Presentation on the principles, philosophy and a few applications of object oriented programming along with a few pointers on how to effectively code. Presented at a session aimed at undergrad computer science students at the University of Pune. Present along with Mr. Anirudh Tomer and Mr. Toshish Jawale.

1. SOLID OOPS
ConvertingReal world entities into programming Objects ;
understanding its applications ; API designing, MVC framework

2.  We apologize for wrong session title 
 Lets know each other
 Your expectations
 Our aim
 Why should you join this session
 Goodies for active participants 
Introduction

3.  What is “Real”?
 Everything outside of your program is
Real.
 Even your own program is a Real World
Entity for some other program or even for
your own program!
 In short
Real World Entity…

4.  Because these are all the “things” on
which we want to work upon.
 Yes, and by work we do not mean, just
writing the code! 
Why do we bother about this?

5.  Objects? Why?
 How are they introduced in the
programming world?
 Where are they used often?
 State and behaviour
 Who should use it?
Correlating to programming
objects

6.  We separate our real world entities in
different groups
 Object is an instance of a class
Ball
instances of
What is this class?

7.  How classes are organized?
 Why classes need to be organized?
 Is there any standard way to do it?
 If yes, whats it?
Organization

8.  How these different attributes of a class
are defined?
 fields/properties - state
 methods/functions - behavior
 constructors/initializers
 destructors
What class contains?

9.  What is the object oriented way of getting
rich ?
— Inheritance
 Relations between the classes
 By the way, are you good at relations?
Relations

10.  Have you watched Television?
Interface

11.  Something you use to keep your stuff from
mixing together
 Folders
 Drives
 A customized, more sophisticated package
 Examples familiar to you are,
◦ ZIP file
◦ EXE file
◦ DLL file etc.
Point is, keep your stuff organized.
Package

12. What is Abstraction?
• Abstraction - a concept or idea not associated with
any specific instance
• It is all about perspective

13. Where does abstraction exist?
• Control abstraction
o Abstraction of actions
• Data abstraction
o Abstraction of information

14. How does this relate to
programming?
• Writing functions/subroutines is control
abstraction.
• Datatypes is data abstraction.

15. Data Abstraction
• Generalization
• Specialization

16. Example
public class Animal extends
LivingThing{ theChicken = new Animal();
private Location loc; theCat = new Animal();if
private double energyReserves;
(theChicken.isHungry())
public boolean isHungry() { {
return energyReserves <
2.5; theChicken.eat(grains);}
} if (theCat.isHungry()) {
public void eat(Food f) { theCat.eat(mouse);}
// Consume food theCat.moveTo(theSofa);
energyReserves +=
f.getCalories();
}
public void moveTo(Location l)
{
// Move to new location
loc = l;
}}

17. It's relevance with OOP
• Object is an attempt to combine data and control
abstraction
• Polymorphism
• Inheritence

18. Why do this?
• Separate the business logic from the underlying
complexity
• Make it easier to parallelize tasks
• Meaningful amount of details are exposed
• Representation in a similar form in semantics
(meaning) while hiding implementation details.

19. Why do we write programs?

20. We have the right objects in
place, now what?
• Let's get them talking to each other
• Let's actually tell them what to talk about

21. What sort of messages?
• Creation
• Invocation
• Destruction

22. Who generates these
messages?
• Aliens? • Platform
• The Government? • User Interaction
• Events

23. API Designing

24. String operations
I need it to be
Hehehe! The menu driven
whole 2 hours I
will just write a
fancy menu
Programming Lab I

25. Set operations
Again! *$%#@ I need it to be
Menu will be menu driven
“Enter 1 to
proceed 0 to
exit”
Programming Lab I

26. Don’ts we do
Monolithic programs
Single file containing all functions
Code repetition
Thinking less about function signature
Reinventing the wheel

27. What we think about API 
API

28. What it actually is 
printf(), scanf(), strcmp()
Easy to use and hard to misuse Spec of DS,
functions,
Can be programming language unspecific!! behavior
etc.
Not necessarily a code library, can be just a spec
You can create your own API too

29. Lets design an API

30. Designing Process (based on suggestions by Joshua Bloch)
 Write 2 programs and not one
 Write API first
◦ Understand the use case
◦ Foresee future extensions (don’t change API often)
◦ A general purpose API vs multiple small API’s
◦ If you can’t name it, its doing either extra or doing less
◦ Don’t surprise the API user, don’t do extra
◦ Remember! You can always add but you can’t remove
◦ Document the API religiously!
◦ Use consistent parameter ordering.
◦ Extra params, use a struct
 Code more! API is living thing
 Expect to make mistakes. Refactor API!
 Encourage others to use it

31. MVC Architecture

32. Programming without MVC
I need it
 Linked List with GUI
o add a node
o remove a node
o reverse a linked list
 Linked list with GUI
______ ______ ______
|__1__| |__5__| |__7__| …

33. Challenges
Data Functions GUI
Structures • Function • Creating
• struct ? signature boxes
• Separate • Flow control • Moving
variables boxes

34. Nightmare begins
typedef struct node{
struct node* nextNode;
…
}Node;
…
Node *linkedlist;
addNewNode(){
while (linkedlist->nextNode!=null){
drawSquare(); //you may have internal D.S. for each square
drawArrow();
}
Node *newNode = (Node*) malloc(sizeof(struct node));
scanf(); // for new values
newNode->val1 = …;
newNode->val2 = …;
linkedlist->nextNode = newNode;
while (linkedlist->nextNode!=null){
drawSquare();
drawArrow();
}
}

35. New requirements
 Keep different colors for each node
 I want oval nodes not rectangular nodes
 I want linked list nodes to be shown in
hierarchy not in straight line.
Make Changes

36. FB Timeline: Full of GUI
Components

37. MVC Framework: Coding vs.
Architecting
Its nothing but
how you design
your code.

38. Model View Controller
• Handling data • Display data • Read data
• Save them on from view
file or in • Control user
internal D.S interaction
• Send new
data to model
Roles: Model, View and Controller

39. M-V-C not MVC
 Keep them separate
 You may create different files
◦ A separate “model.h”
◦ A separate “view.c” (includes model.h)
◦ A separate “controller.c” (includes model.h)
◦ Give deep thought to data structures
 Principle of Agnosticism:
each component is unaware of others presence

40. Model
typedef struct node{ C++ or other
struct node* nextNode;
int id; OOP languages
… make finding the
}Node;
int globalId = 0;
context easy
typedef struct linkedList{
Node * headNode;
int id;
int listLength;
}LinkedList;
LinkedList *linkedListPool[];
void addNode(int linkedListId, int index, Node *newNode){
…
}
void removeNode(int linkedListId, Node *node){
…
}
LinkedList* createNewLinkedList(){
LinkedList* newll = (LinkedList*) malloc(sizeof(struct linkedList));
newll->id = globalId++;
newll->headNode = (Node*) malloc(sizeof(struct node));
newll->length = 0;
linkedListPool[globalId] = newll;
return newll;
}

41. View
typedef struct viewNode{
struct viewNode* nextViewNode;
int xLocation, int yLocation;
String color; //#FF3e2A (in hex)
…
}ViewNode;
//Similar to Model create another struct
typedef struct display{
ViewNode* head;
int id;
int length;
}Display;
Display *displayNodeList[];
void addDisplayNode(int viewNodeId, int index, Node *newNode){
//create new ViewNode
//Render UI
…
}
//create new display node like Model

42. Controller
typedef enum input{
ADD,REMOVE,GET_LENGTH…
}Input;
LinkedList* linkedList = createNewLinkedList();
Display* display = createNewDisplay();
//Show a fancy menu
Input input = read input from user;
switch(input){
case ADD:
Node* newNode = //malloc new node;
addNode(linkedList->id,newNode);
addDisplayNode(display->id,newNode);
break;
}

43. Questions ?