Selenium-Webdriver-Object declaration

Question

What is the difference between below two statement?

WebDriver driver = new FirefoxDriver();

FirefoxDriver driver= new FirefoxDriver();

Answer 1

This is casting.

With WebDriver you are explicitly casting new instance of FirefoxDriver() as WebDriver and same for the FirefoxDriver.

Answer 2

Suppose we want to do cross browser testing. If we use first definition

WebDriver driver = new FirefoxDriver();

Then we can use the same object to run test in chrome or IE-:

driver=new ChromeDriver(); 

or

driver=new InternetExplorerDriver();

But if we use second definition, then we have define another instance-:

ChromeDriver driver2= new ChromeDriver();

or

InternetExplorer driver3= new InternetExplorerDriver();