The Java Tutorial goes on to list bullets for when an abstract class should be considered and for when an interface should be considered. Unsurprisingly, these are derived from the previously ...

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.