In java I have an arraylist that holds the following
List<IMyInterface>
I am returning it in a function
List<? extends IMyInterface> getList()
Now I wanna do the following
getList().add(MyElement)
where MyElement extends the interface.
What I get is a compile error that the method was expecting something else.
here it is:
add (capture ) in list cannot be aplied to (MyElement).
. though MyElement extends th IMyInterface
BTW: What is the word Capture in bold ? Thanks.
Add is a consumer method, it consumes things to be added to the list, so you want any list you add things to to be bounded below (? super Foo) rather than above (Foo extends ?).
See this question on PECS for more detail.
To make it more concrete, imagine the underlying was List<MyBetterInterface>, where MyBetterInterface extends IMyInterface. Now you'd still be OK to implement the getList() method with the same signature - but it is clearly not valid for a caller to add an object which implements only IMyInteface since now you'd have some objects which are not MyBetterInterface in there.
So declare it as
List<? super IMyInterface> getModifiableList();
getList().add(MyElement) will work, but how do you declare the array list? List<? super IMyInterface> list = new ArrayList<A>(); will give compilation error (A implements IMyInterface). Could you post a minimal sample?
ArrayList<IMyInterface>.