Java’s interface language feature confuses many Java newbies. Many mistakenly assume that interfaces only sidestep Java’s failure to support multiple implementation inheritance. In reality ...

You can use multiple inheritance with interfaces, however. The difference between a class and an interface, in this case, is that interfaces don’t keep state.

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.