public static interface Subject.Factory<SubjectT extends Subject<SubjectT,ActualT>,ActualT>

In a fluent assertion chain, the argument to the common overload of about, the method that specifies what kind of Subject to create.

For more information about the fluent chain, see this FAQ entry.

For people extending Truth

When you write a custom subject, see our doc on extensions. It explains where Subject.Factory fits into the process.