Question

I have a following model:

abstract Article {id, name, text}

final NewspaperArticle { printDate } extends Article

final ScientificArticle { quotations, publicationDate } extends Article

final ... { ... } extends Article

I wonder how I could achieve casting the final entities between each other, so that the common fields of Article superclass would be set and the different fields would stay null. Something like:

ScientificArticle scientificArticle = ...;
NewspaperArticle newspaperArticle = new NewspaperArticle();
newspaperArticle.copyOf(scientificArticle);

Is it possible to cast it or I will have to use reflection?

Answer 1

To answer your question in short: No, you can’t cast an object to another class. You may only cast to supertypes of the object’s real class. (A class is also a supertype of itself.)

You could, however, use composition instead of inheritance:

interface Article { ArticleData getArticleData(); }

final ArticleData {id, name, text}

final NewspaperArticle { articleData, printDate } implements Article

final ScientificArticle { articleData, quotations, publicationDate } implements Article

final ... { articleData, ... } implements Article

Then you could add a constructor like NewspaperArticle(Article createFrom) to each class which sets the article data field and leaves the others null:

class NewspaperArticle {
  ArticleData articleData;
  Date printDate = null;

  NewspaperArticle(Article createFrom) {
    this.articleData = createFrom.getArticleData();
  }
}

Your example would then look like:

ScientificArticle scientificArticle = ...;
NewspaperArticle newspaperArticle = new NewspaperArticle(scientificArticle);