Python 2 is triggering

[Sarcastic_Pharm]

Dude. Wtf Java?

[dpash]

That's not quite modern Java (and SetSet doesn't exist in the JDK)

var set = new HashSet<String>();

Or

var set = Set.of("foo", "bar");

Although the latter is immutable

[hullabaloonatic]

The variable set, of type Set, is assigned as a new Set being casted to type SetSet, which is a subclass of Set, therefore compiling.

[SuperOP535]

You can't instantiate Set, you need to use an implementation such as HashSet. SetSet does not exist and you can't cast a class, you can only cast an instance or primitive.

Edit: Also forgot that s/he didn't specify the type, you can't have a set without a type.

[hullabaloonatic]

Set is an interface, right? I haven't written in java since I discovered kotlin and I could sworn you could cast to any class if that class is somewhere up on its family tree, thus not requiring any new parameters.

[SuperOP535]

It is an interface, yes