Java provides a collection framework defining several groups and interfaces to represent groups of objects as a single unit. Collection framework is one of the central and fundamental parts of ...

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

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.