What is a Class and object?
Class is a blue print / template. Objects are instances of classes, in other words they bring life in class. To use a class we need to create an object.
What is nested Classes?
Nested classes are classes within classes.
What are abstract classes?
Abstract class is a half defined parent class. The full implementation of abstract class is defined by the child classes.
For example below code snippet shows a simple abstract class / half defined class called “DatabaseCommon” and later the concrete classes i.e. “SQLServer” and “Oracle” inherit and define a complete implementation for the same.
To define an abstract class we need to use the abstract keyword.
Also do not forget to visit http://www.questpond.com and see following video on Classes and objects: -