Object Implementation

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ObjectImplementation

• Implementation of Classes Relationships In C

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Implementation of Classes In C
Case Study A Library System - Class Diagrams
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/ Generated by Together / ifndef
BOOK_H define BOOK_H class Book public
void display() private string
title string author int price
int number_of_pages endif //BOOK_H
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/ Generated by Together / ifndef
USER_H define USER_H class User public
void displayBooks() void
borrowBook() private string name
string address endif //USER_H
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/ Generated by Together / ifndef
LIBRARY_H define LIBRARY_H class Library
public void addBook() void
displayBooks() void borrowBook() endi
f //LIBRARY_H
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Class Implementation

• So how are classes implemented in C?
• This can be achieved in two ways
• using the struct construct (similar to C)
• using C Class

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Class Implementation
class Book private // this keyword does not
allows access to the //
following members by other objects char
title40 char author25 int
no_of_pages float price public //this keyword
allows other object to invoke the
//following operation on the objects of this
class Book (char bktitle, char aut, int page,
float pr) // constructor. Book ( ) // 2nd
default constructor. Book( ) // Destructor
void display( )

instance variables

operations/methods
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Aspects of a C Class
class Book private // this keyword does not
allows access to the //
following members by other objects char
title40 char author25 int
no_of_pages float price public //this keyword
allows other object to invoke the
//following operation on the objects of this
class Book (char bktitle, char aut, int page,
float pr) // constructor. Book ( ) // 2nd
default constructor. Book( ) // Destructor
void display( )
access modifiers
members
constructors
destructor
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Anatomy of an Object
interface (public)
initialise disable, access functions public
members,
CODE
private members
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Access Modifiers

• enable encapsulation
• data members should be accessible by objects own
  operations in almost all cases
• data members to be accessible by objects own
  operations are designated as private
• members that are to be accessible directly from
  outside the object are defined as public
• private, public and protected are access modifiers

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Constructors

• Constructors are member functions that return
  initialised objects. They however do not have
  return type like ordinary member functions.
• Constructors have the same name as the class
• The most common use of constructors is for
  initialising object instances, ie. giving its
  instance variables values.
• There can be more that one constructor for a class

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Destructor

• Destructors are mainly used for memory management
  techniques.
• A destructor does not have arguments.
• each object type can have only one destructor.

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Defining Member Functions
class Book private // this keyword does not
allows access to the //
following members by other objects char
title40 char author25 int
no_of_pages float price public //this keyword
allows other object to invoke the
//following operation on the objects of this
class Book (char bktitle, char aut, int page,
float pr) // constructor. Book ( ) // 2nd
default constructor. Book( ) // Destructor
void display( )
these member functions must be defined
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Defining Member Functions
Syntax
return_type className methodName(parametersList
) // method statements
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Defining Member Functions

• return_type - any standard built-in types, user
  defined types, void if method does not return any
  values
• className - name of the class
• - scope resolution
• parametersList - parameters which takes values
  into the method. parameters have to be declared
  of some type ie.
• (type param1, type param2,etc)
• method statements - statements which achieve
  the purpose of the method.

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Defining Member Functions
class Book private char title40
char author25 int no_of_pages float
price public Book (char bktitle, char aut,
int page, float pr) Book ( )
Book( ) void display( )
void Bookdisplay() coutltltTitle
ltlttitleltltendl coutltltAuthor
ltltauthorltltendl coutltltPages
ltltno_of_pagesltltendl coutltltPrice
ltltpriceltltendl
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Defining Constructor
class Book private char title40
char author25 int no_of_pages float
price public Book (char bktitle, char aut,
int page, float pr) Book ( )
Book( ) void display( )
BookBook (char bktitle, char aut, int page,
float pr) strcpy(bktitle,title)
strcpy(aut,author)
no_of_Pagespage price pr
BookBook ( )
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Defining Destructor
class Book private char title40
char author25 int no_of_pages float
price public Book (char bktitle, char aut,
int page, float pr) Book ( )
Book( ) void display( )
BookBook( )
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Class Destructor

• a complement of a constructor
• can have at most one destructor
• called when an object is about to be destroyed
• name is the name of the class preceded by a
  tilde, or squiggle character,

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Case Study A Library System - Class Relationship
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/ Generated by Together / class User ifndef
LIBRARY_H define LIBRARY_H include
"Book.h" class Library public void
addBook() void displayBooks() void
borrowBook() private / _at_link
aggregation _at_clientCardinality 1../ Book
lnkBook User lnkUser endif
//LIBRARY_H
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Class Relationship ImplementationAggregation
class User private char name25
char address40 Book books_borrowed5
int noofBorrowedBooks public User (char nme,
char add) User ( ) User( ) void
displayBooks( ) void borrowBook(Book
aBook)
User
displayBooks borrowBook
name address
Class - User
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Class Relationship ImplementationAggregation
class Library private Book
theCollection20 int noofBooks public
Library ( ) Library( ) void addBook(
) void displayBooks( ) void borrowBook(User
aUser)
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Class Relationship Implementation Association
class Library private Book
theCollection20 int noofBooks public
Library ( ) Library( ) void addBook(
) void displayBooks( ) void borrowBook(User
aUser)
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Class Relationship Implementation Association
class Library ... public User newMember(
) .
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Interaction Diagram - Its relation to Methods
implementation
lib1
u1
u2
b1
b2
b3
b4
displayBooks
display
display
display
display
borrowBooku2
borrowBookb2
displayBooks
display
displayBooks
addBook
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C Class - Summary

• facility to create automatic initialisation
  functions through use of constructors
• facility to clean up automatically as an object
  goes out of scope via a destruction function
• constructor(s) have the same name as the class
  itself, and can have parameters lists like normal
  functions
• allow more than one constructor - differentiate
  by a parameter list either in the number or types
  of parameters

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C Class - Summary

• destructor is identified by the name of the class
  preceded by the (tilda) character. The
  destructor cannot have any parameters (so only
  one destructor is allowed)
• the constructor and destructor functions have no
  type specifier, e.g. BookBook( ) instead of
  void BookBook( ) since no return type is
  expected
• all members of a C class are private by
  default
• the public keyword is used to allow access to
  member variables and functions whose declaration
  follow it

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Object Development
A teaching block consists of several rooms
each with a unique room number and specified
seating capacity. Rooms may be booked on a
particular day for lectures. Each booking must
start on the hour and can be of any duration. It
must be possible to book a room in the teaching
block if it is free and generate a display of the
status of each room in the teaching block for a
particular day.
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Object Development

• Identify the major classes present.
• Identify their most important operations and
  properties.
• Construct a class diagram showing any
  associations or aggregations.
• Construct suitable instance diagrams
• Construct message trace diagrams showing
  interactions between objects.
• Construct a model showing how a room in the
  teaching block can be booked.