In Java 8, you can convert a LocalDateTime object to a particular format using the DateTimeFormatter class. Here’s an example:

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class LocalDateTimeFormatExample {
    public static void main(String[] args) {
        // create a LocalDateTime object
        LocalDateTime localDateTime = LocalDateTime.now();

        // create a DateTimeFormatter object with the desired format
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss");

        // format the LocalDateTime object with the formatter
        String formattedDateTime = localDateTime.format(formatter);

        // print the formatted datetime string
        System.out.println(formattedDateTime);
    }
}

In this example, we’re creating a DateTimeFormatter object with the pattern "dd-MM-yyyy HH:mm:ss", which represents the format we want to convert the LocalDateTime object to. Then we’re using the format() method to convert the LocalDateTime object to the desired format. Finally, we’re printing the formatted datetime string.

You can change the pattern to match the desired format you want to convert the LocalDateTime object to.