Set set = new HashSet<>();
List list = new ArrayList<>();
set.add(4);  ==> HashSet overrides add() method from Collection Interface
list.add(8); ==> ArrayList overrides add() method from Collection Interface

WebDriver driver1 = new ChromeDriver();
driver1.get("xxxxxx"); ChromeDriver overrides get/findElement/etc.
                                      methods from WebDriver Interface.

WebDriver driver2 = new FirefoxDriver();
driver2.get("xxxxxx"); FirefoxDriver overrides 
get/findElement/etc. methods from WebDriver Interface.