And differences between abstract classes and interfaces are -

• A child class can only extend one child class but can implement multiple interfaces
• An abstract class can have both defined and undefined methods but an interface can only have undefined methods
• This one is a similarity. None of the abstract class or interface can be instantiated. However both can reference to objects of base class like this

  Webdriver driver;
  driver = new FirefoxDriver(); //FirefoxDriver is a base class and Webdriver is an interface.
  

  We can pass class like this to a function that requires a interface if class implementts that interface

```