When working with immutable objects, what is the best way to return a copy with modified fields?

Question

The Java 8 Streams API allows you to create code functionally, not necessarily. Since we know that immutability provides many advantages, and as such, I try to make objects immutable wherever possible. In everyday programming, I find myself in a situation where I want to "set" a value. My objects are immutable, so I need to create a new object and initialize the field in the constructor.

I am using the Lombok project, which provides annotations, such as @Value, which essentially make the object immutable. It also has @Builderone that uses the builder pattern to provide a builder for an immutable object by setting fields not specified in the free API before null.

The annotation @Builderhas a field with a name toBuilderthat, if true, provides a method toBuilder()that returns a builder filled with the fields of the object, where the developer can "set" the values, call build()and return a new object.

eg. to create Listimmutable objects with modified fields forename, I would do the following:

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

import lombok.Builder;
import lombok.Value;

public class SOExample {

    @Value
    @Builder(toBuilder = true)
    private static class Person {
        private final String forename;
        private final String surname;
        private final int age;
        private final int heightInCm;
    }

    public static void main(String[] args) {
        List<Person> people = Arrays.asList(Person.builder()
                .forename("stack")
                .surname("overflow")
                .age(21)
                .heightInCm(180)
                .build());
        people.stream()
                .map(p -> p.toBuilder()
                        .forename("updatedForename")
                        .build())
                .collect(Collectors.toList());
    }
}

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            .map(p -> p.withForename("updatedForename"))

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