Java – unbounded wildcard passed to method

@H_ 301_ 7@public class ColTest { static
T wildSub(ArrayList holder,T arg){ T t=holder.get(0); return t; } public static void main(String[] args) { ArrayList list=new ArrayList

(Arrays.asList(2L,3L,7L)); Long lng=1L; ColTest.wildSub(list,lng); } }

I'm really interested in why this fragment is legal, because the signature of wildsub only accepts t's ArrayList or derived from t, and the type is t's arg But Meaning – some specific types, unknown, and how does it satisfy the compiler? In all types After that doesn't mean

Solution

This is due to capture conversion Internally, the compiler converts the expression foo Type of To foo < x >, where x is a specific although unknown type