Overview: OO and C++

Software Engineering Goals and Strategies Programming Techniques C++ Structures What to Teach? What to Learn? Why C++? Why not C++?

Why Start with:

Software Engineering Goals Design Strategies Programming Techniques

Design skills are useful in the development of realistic programms.

Without understanding programming in the large, one cannot (and need not) understand the importance of OOP.

Nonfunctional Software Engineering Goals

Reusability Extensibility Flexibility

Design Strategies

Abstraction Simplifying the description of a real-world entity to its essentials.

Separation Treating what an entity does and how it does it independently of

each other.

Composition Building complex systems by assembling simpler parts via

association and aggregation.

Generalization Identifying common elements among different entities via

hierarchy, genericity, polymorphism or patterns.

Programming Techniques

Unstructured Programming Procedural Programming Modular Programming Object-Oriented Programming

Mapping of Abstractions to Software

real world abstractions software

entity

attributes data

Mapping of Abstractions to Software

real world abstractions software

entity

behaviour functions

Mapping of Abstractions to Software

real world abstractions software

entity

attributes

behaviour

data

functions

Unstructured Programming

main programdata

• The main program directly operates on global data.

x- and y-intercepts of ax + by + c = 0

#include <iostream.h>

int main() {

// Read the coefficients of a line equation in the form

// ax+by+c = 0

// then print the line's x- and y-intercepts.

// Read the equation coefficients.

float a, b, c;

cin >> a >> b >> c;

// Print the equation coefficients.

cout << "Coefficients: " << a << ", " << b << ", " << c << endl;

// Compute and print the x-intercept. cout << "x-intercept: ";

if (a != 0) {

cout << -c / a << ", ";

}

else {

cout << "none, ";

}

// Compute and print the y-intercept.

cout << "y-intercept: ";

if (b != 0) {

cout << -c / b << endl;

}

else {

cout << "none" << endl;

}

return 0;

}

Procedural Programming

• The main program coordinates calls to procedures and hands on appropriate data as parameters.

main programdata

function3()function2()function1()

main function

/* Example: Stack C like */

#define MAXVAL 100 /* max stack depth */

int sp = 0; /* Stack pointer */

double val[MAXVAL]; /* Stack */

void push(double f ) {

if (sp < MAXVAL) val[sp++] = f;

else {

cout << "error: stack full\n";

clear();

}

}

double pop () {

if (sp > 0) return val[--sp];

else {

cout << "error: stack empty\n";

clear();

return 0;

}

}

int main() {

...

/* use the stack */

push(1); push(2); push(17);

d = pop();

...

}

Critique:

The code is readable and understandable. Functions (push, pop, ...) are used as

abstraction mechanism. The data contained in the stack cannot be made local

to any of the routines, they must be shared by all.

Solution: Modules

David Parnas 1982: information hiding principle

Provide an user of an abstraction with all information

needed to use it correctly, and nothing more.

Modular Programming

• The main program coordinates calls to procedures in seperate modules. Each module can have its own data.

main programdata

function3()function2()function1()

module 1data 1

module 2data 2

stack.h

#define MAXVAL 100 /* max stack depth */

void push(double f );

double pop ();

UseStack.c

#include "stack.h"

int main() {

...

/* use the stack */

push(1); push(2); push(17);

d = pop();

...

}

stack.c

int sp = 0; /* Stack pointer */

double val[MAXVAL]; /* Stack */

void push(double f ) {

if (sp < MAXVAL) val[sp++] = f;

else {

cout << "error: stack full\n";

clear();

}

}

double pop () {

if (sp > 0) return val[--sp];

else {

cout << "error: stack empty\n";

clear();

return 0;

...

Critique

Modules solve some but not all problems: Moduls permit to hide the implementation details. They do not solve the problem of instantiation,

the ability to make multiple copies of the data areas.

Solution: Classes and Objects What if you need stacks for different types?

Solution: Templates

Object-Oriented Programming

• The main program coordinates calls to procedures in seperate modules. Each module can have its own data.

object 1data 1

object 2data 2

object 4data 4

object 3data 3

class Stack {

public:

void push(double f);

double pop();

...

private:

int sp;

double val[maxval];

...

};

int main() {

Stack s;

Stack t;

s.push(1); t.push(2); s.push(17);

d = s.pop();

t.push(s.pop());

...

}

Stackint spdouble val[]...push(double)double pop()...

Stack s

sp

val

0

Stack t

sp

val

2

2 1

Implementation of the Stack Class

double Stack::push(double f ) {

if (sp < maxval) val[sp++] = f;

else {

cout << "error: stack full\n";

clear();

}

}

double Stack::pop () {

if (sp > 0) return val[--sp];

else {

cout<< "error: stack empty\n";

clear();

return 0;

...

Templates:

template <class T>

class Stack {

public:

void push(T f);

T pop();

...

private:

int sp;

T val[maxval];

...

};

int main() {

Stack<double> s;

Stack<double> t;

s.push(1); t.push(2); s.push(17);

d = s.pop();

t.push(s.pop());

...

}

classes with type parameters, generic classes

Object-Oriented Programming

Object-oriented programming views a program as collection of agents, termed objects. Each object is responsible for specific tasks.

An object is an encapsulation of state (data members) and behavior (operations).

The behavior of objects is dictated by the object class. An object will exhibit its behavior by invoking a

method (similar to executing a procedure). Objects and classes extend the concept of abstract data

types by adding the notion of inheritance.

Topology: Procedural versus OO

f1()

f2()

f3()

f4()f5()

Dataf1()

f2()

f3()

Dataf4()

f5()

Mapping of Abstractions to Software

real world abstractions software

entity

attributes

behaviour

class Entityattribute1...

function1()...

Variety of Classes

Domain Classes / Data Managers / Materials Classes whose principle responsibility is to maintain data

values

Data Sinks or Sources Objects that interface to data generators or consumers, but do

not hold data themselves

View or Observer Classes, Tool Classes Classes that provide the graphical display of an object, but are

not the object themselves

Helper Classes, Container Classes Classes that maintain little or no state information, but assist

in the execution of complex tasks

What Do Classes Represent

Classes that directly reflect concepts in the application domain.

Classes that are artifacts of the implementation.

User-level concepts (e.g. cars and trucks) Generalization of user-level concepts (e.g. vehicles) Hardware ressources (e.g. memory manager) System ressources (e.g. output streams) Helper classes (e.g. lists, queues, locks, ...)

8 5 2.0 6.0 2.0 2.0 4.0 4.0 4.1 1.0 6.0 5.06.0 2.0 8.0 3.0 9.0 1.0 3 1 2 0 3 3 2 13 5 2 3 4 6 4 2 5 3 7 6 5

1 2 3 4 5 6 7 8 9

1

2

3

4

5

6

0

1 2

3

4

(0)

(1)

(2)

(3)

(4)

(5)

(6)

(7)

Example: General Purpose Interface Bus (GPIB)

GPIB

An Acme 130voltage supply

A VoltyMetricsvoltmeter

Acme130

Acme140

Inheritance to Share Implementationclass Acme130 {public: Acme130(GPIBController_Stub& controller,int gpib_address); void set(float volts); double minimum() const; double maximum() const;private: GPIBController_Stub my_controller; int my_gpib_address;};class Acme140 : public Acme130 {public: enum Jumper { J1, J2 }; // Possible jumper settings Acme140(GPIBController& controller, int gpib_address, Jumper j); float maximum() const;private: float max_voltage;};

"interface"

Voltmeter"interface"

GPIBInstrument"interface"

VoltageSupply

VoltyMetrics Acme130 VoltOn59

Inheritance to Share Behavior, Polymorphism

"abstract"

VoltageSupply

void set(float)float minimum()float maximum()

Acme130 VoltOn59

float checkCalibration(VoltageSupply& supply, VoltyMetrics& meter, float tst_voltage) { // Relative error at specified test voltage. supply.set(tst_voltage); return abs(tst_voltage - meter.read()) / tst_voltage;}

class VoltageSupply {public: virtual void set(float volts) = 0; virtual float minimum() = 0; virtual float maximum() = 0; virtual ~VoltageSupply();};

class Acme130_VS : public VoltageSupply { ...};

Ray Tracer

Lamp

Object

Screen

Observer

Ray

Object

Sphere

Triangle

Parallelogram Ring

Quadratic

BBox

Design Patterns

0

10

20

30

40

50

60

70

80

90

1. Qrtl. 2. Qrtl. 3. Qrtl. 4. Qrtl.

0

50

100

1. Qrtl. 2. Qrtl. 3. Qrtl. 4. Qrtl.

OstWest

Nord

1. Qrtl. 2. Qrtl. 3. Qrtl. 4. Qrtl.Ost 20,4 27,4 90 20,4West 30,6 38,6 34,6 31,6Nord 45,9 46,9 45 43,9

20,4 27,4 90 20,430,6 38,6 34,6 31,645,9 46,9 45 43,9 Subject

Observer

Observer Observer

change notification

modificationsrequests

Subject

Attach(Observer)Detach(Observer)Notify()

ConcreteSubjectsubjectStateGetState()SetState()

Observer

Update()

ConcreteObserverobserverStateUpdate()

observes

subject

return subjectState

observerState = subject-> GetState()

for all o in observers { o -> Update()}

C++ Structures:

variables/constants pointer, references, arrays expressions, operators control statements functions exceptions types/objects

builtin types classes

interface data members implementation

inheritance of interface of data members of implementation

polymorphism templates class libraries frameworks design patterns

Connections among Strategies, Structures and Goals

abstraction

separation

composition

generalization

classes/objects

inheritance

templates

design patterns

reusability

extensibility

flexibility

DesignStrategies

C++/OOStructures

SEGoals

Classes of Software

Application Programs Libraries, Toolkits

Applications will use classes from one ore more libraries of predefined classes.

Frameworks A set of cooperating classes that make up a reusable

design for a specific class of software.

Libraries

Application Librarye.g. Simulation

GUI• Graphics• Events

Database• OODBMS

OS Support• Net• Files• ThreadsDatastructures Algorithms

What to Teach? What to Learn?

How to think in objects? How to analyse object-

oriented? How to design object-

oriented? system design class hierarchy design class design

How to program in C++? C++ as better C using classes

class implementation memory management features and pitfalls

What is in the class library/framework? C++ standard library ...

How to use the tools? IDEs Compiler Debugger ...

Why C++ Why not C++

C++ is widely available and used.

C++ is the fastest OO language.

C++ is designed for a variety of programming paradigms.

C++ is mature.

C is a small language, C++ is a big language.

C++ is hard to learn.

C++ has subtle and often hard-to-predict behaviors.

C++ lacks an automatic garbage collection.

60

-

70

-

80

-

90

-

Fortran

PL/I

Ada

Ada 95

Algol 60

Algol68

Pascal

Modula-2

Modula-3

CPL

BCPL

C

ANSI C

C with Classes

C++

C++arm

C++std

Simula 67

CLOS

Lisp

Objective C

Smalltalk 80

Java

ML

Clu

Eiffel