public static class Builder {
        private String firstName;
        private String lastName;
        private DateTime birthDate;
        private String address;
        private int zipCode;
        private String city;
        private String state;
        private String zipCode4;

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

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

        public Builder birthDate(DateTime birthDate) {
            this.birthDate = birthDate;
            return this;
        }

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

        public Builder zipCode(int zipCode) {
            this.zipCode = zipCode;
            return this;
        }

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

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

        public Builder zipCode4(String zipCode4) {
            this.zipCode4 = zipCode4;
            return this;
        }

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

    private User(Builder builder) {
        this.firstName = builder.firstName;
        this.lastName = builder.lastName;
        this.birthDate = builder.birthDate;
        this.address = builder.address;
        this.zipCode = builder.zipCode;
        this.city = builder.city;
        this.state = builder.state;
        this.zipCode4 = builder.zipCode4;
    }