Confusion in generic List<> hierarchy

Question

Wildcards and Subtyping - Oracle Documentation

This document has a diagram shows the relationships between several List classes declared with both upper and lower bounded wildcards. The relationship as depicted in the picture below:

In the right side hierarchy, List<? super Number> is sub type to List<? super Integer>. Isn't it confusing?

As far as I interpret, List<? super Number> can be represented by any List<type> where type is either Number or super class of Number. Same logic holds true for List<? super Integer> also. So how can List<? super Number> be a sub type of List<? super Integer>?

So a `List super Integer>` is a list where `type` is either `Integer` or a super class of `Integer`. Is `Number` a super class of `Integer`? — Sotirios Delimanolis, Nov 01 '16 at 17:49
[This](http://stackoverflow.com/a/19739576/2711488) might be helpful… — Holger, Nov 04 '16 at 14:59

Joffrey · Accepted Answer · 2016-11-01T18:01:10.807

This is because List<? super Number> can only hold Number and its super classes, while List<? super Integer> can hold the same + integers.

You can think about it this way: if the item type is more restrictive, then a list of such items is lower in the inheritance hierarchy. You can put a List<? super Number> in a variable of type List<? super Integer>, but not the other way around.

Look at how the item types include each other, this might help you:

Confusion in generic List<> hierarchy

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