PersonWithBuilder.java

public final class Person {
    private final String firstName;
    private final String lastName;
    private final String middleName;
    private final String facebookId;
    private final String twitterId;

    public static class Builder {
        private final String firstName;
        private final String lastName;
        private String middleName = "";
        private String facebookId = "";
        private String twitterId = "";

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

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

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

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

        public Person build() {
            return new Person(this);
        }
    }

    private Person(Builder builder) {
        this.firstName = builder.firstName;
        this.lastName = builder.lastName;
        this.middleName = builder.middleName;
        this.facebookId = builder.facebookId;
        this.twitterId = builder.twitterId;
    }
}