java.lang.Void and void

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java.lang.Void is analogous to java.lang.Integer. Integer is a way of boxing values of the primitive type int. Void is a way of boxing values of the primitive type void.

"But wait, void doesn‘t have any possible values!"

Right! That‘s what makes java.lang.Void "uninstantiable". :)

It‘s a nice feature of the Java type system that every primitive type has a boxed equivalent. inthas Integer, long has Long, byte has Byte... and void has Void. It would be weird and asymmetrical if Void didn‘t exist.

"So what‘s the difference between java.lang.Void and void?"

Easy. void is a primitive type. Void is an reference type that inherits from Object. They‘re similar in that neither of them has any possible values; but nevertheless they are two very different types, from the type system‘s point of view.

"But I don‘t have any use for Void in my programs."

And I don‘t have any use for GarbageCollectorMXBean in mine. Some features don‘t have non-obscure uses. That‘s okay.

 

The only point of Void is to hold Void.TYPE, which is sort of like void.class. If you have a reflective reference to a method that returns void, and you get its return type, it‘ll return Void.TYPE.

java.lang.Void and void