public final class Person {

    private final String firstName;
    private final String lastName;

    private Person(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public static Builder builder() {
        return new Builder();
    }

    public static final class Builder {
        private String firstName;
        private String lastName;

        private Builder() {
        }

        public Builder firstName(String firstName) {
            this.firstName = firstName;
            return this;
        }

        public Builder lastName(String lastName) {
            this.lastName = lastName;
            return this;
        }

        public Person build() {
            return new Person(firstName, lastName);
        }
    }
}