Who Am I?

• bachelor of eng in eee.
• master's degree in etm.
• softare/r&d engineer.
• denizmemis @linkedin.com
• d8niz @github.com
• deniz.memis @eteration.com

Object Oriented Programming

• objects
• classes
• inheritance
• abstraction
• hierarchies / taxonomies

Story Time :)

Alan Kay

Personal computing pioneer (see Smalltalk), holding a Dynabook

• The best way to predict the future is to invent it.

• Technology is anything invented after you were born.

• The most disastrous thing that you can ever learn is your first programming language.

• A change in perspective is worth 80 IQ points.

OOPs #1: Human Cell Analogy

• Expectation:

  • Inheritance
  • Taxonomy

• Reality:

  • ->Cells
    --> Tissues
    ----> Organs
    --------> Organisms

Contrast: Imperative (Procedural) Style

"...a software development paradigm where functions are implicitly coded in every step required to solve a problem..."

Contrast: Object-Oriented Style

"...a computer programming model that organizes software design around data, or objects, rather than functions and logic..."

OOPs #2: Big Idea

• Expectation:

  • Objects (!)
  • Classes (!)

• Reality:

  • Messaging
  • Late-binding

Objects

• Say objects are like cells
• And big idea is messaging
• How do they even communicate ?

Messages

• Dopamine (look slightly right)
• Receptors acting as communication agents
• Laying out the messaging protocol

Systems

• What do you see here?

• Computers messaging thru an established protocol

• What do we get ?

  • Much larger and flexible system
  • Handles complexity
  • Handles scaling

Typical OOP Syntax

thing.do(some, stuff);
<rec> <---message--->
         <---args--->

• Email format:

- to: thing
- subject: urgent please :)
- message: 'do', some, stuff

What does do do ?

thing.do(some, stuff);
thing.do(other, stuff)
child.do(some, stuff)
thing.do(some, stuff)

• Late binding
• It is up to the thing (object || recipient) to do what to do :)
• Flexible
• Adaptable
• Tolerant to change

End Of Story Time :)

Four Pillars Of OOP

• Abstraction
• Encapsulation
• Inheritance
• Polymorphism

Abstraction

"...the process of considering something independently of its associations or attributes..."

• Hiding implementation details

abstract class Bike{  
  abstract void run();  
}  

class HondaCB250R extends Bike{  
  void run()
  {
    System.out.println("running safely on a 250cc bike");
  }

  public static void main(String args[])
  {  
    Bike obj = new Honda4();  
    obj.run(); //running safely on a 250cc bike
  }  
}  

Encapsulation

"...the action of enclosing something in or as if in a capsule..."

• Bundling the data along with the behaviior

• Facilitates the state management, keeps thing organized, allows read/write access management

class Person {
  private int age;
  private String name;
  private String surname;
  private float salary;
  private String pob;
  private String dob;

  public Person(name,surname){...}

  public int getAge(){...}
  public void setAge(int age) {...}
  .
  .  
  public float calculateSalary(int age, String dob) {...}

}

Inheritance

• Some classes may share commonalities
  • For example HomePolicy, AutoPolicy, LifePolicy classes may all have same state and behavior
• Instead of repeating commonalities in each class, we can abstract them in a common place
• These commonalities can be stored in a super class
• Each subclass inherits state and behavior from its superclass

Inheritance (cont'd)

public class Main {
	public static void main(String[] args) {
		Calc calc = new Calc();
		System.out.println("sum: " + calc.add());

		Calc calcWihParametricConstuctor = new Calc(1, -2);
		System.out.println("sum: " + calcWihParametricConstuctor.add());

		AbsoluteCalc absCal = new AbsoluteCalc(1, -2);
		System.out.println("abs sum: " + absCal.add());
	}
}

class Calc {
	private int first;
	private int second;

	public Calc(int first, int second) {
		this.first = first;
		this.second = second;
	}

	public int add() {
		return this.first + this.second;
	}
}

class AbsoluteCalc extends Calc {

	public AbsoluteCalc(int first, int second) {
		super(first, second);
	}

	@Override
	public int add() {
		return Math.abs(this.getFirst()) + Math.abs(this.getSecond());
	}
}

Polymorphism

• Different objects respond to the same message in different ways
  • For example when asked to talk a dog barks, and a cat meows
• It is often supported by method overriding
  • Overriding means that subclass may implement the same method as superclass, but with different code
  • toString() method in the Object class is an example of often overridden method