Create packages, import packaged classes and interfaces into your programs, move packages, and encapsulate them in jar files.

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.

Okay, so you have an interface Monitor.How would you name classes that monitor Files and Bird Movement? How about in general?Since we have had a few style question recently, it came to mind.

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.