Question

In my code i am using two different class objects empobj & employee.
Eclipse asks to change the code

empobj.addAll(employee);

to

empobj.addAll((Collection<? extends EmpApp>) employee);

What does it mean?
I cannot understand the concept here.
Can I get any clarifications about this?

Answer 1

addAll takes as its parameter a Collection and then adds all the elements of that collection to itself. In your case, you’re trying to give it something that is not a Collection, so the compiler is trying to make it work by casting the argument to the correct type. In this particular case, the correct type is a collection of some object which extends EmpApp, i.e., Collection<? extends EmpApp>.

Judging from the name of your variable, employee probably isn’t a collection, so you need to revisit the API for whatever collection empobj is and find out how you can add a single element to it (likely add).