class abstract code example

Example 1: abstract class in java

Sometimes we may come across a situation where we cannot provide 
implementation to all the methods in a class. We want to leave the 
implementation to a class that extends it. In such case we declare a class
as abstract.To make a class abstract we use key word abstract. 
Any class that contains one or more abstract methods is declared as abstract. 
If we don’t declare class as abstract which contains abstract methods we get 
compile time error.
  
  1)Abstract classes cannot be instantiated
  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.

Example 2: when we should use abstract class

When to use an abstract class
An abstract class is a good choice if we are using the inheritance concept since it provides a common base class implementation to derived classes.
An abstract class is also good if we want to declare non-public members. In an interface, all methods must be public.
If we want to add new methods in the future, then an abstract class is a better choice. Because if we add new methods to an interface, then all of the classes that already implemented that interface will have to be changed to implement the new methods.
If we want to create multiple versions of our component, create an abstract class. Abstract classes provide a simple and easy way to version our components. By updating the base class, all inheriting classes are automatically updated with the change. Interfaces, on the other hand, cannot be changed once created. If a new version of an interface is required, we must create a whole new interface.
Abstract classes have the advantage of allowing better forward compatibility. Once clients use an interface, we cannot change it; if they use an abstract class, we can still add behavior without breaking the existing code.
If we want to provide common, implemented functionality among all implementations of our component, use an abstract class. Abstract classes allow us to partially implement our class, whereas interfaces contain no implementation for any members.

Example 3: abstract class example in java

//abstract parent class
abstract class Animal{
   //abstract method
   public abstract void sound();
}
//Dog class extends Animal class
public class Dog extends Animal{

   public void sound(){
	System.out.println("Woof");
   }
   public static void main(String args[]){
	Animal obj = new Dog();
	obj.sound();
   }
}

Example 4: 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.