CS441 CURRENT TOPICS IN PROGRAMMING LANGUAGES

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CS441CURRENT TOPICS IN PROGRAMMING LANGUAGES

• LECTURE 1
• GEORGE KOUTSOGIANNAKIS
• George Koutsogiannakis / Summer 2011

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Course Objective

• Practice building reliable GUI (Graphical User
  Interface) using Java.
• Create Client Server architectures
• Networking protocols.
• Design of Internet Client Server enterprises
  (applications).
• Java will be used to build Client/Server
  architectures. Other platforms follow similar
  approaches to Java.

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Course Material

• THE PRESENTATIONS PROVIDE A LIST OF TOPICS
  DISCUSSED IN CLASS ON THE DAY OF THE LECTURE.
• A SORT DISCUSSION IS PRESENTED IN THE POWER POINT
  PRESENTATION.
• YOU MUST EITHER KEEP NOTES IN THE LIVE CLASS OR,
  IF YOU ARE A REMOTE STUDENT, WATCH THE TAPE FOR
  THE COMPLETE COVERAGE OF THE TOPICS.
• IN ADDITION YOU CAN DOWNLOAD THE POWER POINT
  PRESENTATIONS FROM THE COURSE S WEB SITE
• http//www.cs.iit.edu/cs441/schedule.html

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Course Material

• THIS SUMMARY DOES NOT NECESSARILLY LIMIT THE
  TOPICS DISCUSSED IN CLASS. TOPICS NOT LISTED HERE
  CAN BE DISCUSSED (FOR INSTANCE SAMPLE COD
  EWRITTEN ON THE WHITE BOARD). IT ONLY SERVES AS
  A GUIDELINE!.
• PROGRAMMING EXAMPLES ARE GIVEN FOR SOME TOPICS IN
  
• http//www.cs.iit.edu/cs441/handoutsnew.htm
  l
• SUPPLEMENT YOUR UNDERSTANDING OF THE MATERIAL BY
  ALSO READING THE RECOMMENDED CHAPTERS FROM THE
  ASSIGNED TEXTS, NOTED ON THE SCHEDULE PAGE OF THE
  COURSES WEB SITE.

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COURSE ADMINISTRATION

• TOPICS DISCUSSED
• COURSE WEB SITE
  http//www.cs.iit.edu/cs441
• USAGE OF BLACKBOARD
• TOOLS NEEDED FOR THE COURSE http//www.cs.iit.edu
  /cs441/tools.html
• OFFICE HOURS
• ASSIGNMENTS / PROJECT.
• COURSE SYLLABUS
• THIS IS AN INTERMEDIATE TO ADVANCE LEVEL COURSE
  IN JAVA. BASIC KNOWLEDGE OF JAVA IS ASSUMED. MUST
  KNOW HOW TO COMPILE AND INTERPRET. MUST KNOW HOW
  TO USE NUMEROUS FILES TOGETHER.

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COURSE ADMINISTRATION

• REVIEW OF COURSE S WEB SITE
• COURSE GRADING
• COURSE ASSIGNMENTS
• DOWNLOADING OF ASSIGNMENTS
• DEADLINES FOR ASSIGNMENT
• TOOLS REQUIRED
• OTHER
• METHOD OF ASSIGNMENTS SUBMISSION.
• BLACKBOARD S INDIVIDUAL ASSIGNMENT FOLDERS- DO
  NOT SUBMIT TO DIGITAL DROP BOX!!!!
• ETHICS

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JAVA FRAMEWORKS AND ACCEPTABLE PLATFORMS

• DISCUSSION OF VARIOUS JAVA FRAMEWORKS AVAILABLE
  AND THEIR FUNCTIONALITY
• JDK1.6 STANDARD EDITION UPDATE 23 or latest
  update. RECOMMEND THAT YOU DOWNLOAD AND INSTALL
  ON YOUR COMPUTER. EARLIER VERSIONS ARE
  ACCEPTABLE.
• JAVA ENTERPRISE EDITION 6 (EE 6) . INCLUDES A
  JDK PLUS OTHER APIs.
• WINDOWS ENVIRONMENT IS THE PREFERRED ENVIRONMENT
  FOR ASSIGNMENTS AND PROJECTS. I WILL BE CHECKING
  YOUR WORK USING WINDOWS.
• If another environment is used you can demo your
  assignment to me on your laptop.

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JAVA FRAMEWORKS AND ACCEPTABLE PLATFORMS

• DURING THE FIRST PART OF THE COURSE EDIT PLUS IS
  THE PREFERRED IDE FOR WRITNG PROGRAMS. DO NOT USE
  NetBeans IN THE FIRST HAL F OF THE COURS
  EASSIGNMENTS UNLESS THE ASSIGNMENT SPECIFICALLY
  SAYS SO.
• YOU CAN USE OTHER JAVA FRIENDLY IDEs AS LONG AS
  THEY DONT USE THEIR OWN JDK.
• YOU MUST INSTALL A VERSION OF THE JDK AND LINK
  YOUR IDE TO THAT INSTALLATION.
• DO NOT USE ECLIPSE AS IT USES ITS OWN JDK. IF
  YORU PROGRAM DOES NOT WORK BECAUSE YOU USED
  ECLIPSE TIME WILL BE WAISTED DEBUGGING IT (IT
  WILL BE RETURNE DTO YOU).
• PREFERRED DATABASES MySQL / ACCESS/DERBY
• WEB SERVER TOMCAT VERSION 6.0 AND UP
• NET BEANS 6.5 AND UP (LATEST VERSION IS 6.9) .
  NOTE THAT EACH VERSION HA SITS OWN ISSUES AND
  PROBLEMS.

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JAVA PROGRAMS

• DIVISION OF JAVA PROGRAMS
• APPLICATIONS.
• APPLETS.
• SERVER SIDE JAVA- SERVLETS, JAVA SERVER PAGES,
  JAVA SERVER FACES.
• ENTERPRISE JAVA BEANS
• WEB SERVICES
• DISTRIBUTED SERVICES USING RMI OR RMI OVER IIOP
  (OR JAVA IDL).
• SOME PROGRAMS REQUIRE SPECIAL TOOLS NOT AVAILABLE
  IN THE STANDARD EDITION JDK (AVAILABLE IN
  ENTERPRISE EDITION)
• SERVLETS AND JAVA SERVER PAGES
• WEB SERVICES
• ENTERPRISE JAVA BEANS

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APPLETS AND BROWSERS

• BROWSERS AND WEB SERVERS (SERVER / CLIENT )
• APPLETS AND THE BROWSER.
• APPLETS AND SECURITY.
• BROWSER ACTS AS A SANDBOX.
• WEB SERVER AND APPLETS.
• WEB SERVER AND SERVLETS.
• WEB SERVER AND JAVA SERVER PAGES.

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Applets
SERVER SIDE
CLIENT SIDE
Internet
1
myApplet.html
1
1
Web Server
Browser
myApplet.class
2
2
2

• 1 Http request/response for html file//file is
  sent to Browser
• Browser interprets the html script
• 2 Http request/response for file
  myApplet.class// file is sent to Browser
• Browser interprets java bytecodes
• File is destroyed when Browser is closed.

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Servelts
Java Client Application
Servlet executes on the server side
Internet
1
myServelt.class
1
1
Web Server
myJavaApplication.class
4
3
2
3

• 1 Http request sent to Web Server for servelt
  file execution
• 2 Servelet executes on the Server side and
  returns response to Web Server
• 3 Http response formed by the Web Server based
  on the response from Servlet
• Http response is sent to Client
  Application
• 4 Http response passes contents to input
  stream of the client application
  (myJavaApplication.class)

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Java Server Pages

• 1 Http request sent to Web Server for jsp file
  execution
• 2 java code of jsp executes on the Server
  side initially
• 3 Http response formed by the Web Server based
  on the response from jsp. The java part of jsp
  is converted to a Servlet
• Http response is sent to Client
  Application
• 4 Http response passes contents to input
  stream of the client application
  (myJavaApplication.class). The browser interprets
  the particular format sent (html, XML etc.).

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Other communication forms

• html -gt applet -gt servlet
• Client (Browser or some Java application
  program) interprets html which calls an applet
  from the server.
• Applet bytecodes are interpreted by the browser
  (or java application program). Applet calls back
  to the server for the execution of a servlet.
• Server executes the servlet.
• The response of the servlet is sent back to the
  browser 9or java application program) in some
  format (like html).
• Browser (or java application program) interprets
  response.

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Other communication forms

• html-gt servlet-gt applet
• In this example of different modules
  communicating with each other, first the html
  code interpreted by the client (Browser or a Java
  application program) calls for a servlet to be
  executed by the server.
• The server executes the servlet and sends the
  http response to the client.
• The client interprets the response and as a
  result a call to an applet is made (to the
  server).
• The server sends the applet to the client.
• The client interprets the applet code.

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Other communication forms

• In this course we will examine some of the
  previous communication architectures as well as
  more complicated architectures on the server side
  i.e.
• The servlet could be calling another server
  called a RMI server which in turn queries a data
  base.
• Or, the servlet calls a session Enterprise Java
  Bean which in turn calls an Entity bean which in
  turn queries a database.

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INHERITANCE REVIEW

• JAVA DOES NOT SUPPORT MULTIPLE INHERITANCE
• SINGLE INHERITANCE IS APPLIED IN JAVA VIA KEYWORD
  extends
• MULTIPLE INHERITANCE CAN BE SIMULATED BY USING
  INTERFACES

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A Sample Vehicle Hierarchy

• This hierarchy is depicted using a Unified
  Modeling Language (UML) diagram.
• In UML diagrams, arrows point from the subclass
  to the superclass.

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Superclasses and Subclasses

• A big advantage of inheritance is that we can
  write code that is common to multiple classes
  once and reuse it in subclasses
• A subclass can define new methods and instance
  variables, some of which may override (hide)
  those of a superclass

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Inheritance Rules

Superclass Members Inherited by subclass? Directly Accessible by Subclass? Directly Accessible by Client of Subclass?
public fields yes yes, by using field name yes
public methods yes yes, by calling method from subclass methods yes
protected fields yes yes, by using field name no, must call accessors and mutators
protected methods yes yes, by calling method from subclass methods no
private fields no no, must call accessors and mutators no, must call accessors and mutators
private methods no no no
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Inheritance Rules for Constructors

Superclass Members Inherited by subclass? Directly Accessible by Subclass? Directly Accessible by Client of Subclass Using a Subclass Reference?
constructors no yes, using super( arg list ) in a subclass constructor no
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Subclass Constructors

• Constructors are not inherited.
• However, the subclass can call the constructors
  of the super class to initialize inherited
  fields.
• Implicit invocation
• The default constructor of the subclass
  automatically calls the default constructor of
  the superclass.
• For explicit invocation, use this syntax
• super( argument list )
• If used, this statement must be the first
  statement in the subclass constructor.

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Multiple Inheritance

• The concept of multiple inheritance is shown
  below (even though Java does not allow it).

Class A
Class B
Class C
Class D
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abstract Classes and Methods

• An abstract class is a class that is not
  completely implemented.
• Usually, the abstract class contains at least one
  abstract method.
• An abstract method specifies an API but does not
  provide an implementation.
• The abstract method is used as a pattern for a
  method the subclasses should implement.

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More on abstract Classes

• An object reference to an abstract class can be
  declared.
• We use this capability in polymorphism, which
  will be discussed later.
• An abstract class cannot be used to instantiate
  objects (because the class is not complete).
• An abstract class can be extended.
• subclasses can complete the implementation and
  objects of those subclasses can be instantiated

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Defining an abstract class

• To declare a class as abstract, include the
  abstract keyword in the class header
• accessModifier abstract class ClassName
• // class body

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Example Hierarchy

• We can define a Figurehierarchy.
• The superclass is Figure,which is abstract. (In
  theUML diagram, Figure is set in italics to
  indicate that it is abstract.)
• We will derive two subclasses Circle andSquare.

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Subclasses of abstract Classes

• A subclass of an abstract class can implement
  all, some, or none of the abstract methods.
• If the subclass does not implement all of the
  abstract methods, it must also be declared as
  abstract.
• Our Circle subclass adds a radius instance
  variable and implements the draw method.
• Our Square subclass adds a length instance
  variable and implements the draw method.

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Restrictions for Defining abstract Classes

• Classes must be declared abstract if the class
  contains any abstract methods
• abstract classes can be extended
• An object reference to an abstract class can be
  declared
• abstract classes cannot be used to instantiate
  objects

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Restrictions for Defining abstract Methods

• abstract methods can be declared only within an
  abstract class
• An abstract method must consist of a method
  header followed by a semicolon
• abstract methods cannot be called
• abstract methods cannot be declared as private or
  static
• A constructor cannot be declared abstract

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The Figure Class

• public abstract class Figure
• private int x
• private int y
• private Color color
• // usual constructors, accessors,
• // and mutators
• // abstract draw method
• public abstract void draw( Graphics g )
• All classes in the hierarchy will have an (x, y)
  coordinate and color. Subclasses will implement
  the draw method.

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Polymorphism

• An important concept in inheritance is that an
  object of a subclass is also an object of any of
  its super classes.
• That concept is the basis for an important OOP
  feature, called polymorphism.
• Polymorphism simplifies the processing of various
  objects in the same class hierarchy because we
  can use the same method call for any object in
  the hierarchy using a super class object
  reference.

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Polymorphism Conditions

• conditions for polymorphism
• The Figure, Circle, and Square classes are in the
  same hierarchy.
• The non-abstract Circle and Square classes
  implement the draw method.
• We assigned the Circle and Square objects to
  Figure references.
• We called the draw method using Figure references.

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Example

• Suppose we have a class FigureClient.
• This class uses the previous classes to actually
  draw figures.
• i.e. (assuming that all classes are in the same
  folder)
• public class FigureClient
• public static void main ( String rags)
• Circle circlenew Circle()
• Square squarenew Square()
• Figure figure //just declaration, no
  instantiation is allowed
• figurecircle
• figure.draw() // a circle will be drawn
• figuresquare
• figure.draw() // a square will be drawn
  now.

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Superclasses and Subclasses

• A big advantage of inheritance is that we can
  write code that is common to multiple classes
  once and reuse it in subclasses
• A subclass can define new methods and instance
  variables, some of which may override (hide)
  those of a superclass

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Interfaces

• A class can inherit directly from only one class,
  that is, a class can extend only one class.
• To allow a class to inherit behavior from
  multiple sources, Java provides the interface.
• An interface typically specifies behavior that a
  class will implement. Interface members can be
  any of the following
•    classes
•    constants
•    abstract methods
•    other interfaces

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Interface Syntax

• To define an interface, use the following
  syntax 
• accessModifier interface InterfaceName
• // body of interface
• All interfaces are abstract thus, they cannot be
  instantiated. The abstract keyword, however, can
  be omitted in the interface definition.

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Finer Points of Interfaces

• An interface's fields are public, static, and
  final. These keywords can be specified or
  omitted.
• When you define a field in an interface, you must
  assign a value to the field. 
• All methods within an interface must be abstract,
  so the method definition must consist of only a
  method header and a semicolon. The abstract
  keyword also can be omitted from the method
  definition.

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Inheriting from an Interface

• To inherit from an interface, a class declares
  that it implements the interface in the class
  definition, using the following syntax  
• accessModifier class ClassName extends
  SuperclassName
• implements Interface1, Interface2,
• The extends clause is optional.
• A class can implement 0, 1, or more interfaces.
• When a class implements an interface, the class
  must provide an implementation for each method in
  the interface.

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Example

• We define an abstract class Animal with one
  abstract method
• public abstract void draw( Graphics g )
• We define a Moveable interface with one abstract
  method
• public interface Moveable
• int FAST 5 // static constant
• int SLOW 1 // static constant
• void move( ) // abstract method

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Derived Classes

• TortoiseRacer class
• extends Animal class
• implements Moveable interface
• implements draw and move methods
• TortoiseNonRacer class
• extends Animal class
• (does not implement Moveable interface)
• implements draw method only

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Multiple Inheritance

• Suppose we have abstract class Student (template
  class).
• This class has abstract method getGPA which
  returns the gpa.
• Suppose we also have abstract class Employee
  (template class)
• This class has abstract method getSalary which
  returns the salary.
• Class StudentEmployee wants to inherit both
  classes and implement both the gpa and the
  salary.
• It can not do that because multiple inheritance
  is not allowed
• public class StudentEmployee extends
  Student extends Employee
• ABOVE IS NOT LEGAL!!!!!!!

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Multiple Inheritance

• Let us leave Employee intact and instead remove
  the abstract method getGPA from the Student
  class.
• Thus there is no need for Student to be abstract
  any more.
• Let us create an interface
• public interface StudentInterface
• defines the method getGPA
• Let us create a class StudentImpl which inherits
  Student and implements interface
  StudentInterface. It implements the method getGPA
  which calculates the gpa.

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Multiple Inheritance

• Now class StudentEmployee extends Employee and it
  also implements the interface StudentInterface.
  Therefore it implements the method getGPA but
  kind of indirectly (via the implementation of the
  method in the StudentImpl class)
• StudentImpl stnew StudentImpl()
• public float getGPA()
• return st.getGPA()
• StudentEmployee object can invoke other
  methods of class Student since StudentImpl also
  inherits student.
• It also can use the class Employee since it
  inherited that class directly.

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Multiple Inheritance
Abstract Employee class

• Student class

Interface StudentInterface
Class StudentEmployee Uses StudentImpl
StudentImpl
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Example of Multiple Inheritance

• Example of a Multiple Inheritance Implementation
  is posted on the Web Site Examples page.
• In the example our goal it create a class called
  Expenses that inherits from both classes Employee
  and OperatingExpenses.
• Class CorporationTest tests the multiple
  inheritance.

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Example of Multiple Inheritance

• Class Employee is abstract because method
  compensation is abstract.
• Classes Engineer, Management, AdministartivePerson
  el inherit Employee and implement compensation
  according to their requirements.
• Interface ExpenseInterface defines method
  getOperatingExpenses
• Class Expense extends Employee and implements
  interface ExpenseInterface
• Class OperatingExpenses has methods that
  calculates different operating expenses for the
  corporation.
• Class ExpenseImpl extends OperatingExpenses and
  implements the interface ExpenseInterface

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Engineer
Administrative Personel
Management
ExpensesInterface
Abstract class Employee
OperatingExpenses
OperatingExpensesImpl
Expenses Uses OperatingExpensesImpl
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Example of Multiple Inheritance

• Study program Multiple Inheritance Example
  available in the Examples (page) of the course s
  web site.