abstraction in programming code example

Example 1: what is abstraction

it is process of hiding implementation details and 
only showing the functionality to the user. 
Abstraction focus on what the object does instead of how it does. 
It is achieved by using Abstract class and Interface. 
abstract methods (methods without body, cannot be static and final), 
interface must implemented and abstract classes must be extended 
by regular classes in order to achieve abstraction 
(because abstract methods can only be exist in abstract class and interface). 
A class can implement multiple interfaces, 
but it can extend only single abstract class.

Ex: In my framework I have achieve abstraction by using collections or 
Map, because it’s all interface. Most of the cases I come across using List. 
If we want to access elements frequently by using index, List is a way to go. 
ArrayList provides faster access if we know index. 
If we want to store elements and want them to maintain an order, 
List is a better choice.

i)List<String> webs=driver.getWindowHandles();
=>create a list first to store web URLs in list

ii)findElements evaluates multiple elements so therefore will assigned 
to List <WebElement>

iii)To handle dynamic elements store it in the list and identify by index:
List<WebElement> all=driver.findElements(By.tagname(“”)); (or other locators).

Example 2: abstractin

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.In my framework I have created my
PageBase class as super
class of the all page classes. 
I have collected all common elements
and functions into PageBase class and
all other page classes extent PageBase class.
By doing so, I don't have to locate very
common WebElements and it provides
reusability in my framework.
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.