Java Type System-Sadness

experiment.java

package com.erinswensonhealey.experiments;

import java.time.Instant;
import java.util.List;
import java.util.stream.Collectors;

public class Experiment {

    public interface HasCreatedAtTimestamp<T extends HasCreatedAtTimestamp<T>> {
        Instant getCreatedAtTimestamp();
        T setCreatedAtTimestamp(Instant ts);
    }

    public class Address implements HasCreatedAtTimestamp<Address> {

        public Address(String city, String state, String code, String country, Instant createdTimestamp) {
            this.city = city;
            this.state = state;
            this.code = code;
            this.country = country;
            this.createdTimestamp = createdTimestamp;
        }

        private String city;
        private String state;
        private String code;
        private String country;
        private Instant createdTimestamp;

        public Instant getCreatedAtTimestamp() {
            return this.createdTimestamp;
        }

        public Address setCreatedAtTimestamp(Instant ts) {
            return new Address(this.city, this.state, this.code, this.country, ts);
        }
    }

    public class Person implements HasCreatedAtTimestamp<Person> {

        public Person(String name, Instant createdTimestamp) {
            this.name = name;
            this.createdTimestamp = createdTimestamp;
        }

        private String name;
        private Instant createdTimestamp;

        public Instant getCreatedAtTimestamp() {
            return this.createdTimestamp;
        }

        public Person setCreatedAtTimestamp(Instant ts) {
            return new Person(this.name, this.createdTimestamp);
        }
    }

    public static class Foo {

        public static <T extends HasCreatedAtTimestamp<T>> List<T> overrideCreatedAtTimestamps(List<T> xs, Instant ts) {
            return xs.stream().map(x -> x.setCreatedAtTimestamp(ts)).collect(Collectors.toList());
        }

        public void savePeople(List<Person> ps) {
            List<Person> updated = overrideCreatedAtTimestamps(ps, Instant.now());
            System.out.println(updated.get(0).name);
        }

        public void saveAddress(List<Address> as) {
            List<Address> updated = overrideCreatedAtTimestamps(as, Instant.now());
            System.out.println(updated.get(0).city);
        }
    }
}