Question

After successfully writing one method which does what it should (much shortened sample below) I want to refactor it to not be limited to return a List of MyEntity but instead a List<SomeType extends MyParentEntity>. So it should be able to accept only those types extending my MyParentEntity but able to specify another type (List<MyOtherEntity>, List<MyAwesomeEntity> etc.).

Shortened example:

 public static List<MyEntity> getFavList(Context context) {

        String prefKey = buildKey( new MyEntity() );
        List<MyEntity> entityList = new ArrayList<MyEntity>();

        SharedPreferences settings = context.getSharedPreferences(prefKey, 0);

        GSON gson = new GSON();
        MyEntity entity = gson.fromJson(settings.getString(0, null), MyEntity.class);

        entityList.add(entity);

        return entityList;
    }

I googled a lot but I didn’t find the correct approach to make this work without any compiler errors. I’d appreciate any pointers leading to a solution.

Answer 1

You will need to pass in the Class and the object you are passing to buildKey.

public static <T extend MyParentEntity> List<T> getFavList(
    Context context, Class<T> clazz, T key
) {

    String prefKey = buildKey(key);
    List<T> entityList = new ArrayList<T>();

    SharedPreferences settings = context.getSharedPreferences(prefKey, 0);

    GSON gson = new GSON();
    MyEntity entity = gson.fromJson(settings.getString(0, null), clazz);

    entityList.add(entity);

    return entityList;
}

(I don’t know what buildKey is supposed to be.)