What is the use and point of unbound wildcards generics in Java?

Question

I don\'t understand what is the use of unbound wildcards generics. Bound wildcards generics with upper boundary makes perfect sense, be

Answer 1

There are (rare) perfectly correct use cases for unbound wildcards. The SDK contains some of them.

One example is a method that does a definite action on a list of any kind and does not return anything as rotate in Collections:

static void rotate(List list, int distance)

Another example is when you want to list the possible constructors for a class, the method is :

Constructor[] getConstructors()

Here it in not even possible to use a generic, because by definition the array will contain different constructor each with its own actual class. By contrast, the API does use a generic signature for getting one single constructor : Constructor getConstructor(Class... parameterTypes).

The conclusion is that even if it is mainly used for compatibility with older code, there are still places where unbound wildcard generics are the correct way.