Decouple structure and implementation and delay the coupling to another time.

Comment.java

interface Length {
    int getLength();
}

class CommentStruct {
    protected String author;
    protected String content;
}

public class Comment extends CommentStruct implements Length{
    public int getLength() {
        return content.length();
    }
}

// https://youtu.be/5QFDQRkbllo?si=3IY7T8DMM6aXbOWO&t=118