PAGE-4 : HOW WebDriver driver = new FirefoxDriver() WORKS INTERNALLY

When we first start with selenium automation our very first line code comes as  :

WebDriver driver = new FireFoxDriver

Simple answer to this is WebDriver is an Interface,and we are defining a reference variable(driver) whose type is an interface .Now any object we assign to it must be an instance of a class(FireFoxDriver) that implements the interface."

Note : Firefox driver is included in the selenium-server-stanalone.jar available in the downloads. The driver comes in the form of an xpi (firefox extension) which is added to the firefox profile when you start a new instance of FirefoxDriver.

WHAT IS AN INTERFACE

Interface is like a blueprint of Class. It contains variables and body less methods(Abstract methods), where we just declare methods but we implement them inside the class which inherit Interface.

EXAMPLE

package com.package1;

public interface WebDriver {

       public void getUrl(String Url);

      

}

Above example just contain the structure of a get method, now a class which would implement this interface need to define the method.

Now we will create a class which will implement the interface

package com.package1;

public class FirefoxDriver implements WebDriver{

       @Override

       public void getUrl(String Url) {

              System.out.println("Url is :" + Url);

             

       }

}

Class that implements an interface must implement all the methods declared in the interface. Now our FirefoxDriver class should implement all the methods declared inside an WebDriver interface, same is the case with ChromeDriver or IEDriver classes.

package com.package1;

import org.testng.annotations.Test;

public class ImplementationClass {

      

       @Test

       public void test(){

              WebDriver driver=new FirefoxDriver();

              driver.getUrl("http://facebook.com");

       }

      

}

So from here we have understood that “Webdriver” is an interface and “FirefoxDriver”  is an implementation class of the interface.

INTERFACE INSTANCE

We can create a reference variable of an interface but we can't instantiate any interface since it is just a contract to be implemented in a Class.

WebDriver driver = New WebDriver()

To understand the concept of WebDriver driver=new WebDriver() , you have to know the concept behind the anonymous inner class using Interface.

package com.package1;

public interface WebDriver {

       void eat();

}

package com.package1;

public class ImplementationClass {

public static void main(String[] args) {

       WebDriver driver= new WebDriver() {

             

              @Override

              public void eat() {

                     System.out.println("Nice Fruits");

                    

              }

       };

       driver.eat();

}

}

Output here is :  nice fruits

INTERNAL WORKING OF THE CODE 

It performs two main tasks behind this code:

WebDriver driver= new WebDriver(){ 

void eat(){

System.out.println("nice fruits");} 

}; 

A class is created but its name is decided by the compiler which implements the Eatable interface and provides the implementation of the eat() method.

An object of Anonymous class is created that is referred by p reference variable of Eatable type.

INTERNAL CLASS GENERATED BY THE COMPILER

import java.io.PrintStream; 

static class TestAnonymousInner1$1 implements WebDriver 

{ 

TestAnonymousInnerClass(){} 

void eat(){System.out.println("nice fruits");} 

} 

So coming on to our topic : WebDriver driver = new WebDriver();

This means that we are simultaneously creating an anonymous class that implements the WebDriver interface and also creating an instance of that anonymous class.