar.DAY_OF_MONTH, -1);
c.add(Calendar.WEEK_OF_YEAR, 1);
System.out.println("After one week: " + formatter.format(c.getTimeInMillis()));
c.add(Calendar.WEEK_OF_YEAR, -1);
c.add(Calendar.MONTH, 1);
System.out.println("After one month: " + formatter.format(c.getTimeInMillis()));
c.add(Calendar.MONTH, -1);
c.add(Calendar.YEAR, 1);
System.out.println("After one year: " + formatter.format(c.getTimeInMillis()));
c.add(Calendar.YEAR, -1);
Output:
After one day: 17/09/2014
After one week: 23/09/2014
After one month: 16/10/2014
After one year: 16/09/2015
With Joda-time:
DateTimeFormatter formatter = DateTimeFormat.forPattern("dd/MM/yyyy");
LocalDate date = LocalDate.parse("16/09/2014", formatter);
System.out.println(date.toString(formatter));
System.out.println(date.plusDays(1).toString(formatter));
System.out.println(date.plusWeeks(1).toString(formatter));
System.out.println(date.plusMonths(1).toString(formatter));
System.out.println(date.plusYears(1).toString(formatter));
Output:
16/09/2014
17/09/2014
23/09/2014
16/10/2014
16/09/2015
Use Calendar api of Java/Android as follow:
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
Date date;
try {
date = sdf.parse(dateStr);
Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.add(Calendar.DAY_OF_MONTH, 1); //add one day to your date
cal.add(Calendar.MONTH, 1); //add 1 month to your date
cal.add(Calendar.YEAR, 1); //add 1 year to current date
System.out.println(sdf.format(cal.getTimeInMillis()));
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Here is the example:
String strDate = "16/09/2014";
int noOfDays = 1;
SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
Date date = formatter.parse(strDate);
Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.add(Calendar.DATE, noOfDays);
tl;dr
LocalDate.parse(
"16/09/2014" ,
DateTimeFormatter.ofPattern( "dd/MM/uuuu" )
)
.plusDays( 1 )
.format( DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) )
Details
Tip: Use date-time data types for date-time values. You should be using a date-oriented type to define your column in your database to store a date value rather than as text.
Tip # 2: When you do serialize a date value to text, use the standard ISO 8601 formats. These are sensible, practical, and sort chronologically when alphabetical.
Use the java.time classes rather than the troublesome old date-time classes that are now legacy. For Android, see bullets below.
DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) ;
LocalDate ld = LocalDate.parse( "16/09/2014" , f ) ;
LocalDate dayAfter = ld.plusDays( 1 ) ;
LocalDate weekAfter = ld.plusWeeks( 1 ) ;
LocalDate monthAfter = ld.plusMonths( 1 ) ;
LocalDate yearAfter = ld.plusYears( 1 ) ;
To generate a string in standard format, simply call toString.
String output = dayAfter.toString() ; // YYYY-MM-DD standard format.
2014-09-17
For other formats, use a DateTimeFormatter as seen above.
String output = dayAfter.format( f ) ;
17/09/2014
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Where to obtain the java.time classes?
Java SE 8, Java SE 9, and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
See How to use ThreeTenABP….
I am taking in two dates as command line arguments and want to check if the first one is after the second date. the format of the date it "dd/MM/yyy".
Example: java dateCheck 01/01/2014 15/03/2014
also i will need to check if a third date hardcoded into the program is before the second date.
try {
System.out.println("Enter first date : (dd/MM/yyyy)");
BufferedReader bufferRead = new BufferedReader(new InputStreamReader(System.in));
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
Date date1 = sdf.parse(bufferRead.readLine());
System.out.println("Enter second date : (dd/MM/yyyy)");
Date date2 = sdf.parse(bufferRead.readLine());
System.out.println(date1 + "\n" + date2);
if (date1.after(date2)) {
System.out.println("Date1 is after Date2");
} else {
System.out.println("Date2 is after Date1");
}
} catch (IOException e) {
e.printStackTrace();
}
To compare two dates :
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyy");
Date firstDate = sdf.parse("01/01/2014");
Date secondDate = sdf.parse("15/03/2014");
if(firstDate.before(secondDate)){
System.out.println("firstDate < secondDate");
}
else if(firstDate.after(secondDate)){
System.out.println("firstDate > secondDate");
}
else if(firstDate.equals(secondDate)){
System.out.println("firstDate = secondDate");
}
tl;dr
LocalDate ld1 = LocalDate.parse( "01/01/2014" , DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) ) ;
LocalDate ld2 = LocalDate.parse( "15/03/2014" , DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) ) ;
LocalDate ld3 = LocalDate.of( 2014 , Month.JULY , 1 ) ;
Boolean isFirstDateBeforeSecondDate = ld1.isBefore( ld2 ) ;
Boolean isThirdDateBeforeSecondDate = ld3.isBefore( ld2 ) ;
Boolean result = ( isFirstDateBeforeSecondDate && isThirdDateBeforeSecondDate ) ;
return result ;
Using java.time
The modern approach uses the java.time classes rather than the troublesome old legacy date-time classes (Date, Calendar, etc.).
The LocalDate class represents a date-only value without time-of-day and without time zone.
Define a formatting pattern to match your input strings using the DateTimeFormatter class.
String input = "15/03/2014" ;
DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd/MM/uuuu" );
LocalDate ld = LocalDate.parse( input , f );
ld.toString(): 2014-03-15
To specify a fixed date, pass year, month, and dayOfMonth. For the month, you may specify a number, sanely numbered 1-12 for January-December (unlike the crazy 0-11 in the legacy classes!). Or you may choose to use the Month enum objects.
LocalDate firstOf2014 = LocalDate.of( 2014 , Month.JANUARY , 1 );
Compare using isBefore, isEqual, or isAfter methods.
Boolean isInputDateBeforeFixedDate = ld.isBefore( firstOf2014 ) ;
isInputDateBeforeFixedDate.toString(): false
ISO 8601
If possible, replace your particular date string format with the standard ISO 8601 format. That standard defines many useful practical unambiguous string formats for date-time values.
The java.time classes use the standard formats by default when parsing/generating strings. You can see examples in the code above. For a date-only value, the standard format is YYYY-MM-DD.
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Where to obtain the java.time classes?
Java SE 8, Java SE 9, and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
See How to use ThreeTenABP….
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.
Use SimpleDateFormat to convert a string to Date.
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
Date date1 = sdf.parse("01/01/2017");
Date has before and after methods and can be compared to each other as follows:
if(todayDate.after(historyDate) && todayDate.before(futureDate)) {
// In between
}
For an inclusive comparison:
if(!historyDate.after(todayDate) && !futureDate.before(todayDate)) {
/* historyDate <= todayDate <= futureDate */
}
To read a date and check before:
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyy");
try {
Date date1 = sdf.parse(string1);
Date date2 = sdf.parse(string2);
if(date1.before(date2)) {
// do something
}
} catch(ParseException e) {
// the format of the read dates is not the expected one
}
I recently came across a task where i have to get all Fridays in a date range. I wrote a small piece of code and was surprised see some strange behaviour.
Below is my code:
public class Friday {
public static void main(String[]args){
String start = "01/01/2009";
String end = "12/09/2013";
String[] startTokens = start.split("/");
String[] endTokens = end.split("/");
Calendar startCal = new GregorianCalendar(Integer.parseInt(startTokens[2]),Integer.parseInt(startTokens[1])-1,Integer.parseInt(startTokens[0]));
Calendar endCal = new GregorianCalendar(Integer.parseInt(endTokens[2]),Integer.parseInt(endTokens[1])-1, Integer.parseInt(endTokens[0]));
int startYear = Integer.parseInt(startTokens[2]);
int endYear = Integer.parseInt(endTokens[2]);
int startWeek = startCal.get(Calendar.WEEK_OF_YEAR);
int endWeek = endCal.get(Calendar.WEEK_OF_YEAR);
Calendar cal = new GregorianCalendar();
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);
// cal.setMinimalDaysInFirstWeek(7);
ArrayList<String> main = new ArrayList<String>();
while(startYear <= endYear ){
cal.set(Calendar.YEAR, startYear);
System.out.println(cal.getMinimalDaysInFirstWeek());
if(startYear == endYear){
main.addAll(getFridays(startWeek, endWeek, cal));
}
else{
main.addAll(getFridays(startWeek, 52, cal));
startWeek = 1;
}
startYear =startYear +1;
}
for(String s: main){
System.err.println(s);
}
}
public static ArrayList<String> getFridays(int startWeek, int endWeek, Calendar cal){
ArrayList<String> fridays = new ArrayList<String>();
while(startWeek <= endWeek){
cal.set(Calendar.WEEK_OF_YEAR, startWeek);
fridays.add(cal.getTime().toString());
startWeek = startWeek+1;
}
return fridays;
}
}
Now when I ran the code i noticed that Fridays of 2011 are missing. After some debugging and online browsing i figured that Calendar.WEEK_OF_YEAR is locale specific and I have to use setMinimalDaysInFirstWeek(7) to fix it.
So uncommented the related line in the above code.
From what I understood now first week of year should start from full week of year.
For example Jan 1 2010 is friday. But it should not show up in results as i configured it to treat that week begins from Jan 3rd. But Now i still see the Jan 1 as friday
I am very much confused. Can some one explain why it is happening?
These Stackoverflow articles helped me a bit:
Why dec 31 2010 returns 1 as week of year?
Understanding java.util.Calendar WEEK_OF_YEAR
Here is an easier method, using the wonderful http://www.joda.org/joda-time/ library:
String start = "01/01/2009";
String end = "12/09/2013";
DateTimeFormatter pattern = DateTimeFormat.forPattern("dd/MM/yyyy");
DateTime startDate = pattern.parseDateTime(start);
DateTime endDate = pattern.parseDateTime(end);
List<DateTime> fridays = new ArrayList<>();
while (startDate.isBefore(endDate)){
if ( startDate.getDayOfWeek() == DateTimeConstants.FRIDAY ){
fridays.add(startDate);
}
startDate = startDate.plusDays(1);
}
at the end of this, you'd have the fridays in the fridays array. Simple?
Or if you want to speed things up, once you have gotten a friday, you can switch from using days, to using weeks:
String start = "01/01/2009";
String end = "12/09/2013";
DateTimeFormatter pattern = DateTimeFormat.forPattern("dd/MM/yyyy");
DateTime startDate = pattern.parseDateTime(start);
DateTime endDate = pattern.parseDateTime(end);
List<DateTime> fridays = new ArrayList<>();
boolean reachedAFriday = false;
while (startDate.isBefore(endDate)){
if ( startDate.getDayOfWeek() == DateTimeConstants.FRIDAY ){
fridays.add(startDate);
reachedAFriday = true;
}
if ( reachedAFriday ){
startDate = startDate.plusWeeks(1);
} else {
startDate = startDate.plusDays(1);
}
}
First off, I would not bother with weeks. Set the Calendar to the beginning of the range, and figure out which DOW it is, then increment to get to the next Friday, then simply loop adding 7 days until you are at the end of the range.
Actually, since you are always only going forward, should be something like:
int daysToAdd = FridayDOW - currentDOW;
if (daysToAdd < 0) daysToAdd += 7;
Date startDate = currentDate.add(Calendar.DAYS, daysToAdd);
Yeah, like that.
Ok, actually, for kicks, here it is in Java 8:
#Test
public void canFindAllFridaysInRange(){
start = LocalDate.of(2013, 5, 10);
end = LocalDate.of(2013, 8,30);
DayOfWeek dowOfStart = start.getDayOfWeek();
int difference = DayOfWeek.FRIDAY.getValue() - dowOfStart.getValue();
if (difference < 0) difference += 7;
List<LocalDate> fridaysInRange = new ArrayList<LocalDate>();
LocalDate currentFriday = start.plusDays(difference);
do {
fridaysInRange.add(currentFriday);
currentFriday = currentFriday.plusDays(7);
} while (currentFriday.isBefore(end));
System.out.println("Fridays in range: " + fridaysInRange);
}
Got to love the new date classes!! Of course a lambda would condense this further.
tl;dr
someLocalDate.with( // Date-only value without time-of-day and without time zone, represented by `LocalDate` class.
TemporalAdjusters.nextOrSame ( DayOfWeek.FRIDAY ) ) // Moving from one `LocalDate` object to another, to find the next Friday unless the starting date is already a Friday.
) // Return a `LocalDate` object.
java.time
The other Answers are outdated. The old java.util.Date/.Calendar classes have been supplanted in Java 8 and later by the new java.time framework. Joda-Time library is excellent, continues to be maintained, and even inspired java.time. But the Joda-Time team recommends moving on to java.time as soon as is convenient.
LocalDate
The java.time classes include LocalDate for a date-only value without time-of-day nor time zone. See Tutorial.
First parse your input strings to get LocalDate objects.
String inputStart = "01/01/2009";
String inputStop = "12/09/2013"; // 258 Fridays.
// String inputStop = "01/01/2009"; // 0 Friday.
// String inputStop = "01/02/2009"; // 1 Friday.
DateTimeFormatter formatter = DateTimeFormatter.ofPattern ( "MM/dd/yyyy" );
LocalDate start = LocalDate.parse ( inputStart , formatter );
LocalDate stop = LocalDate.parse ( inputStop , formatter );
In your own code, try-catch for exception in case of bad inputs. And verify that stop is indeed the same or later than start.
TemporalAdjusters
The java.time framework includes the TemporalAdjuster interface as a way of shifting date-time values. For example, getting the next or same Friday for any particular date. On your starting date, call with(TemporalAdjuster adjuster) and pass a pre-defined implementation of a TemporalAdjuster from the class TemporalAdjusters (note the plural s). See Tutorial.
List<LocalDate> fridays = new ArrayList<> (); // Collect each Friday found.
LocalDate nextOrSameFriday = start.with ( TemporalAdjusters.nextOrSame ( DayOfWeek.FRIDAY ) );
// Loop while we have a friday in hand (non-null) AND that friday is not after our stop date (isBefore or isEqual the stop date).
while ( ( null != nextOrSameFriday ) & ( ! nextOrSameFriday.isAfter ( stop ) ) ) {
fridays.add ( nextOrSameFriday ); // Remember this friday.
nextOrSameFriday = nextOrSameFriday.plusWeeks ( 1 ); // Move to the next Friday, setting up for next iteration of this loop.
}
Dump to console.
System.out.println ( "From: " + start + " to: " + stop + " are " + fridays.size () + " Fridays: " + fridays );
From: 2009-01-01 to: 2013-12-09 are 258 Fridays: [2009-01-02, 2009-01-09, 2009-01-16, 2009-01-23, 2009-01-30, 2009-02-06, 2009-02-13, 2009-02-20, 2009-02-27, 2009-03-06, 2009-03-13, 2009-03-20, 2009-03-27, 2009-04-03, 2009-04-10, 2009-04-17, 2009-04-24, 2009-05-01, 2009-05-08, 2009-05-15, 2009-05-22, 2009-05-29, 2009-06-05, 2009-06-12, 2009-06-19, 2009-06-26, 2009-07-03, 2009-07-10, 2009-07-17, 2009-07-24, 2009-07-31, 2009-08-07, 2009-08-14, 2009-08-21, 2009-08-28, 2009-09-04, 2009-09-11, 2009-09-18, 2009-09-25, 2009-10-02, 2009-10-09, 2009-10-16, 2009-10-23, 2009-10-30, 2009-11-06, 2009-11-13, 2009-11-20, 2009-11-27, 2009-12-04, 2009-12-11, 2009-12-18, 2009-12-25, 2010-01-01, 2010-01-08, 2010-01-15, 2010-01-22, 2010-01-29, 2010-02-05, 2010-02-12, 2010-02-19, 2010-02-26, 2010-03-05, 2010-03-12, 2010-03-19, 2010-03-26, 2010-04-02, 2010-04-09, 2010-04-16, 2010-04-23, 2010-04-30, 2010-05-07, 2010-05-14, 2010-05-21, 2010-05-28, 2010-06-04, 2010-06-11, 2010-06-18, 2010-06-25, 2010-07-02, 2010-07-09, 2010-07-16, 2010-07-23, 2010-07-30, 2010-08-06, 2010-08-13, 2010-08-20, 2010-08-27, 2010-09-03, 2010-09-10, 2010-09-17, 2010-09-24, 2010-10-01, 2010-10-08, 2010-10-15, 2010-10-22, 2010-10-29, 2010-11-05, 2010-11-12, 2010-11-19, 2010-11-26, 2010-12-03, 2010-12-10, 2010-12-17, 2010-12-24, 2010-12-31, 2011-01-07, 2011-01-14, 2011-01-21, 2011-01-28, 2011-02-04, 2011-02-11, 2011-02-18, 2011-02-25, 2011-03-04, 2011-03-11, 2011-03-18, 2011-03-25, 2011-04-01, 2011-04-08, 2011-04-15, 2011-04-22, 2011-04-29, 2011-05-06, 2011-05-13, 2011-05-20, 2011-05-27, 2011-06-03, 2011-06-10, 2011-06-17, 2011-06-24, 2011-07-01, 2011-07-08, 2011-07-15, 2011-07-22, 2011-07-29, 2011-08-05, 2011-08-12, 2011-08-19, 2011-08-26, 2011-09-02, 2011-09-09, 2011-09-16, 2011-09-23, 2011-09-30, 2011-10-07, 2011-10-14, 2011-10-21, 2011-10-28, 2011-11-04, 2011-11-11, 2011-11-18, 2011-11-25, 2011-12-02, 2011-12-09, 2011-12-16, 2011-12-23, 2011-12-30, 2012-01-06, 2012-01-13, 2012-01-20, 2012-01-27, 2012-02-03, 2012-02-10, 2012-02-17, 2012-02-24, 2012-03-02, 2012-03-09, 2012-03-16, 2012-03-23, 2012-03-30, 2012-04-06, 2012-04-13, 2012-04-20, 2012-04-27, 2012-05-04, 2012-05-11, 2012-05-18, 2012-05-25, 2012-06-01, 2012-06-08, 2012-06-15, 2012-06-22, 2012-06-29, 2012-07-06, 2012-07-13, 2012-07-20, 2012-07-27, 2012-08-03, 2012-08-10, 2012-08-17, 2012-08-24, 2012-08-31, 2012-09-07, 2012-09-14, 2012-09-21, 2012-09-28, 2012-10-05, 2012-10-12, 2012-10-19, 2012-10-26, 2012-11-02, 2012-11-09, 2012-11-16, 2012-11-23, 2012-11-30, 2012-12-07, 2012-12-14, 2012-12-21, 2012-12-28, 2013-01-04, 2013-01-11, 2013-01-18, 2013-01-25, 2013-02-01, 2013-02-08, 2013-02-15, 2013-02-22, 2013-03-01, 2013-03-08, 2013-03-15, 2013-03-22, 2013-03-29, 2013-04-05, 2013-04-12, 2013-04-19, 2013-04-26, 2013-05-03, 2013-05-10, 2013-05-17, 2013-05-24, 2013-05-31, 2013-06-07, 2013-06-14, 2013-06-21, 2013-06-28, 2013-07-05, 2013-07-12, 2013-07-19, 2013-07-26, 2013-08-02, 2013-08-09, 2013-08-16, 2013-08-23, 2013-08-30, 2013-09-06, 2013-09-13, 2013-09-20, 2013-09-27, 2013-10-04, 2013-10-11, 2013-10-18, 2013-10-25, 2013-11-01, 2013-11-08, 2013-11-15, 2013-11-22, 2013-11-29, 2013-12-06]
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Using a JDBC driver compliant with JDBC 4.2 or later, you may exchange java.time objects directly with your database. No need for strings nor java.sql.* classes.
Where to obtain the java.time classes?
Java SE 8, Java SE 9, and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
Later versions of Android bundle implementations of the java.time classes.
For earlier Android, 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.
This code will print all dates having Friday.
public class Friday {
public static void main(String[] args) throws ParseException {
String start = "01/01/2013";
String end = "12/01/2013";
SimpleDateFormat dateFormat=new SimpleDateFormat("dd/MM/yyyy");
Calendar scal=Calendar.getInstance();
scal.setTime(dateFormat.parse(start));
Calendar ecal=Calendar.getInstance();
ecal.setTime(dateFormat.parse(end));
ArrayList<Date> fridayDates=new ArrayList<>();
while(!scal.equals(ecal)){
scal.add(Calendar.DATE, 1);
if(scal.get(Calendar.DAY_OF_WEEK)==Calendar.FRIDAY){
fridayDates.add(scal.getTime());
}
}
System.out.println(fridayDates);
}
}
Here a solution based on new stream-features of Java-8 and using my library Time4J (v4.18 or later):
String start = "01/01/2009";
String end = "12/09/2013";
ChronoFormatter<PlainDate> f =
ChronoFormatter.ofDatePattern("dd/MM/yyyy", PatternType.CLDR, Locale.ROOT);
PlainDate startDate =
f.parse(start).with(PlainDate.DAY_OF_WEEK.setToNextOrSame(Weekday.FRIDAY));
PlainDate endDate = f.parse(end);
Stream<PlainDate> fridays =
DateInterval.stream(Duration.of(1, CalendarUnit.WEEKS), startDate, endDate);
fridays.forEachOrdered(System.out::println);
// output
2009-01-02
2009-01-09
...
2013-08-30
2013-09-06
// other example: list of fridays in ISO-8601-format
List<String> result =
DateInterval.between(startDate, endDate)
.stream(Duration.of(1, CalendarUnit.WEEKS))
.map((date) -> date.toString()) // or maybe use dd/MM/yyyy => f.format(date)
.collect(Collectors.toList());
By the way, Java-9 will offer a similar solution (but with exclusive end date boundary), see also this enhancement-issue.
with Lamma Date :
List<Date> fridays = Dates.from(2015, 12, 1).to(2016, 1, 1).byWeek().on(DayOfWeek.FRIDAY).build();
for (Date friday: fridays) {
System.out.println(friday);
}
public static List<Date> getWeekNumberList(Date currentMonthDate) {
List<Date> dates = new ArrayList<>(10);
Calendar startCalendar = Calendar.getInstance();
startCalendar.setTime(currentMonthDate);
startCalendar.set(Calendar.DAY_OF_MONTH,
startCalendar.getActualMinimum(Calendar.DAY_OF_MONTH));
Calendar endCalendar = Calendar.getInstance();
endCalendar.setTime(currentMonthDate);
endCalendar.set(Calendar.DAY_OF_MONTH,
endCalendar.getActualMaximum(Calendar.DAY_OF_MONTH));
Date enddate = endCalendar.getTime();
while (startCalendar.getTime().before(enddate)) {
if (startCalendar.get(Calendar.DAY_OF_WEEK) == Calendar.MONDAY) {
Date result = startCalendar.getTime();
dates.add(result);
startCalendar.add(Calendar.WEEK_OF_MONTH, 1);
} else {
startCalendar.add(Calendar.DAY_OF_MONTH, 1);
}
}
return dates;
}
Using Java 8+
LocalDate s= LocalDate.now();
LocalDate e= LocalDate.now().plusMonths(5);
List<LocalDate> dates2 = s.with(TemporalAdjusters.next(DayOfWeek.FRIDAY)).datesUntil(e, Period.ofWeeks(1)).collect(Collectors.toList());
dates2.forEach(x->System.out.println(x));
I am having a bit of trouble parsing a string date to a Date object. I use a DateFormat to parse the string, and when I print the value of the date, it gives me what I expect.
But when I try get the day, the month or the year it gives me the wrong values. For instance, the year is 2011, but when I do .getYear() it gives me 111. I have no idea why this is happening. Here is the relevant code segment:
Date dateFrom = null;
String gDFString = g.getDateFrom();
System.out.println(gDFString);
DateFormat df = new SimpleDateFormat("dd/MM/yyyy");
try {
dateFrom = df.parse("04/12/2011");
System.out.println(dateFrom);
System.out.println(dateFrom.getYear());
} catch (ParseException e) {
e.printStackTrace();
}
When I out print dateFrom, I get Sun Dec 04 00:00:00 GMT 2011, which is what you would expect. But printing .getYear() returns 111.
I need to be able to get the day, month and year of the date for a time series graph.
Those methods have been deprecated. Instead, use the Calendar class.
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
public final class DateParseDemo {
public static void main(String[] args){
final DateFormat df = new SimpleDateFormat("MM/dd/yyyy");
final Calendar c = Calendar.getInstance();
try {
c.setTime(df.parse("04/12/2011"));
System.out.println("Year = " + c.get(Calendar.YEAR));
System.out.println("Month = " + (c.get(Calendar.MONTH)));
System.out.println("Day = " + c.get(Calendar.DAY_OF_MONTH));
}
catch (ParseException e) {
e.printStackTrace();
}
}
}
Output:
Year = 2011
Month = 3
Day = 12
And as for the month field, this is 0-based. This means that January = 0 and December = 11. As stated by the javadoc,
Field number for get and set indicating the month. This is a
calendar-specific value. The first month of the year in the Gregorian
and Julian calendars is JANUARY which is 0; the last depends on the
number of months in a year.
Javadoc to the rescue:
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.
You should not use deprecated methods. Deprecated methods are methods which should not be used anymore. But whatever the method you're using, read its javadoc to know what it does.
President Evil nailed it, Date.getYear() returns a value that is the result of subtracting 1900 from the year that contains. And you you shouldn't use it.
But quick fix for the code in the question is:
Date dateFrom = null;
String gDFString = g.getDateFrom();
System.out.println(gDFString);
DateFormat df = new SimpleDateFormat("dd/MM/yyyy");
try {
dateFrom = df.parse("04/12/2011");
System.out.println(dateFrom);
// Add 1900 to dateFrom.getYear()
System.out.println(dateFrom.getYear()+1900);
} catch (ParseException e) {
e.printStackTrace();
}
http://download.oracle.com/javase/1.4.2/docs/api/java/util/Date.html#getYear%28%29
The specification states that it returns the year minus 1900. Probably a good idea to avoid deprecated methods as well.
tl;dr
int year =
LocalDate.parse(
"04/12/2011" ,
DateTimeFormatter.ofLocalizedDate( FormatStyle.SHORT ).withLocale( Locale.US )
).getYear() ;
2011
java.time
The troublesome java.util.Date class and its siblings are now supplanted by the excellent java.time classes.
String input = "04/12/2011";
Locale locale = Locale.US;
DateTimeFormatter f = DateTimeFormatter.ofLocalizedDate( FormatStyle.SHORT ).withLocale( locale );
LocalDate ld = LocalDate.parse( input , f );
The java.time classes utilize sane numbering, with:
Months 1-12 for January-December
2011 means 2011
Days of week are 1-7 for Monday-Sunday (per ISO 8601).
Interrogate the LocalDate for its constituent parts.
int year = ld.getYear(); // 2011
int month = ld.getMonthValue(); // 4
int dayOfMonth = ld.getDayOfMonth(); // 12
You can even ask for automatically localized name of month and name of day-of-week.
String monthName = ld.getMonth().getDisplayName( TextStyle.FULL_STANDALONE , Locale.CANDA_FRENCH ); // avril
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.
This is only a guess, but the 111 could be the number of years since 1900. Take a look at documentation/do some tests to verify this (I can't check at the moment)