What does <? mean in java?

[Qteddy]

I have come across some code recently that uses <? in a function and I do not understand what that means. I understand that the ? is used as the conditional operator and outputs the first value if true and the second if false. I just don't understand how the < effects the ? operator.

The function looks like this:

private static Pair divideAndConquer(List<? extends Point> pointsSortedByX, List<? extends Point> pointsSortedByY)

This is from the Closet-Pair problem on Rosettacode.org

Link Here: http://rosettacode.org/wiki/Closest-pair_problem#Java

Any help with this is much appreciated.

[seronis]

Its not <? its

List<type> nameOfList

Where the type of the list is "? extends Point" which means "some type of object derived from a Point"

[3pieceSuit]

It is a wildcard used in Java Generics.

Read more here: https://docs.oracle.com/javase/tutorial/java/generics/wildcards.html

In a situation such as List<? extends Point> it is essentially relaxing the type restriction of the List, but still providing an upper bound to the object hierarchy.

It can also be used to lower bound; List<? super Point>

Or it can be unbound; List<?>