What is the purpose of List?

Question

I didn\'t even know this was doable, but I saw while perusing some code online a method with a signature like this:

public List read( ... )
         


        

Answer 1

List is weird. It can only have null elements, since you can't create an object of type Void. I don't think there is a practical use for such a thing.

Void is part of java.lang. It's not a special keyword or anything. It's a "pseudo-type" (according to the docs) used to as a place-holder to represent the Class object corresponding to void, as in Class. From the docs for Class:

The primitive Java types (boolean, byte, char, short, int, long, float, and double), and the keyword void are also represented as Class objects.

The Void class exists mainly for the sake of the last part of this, so you can write:

Class voidType = void.class; // == Void.TYPE

just like you can write:

Class intType = int.class; // == Integer.TYPE