Question

My Question might be very simple,

I have a class Result with some inner fields , setters and getters.

Additionally, i have class Special1Result which extends Result and includes several more fields and Special2Result with some more data.

In different class Dispatcher, i have written the following method:

processResults(List<? extends Result> results), which is only familiar with Result (I need this method to query if there is specific field in the extended Result object – i am using annotations).

So i have decided to use the extended for-each loop: for (Result res : results) {}

So what is my question ? i am trying to find over the web how to write this for loop for extended objects, e.g. something like this for (? extends Results res: results){}

Is it possible? How is the correct way to write it?

Answer 1

I am trying to find over the web how to write this for loop for extended objects, e.g. something like this

for (? extends Results res: results){}

No, this is not possible: you cannot statically type items supplied dynamically at run-time.

How is the correct way to write it?

You are already doing it:

for (Results res: results) {
}

If you would like to test for Special2Result inside that loop, you can do it, but usually it tells that your design can be improved. A better alternative is to use a mechanism of double dispatch, such as the Visitor Pattern, to hide the details of special treatment for your subclasses.