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This may be a stupid question, but ... "What is the difference between specifying a wildcard for a genericized type and not using the generic notation at all?"

First thoughts:

Take this for example:

interface Example {
  public List<?> getList();
}
 
class ExampleImpl implements Example {
  public List getList() { return new ArrayList(); } // warning: needs unchecked conversion to conform to List<?>
}

ExampleImpl successfully implements Example, but the compiler warns me about the conversion of List to List<?>. I don't see how it's even possible to return a List from the method in ExampleImpl that is not conformable List<?>--if that's truly the case, why does the compiler even warn me at all?

It makes me wonder what the benefit is for specifying wildcard generic types for an API. If I were to rewrite the interface's method to return a plain old List, then I wouldn't receive any warnings.

So I don't get it:

What's the point of specifying a wildcard for a genericized type, when you can just omit the generics altogether?