Question

Is there a way to avoid using @SuppressWarnings below and to keep the same functionality without the warning ‘Type safety: Unchecked cast from AbstractDO[] to E[]’:

public MyClass {
  ...
  private Map<Class<? extends AbstractDO>, AbstractDO[]> map;
  ...
  private void saveConcreteDOs(AbstractDO[] theEntities) {        
    entityMap.put(theEntities[0].getClass(), theEntities);
  }

  @SuppressWarnings("unchecked")
  protected <E extends AbstractDO> E[] getConcreteDOs(Class<E> theType) {
    return (E[]) map.get(theType);
  }
  ...
}

Maybe enhance map declaration?

Answer 1

You have a choice: either suppress the warning for a cast you know will always succeed, or avoid the warning and verify that the cast succeeded with a try/catch block.

There are only those two choices.

maybe there is a way to enhance map declaration?

In your case, I’d say you have a few options.

I think your best bet is to add a throws ClassCastException clause to your getConcreteDOs method and let the caller deal with an invalid cast brought on by an invalid use of the method — assuming they could get it to compile around your extends AbstractDO clause. This has the unfortunate side effect of forcing the consumer to wrap the call in a try/catch block or declare their own throws clause to force a try/catch block higher up the stack.

You could just swallow the exception with an empty catch block; frankly I’d prefer the @SuppressWarning over that.

Or you could drop the method entirely and only deal in abstract entities, effectively making the consumer of your repository deal with the cast.

Bottom line: you’re going to have these issues whenever you try to build generic repositories. You might be better off with a concrete-repository-per-entity-type pattern.