Introduction to ObjectOriented Paradigm

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Introduction to Object-Oriented Paradigm String
Objects

• Reading Chapter 19

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Function-Oriented Programming

• Views a program as a collection of functions with
  a controller
• Uses design strategies to isolate (to the extent
  possible) each function in a separate component
  of the program
• Uses functions, procedures, subroutines, etc. to
  implement the primary structure
• Uses structure charts to describe the program
  structure

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Object-Oriented Programming

• Views a program as a collection of cooperating
  objects
• Uses design strategies to isolate objects in
  separate component of the program
• Uses classes to implement the primary program
  structure
• Uses object diagrams to describe the program
  structure

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Name the objects in this classroom
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An Object

• has a state which is described by attributes
• has behavior which is defined through methods
• has an identity which is a name

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Example Object Door
Attributes? Behavior? Identity?
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OOP

• Object-oriented programming (OOP) models
  real-world objects with software counterparts.
• Takes advantage of class relationships
• Objects of a certain class have common
  characteristics
• Example class vehicles

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Objects of Type Vehicle
Land Vehicle
Vehicle
Car
Air Vehicle
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Major Elements of OO Model (Booch)

• Abstraction
• Describing the essential characteristics of an
  object that distinguish it from other kinds of
  objects
• Encapsulation (information hiding)
• Hiding all the details of an object that do not
  contribute to its essential characteristics
• Modularity
• Decomposition of domain into a set of cohesive
  and loosely coupled modules
• Hierarchy
• Ranking or ordering of abstractions

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Abstraction
Process of extracting relevant properties of an
object while ignoring nonessential details
Major Repairs?
Price?
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Encapsulation
Separating the aspects of an object into external
and internal aspects.
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Modularity
Complex systems are modularconstructed by
combining simpler working components.
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Hierarchy
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Basic Concepts of OOClasses and Objects

• A class is a definition of a general type of
  object (attributes and methods)
• An object is an instance of a class
• Analogy
• Class is a blueprint
• Object is an house built by the blueprint

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Example A Circle Class

• Attributes (describe state)
• radius
• location of center (x, y)
• Methods (define behavior)
• set its center
• set its radius
• draw itself
• calculate its area

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Example A Circle Object
Name theCircle (identity)
radius
centerX
centerY
SetCenter
(attributes)
SetRadius
(methods)
Draw
Area
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Example A Circle Object
Declare theCircle to be a Circle object
//This process is called instantiation begin SetR
adius of theCircle to 3 SetCenter of theCircle
to (2.5, 4.5) Draw theCircle display Area of
theCircle end
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First Look at a Class

• Character strings are commonly used in many
  applications
• There are some standard operations that one would
  like to perform on strings
• We will look at a class for character strings
  that is defined in C in the standard library.

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String Class

• A string is a sequence of characters treated as a
  single object.
• A string constant is a sequence of zero or more
  characters enclosed in double quotes.
• C provides a standard library that defines a
  class that can be used to create and manipulate
  string objects
• To use the string class, include the following
  directive
• include ltstringgt

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Creating Objects

• Create (or instantiate) an object of the class
  string the same way you declare variables
• string greeting Hello
• The above statement creates an object of the
  class string and initializes it to a value

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Attributes of string Objects

• The characters that comprise the string
• The number of characters in the string
• string message Help!

message
H e l p !
Length
5
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Behaviors of String Objects

• When you want an object to do something, you can
  use operators that are defined for the string or
  send it a messages that it understands.
• There are many operators and messages that string
  objects understand.
• The operations include
• Assignment
• Extraction gtgt
• Insertion ltlt
• Concatenation
• Appending

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Assignment
string message1 Hello! string message2
message2 message1
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Examples

• string prompt
• string firstName, lastName
• prompt Enter your first name and last name
• cout ltlt prompt
• cin gtgt firstName gtgt lastName

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Extracting strings from cin

• Skips initial white space
• Reads a white space terminated word
• What is read by previous code with each of the
  following sets of input?
• Set 1 John Doe
• Set 2 Doe John
• Set 3 JohnDoe

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The Concatenation Operation

• string firstName Tiger
• string lastName Wood
• string fullName
• fullName firstName lastName

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The Append Operation

• The append operation () adds characters to the
  end of a string.
• Examples
• string message Help
• message !
• message Wow
• string who Me
• who message

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C Syntax for Sending Messages
Object name Message type Optional
list of arguments
(contents of the
message)
Identifier.Message(Arg1, Arg2, Argn)
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The size message

• string date
• int i
• date August 28, 2000
• i date.size()
• cout ltlt i

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The substr message

• Returns a substring of a string
• Has two arguments
• Starting position of substringfirst position is
  position 0
• Length of substring
• Technicalities
• A starting position beyond the end is an error
• If the length is too long, just return what is
  there

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Example

• string somestring Merry Christmas
• string otherstring
• otherstring somestring.substr(0,5)
• otherstring somestring.substr(5,2)
• somestring otherstring.substr(0,4)
• somestring otherstring.substr(15,10)

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The find message

• Two arguments
• A substring to find
• The position in the string to start the search
• Returns the position within the string where the
  substring is found
• If substring not found, returns a number that is
  larger than any legal position in the string.

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Example

• string spockSays Live long and prosper!
• int i
• i spockSays.find(and, 0)
• cout ltlt i is ltlt i ltlt endl
• i spockSays.find(and, 5)
• cout ltlt i is ltlt i ltlt endl
• i spockSays.find(and, 11)
• cout ltlt i is ltlt i ltlt endl
• (Note See next slide for details on MSV C
  behavior of this function.)

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Example (Cont..)

• string spockSays Live long and prosper!
• unsigned long int i
• i spockSays.find(and, 11)
• cout ltlt i is ltlt i ltlt endl
• (Note i must be declared unsigned long int or
  MSV C will return 1.)

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The getline auxillary function

• Reads an entire line into a string
• Not a message, but is an auxillary function
• Arguments
• Stream to read from
• String to receive the input line
• Character that terminates the extraction

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Example

• string inputLine
• cout ltlt Please enter some text
• getline(cin, inputLine, \n)
• cout ltlt Your input is \ ltlt inputLine
• ltlt \ ltlt endl

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Example Program

• Write a program to read in a date in American
  format (e.g. August 28, 2000) and print the date
  in international format (e.g. 28 August 2000).