How to Change the Day in The Date Using Java?

The Java Calendar class (java.util.Calendar) is a very helpful and practical class for manipulating dates and times in Java. Here, I'll show you how to change the date and time using the calendar class.

Get today's date and time using a calendar() class method.

DateFormat dF = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Calendar c = Calendar.getInstance();
System.out.println(" Present Date Time is : " + dF.format(c.getTime()));

Change the date or time on a calendar.

// Date and time are current plus one day.
cal.add(Calendar.DATE, 1);
// Date and time are current plus one month.
c.add(Calendar.MONTH, 1);
// Date and time are current plus one year.
c.add(Calendar.YEAR, 1);
// Date and time are current plus one hour.
c.add(Calendar.HOUR, 1);
// Date and time are current plus one minute.
c.add(Calendar.MINUTE, 1);
// Date and time are current plus one second.
c.add(Calendar.SECOND, 1);
// Take a day out of the current date.
c.add(Calendar.DATE, -1);
// Take a month out of the current date.
c.add(Calendar.MONTH, -1);
// Take a year out of the current date.
c.add(Calendar.YEAR, -1);
// Take an hour out of the current date.
c.add(Calendar.HOUR, -1);

// Take a minute out of the current date.
c.add(Calendar.MINUTE, -1);

// Take a second out of the current date.
c.add(Calendar.SECOND, -1);

This complete source code demonstrates how to change the date and time in Java.

// File name: DateTimeChanging.java

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
public class DateTimeChanging {
  public static void main(String args[]) {
 
	   DateFormat dF = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
	   // retrieve the current time and date with a calendar ()
	   Calendar c = Calendar.getInstance();
	   System.out.println(" Present Date Time is : " + dF.format(c.getTime()));
	   // Date and time are current plus one day.
	   c.add(Calendar.DATE, 1);
	   System.out.println(" Adding one day to the present date : " + dF.format(c.getTime()));
	   // Date and time are current plus one month.
	   c = Calendar.getInstance();
	   c.add(Calendar.MONTH, 1);
	   System.out.println(" Adding one month to the present date : " + dF.format(c.getTime()));
	   // Date and time are current plus one year.
	   c = Calendar.getInstance();
	   c.add(Calendar.YEAR, 1);
	   System.out.println(" Adding one year to the present date : " + dF.format(c.getTime()));
	   // Date and time are current plus one hour.
	   c = Calendar.getInstance();
	   c.add(Calendar.HOUR, 1);
	   System.out.println(" Adding one hour to the present date : " + dF.format(c.getTime()));
	   // Date and time are current plus one minute.
	   c = Calendar.getInstance();
	   c.add(Calendar.MINUTE, 1);
	   System.out.println(" Adding one minute to the present date : " + dF.format(c.getTime()));
	   // Date and time are current plus one second.
	   c = Calendar.getInstance();
	   c.add(Calendar.SECOND, 1);
	   System.out.println(" Adding one second to the present date : " + dF.format(c.getTime()));
	   // Take a day out of the current date.
	   c = Calendar.getInstance();
	   c.add(Calendar.DATE, -1);
	   System.out.println(" Subtracting one day from the present date : " + dF.format(c.getTime()));
	   // Take a day out of the current month.
	   c = Calendar.getInstance();
	   c.add(Calendar.MONTH, -1);
	   System.out.println(" Subtracting one month from the present date : " + dF.format(c.getTime()));
	   // Take a day out of the current year.
	   c = Calendar.getInstance();
	   c.add(Calendar.YEAR, -1);
	   System.out.println(" Subtracting one year from the present date : " + dF.format(c.getTime()));
	   // Take a day out of the current hour.
	   c = Calendar.getInstance();
	   c.add(Calendar.HOUR, -1);
	   System.out.println(" Subtracting one hour from the present date : " + dF.format(c.getTime()));
	   // Take a day out of the current minute.
	   c = Calendar.getInstance();
	   c.add(Calendar.MINUTE, -1);
	   System.out.println(" Subtracting one minute from the present date : " + dF.format(c.getTime()));
	   // Take a day out of the current second.
	   c = Calendar.getInstance();
	   c.add(Calendar.SECOND, -1);
	   System.out.println(" Subtracting one second from the present date : " + dF.format(c.getTime()));	   
 
  }
}

Output:

Present Date Time is : 2023/01/14 18:15:26
 Adding one day to the present date : 2023/01/15 18:15:26
 Adding one month to the present date : 2023/02/14 18:15:26
 Adding one year to the present date : 2024/01/14 18:15:26
 Adding one hour to the present date : 2023/01/14 19:15:26
 Adding one minute to the present date : 2023/01/14 18:16:26
 Adding one second to the present date : 2023/01/14 18:15:27
 Subtracting one day from the present date : 2023/01/13 18:15:26
 Subtracting one month from the present date : 2022/12/14 18:15:26
 Subtracting one year from the present date : 2022/01/14 18:15:26
 Subtracting one hour from present date : 2023/01/14 17:15:26
 Subtracting one minute from the present date : 2023/01/14 18:14:26
 Subtracting one second from the present date : 2023/01/14 18:15:25

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