The Big PictureChapter 1

Copyright © 1998-2004 Delroy A. Brinkerhoff. All Rights Reserved.CS 1410 Chapter 1 Slide 1 of 18

Language LevelsWhere do they all go?

PHigh-level< Close to problem< System independent

PLow-level< Close to system< Doesn’t reflect problem

Java, C#

FORTRAN, COBOL, C++

C/C++

AssemblerMachine

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Relationship Between C and C++C++ is (almost) a perfect subset of C

ANSIC

C++

mainfunctionssyntaxoperatorsflow of controlorganizationcompilationlibraries

object-orientedmodel

prototypesconstinlinereferencesnew / delete

classesencapsulationinheritancepolymorphismRTTItemplatesctors/dtorsoverloading

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Computer LanguagesThe Lineage

FORTRAN º ALGOL58 (IAL) º ALGOL60 º CPL º BCPL º B

CObjective C

C++ º Java º C#

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The Development GoalFrom problem domain to working system

Procedural / Structured

Data Driven

Object-Oriented

Ad Hoc

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Procedural ModelThe oldest model

PFocuses on how (i.e., the algorithms) to solve a problemPDecomposes problem into procedures or subroutinesPTwo kinds of data (i.e., data defined in two different scopes)< Local data is defined in and is only accessible within a procedure< Global data is defined outside of a procedure and is accessible

throughout the programPGlobal data results in procedural coupling< Changes have wide spread and often unexpected effects< Global data makes the program fragile

PCoupled procedures must be< Developed as a unit< Debugged as a unit< Validated as a unit

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Data Driven ModelsAn early attempt to improve procedural programming

PData flow< Maps data input to data output< Design data structures first< Design processes / functions last

PData hiding< Packages data and the procedures that work

on the data together in a module (a file in C)< Data is still in global scope but access is

allowed only through the module functionsPAbstract Data Type (ADT)< Programmer created data type< struct in C

process

data

data

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Object ModelState of the art

PCharacteristics of functional & data modelsPA tool for managing complexityPChange resilient < Change is localized< Intra-object functions may be coupled< Extra-object functions are decoupled

PNatural organization for data and functions< Objects encapsulate data and functions

together< Supports ADTs: multiple objects of a type may

be created (class is a type specifier or ADT)< Supports data hiding: data access is controlled

through key words

Name

AttributesData / variables

BehaviorsOperationsFunctions

UML classsymbol

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Object-Oriented ModelThe big picture

P “Object-oriented modeling and design is a new way ofthinking about problems using models organized aroundreal-world concepts. The fundamental construct is theobject, which combines both data structure and behavior in asingle entity.”

James Rumbaugh, Object-Oriented Modeling and DesignPData Structure (attribute)< variable < instance field < data < data field< data member < instance variable < state

PBehavior< method < function< member function < operation< service< sending a message is equivalent to calling a function

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ObjectsThe central actor in the object model

PEntities that make sense in an application contextPSingle, specific instance of a class< Objects with the same attributes and data types are described by a

single class< Each object has a distinct identity or handle and is uniquely

addressablePData in each object is distinct from the data in all other

objects instantiated from the same class< An object has explicit boundaries

PEncapsulation is the first defining characteristic of the objectmodel< Objects and encapsulation are synonymous< Seals attributes and behaviors together into a single unit

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ClassesDefining characteristics

PAn abstraction of one or more objectsPDescribe “things” with similar attributes and behaviorsPProvides data hiding< Data is in a unique scope and access is controlled< Accessed through public interface (methods or member functions)

P Implements Abstract Data Types (ADT)< Creates a new type specifier< Separates implementation (data) from the interface (public

functions)PTemplate, blueprint, or cookie cutter

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AttributesDescribe an object

PCharacterize or distinguish an objectPAre data values (variables) held by objectsPAre the data an object is responsible for maintainingPShould be placed at the highest level in an inheritance

hierarchy where they remain applicable to each descendantP “Good” attributes depend on what is being modeled

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Behaviors / OperationsMember functions or methods

PA function or transformation that may be applied to or by anobject

POperations, behaviors, and services are logical (user visible);member functions are the physical functions that implementbehaviors or operations

PCalled through or bound to an object; that object is an implicittarget (the function operates on the data stored in the object)

PSome operations may be applied to many classes and arepolymorphic (i.e., implemented through multiple methods)

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foo my_foo;my_foo.function();

Class RelationshipsRepresenting systems as collections of related classes

PAttempt to mimic the relationships between objects in thereal world

PAre depicted as diagrams or connected graphs< Nodes or vertices are classes< Edges, arcs, or paths denote the relationship

PAllow objects to cooperate in the overall solution of aproblem

PAre supported by specific computer-language syntax

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InheritanceGeneralization, gen-spec, is-a, is-a-kind-of; is-like-a, simile

PThe child class inherits all ofthe attributes and memberfunctions collectively calledfeatures) owned by the parentclass

PThe second definingcharacteristic of the objectmodel

Base ClassSuperclassParent ClassGeneralizationAncestor

Derived ClassSubclassChild ClassSpecializationDescendantUML

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Methods With The Same NameOverloading vs Overriding

POverloading functions (and operators)< Defined in the same class< Have the same name < Must have different signatures< May have different return types

POverriding functions< Two or more classes related through inheritance< One function defined in a super class, an other in

a subclass class< Have the same name< Have the same signatures and return type

PCircle::draw overrides or hides Shape::drawPThe move functions are overloaded

Shape

Circle

draw( )

draw( )move(int,int)move(int)

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PolymorphismMany shapes: late, run-time, or dynamic binding; also dynamic dispatch

PSelection of the correct method is deferred until run-timewhen the selection is based on the current object

PObjects respond differently to the same messagePRequires Inheritance; virtual, overridden functions; address

variables (pointer or reference)PThird defining feature of the object-oriented model

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Polymorphism ExampleDynamic binding

positioncolor

draw( )erase( )move( )

Shape

radius

draw( )erase( )

Squareside

draw( )erase( )

Triangleside1side2side3

draw( )erase( )

Circle

Shape* s

Exact shape selecteddynamically at runtime,perhaps in response touser input.

s->draw( ); Which draw method iscalled? Cannotdetermine at compiletime-- selection deferreduntil runtime.

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