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javagenericsbounded-wildcard

are these wildcards redundant?

I have two examples of methods that uses wildcard generics.

First example:

public static <T extends Comparable> T findMax(List<T> list)

Second example: 

public static <T extends Comparable<? super T>> T findMax(List<? extends T> list)

I want to know if these two examples are redundant. If yes, why?

Solution

  • The two examples are telling you different things, so they are not redundant, they give different information and restricts the type in a different way.

    public static <T extends Comparable> T findMax(List<T> list)

    In this example, you are telling your T variable can be of any type that implements or extends Comparable (if it is a class or an interface)

    public static <T extends Comparable<? super T>> T findMax(List<? extends T> list)

    In this example, you are telling that the T type should extends comparable and also telling that the type must be a super class of T (inside comparable) but it can be a sub-type of T in the list.