Is there any special meaning to the text "<?>"?

Question

private final Class<? extends FragmentActivity> activityClass; 

I understand the definition, except for the <? > <? > .

Is there any reason for the extensions to be enclosed in this special text?

Answer 1

which is a wild card symbol that says any of them can take any type that extends FragmentActivity

Answer 2

This is part of Java generics , and this means that the activityClass type extends FragmentActivity.