Answers for "interface vs abstract class java"

difference between abstract and interface

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.

abstract class vs interface

***************************Abstract class*****************************
1) Abstract class can have abstract and non-abstract methods.
2) Abstract class doesn't support multiple inheritance.
3) Abstract class can have final, non-final, static and non-static variables.
4) Abstract class can provide the implementation of interface.
5) The abstract keyword is used to declare abstract class.
6) An abstract class can extend another Java class and implement multiple Java interfaces.
7) An abstract class can be extended using keyword "extends".
8) A Java abstract class can have class members like private, protected, etc.
9)Example:
public abstract class Shape{
public abstract void draw();
}


*****************************Interface********************************
1) Interface can have only abstract methods. Since Java 8, it can have default and static methods also.
2) Interface supports multiple inheritance.
3) Interface has only static and final variable
4) Interface can't provide the implementation of abstract class.
5) The interface keyword is used to declare interface.
6) An interface can extend another Java interface only.
7) An interface can be implemented using keyword "implements".
8) Members of a Java interface are public by default.
9) Example:
public interface Drawable{
void draw();
}

interface vs abstract class java

Interfaces specify what a class must do. 
It is the blueprint of the class.
It is used to achieve total abstraction. 
We are using implements keyword for interface.

Basic statement we all know in Selenium is
WebDriver driver = new FirefoxDriver();
WebDriver itself is an Interface.
So we are initializing Firefox browser
using Selenium WebDriver.
It means we are creating a reference variable
of the interface and creating an Object.
So WebDriver is an Interface and
FirefoxDriver is a class.

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.

difference between interface and abstract class

Interfaces specify what a class must do. 
It is the blueprint of the class.
It is used to achieve total abstraction. 
We are using implements keyword for interface.

Basic statement we all know in Selenium is
WebDriver driver = new FirefoxDriver();
WebDriver itself is an Interface.
So we are initializing Firefox browser
using Selenium WebDriver.
It means we are creating a reference variable
of the interface and creating an Object.
So WebDriver is an Interface and
FirefoxDriver is a class.

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.

how to use an abstract class in java

interface methods{
    public void hey();
    public void bye();
}

//unable to implement all the abstract methods in the interface so 
// the other class automatically becomes abstract
abstract class other implements methods{
    public void hey(){
        System.out.println("Hey");
    }
}

//able to implement all the methods so is not abstract
class scratch implements methods {
    public void hey(){
        System.out.println("Hey");
    }
    public void bye() {
        System.out.println("Hey");
    }
}