OOP Class 2

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• OOPClass 2

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An Object of class Time
OPERATIONS DATA
Set
Private data hrs 8 mins 25 secs
42
Increment
Write . . .
Time
3

• Definitions

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Definitions

• Definitions of object on the Web
• a tangible and visible entity an entity that can
  cast a shadow "it was full of rackets, balls and
  other objects"
• Definitions of object-oriented on the Web
• object-oriented ... techniques where data
  carries with itself the "methods" (also known as
  "functions") used to handle that data. An OO
  programmer, for instance, can write a statement
  such as "object.print()" without having to be
  concerned about what kind of object will be
  involved at "run time" or what its printing
  method is. Object-oriented code is both more
  flexible and more organized, so it is far easier
  to write, read, and change than procedural code
  www.3dartist.com/WP/dempy/help/glossary.htm
• A style of software development and packaging
  based on how real world objects relate to one
  another. Data and procedures are combined in
  objects objects communicate with each other via
  messages similar objects are grouped together
  into classes data and procedures are inherited
  through a class hierarchywww.olenick.com/html/gl
  ossary.html

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Definitions

• Definitions of object-oriented design on the Web
• entails transforming the analysis model into a
  feasible design. kaykeys.net/science/computerwork/
  oodesign/
• A software design method that models the
  characteristics of abstract or real objects using
  classes and objects. software.allindiansite.com/ja
  va/ojava.html
• Object-oriented design (OOD) is a design method
  in which a system is modeled as a collection of
  cooperating objects and individual objects are
  treated as instances of a class within a class
  hierarchy.
• en.wikipedia.org/wiki/Object-oriented_design

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Definitions of object-oriented analysis on the
Web

• Object-oriented analysis
• builds a model of a system that is composed of
  objects. The behavior of the system is achieved
  through collaboration between these objects, and
  the state of the system is the combined state of
  all the objects in it. Collaboration between
  objects involves them sending messages to each
  other.
• Definitions of object-oriented programming on the
  Web
• A programming approach based on the concepts
  of data abstraction and inheritance. Unlike
  procedural programming techniques,
• Style of programming characterized by the use
  of separate "objects" to perform different tasks
  within a program. These "objects" usually consist
  of an abstract data type or class, along with the
  methods used to manipulate that abstract data
  type
• A programming methodology built around objects
  and based on sending messages back and forth
  between those objects. The basic concepts of
  object-oriented programming are encapsulation,
  inheritance, and polymorphism

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Modeling the Real World

• Components of a software system is an
  interpretation of the real world
• Model , a representation of parts of the real
  world
• Algorithm, capture the computation needed to
  manipulate the model
• Object Orientation is a software development
  model that makes use of objects as a
  representation of the real world
• An object represents anything in the real world
  that can be distinctly identified.
• A class represents a set of objects with similar
  characteristics and behavior

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History
9
Module Structure Chart
Main
Get Data
Prepare File for Reading
Print Data
Print Heading
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Two Design Strategies
FUNCTIONAL OBJECT-ORIENTED
DECOMPOSITION DESIGN
OBJECT
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• Software Process Models

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Unified Process

• a use-case driven, architecture-centric,
  iterative and incremental software process
  closely aligned with the Unified Modeling
  Language (UML)
• Tools are used to describe customer views (use
  cases)
• Used mainly for OO based methodologies
• Runs in phases

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The Unified Process (UP)
inception
Phase 1 Communication Planning
Phase 2 Planning Modeling
elaboration
inception
Phase 3 Coding, unit test integrate Components
result
Phase 4 Deployment
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UP Phases
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UP Work Products
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Agile Development
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The Manifesto for Agile Software Development

• We are uncovering better ways of developing
  software by doing it and helping others do it.
  Through this work we have come to value
• Individuals and interactions over processes and
  tools
• Working software over comprehensive documentation
  
• Customer collaboration over contract negotiation
• Responding to change over following a plan
• That is, while there is value in the items on the
  right, we value the items on the left more.

Kent Beck et al
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What is Agility?

• Effective (rapid and adaptive) response to change
• Effective communication among all stakeholders
• Drawing the customer onto the team
• Organizing a team so that it is in control of the
  work performed
• Yielding
• Rapid, incremental delivery of software

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An Agile Process

• Is driven by customer descriptions of what is
  required (scenarios)
• Recognizes that plans are short-lived
• Develops software iteratively with a heavy
  emphasis on construction activities
• Delivers multiple software increments
• Adapts as changes occur

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Extreme Programming (XP)

• The most widely used agile process, originally
  proposed by Kent Beck
• XP Planning
• Begins with the creation of user stories
• Agile team assesses each story and assigns a cost
• Stories are grouped to for a deliverable
  increment
• A commitment is made on delivery date
• After the first increment project velocity is
  used to help define subsequent delivery dates for
  other increments

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Extreme Programming (XP)

• XP Design
• Follows the KIS principle
• Encourage the use of CRC cards (see Chapter 8)
• For difficult design problems, suggests the
  creation of spike solutionsa design prototype
• Encourages refactoringan iterative refinement
  of the internal program design
• XP Coding
• Recommends the construction of a unit test for a
  store before coding commences
• Encourages pair programming
• XP Testing
• All unit tests are executed daily
• Acceptance tests are defined by the customer
  and executed to assess customer visible
  functionality

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Extreme Programming (XP)
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• OO Design Programming
• Java Basics

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Classes and Objects
Class Point Int x, y Public void move
(intd dx, int dy) x dx
y dy

• An object
• point1
• Attributes or fields
• int x, y
• A method
• void move(int dx, int dy)
• A message
• point1.move(10, 10)

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An Object of class Time
OPERATIONS DATA
Modularity Abstraction Encapsulation Inheritance P
olymorphism Message Passing
Set
Private data hrs 8 mins 25 secs
42
Increment
Write . . .
Time
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Developing a Java Application

• Write the source code
• Using an Integrated Development Environment (IDE)
  or text editor
• Save in a .java file
• Compile the source code
• javac ClassName.java
• Creates .class file
• Execute the application
• java ClassName
• Run by the Java Virtual Machine (JVM)

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A First Application

• 1 // First program in Java
• 2 // FirstProgram.java
• 3
• 4 public class FirstProgram
• 5
• 6 public static void main( String args )
• 7
• 8 System.out.println( "Programming is not "
  
• 9 " a spectator sport!" )
• 10 System.exit( 0 )
• 11
• 12

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• Class FirstProgram
• Method main(...)
• Statement System.out.println(...)
• Comments
• // a comment
• / another comment /
• Source file FirstProgram.java

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Program Errors

• Compiler errors
• Found by the compiler.
• Usually caused by incorrect syntax or spelling
• Run-time errors
• Reported by the JVM
• Usually caused by incorrect use of prewritten
  classes or invalid data
• Logic errors
• Found by testing the program
• Incorrect program design or incorrect execution
  of the design

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Program Life Cycle
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Introduction Java Platform

• JavaTM platform is based on the idea that the
  same software should run on many different kinds
  of computers, consumer gadgets, and other
  devices.
• Portability
• Java platform allows you to run the same Java
  application on lots of different kinds of
  computers.

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JVM

• Java virtual machine or "JVMTM
• a translator that turns general Java platform
  instructions into tailored commands that make the
  devices do their work

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Java Program Phases

• Edit
• IDE, vi, emacs, notepad
• Compile
• javac
• Load
• Class Loader
• Verify
• Verifier (Security and Validation)
• Execute
• Java Interpreter (java or appletviewer)

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The java Compiler

• javac
• Creates bytecodes
• Stored on disk as .class
• Each file contains bytecode for one and only one
  class

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The java Class Loader

• Loads bytecodes in memory
• Loads .class files from disk into memory

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The java Bytecode Verifier

• Confirms that all bytecodes are
• Valid and
• Don't violate Javas Security restrictions
• Works on bytecodes from memory

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The java Interpreter

• Reads bytecodes and translate them into a
  language that is relevant to the targeted
  computer architecture
• PC
• Machintosh
• Cell Phone
• For applets execution its built into the browser
  or the appletviewer

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Your first program HelloWorldApp.java

• Displays the greeting "Hello world!". To create
  this program, you will 
• Create a source file
• A source file contains text, written in Java.
• Compile the source file into a bytecode file.
• The compiler, javac, converts these instructions
  into a bytecode file

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Your first program HelloWorldApp

• Run the program contained in the bytecode file
• The Java interpreter implements the Java VM
• This interpreter takes your bytecode file and
  carries out the instructions by translating them
  into instructions that your computer can
  understand.

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JRE
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JAVA Program

• public class HelloWorldApp
• public static void main(String args)
• System.out.println("Hello World")

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Steps

• Save the file as HellowWordApp.java
• Compile
• Javac HellowWordApp.java ? HellowWordApp.class
• Run the program
• Java HellowWordApp

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Output
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What Can be a Class?

• Physical Objects equipments, devices, products
• People Students, Faculty, Customers
• Organizations Universities, Companies,
  Departments, Bank
• Places Buildings, Rooms, Seats
• Events Mouse click, order request, purchase
  orders
• Concepts Transaction

• The domain determines the classes

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What Features Should a Class Have?

• Actions should be modeled as methods of a class
• Verb phrases
• Underline the verbs and nouns in the description
  of the requirements and use cases
• Nouns are candidate classes or attributes
• Verbs are candidate methods

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Java Programming Language

• Java Basics
• OO Basics
• UML Basics

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Data Types, Variables, and Constants

• We use Symbolic Names to refer to data
• We must assign a data type for very identifier
  (symbolic name)
• Declaring Variables
• Primitive Data Types
• Initial Values and Literals
• String Literals and Escape Sequences
• Constants

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Data Types

• For all data, assign a name (identifier) and a
  data type
• Data type tells compiler
• How much memory to allocate
• Format in which to store data
• Types of operations you will perform on data
• Compiler monitors use of data
• Java is a "strongly typed" language
• Java "primitive data types"
• byte, short, int, long, float, double, char,
  boolean

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Declaring Variables

• Every Variable must be given a name and a data
  type
• Variables hold one value at a time, but that
  value can change
• Syntax
• dataType identifier
• or
• dataType identifier1, identifier2,
• Naming convention for variable names
• first letter is lowercase
• embedded words begin with uppercase letter

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Java Primitive Data Types

• byte, short, int, long , float, double, char,
  boolean

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OO Design
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Topics

• Class Basics and Benefits
• Creating Objects Using Constructors
• Calling Methods
• Using Object References

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Object-Oriented Programming

• Classes combine data and the methods (code) to
  manipulate the data
• Classes are a template used to create specific
  objects
• All Java programs consist of at least one class.
• Two types of classes
• Application/Applet classes
• Service classes

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Example

• Student class
• Data name, year, and grade point average
• Methods store/get the value of each piece of
  data, promote to next year, etc.
• Student Object student1
• Data Maria Gonzales, Sophomore, 3.5

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Some Terminology

• Object reference identifier of the object
• Instantiating an object creating an object of a
  class
• Instance of the class the object
• Methods the code to manipulate the object data
• Calling a method invoking a service for an
  object.

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Class Data

• Instance variables variables defined in the
  class and given values in the object
• Fields instance variables and static variables
  (we'll define static later)
• Members of a class the class's fields and
  methods
• Fields can be
• any primitive data type (int, double, etc.)
• objects

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Encapsulation

• Implementation of a module should be separated
  from its users.
• Instance variables are usually declared to be
  private, which means users of the class must
  reference the data of an object by calling
  methods of the class.
• Thus the methods provide a protective shell
  around the data. We call this encapsulation.
• Benefit the class methods can ensure that the
  object data is always valid.

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Modularity

• Divide-and-conquer
• Decompose a complex system into a highly cohesive
  loosely coupled modules.
• Cohesion single-mind-ness of a module
• Each module should small and simple
• Coupling the degree of connectivity between
  modules
• Interactions between modules should be simple

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Abstraction

• Separating the essential from the nonessential
• The behaviors of a module should be characterized
  in a precise way using its interfaces.
• Server provider for example is a client that
  provide services (methods) to its clients.
• Clients need to know only the contract API.

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Polymorphism

• Many shapes
• Same method many ways to call it (dynamic)
• Replacing an object with its parent

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Reusability

• Reuse class code is already written and tested,
  so you build a new application faster and it is
  more reliable
• Example A Date class could be used in a
  calendar program, appointment-scheduling program,
  online shopping program, etc.

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How To Reuse A Class

• You don't need to know how the class is written.
• You do need to know the application programming
  interface (API) of the class.
• The API is published and tells you
• How to create objects
• What methods are available
• How to call the methods

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Declare an Object Reference

• Syntax
• ClassName objectReference
• or
• ClassName objectRef1, objectRef2
• Object reference holds address of object
• Example
• Date d1

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Instantiate an Object

• Objects MUST be instantiated before they can be
  used
• Call a constructor using new keyword
• Constructor has same name as class.
• Syntax
• objectReference
• new ClassName( arg list )
• Arg list (argument list) is comma-separated list
  of initial values to assign to object data

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Constructor

• Constructor method special method with the same
  name as the class that is used with new when a
  class is instantiated
• public class name
• public name(String frst,String lst)
• first frst
• last lst
• Name name
• name new Name(john, Dewey)

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Date Class API

• constructor special method that creates an
  object and assigns initial values to data

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Instantiation Examples

• Date independenceDay
• independenceDay new Date( 7, 4, 1776 )
• Date graduationDate
• new Date( 5, 15, 2008 )
• Date defaultDate new Date( )

Example Next Slide
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Constructors.java

• public class Constructors
• public static void main( String args )
• Date independenceDay
• independenceDay new Date( 7, 4, 1776 )
• Date graduationDate new Date( 5, 15, 2008
  )
• Date defaultDate new Date( )

Figure Next Slide
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Objects After Instantiation
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Calling a Method
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Method Classifications

• Accessor methods
• get
• gives values of object data
• Mutator methods
• set
• change values of object data

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Date Class Methods

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The Argument List in an API

• Pairs of
• dataType variableName
• Specify
• Order of arguments
• Data type of each argument
• Arguments can be
• Any expression that evaluates to the specified
  data type

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Modeling Relationships and Structures

• UML

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UML Class Diagram

• Used to model the static structure and
  relationships among the classes of an OO software
  system
• A class diagram is made of
• Nodes (Classes and Interfaces)
• Links (Relationships)

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Relationships

• Inheritance
• Extension Relationship (specialization and
  generalization)
• Extension between two interfaces
• Implementation (when a class implements an
  interface)
• UML uses hollow triangle pointing toward the
  super class
• See Page 30 for an example
• Association
• Aggregation and Composition
• Dependency

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Read Ahead

• Chapter 2 including the case study on page 44