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CS441CURRENT TOPICS IN

PROGRAMMING LANGUAGES

LECTURE 1

GEORGE KOUTSOGIANNAKIS

George Koutsogiannakis / Summer 2011

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

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.html• SUPPLEMENT YOUR UNDERSTANDING OF THE MATERIAL

BY ALSO READING THE RECOMMENDED CHAPTERS FROM THE ASSIGNED TEXTS, NOTED ON THE SCHEDULE PAGE OF THE COURSE’S 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.

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.

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 DON’T 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.

Applets

Notice that the Java code is executed by the

client (Browser)

Browser Web ServerInternet

myApplet.html#1 #1

#1

• #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.

myApplet.class

#2 #2 #2

CLIENT SIDESERVER SIDE

Servelts

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Web ServerInternet

#1 #1

#1

• #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)

myServelt.class

#3 #3 #2

myJavaApplication.class

Java Client Application Servlet executes on the server side

#4

Java Server Pages

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Web ServerInternet

#1 #1

#1

myJSP.class

#3 #3 #2

myJavaApplication.class

Java Client Application JSP contains java code andOther formats such as html, XML, special tags.

#4

• #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.).

Other communication forms

• html -> applet -> 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-> servlet-> 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. 18

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

MembersInherited 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 no20

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.33

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 circle=new Circle();

Square square=new Square();

Figure figure; //just declaration, no instantiation is allowed

figure=circle;

figure.draw(); // a circle will be drawn

figure=square;

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 st=new 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

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Abstract Employee

class

Student class

Class StudentEmplo

yeeUses StudentImpl

StudentImpl

Interface StudentInter

face

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, AdministartivePersonel 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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Abstract class Employee

OperatingExpenses ExpensesInterface

OperatingExpensesImplExpenses

Uses OperatingExpensesImpl

Engineer ManagementAdministrativePersonel

Example of Multiple Inheritance

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

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