Java replace part of the string before a comma

Question

I have a string in data format, apr 17,2016.

For instance, I would like to go back 1 day, so I would like to get apr 16,2016.

How can I do that?

Please note, it could be mar 1,2016 as well so the replacement at index cannot work.

Answer 1

You can use Java 8 for this.

Just convert to LocalDate. It has flexible API for many reasons.

Here is code snippet:

public static void main(String[] args) throws ParseException {
    String dateStr = "apr 17,2016";
    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMM dd,uuuu");

    // convert to local date
    LocalDate localDate = LocalDate.parse(dateStr, formatter.withLocale(Locale.ITALIAN));
    System.out.println("START DATE:\n" + localDate);

    // use all power of new java.time
    LocalDate oneDayBefore = localDate.minusDays(1);
    LocalDate oneMonthBefore = localDate.minusMonths(1);
    LocalDate oneWeekBefore = localDate.minusWeeks(1);
    LocalDate oneYearBefore = localDate.minusYears(1);

    System.out.println("RESULTS:");
    System.out.println(oneDayBefore);
    System.out.println(oneMonthBefore);
    System.out.println(oneWeekBefore);
    System.out.println(oneYearBefore);
}

Output:

START DATE:
2016-04-17
RESULTS:
2016-04-16
2016-03-17
2016-04-10
2015-04-17

Now you need to print local date as a string.

Here is example:

    // use Java 8 features
    DateTimeFormatter dtf = DateTimeFormatter.ofPattern("MMM dd,yyyy");
    String dt = dtf.format(oneDayBefore);
    System.out.println(dt);

Output:

Apr 16,2016

Answer 2

tl;dr

LocalDate.parse ( 
    "apr 17,2016" , 
    DateTimeFormatter.ofPattern ( "MMM dd,uuuu" ).withLocale( locale ) 
)

Using java.time

The modern way is with the java.time classes.

You do not specify the locale or human language intended for your input strings. The initial lowercase letter in the month name abbreviation is not appropriate to US English. So I tried all the locales provided with Java 8 Update 121, ignoring any parsing attempts that failed with an exception.

Note how we call DateTimeFormatter::withLocale inside the loop. Locale determines (a) the human language for translation of name of day, name of month, and such, and (b) the cultural norms deciding issues of abbreviation, capitalization, punctuation, separators, and such.

You can do date-time math to get the previous day by calling LocalDate::minusDays.

String input = "apr 17,2016";
DateTimeFormatter f = DateTimeFormatter.ofPattern ( "MMM dd,uuuu" );

for ( Locale locale : Locale.getAvailableLocales ( ) ) {
    try {
        LocalDate ld = LocalDate.parse ( input, f.withLocale ( locale ) );
        System.out.println ( locale.getDisplayName ( ) + " → " + ld + " | day before: " + ld.minusDays ( 1 ) );
    } catch ( java.time.format.DateTimeParseException e ) {
        // Swallow this expected exception. No code needed here.
    }
}
System.out.println ( "Done." );

Nineteen worked.

Italian → 2016-04-17 | day before: 2016-04-16
Swedish (Sweden) → 2016-04-17 | day before: 2016-04-16
Slovak → 2016-04-17 | day before: 2016-04-16
Estonian → 2016-04-17 | day before: 2016-04-16
Swedish → 2016-04-17 | day before: 2016-04-16
Serbian (Latin,Bosnia and Herzegovina) → 2016-04-17 | day before: 2016-04-16
Serbian (Latin,Montenegro) → 2016-04-17 | day before: 2016-04-16
Norwegian (Norway,Nynorsk) → 2016-04-17 | day before: 2016-04-16
Estonian (Estonia) → 2016-04-17 | day before: 2016-04-16
Serbian (Latin) → 2016-04-17 | day before: 2016-04-16
Dutch → 2016-04-17 | day before: 2016-04-16
Norwegian (Norway) → 2016-04-17 | day before: 2016-04-16
Dutch (Netherlands) → 2016-04-17 | day before: 2016-04-16
Italian (Switzerland) → 2016-04-17 | day before: 2016-04-16
Slovak (Slovakia) → 2016-04-17 | day before: 2016-04-16
Italian (Italy) → 2016-04-17 | day before: 2016-04-16
Dutch (Belgium) → 2016-04-17 | day before: 2016-04-16
Norwegian → 2016-04-17 | day before: 2016-04-16
Serbian (Latin,Serbia) → 2016-04-17 | day before: 2016-04-16
Done.

---

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

Where to obtain the java.time classes?

• Java SE 8 and SE 9 and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

Answer 3

**Note : you should use a date class instead of strings, but there are better classes available than the ones I used here. ** I will edit this answer to reflect this, but you should look below at solutions that are more appropriate for current Java versions and to the precision (day instead of millisecond) requested here.

The most robust way is to convert your string into a date class, manipulate the date, then reformat it back. The conversion in each direction can be done with the SimpleDateFormat class (Api docs) and the changing of the date is easily done with the Calendar class (API docs)

This runs and takes the date from the argument and outputs the format with one day subtracted, as you asked.

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Calendar;

public class DateSubtractExample{
    public static String backOneDay(String inDate){
      SimpleDateFormat formatter = new SimpleDateFormat("MMM dd,yyyy");
      try{
          // turn your string into a date (if formatting is right)
          Date date1 = formatter.parse(inDate);
          // make a calendar, set it to the date, and subtract one day.
          Calendar cal = Calendar.getInstance();
          cal.setTime(date1);
          cal.add(Calendar.DATE,-1);
          // convert date back to input format. 
          return formatter.format(cal.getTime());
        }
        catch (ParseException bad){
                bad.printStackTrace();
                return "UNREADABLE DATE "+inDate+":"+bad;

        }
    }

    public static void main(String[] args) throws ParseException{
       System.out.println(DateSubtractExample.backOneDay(args[0]));
    }
}

Answer 4

public String getPreviousDate(String oldDate) {
    String[] parts1 = oldDate.split(" "); // split the oldDate around " "
    String[] parts2 = parts1[1].split(","); // split the second part of oldDate around ","

    String month = parts1[0];
    int day = Integer.parseInt(parts2[0]);
    int year = Integer.parseInt(parts2[1]);
    ...
    return newDate;
}

Answer 5

This will work as per your requirement please try this, tested program so no need to worry

import java.text.SimpleDateFormat;  
import java.util.*;

public class DateExample{
    public static void main(String args[]) throws Exception {

        String date = "apr 16,2016";
    SimpleDateFormat formatter=new SimpleDateFormat("MMM dd,yyyy");  

    Date dateFormated =formatter.parse(date);  
    System.out.println(dateFormated);

    GregorianCalendar cal = new GregorianCalendar();
    cal.setTime(dateFormated);
    cal.add(Calendar.DATE, -1);

        Date newDate = cal.getTime();
    String stringDate = formatter.format(newDate);
        System.out.println(stringDate);
    }

}

Answer 6

I feel I am not clear in the question you are asking. I saw two questions, one related to replace part of string and another about date. I assume you question is about the date. So I tried to reply your question thinking you want to decrease the current date by one day.

For this you can use Calendar interface.

Calendar cal = Calendar.getInstance();
cal.setTime(myDate);
cal.add(Calendar.DAY_OF_YEAR,-1);
Date oneDayBefore= cal.getTime();

Answer 7

So, Id use string.split(","). Example Code :

String date="apr 1,2016";
String[] parts=date.split(",");
String month_and_day=parts[0];
String year=parts[1];
String[] parts_of_month_and_day=month_and_day.split(" ");
String month=parts_of_month_and_day[0];
String day=parts_of_month_and_day[1];
int m;
int d;
int y;
y=Integer.parseInt(year);
d=Integer.parseInt(day);
String[] months=new String[] {"jan","feb","mar","apr","may","jun","jul","aug","sep","okt","nov","dez"};
for (int i=0; i < 12 /*length of months*/; i++) {
     if (months[i].equals(month)) {
         m=i;
     }
}