how elements total wildcard general collection?

why i compiler errors java code?

1  open list<? extends foo> getfoos()
2  {
3    list<? extends foo> foos = new arraylist<? extends foo>();
4    foos.add(new subfoo());
5    relapse foos;
6  }

where 'subfoo' petrify category implements foo, foo an interface.

errors i code:

• on line 3: "cannot instantiate arraylist<? extends foo>"


• on line 4: "the slight add(capture#1-of ? extends foo) form list<capture#1-of ? extends foo> convenient arguments (subfoo)"

update: interjection jeff c, i change line 3 contend "new arraylist<foo>();". nonetheless i'm still carrying emanate line 4.