Chapter 14 Object Oriented Design

1
Chapter 14 Object Oriented Design
2
Copy Constructor

• Called with an object as an argument
• General declarator Class Class (Class
  alias)
• Class is class name
• alias is alias for object being copied
• Values directly copied can be listed in
  initialization section
• member1 (alias.member1), member2 (alias.member2)

Lesson 14.1
3
Destructor

• Member function automatically called when object
  goes out of scope
• Name of destructor function required to be class
  name preceded by tilde ()
• Cannot return a value or contain arguments
• General destructor declaration and declarator

Class ( ) Class Class ( )
Declarator in function definition
Lesson 14.1
4
static Storage Class Specifier

• Gives permanent storage for variable
• Persists through entire program execution
• Memory accessibility
• static used with local variable
• Access allowed only from function where declared
• static used with global variable
• Access allowed from file with declaration
• static used with data member of a class
• access allowed by all objects of the class

Lesson 14.2
5
static Data Members

• Shared by all objects of a class
• Declared by keyword static in class definition
• Initialized outside any member functions
• type Class variable value
• Accessible and modifiable by invoking ordinary
  member function on any object
• Accessible and modifiable by invoking static
  member function on class
• Specified as public or private in accessibility

Lesson 14.2
6
static Function Members

• Declared static by preceding declaration with
  keyword static
• Not necessarily invoked using object and dot
  operator
• Without keyword static in function declarator
• Not allowed to access to nonstatic data and
  function members
• Allowed to be called even when no class objects
  exist in program

Lesson 14.2
7
const Special Qualifier

• Data members and objects qualified by const
  cannot be modified after initialization
• Function members qualified with const do not
  modify invoking object's data

Lesson 14.3
8
Pointer Data Members with const

• Three options
• Using const before the data type
• value pointed to cannot be modified
• Using const after the data type
• Address stored by pointer variable cannot be
  modified
• Using const before and after the data type
• Neither value pointed to nor address stored can
  be modified

Lesson 14.3
9
const Reference Data Member

• General form const type ref
  Class Class (const type ref_var)
  ref (ref_var) Class object
  (base_variable)

Class definition
Constructor function
Declaration of object
Lesson 14.3
10
Constant Member Functions

• Protects data members from being inadvertently
  modified
• To declare function (with 2 arguments) const
  type function (type, type) const
• Form of declarator for above functiontype Class
  function (type arg1, type arg2) const

Lesson 14.3
11
Constant Objects

• Effectively makes all data members const
• None of data members of const object can be
  changed after initialization
• Form declare const object with 3 arguments
  const Class object (arg1, arg2, arg3)
• Can use const object to call function
  object.function (arg1b, arg2b)

Lesson 14.3
12
Mutable Data Members

• mutable used with non constant data members
• Can be modified by constant member function
• Can overrides the const of a function and change
  the non constant data member

Lesson 14.3
13
friend Function

• Indicates that function has special relationship
  with a class
• friend specified for function that is not member
  of any class
• Allows function to access private data members
  directly
• Form for declaration with 2 arguments
  friend type function (type, type)

Lesson 14.4
14
friend Functions

• Defining friend functions
• Keyword not used in function definition
• Directly accesses private data members of object
  (where class declared friend)
• Calling friend functions
• No invoking object used since friend not a member
  function function (arg1, arg2)

Lesson 14.4
15
Class That Grants Friendship
Granting class object 1
Granting class object 2
Private data members for object 1, granting class
Private data members for object 2, granting class
Friend function (nonmember)
Public function members, granting class
Lesson 14.4
16
Member Functions As Friends

• Can be member of another class
• General form (with 2 arguments)

class Class1 friend Class2
function (type, type)
Lesson 14.4
17
friend Class

• All member functions of friend class can access
  all private data and function member of class
  granting friendship
• General form for declaring friend
  class Name
• Common practice to list friend classes before
  public and private access specifiers

Lesson 14.5
18
Defining a Friend Class

• Basic general form for defining class
  Friend public
  type functionf (Granting)
• Basic general form for member function type
  Friend functionf (Granting objectga)
  objectga.functiong ( )
  objectga.datag

Lesson 14.5
19
Calling Function of Friend Class

• Basic form for calling friend class objectf
  . functionf (objectg)
• objectf is the friend class object
• functionf is the friend class member function
  name
• objectg is the granting class object

Lesson 14.5
20
Operator Overloading

• Creates new definitions of operators for use with
  objects
• Create function for a class called operator
• operator is the keyword
• Follow by math operator of your choice
• Write code to perform member-by-member addition
  within function body
• When client of class, adds two objects, operator
  ( ) function automatically called

Lesson 14.6
21
Equivalent Function Calls

• Generated by the operator expression
• Dependent upon classification of the operator
  function being friend or member, binary or unary
• Binary friend functions
• Binary member functions
• Unary member functions
• Unary friend functions (not commonly used)

Lesson 14.6
22
Binary friend Functions
object1 object2 operator (object1, object2)
Expression
Equivalent Function Call
Lesson 14.6
23
Binary Member Functions

• Different type call because have invoking objects

Expression
object1 object2 object1 . operator
(object2)
Equivalent Function Call
Lesson 14.6
24
Unary Member Functions

• Additional complication of being either prefix or
  postfix

object1object1.operator ( )
object1 object1.operator (dummy)
Expression
Equivalent Function Call
Lesson 14.6
25
Binary friend Functions

• General form example

Class1 operator- (const Class1 objecta, const
Class1 objectb) Class1 temp
temp.member1 objecta.member1 -
objectb.member1 temp.member2
objecta.member2 - objectb.member2
return temp
Lesson 14.6
26
Rules for Operator Overloading

• Set of available and unavailable operators
• Table 14.3 in text
• Cannot change classification of operator
• Operator precedence rules still apply
• Each friend or freestanding operator function
  must take at least one object as argument
• Equivalent function call for each operator cannot
  be modified

Lesson 14.6
27
Operator Overloading

• Table 14.5 shows many examples
• Only member functions can return this
• Comparison operators return a bool
• gtgt and ltlt operators are commonly overloaded to
  simplify input and output
• ( ) operator is called using an object name
  followed by an argument list enclosed in ( )

Lesson 14.6
28
UML

• Unified Modeling Language
• Developed by James Rumbaugh, Grady Booch, and
  Ivar Jacobson in mid 1990s
• Create diagrams to develop program
• Collaboration
• Use case
• State chart
• Class
• Many others

Lesson 14.7
29
UML Class Diagram Symbols

• Rectangles used to enclose classes
• Lines used to connect classes that interact
• Arrows and descriptors used to indicate type and
  direction of interaction
• Small filled diamond heads used to indicate
  objects of one class are members of another class
• Numbers next to rectangles used to indicate
  number of objects of a class

Lesson 14.7
30
Composition

• "Has a" relationship
• Quite commonly in object-oriented programming
• Objects contained within another object

Car class
Engine class
Wheel class
Lesson 14.7
31
Association

• "uses" or client-server relationship
• Keeps server class independent of client class
• Has simple interface between the two classes
• Server class designer must create both interface
  and implementation

Lesson 14.7
32
Summary
Learned how to

• Use the special class specifiers static and const
• Work with friend functions and classes
• Overload operators
• Read some UML and the difference between "has a"
  and "uses" relationships