How do I modified the value of LocalDate and LocalTime object?

The easiest way to modify the value of a LocalDate, LocalTime or LocalDateTime object is to use the with() method of the corresponding object. These methods will return a modified version of the object, it doesn’t change the attribute of the original object. All the methods, like withYear(), withDayOfMonth() or the with(ChronoField) of the LocalDate object will return a new object with the modified attribute.

With the LocalTime object you can use the withHour(), withMinute(), withSecond() or the more generic with(ChronoField) method to modified the attribute of a LocalTime object. You can also modified a LocalDateTime object using these with() method. Let’s see the example in the code snippet below.

package org.kodejava.example.datetime;

import java.time.LocalDate;
import java.time.LocalTime;
import java.time.temporal.ChronoField;

public class ManipulatingDateTime {
    public static void main(String[] args) {
        LocalDate date1 = LocalDate.of(2020, 4, 21);
        System.out.println("date1 = " + date1);
        LocalDate date2 = date1.withYear(2019);
        System.out.println("date2 = " + date2);
        LocalDate date3 = date2.withDayOfMonth(10);
        System.out.println("date3 = " + date3);
        LocalDate date4 = date3.with(ChronoField.MONTH_OF_YEAR, 12);
        System.out.println("date4 = " + date4);

        LocalTime time1 = LocalTime.of(1, 5, 10);
        System.out.println("time1 = " + time1);
        LocalTime time2 = time1.withHour(6);
        System.out.println("time2 = " + time2);
        LocalTime time3 = time2.withMinute(45);
        System.out.println("time3 = " + time3);
        LocalTime time4 = time3.with(ChronoField.SECOND_OF_MINUTE, 25);
        System.out.println("time4 = " + time4);

        LocalDate now1 = LocalDate.now();
        System.out.println("now1 = " + now1);
        LocalDate now2 = now1.plusWeeks(1);
        System.out.println("now2 = " + now2);
        LocalDate now3 = now2.minusMonths(2);
        System.out.println("now3 = " + now3);
        LocalDate now4 = now3.plus(15, ChronoUnit.DAYS);
        System.out.println("now4 = " + now4);
    }
}

The output of this code snippet are:

date1 = 2020-04-21
date2 = 2019-04-21
date3 = 2019-04-10
date4 = 2019-12-10
time1 = 01:05:10
time2 = 06:05:10
time3 = 06:45:10
time4 = 06:45:25
now1 = 2020-04-21
now2 = 2020-04-28
now3 = 2020-02-28
now4 = 2020-03-14

These with() methods is the counterpart of the get() methods. Where the get() methods will give you the value of the corresponding LocalDate or LocalTime attribute, the with() method will change the attribute value and return a new object. It didn’t call set because the object is immutable, which means it value cannot be changed.

While with the with() method you can change the value of date time attribute in an absolute way using the plus() or minus() method can help you change the date and time attribute in a relative way. The plus() and minus() method allows you to move a Temporal back or forward a give amount of time, defined by a number plus a TemporalUnit, in this case we use the ChronoUnit enumeration which implements this interface.