The Javadoc explains that "The Void class is an uninstantiable placeholder class to hold a reference to the Class object representing the Java keyword void.". The reflection API is a set of classes and methods that let you find out things about Java classes at runtime -- i.e., you can ask what methods a class has, what its superclass is, etc. You can also ask what a method's return type is, what its argument types are, etc.
If you ask what a method's return type is, and that method returns void, you get the static final member Void.TYPE . That is the only purpose of the Void class.