abstract vs. intervace java code example

Example 1: java abstract vs interface

you can extend only one abstract class, but you can implement as much interfaces as you would need

Example 2: abstract class vs interface 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.

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.For example in my framework I am using
page object model design pattern and I keep all
locators under Page class. I utilize this locators
in tests but we can't see them in the tests.
Literally we are hiding locators from the test.
Abstraction is methodology of hiding implementation
of internal details and showing the functionality to
users.
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.