OOP, API Design and MVP

SOLID OOPSConverting Real world entities into programming Objects ;

understanding its applications ; API designing, MVC framework

Introduction

We apologize for wrong session title Lets know each otherYour expectationsOur aimWhy should you join this sessionGoodies for active participants

Real World Entity…

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

“EVERYTHING IS REAL”

Why do we bother about this?

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!

Work?

Still, how are they related to programming?

Correlating to programming objects

Objects? Why?How are they introduced in the

programming world?Where are they used often?State and behaviourWho should use it?

What is this class?

We separate our real world entities in different groups

Object is an instance of a class

Ball

instances of

Organization

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

What class contains?

How these different attributes of a class are defined?

fields/properties - statemethods/functions - behaviorconstructors/initializers destructors

Relations

What is the object oriented way of getting rich ?

— Inheritance Relations between the classesBy the way, are you good at relations?

Interface

Have you watched Television?

Package

Something you use to keep your stuff from mixing together

FoldersDrivesA customized, more sophisticated packageExamples familiar to you are,

◦ZIP file◦EXE file◦DLL file etc.

Point is, keep your stuff organized.

What is Abstraction?

• Abstraction - a concept or idea not associated with any specific instance

• It is all about perspective

Where does abstraction exist?

• Control abstractiono Abstraction of actions

• Data abstractiono Abstraction of information

How does this relate to programming?

• Writing functions/subroutines is control abstraction.

• Datatypes is data abstraction.

Data Abstraction

• Generalization

• Specialization

Examplepublic class Animal extends

LivingThing{ private Location loc; private double energyReserves; public boolean isHungry() { return energyReserves < 2.5; } public void eat(Food f) { // Consume food energyReserves += f.getCalories(); } public void moveTo(Location l) { // Move to new location loc = l; }}

theChicken = new Animal();theCat = new Animal();if (theChicken.isHungry()) { theChicken.eat(grains);}if (theCat.isHungry()) { theCat.eat(mouse);}theCat.moveTo(theSofa);

It's relevance with OOP

• Object is an attempt to combine data and control abstraction

• Polymorphism

• Inheritence

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.

Why do we write programs?

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

What sort of messages?

• Creation

• Invocation

• Destruction

Who generates these messages?

• Aliens?

• The Government?• Platform

• User Interaction

• Events

API Designing

String operations

I need it to be menu drivenHehehe! The

whole 2 hours I will just write a

fancy menu

Programming Lab I

Set operations

Again! *$%#@Menu will be “Enter 1 to

proceed 0 to exit”

Programming Lab I

I need it to be menu driven

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

What we think about API

API

What it actually is

printf(), scanf(), strcmp()

Easy to use and hard to misuse

Can be programming language unspecific!!

Not necessarily a code library, can be just a spec

You can create your own API too

Spec of DS, functions, behavior

etc.

Lets design an API

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

MVC Architecture

Programming without MVCLinked Listo add a nodeo remove a nodeo reverse a linked list

Linked list with GUI ______ ______ ______|__1__| |__5__| |__7__| …

I need it with GUI

Challenges

Data Structures• struct ?• Separate

variables

Functions• Function

signature• Flow control

GUI• Creating

boxes• Moving

boxes

Nightmare beginstypedef struct node{

struct node* nextNode;…}Node;…Node *linkedlist;

addNewNode(){while (linkedlist->nextNode!=null){

drawSquare(); //you may have internal D.S. for each squaredrawArrow();

}

Node *newNode = (Node*) malloc(sizeof(struct node));

scanf(); // for new valuesnewNode->val1 = …;newNode->val2 = …;linkedlist->nextNode = newNode;

while (linkedlist->nextNode!=null){drawSquare();drawArrow();

}}

New requirements

Keep different colors for each nodeI want oval nodes not rectangular nodesI want linked list nodes to be shown in

hierarchy not in straight line.

Make Changes

FB Timeline: Full of GUI Components

MVC Framework: Coding vs. Architecting

Its nothing but how you design your code.

Roles: Model, View and Controller

Model• Handling data• Save them on

file or in internal D.S

View• Display data

Controller• Read data

from view• Control user

interaction• Send new

data to model

M-V-C not MVCKeep them separateYou 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

Modeltypedef struct node{

struct node* nextNode;int id;…

}Node;int globalId = 0;

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;

}

C++ or other OOP languages make

finding the context easy

Viewtypedef struct viewNode{

struct viewNode* nextViewNode;int xLocation, int yLocation;String color; //#FF3e2A (in hex)

…}ViewNode;

//Similar to Model create another structtypedef 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

Controllertypedef enum input{ADD,REMOVE,GET_LENGTH…

}Input;

LinkedList* linkedList = createNewLinkedList(); Display* display = createNewDisplay();

//Show a fancy menuInput input = read input from user;switch(input){

case ADD:Node* newNode = //malloc new node;addNode(linkedList->id,newNode);addDisplayNode(display->id,newNode);break;

}

Questions ?