Object Oriented Design
Advanced Programming
SUT • Spring 2019
Outline
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Object Oriented Programming
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Characteristics of objects
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Interface
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Encapsulation
Abstraction
Abstraction
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Machine language
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Assembly: an abstraction of the machine language
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Many languages are abstraction of assembly language
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Fortran, Basic, C
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Big improvement
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But they still require you to think in terms of the structure of the computer
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Rather than the structure of the problem
Different Contexts
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Problem Space
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the place where the problem exists
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such as a business
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Solution Space
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the place where you’re implementing that solution such as a computer
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The effort required to perform this mapping
Library Problem
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Suppose you want to write a library program
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What are the elements of your program?
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We think about functions and variables…
Object Oriented Approach
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A step further
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Represent problem space elements
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This representation is general enough
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Is not constrained to any particular type of problem.
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The elements in the problem space and their representations in the solution space are referred to as “objects”
Object Oriented Principle
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The program is allowed to adapt itself to the lingo of the problem
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by adding new types of objects
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when you read the code, you’re reading words that also express the problem.
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This is a more flexible and powerful language abstraction
Object Oriented Languages
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Smalltalk
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The first successful object-oriented language
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One of the languages upon which Java is based
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Java
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C++
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C##
OOP vs. Procedural Approach
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Elements of OOP
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Objects
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Message passing between objects
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Elements of procedural programming
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Functions
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Variables
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Function invocation
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The way of thinking
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Thinking about objects and relations
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Thinking about functions and computer structure
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OOP Characteristics
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basic characteristics of Smalltalk:
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Everything is an object
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A program is a bunch of objects telling each other what to do
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by sending messages
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Each object has its own memory
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made up of other objects
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Every object has a type
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All objects of a particular type can receive the same messages
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Booch’s description of an Object
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An object has state, behavior and identity
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Booch added identity to the description
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An object (may) have internal data
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which gives it state
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An object (may) have methods
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to produce behavior
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And each object can be uniquely distinguished from every other object
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Each object has a unique address in memory
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Interface
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Each object can satisfy only certain requests
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The requests you can make of an object are defined by its interface
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The type is what determines the interface
Representation of a light bulb
public class Main {
public static void main(String[] args) {
// Turn On the Light
Light lt = new Light();
lt.on();
}
}
Person in an Education System
public class Main {
public static void main(String[] args) {
// Person in Education System
Person person = new Person();
person.setName("Taghi Taghavi");
person.setPhoneNumber(66166601L);
person.showInformation();
}
}
New names in OOP
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Function: Method, Service
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Variable: Property, State
Encapsulation
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Commercial products are encapsulated
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Remote control
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TV
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Cell phone
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They are Black Boxes
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Hidden Implementations
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Public interface
Why Encapsulation?
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Simplified use
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Even for the producer
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Open implementation: bad use
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Hiding the implementation reduces bugs
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It is more beautiful!
Object Encapsulation
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Encapsulation of a problem-space concept into a class of objects
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Define interface
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Hide the implementation
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Black box
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The client may see the implementation
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But can not use it directly
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This is better even for the producer (programmer)
Access Control
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Access to some parts of the class is restricted
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Public and Private area of the class
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The client of a class can use only public area
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Public area = class interface
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Public methods
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Public variables
Example: Rectangle
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Lets encapsulate a rectangle
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What is a rectangle?
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An object
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Which has length and width (properties)
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Lets you specify its length and width
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Can calculate its area and perimeter
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Class Declaration
public class Rectangle {
private int width, length;
public void setWidth(int w) {
width = w;
}
public void setLength(int l) {
length = l;
}
public int calculateArea() {
return width * length;
}
public int calculatePerimeter() {
return (width + length) * 2;
}
}
How to Use Rectangle?
public class Main {
public static void main(String[] args) {
// Rectangle Usage
Rectangle rect = new Rectangle();
rect.setWidth(2);
rect.setLength(7);
System.out.println(rect.calculateArea());
System.out.println(rect.calculatePerimeter());
}
}
Title Text
Object Oriented Design
By Behnam Hatami
Object Oriented Design
Object Oriented Design / Advanced Programming Course @ SUT, Spring 2019
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