Month adjustInto() method in Java

The adjustInto() method of java.time.Month ENUM is an in-built function in Java which takes a Temporal object specifying a date and returns a new Temporal object of the same observable type as the input with the month replaced with this month-of-year.

Method Declaration:

public Temporal adjustInto(Temporal temporal)

Syntax:

Temporal newLocalDate = Month.ANYMONTH.adjustInto(Temporal temporal)

Parameters: This method takes temporal as parameter where:

• temporal – is the specified date to be adjusted.
• ANYMONTH – is the specified month to which the date is to be adjusted, e.g., JANUARY, FEBRUARY, etc.
• newLocalDate – is the modified date.

Return Value: The function returns an adjusted Temporal object which is the date adjusted according to specified Month.

Exceptions:

• DateTimeException: This method throws this exception if it is not possible to make the adjustment.
• ArithmeticException: This exception is thrown if numeric overflow occurs.

Below programs illustrate the above method:

Program 1:

import java.time.*;
import java.time.Month;
import java.time.temporal.Temporal;

class DayOfWeekExample {
    public static void main(String[] args)
    {
        // Set a Local Date whose month is found
        LocalDate localDate1
            = LocalDate.of(1947, Month.AUGUST, 15);

        // Find the month from the Local Date
        Month monthOfYear1
            = Month.from(localDate1);

        // Printing the Local Date
        System.out.println(localDate1
                           + " which is "
                           + monthOfYear1.name());

        // Adjust the month to JANUARY from AUGUST
        Temporal localDate2
            = Month.JANUARY
                  .adjustInto(localDate1);

        // Find the day from the new Local date
        Month monthOfYear2
            = Month.from(localDate2);

        // Printing the new Local Date
        System.out.println(localDate2
                           + " which is "
                           + monthOfYear2.name());
    }
}

Output:

1947-08-15 which is AUGUST
1947-01-15 which is JANUARY

Program 2:

import java.time.*;
import java.time.Month;
import java.time.temporal.Temporal;

class DayOfWeekExample {
    public static void main(String[] args)
    {
        // Set a Local Date whose month is found
        LocalDate localDate1
            = LocalDate.of(2019, Month.MARCH, 18);

        // Find the month from the Local Date
        Month monthOfYear1
            = Month.from(localDate1);

        // Printing the Local Date
        System.out.println(localDate1
                           + " which is "
                           + monthOfYear1.name());

        // Adjust the month to December from March
        Temporal localDate2
            = Month.DECEMBER
                  .adjustInto(localDate1);

        // Find the day from the new Local date
        Month monthOfYear2
            = Month.from(localDate2);

        // Printing the new Local Date
        System.out.println(localDate2
                           + " which is "
                           + monthOfYear2.name());
    }
}

Output:

2019-03-18 which is MARCH
2019-12-18 which is DECEMBER

Reference: https://docs.oracle.com/javase/8/docs/api/java/time/Month.html#adjustInto-java.time.temporal.Temporal-