abstract classes and interfaces 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.

An abstract method is the method which does’nt have any body. Abstract method is declared with keyword abstract and semicolon in place of method body. public abstract void <method name>(); Ex : public abstract void getDetails(); It is the responsibility of subclass to provide implementation to abstract method defined in abstract class

Interface 1) Interface contains only abstract methods 2) Access Specifiers for methods in interface must be public 3) Variables defined must be public , static , final 4) Multiple Inheritance in java is implemented using interface 5) To implement an interface we use implements keyword Abstract Class 1) Abstract class can contain abstract methods, concrete methods or both 2) Except private we can have any access specifier for methods in abstract class. 3) Except private variables can have any access specifiers 4)We cannot achieve multiple inheritance using abstract class. 5)To implement an interface we use implements keyword

abstract class vs interface

Interfaces specify what a class must do and not how. 
It is the blueprint of the class.
It is used to achieve total abstraction. 

We are using implements keyword for interface.

Abstract=
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 that case we declare a class
as abstract by using abstract keyword on method
signature.In my framework I have created my
PageBase 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)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.

Posted by: Guest on December-05-2020

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