Message.java

public class Message {
    private long id;
    private long userId;
    private long postedTs;
    private String content;

    public Message(long id, long userId, long postedTs, String content) {
        this.id = id;
        this.userId = userId;
        this.postedTs = postedTs;
        this.content = content;
    }

    public long getId() {
        return id;
    }

    public long getUserId() {
        return userId;
    }

    public long getPostedTs() {
        return postedTs;
    }

    public String getContent() {
        return content;
    }
}

User.java

public class User {
    private long id;
    private String name;
    private String avatarUrl;

    public User(long id, String name, String avatarUrl) {
        this.id = id;
        this.name = name;
        this.avatarUrl = avatarUrl;
    }

    public long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getAvatarUrl() {
        return avatarUrl;
    }
}