In Java 1.0 and 1.1, the two primary collection classes were Vector and Hashtable, and the Iterator design pattern was implemented in a class called Enumeration.

Abstract classes and interfaces in Java serve fundamentally different purposes. Learn the differences between these Java language elements and how to use them in your programs.

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.