Oop Rosen Schein

8/10/2019 Oop Rosen Schein

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Object Oriented Programming:Its Origins and Importance in

Computer Science

Prof. Jeffrey S. Rosenschein

School of Computer Science and Engineering

Hebrew University, Jerusalem, Israel


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Computer Programming

The history of computerprogramming is a steady move

away from machine-oriented

views of programming towardsconcepts and metaphors that

more closely reflect the way in

which we ourselves understand

the world


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Programming progression

Programming has progressed through:

machine code

assembly language machine-independent programming

languages

procedures & functions

objects


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Machine languageMark I


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Machine Language

0000 1001 1100 0110 1010 1111 0101 1000

1010 1111 0101 1000 0000 1001 1100 0110

1100 0110 1010 1111 0101 1000 0000 1001

0101 1000 0000 1001 1100 0110 1010 1111


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Assembly LanguagePDP-11


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Assembly LanguageMacro-11

GCD: TST B

BEQ SIMPLE

MOV A, R5

SXT R4DIV B, R4

MOV B, A

MOV R5, BCALL GCD

SIMPLE: RETURN


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Assembly LanguageMacro-11

GCD: TST B

BEQ SIMPLE

MOV A, R5

SXT R4DIV B, R4

MOV B, A

MOV R5, BCALL GCD

SIMPLE: RETURN


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Machine-Independent Programming Languages

Fortran ! This example program solves for roots of the quadratic equation,! ax^2 +bx +c =0,for given values of a, b and c.

!PROGRAM bisection

IMPLICIT NONE

INTEGER :: iteration

DOUBLE PRECISION :: CC, Er, xl, x0, x0_old, xr

! Set convergence criterion and guess for xl, xr.

CC = 1.d-4

xl = 8.d-1xr = 11.d-1

! Bisection method.

Er =CC +1

iteration = 0

DO WHILE (Er > CC)

iteration = iteration + 1

! Compute x0 and the error.

x0_old = x0

x0 = (xl + xr) / 2.d0

Er = DABS((x0 - x0_old)/x0)*100.d0

WRITE (*,10) iteration, x0_old, x0, Er

10 FORMAT (1X,I4,3(2X,E10.4)) this is partial


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Procedures & FunctionsPascal

program ValueArg(output);

{Shows how to arrange for a procedure to have arguments.}

procedure PrintInitials(First, Last : char);

{Within this procedure, the names First and Last represent theargument values. Well call write to print them.}

begin

write(My initials are: );

write(First);

writeln(Last)

end; {PrintInitials}

beginPrintInitials (D, C); {Any two characters can be arguments.}

PrintInitials (Q, T); {Like strings, characters are quoted.}

PrintInitials (&, #)

end. {ValueArg}


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Objects

(My examples will be from Java)classTime {

private inthour, minute;

publicTime (inth, intm) {

hour = h;minute = m;}

publicvoid addMinutes (intm) {inttotalMinutes =

((60*hour) + minute + m) % (24*60);if(totalMinutes


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Intrinsic Power vs. Effective Power

This progression is nota matter of intrinsic power

Anything you can do with a minimally capable

computer language, you can theoretically do with

any other minimally capable computer language

But that is like saying a shovel is theoretically ascapable as a tractor. In practice, using a shovel

might make things very hard


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Objects

hour

minute

void addMinutes( int m )

TimeinTimeAttributes:

hour = 8minute = 30

Methods:void addMinutes(int m)

outTimeAttributes:

hour = 17

minute = 35Methods:

void addMinutes(int m)

class

objects


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Classes and Objects

A classis a prototype for creatingobjects

When we write a program in an

object-oriented language like Java,we define classes, which in turn are

used to create objects

A class has a constructorforcreating objects


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classTime {


publicTime (inth, intm) {hour = h;minute = m;

}




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Definition of an Object

An object is a computational entity that:

1. Encapsulatessome state

2. Is able to perform actions, or methods, on this

state3. Communicates with other objects via message

passing


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1)Encapsulatessome state

Like a record in Pascal, it has a set ofvariables (of possibly different types)

that describe an objects state

These variables are sometimes calledan objects attributes(or fields, or

instance variables, or datamembers,

or )


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Pascal Example: Represent a Time

type TimeTYPE = record

Hour: 1..23;

Minute: 0..59;end;

var inToWork, outFromWork: TimeTYPE;


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Java Example: Represent a TimeclassTime {


publicTime (inth, intm) {

hour = h;minute = m;}

}

Time inToWork = newTime 8, 30);

Time outFromWork = newTime 17, 35);

constructorfor Time

attributesof Time


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Objects

hour

minute


TimeinToWork

Attributes:hour = 8minute = 30


outFromWork

Attributes:

hour = 17minute = 35Methods:

void addMinutes(int m)

class

objects


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classTime {


publicTime (inth, intm) {hour = h;minute = m;

}




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3) Communicates with other objects via

message passing

Sends messages to objects, triggering

methods in those objects

void


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Example of Object Creation

and Message Passing

bill

Attributes:

Methods:


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and Message Passing

bill

Attributes:

Methods:

In one of bills methods, the following code appears:

Time inToWork = new Time(8, 30);

inToWork.addMinutes(15);


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and Message Passing

inToWorkAttributes:hour = 8minute = 30


bill

Attributes:

Methods:





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and Message Passing



inToWork.addMinutes(15)

bill

Attributes:

Methods:





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and Message Passing



bill

Attributes:

Methods:





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Structure of a Class Definition

class

name{

declarations

constructor definition(s)

method definitions

}

attributes andsymbolic constants

how to create andinitialize objects

how to manipulatethe state of objects

These parts of a class can

actually be in any order


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History of Object-Oriented Programming

Started out for simulation of complex man-machine systems, but was soon realized thatit was suitable for all complex programmingprojects

SIMULA I (1962-65) and Simula 67 (1967)were the first two object-oriented languages Developed at the Norwegian Computing Center,

Oslo, Norway by Ole-Johan Dahl and Kristen

Nygaard Simula 67 introduced most of the key concepts of

object-oriented programming: objects and classes,subclasses (inheritance), virtual procedures


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The Ideas Spread

Alan Kay, Adele Goldberg and colleagues atXerox PARC extend the ideas of Simula indeveloping Smalltalk (1970s) Kay coins the term object oriented

Smalltalk is first fully object oriented language Grasps that this is a new programming paradigm

Integration of graphical user interfaces andinteractive program execution

Bjarne Stroustrup develops C++ (1980s) Brings object oriented concepts into the C

programming language


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Other Object Oriented Languages

Eiffel (B. Meyer) CLOS (D. Bobrow, G. Kiczales)

SELF (D. Ungar et al.)

Java (J. Gosling et al.) BETA (B. Bruun-Kristensen, O. Lehrmann

Madsen, B. Mller-Pedersen, K. Nygaard)

Other languages add object dialects, such asTurboPascal


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REVIEW:Definition of an Object

An object is a computational entity that:

Encapsulatessome state

Is able to perform actions, or methods, on this

state Communicates with other objects via message

passing


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Encapsulation The main point is that by thinking of the

system as composed of independent objects,we keep sub-parts reallyindependent

They communicate only through well-defined

message passing Different groups of programmers can work on

different parts of the project, just making sure

they comply with an interface

It is possible to build larger systems with less

effort


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Advantages

Building the system as a group of interactingobjects:

Allows extreme modularity between

pieces of the system May better match the way we (humans)

think about the problem

Avoids recoding, increases code-reuse


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But theres more

Classes can be arranged in a hierarchy

Subclasses inheritattributes and

methods from their parent classes

This allows us to organize classes, andto avoid rewriting codenew classes

extendold classes, with little extra work!

Allows for large, structured definitions


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Example of Class Inheritance

extends

extends

toString( )equals( Object obj )getClass( )

Shape

Rectangle

Time

extends

extends

Objects made from this

class, for example, have

allthe attributesand

methodsof the classes

above them, all the way

up the tree

Object

Circle Triangleextends


hourminute

colorborderWidth

Color getColor( )void setBorderWidth( int m )

int computeArea( )

lengthwidth

int computeArea( )

radius baseheight

int computeArea( )


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Java Class Hierarchy


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Java Class Hierarchy, another view


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Polymorphism An object has multiple identities, based on

its class inheritance tree It can be used in different ways


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A Circle is-a Shape is-a Object


Shapeextends

extends

Object

Circle

colorborderWidth


int computeArea( )

radius


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A Circle is-a Shape is-a Object


Shapeextends

extends

Object

Circle

colorborderWidth


int computeArea( )

radius

Shape

Circle

Object

A Circle object really has 3 parts


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How Objects are CreatedCircle c = newCircle );


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c

Shape

Circle

Object

1.

Execution Time


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c

Shape

Circle

Object

c

Shape

Circle

Object

1. 2.

Execution Time


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c

Shape

Circle

Object

c

Shape

Circle

Object

c

Shape

Circle

Object

1. 2. 3.

Execution Time


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Three Common Uses for Polymorphism

1. Using Polymorphism in Arrays

2. Using Polymorphism for Method

Arguments3. Using Polymorphism for Method

Return Type


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1) Using Polymorphism in Arrays

We can declare an array to be filled with Shape

objects, then put in Rectangles, Circles, orTriangles

extends


Shape

Rectangle

extends

extends

Object

Circle Triangleextends

colorborderWidth


int computeArea( )

lengthwidth

int computeArea( )

radius baseheight

int computeArea( )


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samples(an arrayof Shapeobjects)

[0] [1] [2]


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[0] [1] [2]

[2]

firstShape

Attributes:length = 17width = 35

Methods:int computeArea( )

secondShape

Attributes:radius = 11


thirdShape

Attributes:base = 15height = 7




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[0] [1] [2]

[2]

firstShape

Attributes:length = 17width = 35


secondShape

Attributes:radius = 11


thirdShape

Attributes:base = 15height = 7




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2) Using Polymorphism for Method

Arguments

We can create a procedure that has Shape as

the type of its argument, then use it for objects

of type Rectangle, Circle, and Triangle

publicintcalculatePaint (ShapemyFigure) {

finalintPRICE = 5;

inttotalCost = PRICE * myFigure.computeArea( );return totalCost;

}

The actual definition of computeArea( ) is known only at

runtime, not compile timethis is dynamic binding


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Arguments

Polymorphism give us a powerful way of

writing code that can handle multiple types

of objects, in a unified way

publicintcalculatePaint (ShapemyFigure) {

finalintPRICE = 5;

inttotalCost = PRICE * myFigure.computeArea( );return totalCost;

}

To do this, we need to declare in Shapes class definition

that its subclasses will define the method computeArea( )


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Return Type

We can write general code, leaving the typeof object to be decided at runtime

publicShapecreatePicture ( ) {

/* Read in choice from user */System.out.println(1 for rectangle, +2 for circle, 3 for triangle:);

SimpleInput sp = new SimpleInput(System.in);

inti = sp.readInt( );if( i == 1 ) return newRectangle(17, 35);if( i == 2 ) return newCircle(11);if( i == 3 ) return newTriangle(15, 7);

}


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Java Convinced Me to Start Teaching

Object-Oriented in Intro to CS

Java is Object-Oriented from the Ground Up

Java has the elegance that comes from being

designed afterother OO languages had been in use

for many years Java has strong type checking

Java handles its own memory allocation

Javas syntax is standard (similar to C and C++)

Java is a good teaching language, but it (or

something close) will also be seen by students in

industry

b d d


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Object-Oriented Programming in Industry

Large projects are routinely programmed

using object-oriented languages

nowadays

MS-Windows and applications in MS-Officeall developed using object-

oriented languages

This is the world into which our studentsare graduating


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Conclusions

Object-oriented programming provides a superior

way of organizing programming projects

It encourages a high degree of modularity in

programming, making large projects easier to

implement

It provides powerful techniques like inheritance and

polymorphism to help organize and reuse code

Object-oriented languages like Java both provide

a good environment for beginning students tolearn programming, and match real-world

developments in computer programming

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Oop Rosen Schein