Question

I want to have my models wrapped up in a ModelCollection which is mostly used for a ListView. The Collection has always the same attributes like title, totalResults (for Pagination) and it shall contain the listItem-Models in the ArrayList “items”.
However, these models have different types like “ModelCategory” or “ModelChain” and often have different Properties and Methods.

How can I achieve this in java with strong Typing discipline? I heart interface a the right way to do this. WHERE do I have to implement them?

public class ModelCollection {

              public ArrayList< ModelCategory OR ModelChain OR ModelXyz> items = new ArrayList<ModelCategory OR ModelChain OR ModelXyz>();

              private String id;
              private String title;
              private Long updated;

              private String linkSelf;
              private int totalResults;
              private int startIndex;

    /*
     more stuff like parsing a feed
    */

    }

Answer 1

Make your ModelCategory, ModelChain, and ModelXyz implement an interface. Then have your collection be on that interface.

For instance:

public interface MyModel {
}

public class ModelCategory implements MyModel {
}

List<MyModel> list = new ArrayList<MyModel>();

To reference specific methods of each class, you will need to cast your list objects to the correct type.

List<MyModel> list = new ArrayList<MyModel>();
list.add(new ModelCategory());

ModelCategory model = (ModelCategory) list.elementAt(0);

Obviously, you can use whatever methods you need to iterate through your collections.