Java also lets you nest interfaces in interfaces and classes in interfaces. Check out this article on nested interfaces to learn about this strange but occasionally useful Java language feature.

Java lets you declare interfaces inside of classes. Once declared, an interface is automatically a static member of the class. There is no need to declare the interface with the static keyword.

Sealed classes in Java let developers limit the creation and use of subclasses and preserve the class hierarchy. Here is how sealed classes in Java work.