Uses for the Java Void Reference Type?

Question

There is a Java Void -- uppercase V-- reference type. The only situation I have ever seen it used is to parameterize Callables

final Callable<Void> callable = new Callable<Void>() {
            public Void call() {
                foobar();
                return null;
            }
        };

Are there any other uses for the Java Void reference type? Can it ever be assigned anything other than null? If yes, do you have examples?

Answer 1

Void has become convention for a generic argument that you are not interested in. There is no reason why you should use any other non-instantiable type, such as System.

It is also often used in for example Map values (although Collections.newSetFromMap uses Boolean as maps don't have to accept null values) and java.security.PrivilegedAction.

I wrote a weblog entry on Void a few years back.