Several approach to remove duplicates from list of beans in Java

DuplicatesRemoval.java

import org.eclipse.jetty.util.ConcurrentHashSet;

import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;

import io.reactivex.Observable;

import static java.util.Comparator.comparing;
import static java.util.stream.Collectors.toCollection;
import static org.hamcrest.Matchers.hasSize;
import static org.junit.Assert.assertThat;

/**
 * @author Lei Sun <[email protected]>
 */
public class DuplicatesRemoval {
    public static void main(String[] args) {
        List<UserBean> users = Arrays.asList(
                new UserBean("u1", "Lei"),
                new UserBean("u2", "Meimei"),
                new UserBean("u1", "Allen"),
                new UserBean("u3", "Tom"),
                new UserBean("u2", "Alice"));

        DuplicatesRemoval test = new DuplicatesRemoval();
        Collection<UserBean> resultOldFashion = test.removeDuplicatesOldFashion(users);
        System.out.println(resultOldFashion);
        assertThat(resultOldFashion, hasSize(3));

        Collection<UserBean> resultFancy = test.removeDuplicatesFancyStream(users);
        System.out.println(resultFancy);
        assertThat(resultFancy, hasSize(3));

        Collection<UserBean> resultFancyAlt = test.removeDuplicatesFancyStreamAlt(users);
        System.out.println(resultFancyAlt);
        assertThat(resultFancyAlt, hasSize(3));

        Collection<UserBean> resultFancyAlt2 = test.removeDuplicatesFancyStreamAlt2(users);
        System.out.println(resultFancyAlt2);
        assertThat(resultFancyAlt2, hasSize(3));

        Collection<UserBean> resultRxAha = test.removeDuplicatesRxAha(users);
        System.out.println(resultRxAha);
        assertThat(resultRxAha, hasSize(3));
    }

    private Collection<UserBean> removeDuplicatesOldFashion(List<UserBean> users) {
        Map<String, UserBean> map = new HashMap<>();
        users.forEach(u -> map.put(u.getCode(), u));
        return map.values();
    }

    private Collection<UserBean> removeDuplicatesFancyStream(List<UserBean> users) {
        return users.stream().collect(Collectors.toMap(UserBean::getCode, Function.identity(), (p, q) -> p)).values();
    }

    private Collection<UserBean> removeDuplicatesFancyStreamAlt(List<UserBean> users) {
        return users.stream().collect(toCollection(() -> new TreeSet<>(comparing(UserBean::getCode))));
    }

    private Collection<UserBean> removeDuplicatesFancyStreamAlt2(List<UserBean> users) {
        Set<String> seen = new HashSet<>();
        return users.stream().filter(u -> seen.add(u.getCode())).collect(Collectors.toList());
    }

    private Collection<UserBean> removeDuplicatesRxAha(List<UserBean> users) {
        return Observable.fromIterable(users).distinct(UserBean::getCode).toList().blockingGet();
    }

    static class UserBean {
        private String code;
        private String nickname;

        public UserBean(String code, String nickname) {
            this.code = code;
            this.nickname = nickname;
        }

        public String getCode() {
            return code;
        }

        public void setCode(String code) {
            this.code = code;
        }

        public String getNickname() {
            return nickname;
        }

        public void setNickname(String nickname) {
            this.nickname = nickname;
        }

        @Override
        public String toString() {
            return "UserBean{" +
                    "code='" + code + '\'' +
                    ", nickname='" + nickname + '\'' +
                    '}';
        }
    }
}