A subclass is a class defined as an extension or modification of another class. Inheritance is the way a subclass uses method definitions and variables from a superclass just if they had belonged to the subclass itself. Usually a collection of classes has a certain relationship. For this, a package concept is introduced, which offers information hiding concept well-known from modular programming. If you want to use a class you have to import it by specifying the package name.
Packages are a mechanism for building libraries.
Object-oriented programming is not at all new. Its history goes back to 1991 when a group of SUN engineers led by James Gosling wanted to design a small computer language that could be used for consumer devices like cable TV switchboxes. This course is divided into 14 lessons which are themselves structured into a sequence of units . We have plans for advanced courses on Java programming and related parts in later semesters. This course will set the foundation for later courses.