syntax - What does Class<?> mean in Java?

Question

My question is as above. Sorry, it's probably a duplicate but I couldn't find an example with the <?> on the end.

Why would you not just use Class as the parameter?

Answer 1

Class is a parameterizable class, hence you can use the syntax Class<T> where T is a type. By writing Class<?>, you're declaring a Class object which can be of any type (? is a wildcard). The Class type is a type that contains meta-information about a class.

It's always good practice to refer to a generic type by specifying his specific type, by using Class<?> you're respecting this practice (you're aware of Class to be parameterizable) but you're not restricting your parameter to have a specific type.

Reference about Generics and Wildcards: http://docs.oracle.com/javase/tutorial/java/generics/wildcards.html

Reference about Class object and reflection (the feature of Java language used to introspect itself): https://www.oracle.com/technetwork/articles/java/javareflection-1536171.html