LocalDateTime plus() method in Java with Examples

In LocalDateTime class, there are two types of plus() method depending upon the parameters passed to it.

plus(long amountToAdd, TemporalUnit unit)

plus() method of a LocalDateTime class used to return a copy of this LocalDateTime with the specified amount of unit added.If it is not possible to add the amount, because the unit is not supported or for some other reason, an exception is thrown. This instance is immutable and unaffected by this method call.

Syntax:

public LocalDateTime plus(long amountToAdd,
                          TemporalUnit unit)

Parameters: This method accepts two parameters amountToAdd which is the amount of the unit to add to the result, may be negative and unit which is the unit of the amount to add, not null.

Return value: This method returns LocalDateTime based on this LocalDateTime with the specified amount added.

Below programs illustrate the plus() method:
Program 1:

// Java program to demonstrate
// LocalDateTime.plus() method

import java.time.*;
import java.time.temporal.ChronoUnit;

public class GFG {
    public static void main(String[] args)
    {

        // Get the LocalDateTime instance
        LocalDateTime ldt
            = LocalDateTime
                  .parse("2019-12-31T19:15:30");

        // Get the String representation
        // of this LocalDateTime
        System.out.println("Original LocalDateTime: "
                           + ldt.toString());

        // add 90 DAYS to LocalDateTime
        LocalDateTime value
            = ldt.plus(90, ChronoUnit.DAYS);

        // print result
        System.out.println("LocalDateTime after"
                           + " adding 30 DAYS: "
                           + value);
    }
}

Output:

Original LocalDateTime: 2019-12-31T19:15:30
LocalDateTime after adding 30 DAYS: 2020-03-30T19:15:30

plus(TemporalAmount amountToAdd)

plus() method of a LocalDateTime class used to return a copy of this LocalDateTime with the specified amount added to date-time.The amount is typically Period or Duration but may be any other type implementing the TemporalAmount interface.

Syntax:

public LocalDateTime plus(TemporalAmount amountToAdd)

Parameters: This method accepts one single parameter amountToAdd which is the amount to add, It should not be null.

Return value: This method returns LocalDateTime based on this LocalDateTime with the addition made, not null

Below programs illustrate the plus() method:
Program 1:

// Java program to demonstrate
// LocalDateTime.plus() method

import java.time.*;
public class GFG {
    public static void main(String[] args)
    {

        // Get the LocalDateTime instance
        LocalDateTime ldt
            = LocalDateTime
                  .parse("2019-12-31T19:15:30");

        // Get the String representation
        // of this LocalDateTime
        System.out.println("Original LocalDateTime: "
                           + ldt.toString());

        // add 20 Days to LocalDateTime
        LocalDateTime value
            = ldt.plus(Period.ofDays(10));

        // print result
        System.out.println("LocalDateTime after"
                           + " adding Days: "
                           + value);
    }
}

Output:

Original LocalDateTime: 2019-12-31T19:15:30
LocalDateTime after adding Days: 2020-01-10T19:15:30

References:
https://docs.oracle.com/javase/10/docs/api/java/time/LocalDateTime.html#plus(java.time.temporal.TemporalAmount)
https://docs.oracle.com/javase/10/docs/api/java/time/LocalDateTime.html#plus(long, java.time.temporal.TemporalUnit)