abstract class
Abstract class is used in defining a common super class while writing Page Object Model layer of the framework. We usually create an abstract class named BasePage to have all common members for every page written in this class example getPageTitle(). Then each Page class (HomePage, LoginPage, DashboardPage etc.) inherit from BasePage. Sometimes one may need to change the behavior of methods implemented in superclass. So, subclass has freedom to override that method where we use polymorphism. This is how we use Abstract class in real projects. .In my framework I have created my BasePage class as super class of the all page classes. I have collected all common elements and functions into PageBase class and all other page classes extent PageBase class. By doing so, I don't have to locate very common WebElements and it provides reusability in my framework. Also 1)Abstract classes cannot be instantiated 2)Abstract class meant to be inherited so can not be final,static and private 2)An abstarct classes contains abstract method, concrete methods or both. 3)Any class which extends abstarct class must override all methods of abstract class 4)An abstarct class can contain either 0 or more abstract method.