Question

I want to do something like this

private <T extends List<?>> List<?> getFirstFiveElements(T list) {
    //body
}

However when I tray to pass in the arguments it is not working

List<A> a = new LinkedList<A>;
List<B> b = new LinkedList<B>; 
getFirstFiveElements(a);
getFirstFiveElements(b);

so any suggestion how I cam make this work.

Answer 1

The following should work just fine.

private static <A, T extends List<A>> List<A> getFirstFiveElements(T list) {
   //
}

T serves no useful purpose here, and therefore can be eliminated.

private static <A> List<A> getFirstFiveElements(List<A> list) {
   //
}

If you want the method to return the same type that it takes (i.e. ArrayList for ArrayList, LinkedList for LinkedList), then sorry to tell you, Java’s type system is not capable of that.