Object Oriented Development Java Objectives Develop a basic understanding of: OO Concepts Networking...

Object Oriented DevelopmentObject Oriented DevelopmentJava

ObjectivesObjectivesDevelop a basic understanding of:OO ConceptsNetworkingWeb serversServlets (live reports from databases)Using an IDE to develop applications.Learn enough Java to enable you to

continue learning on your own.

Non-objectivesNon-objectivesLanguage theory.Thorough tour of the Java API

Application Programmer InterfaceDiscussion of inner-workings of Java.GUI application development

(Swing/AWT)Why the designers of Java did what they

did.

PrerequisitesPrerequisitesClasses assume basic knowledge of:AlgorithmsNetworksWorld Wide WebDatabases

Class FormatClass Format1. Lectures.2. Review Questions.3. Lab work.All lab work is limited to the

illustrating the subject material presented. Lab work algorithms are simple.

Ask questions.

Object Oriented DevelopmentObject Oriented Development

Other MethodologiesOther Methodologies

For example:– Procedural– Aspect Oriented Programming– Integration Oriented Programming– etc…

Introduction Introduction

First primitive Object Oriented Programming (OOP) language, Simula, released in 1967

Some think it simplifies coding as opposed to Procedural, or Aspect Oriented Programming.

Coded from the point of view of items in a problem rather than a set of procedures.

Office Example.

Object Oriented ProgrammingObject Oriented Programming

A PIE– Abstraction– Polymorphism– Inheritance– Encapsulation

AbstractionAbstraction

Representing the essential parts of a real-world thing as data.

What’s needed for your solution.Some abstractions of a Car

– VIN, Color, Make, Model, Year (Manufacturer)

– Transponder ID, License Plate Number, Account Number (Fast Lane)

EncapsulationEncapsulation

Binding data together with its functionality (methods)

– Department.addEmployee()– Car.drive()– Door.open()– File.open()

InheritanceInheritance

Building on an existing concept by adding new properties or functionality.

Fruit– grams– calories per gram

Citrus is a Fruit– can be squeezed into juice

“Is A” implies inheritance

PolymorphismPolymorphism

Scary name; simple concept.Literally: “Many shapes”

Overloading– Traditionally we have

square(int), squareF(float)…– In OO we have square(int), square(float) …

Overriding– Same function as parent class being

respecified in child class.

ExampleExample

Carint speeddrive()

drive(int speed)

SportsCardrive()

overdrive()

1. Sports Car inherits from car

2. Drive method is overriden as well as overloaded.

3. Car and SportsCar abstract the “concept” of a car.

4. Car and SportsCar encapsulate the functionality of a car.

Classes and ObjectsClasses and Objects

A Class is a collection of properties (also called fields or member variables) and methods that define a new data type

An Object is an instance of a class.

Example– If Person is a class– Bob, Jim, and Mary are all objects (instances

of the Person Class)

JAVAJAVAObject Based from the Start

What is Java?What is Java?

The Java LanguageJava Virtual MachineJava API

The Java LanguageThe Java Language

Developed at Sun Microsystems in 1991, released to the public in 1994

Based upon C++, but it was made to be accessible to more programmers.

Object Oriented. Everything is a class (i.e no stand-alone functions)

Delivers secure, portable, multi-threaded, networking related applications

Case-sensitive

Java Virtual MachineJava Virtual Machine

Referred to as the Sandbox or JVM Java code compiles into bytecode, unlike

most other languages that compile to machine code.

Since bytecode is readable to the JVM, Java is portable to any operating system that has a Java Virtual Machine built for it.

Java APIJava APIApplication Programmer InterfaceApplication Programmer Interface

A collection of software libraries, called packages, that contain Java classes

As testimony to the reusability of Java code, you use the Java API to create functionality.

Use the import keyword to access a software library

Example:import java.io.*;

Programming Java ApplicationsProgramming Java ApplicationsA Java application is a collection of

classes with one class that contains a main method as an entry point.

Most classes must reside in a file with the same name e.g. A public class called Learning must reside in

a file called Learning.java Class declarations and control flow structures are

contained in {} Variable declarations, expressions, functions and

library calls end with semi-colons

Main MethodMain Method

public static void main(String[] args){ }

Accessible to any class

Class method

No return value

An array of String objects

Method name

CommentsComments

Java uses C/C++ commenting styles.Single line comments are denoted by //

int a; // a will be used to count sheep

Block comments begin with /* and end with */ /* Author: Joe Smith

Date: Jan 7th, 2002 Description: First lines of code */

public class HelloWorld {public static void main( String[] args){

System.out.println(“Hello World”);}

}Static object

Object contained in System

Method of out object

Declaration of class Entrance point for application

Compiling and Running Compiling and Running Java ApplicationsJava ApplicationsTo transform files into bytecode, use the

javac (abbreviated java compile) command javac [filename] java [classname]

Review QuestionsReview Questions

1. What is the purpose of the main method?2. What is the difference between a Class and an

Object?3. Given a cookie cutter and cookies, which

would best represent an object, and which best represents a class?

4. What two ways are comments marked in a Java program?

5. How do you include other libraries so that your class can use them?

Lab 1Lab 1

Hola.java

public class Hola {public static void main( String args[]){


}

Borland’s JBuilderBorland’s JBuilder

An Integrated Development Environment (IDE)

Project– A collection of source files that solve a

problem.

Creating a New ProjectCreating a New Project

Using the Project WizardUsing the Project Wizard

Creating a New ClassCreating a New Class

Using the Class WizardUsing the Class Wizard

Create Your Class.Create Your Class.

To Run a ProjectTo Run a ProjectWe have to tell Jbuilder which We have to tell Jbuilder which class has the main method.class has the main method.

Click on the Click on Select HelloWorld

Lab 2Lab 2

Hello World in Jbuilder

public class HelloWorld {

public Helloword() { }

public static void main( String args[]){


}

Variables and OperatorsVariables and Operators

Primitive Data-typesClasses and ObjectsOperators

Primitive Data-typesPrimitive Data-types

A data-type that does not contain any other data-types

List of Primitive Data-types– boolean byte

– int long

– float double

– char short

JVM ensures these types are identical on all platforms

Defining VariablesDefining Variables

Format:– datatype variableName;

Examples:int a;boolean done;float salary;

Using Identifiers of VariablesUsing Identifiers of Variables

Identifiers are the names of the variables that a programmers assigns.

Identifiers can consist of alphanumeric symbols, underscores and dollar signs, but cannot be reserved operator symbols.

Identifiers may not begin with numeric symbols.

Identifiers are case sensitive.

Variable NamesVariable Names

Examples of Valid Identifiers $joe J3_the_robot _this4$ i

Style: stusCar

employeeJohnmyRedRobot

vPawns

Classes and ObjectsClasses and Objects

Class– A collection of properties (also called fields or

member variables) and methods that define a new data type

like metadata (like the def. of a db table)Object

– A particular instance of a class. like data (the rows in a database table)

ClassClass

A class is a description of what an object will look like and how it will behave.

Classes are like an idea. You cannot use them until you make an object out of the class.

Reference Variables & ObjectsReference Variables & ObjectsReference Variables point to objects

datatype refVarWhen they are first defined, they point

nowhere.

Pawn stusPawn;Pawn jeffsPawn;

newnew

new reserves memory for an object of a specified class and returns a reference to it.

ClassName myObj;myObj = new Constructor();

Pawn p;p = new Pawn();

Constructing ObjectsConstructing ObjectsBecause objects are complex datatypes,

(classes) they need to be “constructed”.Format:

refVar = new [constructor()] ;

Pawn stusPawn;Pawn jeffsPawn;stusPawn = new Pawn();

Construction Construction ContinuedContinued

Pawn stusPawn;Pawn jeffsPawn;stusPawn = new Pawn();stusPawn = new Pawn();stusPawn = new Pawn();

Garbage CollectionGarbage Collection

Garbage Collection automatically reclaims an object when its reference count is zero

Objects have a reference Count


1. Is int a class or a primitive datatype?

2. When you declare a reference variable, what does it point to? Pawn p;

3. What does the Garbage Collector do?

Defining a classDefining a class

Format:

[visibility] class ClassName{[properties] the order[constructor methods] does not[methods] matter

}

PropertiesProperties

Properties are variables that are encapsulated by a class

Class Person {int age;boolean male;float salary;

}

Defining a classDefining a class

Format:


}

ConstructorsConstructors

Constructors are special methods called upon the creation of an object

Any initialization of an object should take place in a constructor

If omitted, a default constructor is called setting all values to null.

Always have the same name as the classAlways have the same name as the classAlways have the same name as the class

ConstructorConstructorpublic class Pawn{

String color;int xPosition;int yPosition;

public Pawn() {color=“Black”;xPosition=0;yPosition=1;

}}

Somewhere in your code:Pawn x;x = new Pawn();

Instantiation of ObjectsInstantiation of ObjectsCreating a working copy of a class (Making

an Object).class Pawn {

String color;int xPosition;int yPosition;

}

Somewhere in your code:Pawn stusPawn;

stusPawn = new Pawn();

Shortcut:[datatype] [refVar] = new [constructor()]

Pawn stusPawn = new Pawn();

Using Multiple ConstructorsUsing Multiple Constructors

Format of a classFormat of a class


}

MethodsMethods

Methods are functions encapsulated by the class.

jeffsCar.drive();mikesOven.setTemperature(350);

Methods can have any number of parameters including zero.

Methods may return one or no variables.

mikesOven.setTemperature(350);int y;y = mikesOven.getTemperature();

Coding A MethodCoding A Method

visibility return-type name(parameters) {do stuff

}

public float getDegrees() {float d;d = (9/5)*celsius+32;return d;

}

voidvoid Methods Methods

Methods don’t always have to return something.

Use the return type of void when you do not want to return anything.

Format of a classFormat of a class


}

Introduction to two classesIntroduction to two classes

StringHolds fixed length, non-changeable strings.

StringBufferHolds variable, changeable length strings.

StringStringInstantiation (Creating one for use)

– String blah1 = new String(“Hello”);

Fixed length, cannot change.– blah1=new String( new String(“Hello”) + new

String(“Goodbye”));

StringStringInstantiation

String blah1 = new String(“Hello”);

String blah2 = “Hello”;

Fixed length, cannot change.blah1 = “Hello” + “Goodbye”;

Same as blah1=new String( new String(“Hello”) +

new String(“Goodbye”));

StringBufferStringBuffer

A string buffer is a variable length String whose contents can be modified.

Provides methods to manipulate its contents.

Use sparingly because of performance issues, but better memory-wise.

StringBuffer y = new StringBuffer(“Hello”);

Calling an Object’s MethodsCalling an Object’s Methods

object.method()

Pawn p = new Pawn();p.move();int x = p.getXposition();myOven.beginBake(30,450);

Calling an Object’s MethodsCalling an Object’s Methods

object.method()

String cow;cow = new String(“ Hello Mr. Smith. ”);String x = cow.toLowerCase().trim();System.out.println (“[” +x + “]”);

[hello mr. smith]

System.out.println(String str)System.out.println(String str)

Here’s a method you’ve already used:the .println() method of the System.out object.

System.out.println (“Hello World”);System.out.println (“He is ”+ x +“ years old”);

Method OverloadingMethod Overloading

Creating a method with the same name, but with a different set of parameters, so either version can be called.

Using an existing method name with a different set of parameters.

A signature is the combination of a method name and its parameter types.

Creating two methods with the same signature, but with a different return type is erroneous.

Method OverloadingMethod Overloading

“It’s like, two, two, two mints in one…”

public void setDuration(int mins) {duration = mins;

}

public void setDuration(int hours, int mins) {duration = (hours*60) + mins;

}

Calling code:myClass.setDuration(5);myClass.setDuration(4,20);

DocumentationDocumentation

In Jbuilder, press [F1] http://java.sun.com/j2se/1.3/docs/api/index.html Sun Microsystems provides all of their

documentation in the JavaDoc template so that information is easy to find

JavaDocJavaDoc

Left-hand side lists all classes. Right-hand side lists information about a

specific class.1. An overview2. Field Summary 3. Constructor Summary4. Method Summary5. Field Detail6. Constructor Detail7. Method Detail


1. What does new do?2. What is the primary difference between the

String and StringBuffer classes?3. How can you tell if a method is a constructor?4. Assuming you have a class Pie which has a

bake method. How would you write the method call on an object of class Pie referenced by the variable blueberryPie as coded below?

Pie blueberryPie = new Pie();

Lab 3Lab 3

Mary Had A Little Lamb

Topics:String ManipulationUsing the Doc set

VisibilityVisibility

Visibility is useful in hiding properties or methods that could be potentially harmful to other classes.

Types of Visibility– public - accessible to all

– private - accessible to none

– package – accessible to all classes in the package

– protected - only specific classes gain access

OperatorsOperators Type of operators

– Arithmetic– Assignment– Equality and Relational– Memory Allocation– Conditional– Incremental/Decremental

Unlike C and C++, you can not overload operators

Arithmetic OperatorsArithmetic Operators

Binary operators for algebraic computation, logical expressions and bit shifting

List of Arithmetic Operators+ - * /

% &^ |>> >>>>> ~

Assignment Operator (=)Assignment Operator (=)

Binary operator that assigns the variable or reference on the left to the expression on the right.

Special Assignment Operators Special Assignment Operators

Operators that combine arithmetic operations with the assignment operator

Increases readability and performance List of Special Assignment Operators

+= ~= -= *= /= %= &= ^= |= <<= >>= >>>=

Equality & Relational OperatorsEquality & Relational Operators

Used primarily in conditional statementsEquality operators used with reference

variables determine only if an object is the same, not if its properties all match

Equality Operators == !=

Relational Operators > < >= <=

NotNot

! NOT

boolean done = true;if (!done) { System.out.println(“keep going”);}

And and OrAnd and Or

&& AND

if ((a==1)&&(b==2)) {do something;

|| OR

if ((a==1)||(b==2)) {do something;

Incremental / Decremental Incremental / Decremental OperatorsOperators ++ or -- before a variable means that the value

should be appropriately incremented or decremented, then evaluated

Incremental or decremental operators may only be used on variables or expression that can be on the left side of an assignment operator.

a++; a--;quantity++; quantity--;++remaining; --remaining;

Incremental / Decremental Incremental / Decremental OperatorsOperators ++ or -- after a variable means that the value

should be evaluated, then appropriately incremented or decremented.

int a = 1; if (a++ == 2) {

System.out.println (“Hello”); }

int a = 1; if (++a == 2) {

System.out.println (“Hello”); }

Control FlowControl Flow

Sequence structureSelection structures

if if/elseswitch

Repetition structures forwhiledo/while

Sequence StructureSequence Structure

General structure of Java programs. Unless told otherwise, continue on to the

next line of code.

Try / Catch / FinallyTry / Catch / Finally

These control structures handle errors. try

– A block of code to be processedcatch

– A block of code that is called if the try failsfinally

– A block of code that is processed regardless of the success of the try

Selection Structure - Part ISelection Structure - Part I

Using if– Process if block when the condition is

successfully met; otherwise, ignore it.Using if/else

– Process if block when condition is successfully met; otherwise, process else block

Selection Structure – Part IISelection Structure – Part II

Using switch– Allows for multiple selections– Process each case block when the condition is

successfully met. If no case is met, process default block if it exists.

Repetition Structures – Part IRepetition Structures – Part I

Using for– Keeps processing for block if the loop condition is

met.

for (initial; termination; increment) {block;

}

for (i=1; i<10; i++)

for (int i=1; i<10; i++)

for (int i=1; (i<10)&&(!done)); i++)

Repetition Structures – Part IIRepetition Structures – Part II

Using while

– Keeps processing while block if the loop condition is met

while(condition){

block;

}

You must make sure the condition eventually becomes false!

Repetition Structures – Part IIIRepetition Structures – Part III

Using do/while– Processes do block at least once before testing

the loop condition to continue with processing

do{block;

} while(condition)

You must make sure the condition eventually becomes false!

StringTokenizerStringTokenizer

The StringTokenizer class allows an application to break a string into tokens.

Tokens are determined by delimiters. Example: Spaces act as delimiters in sentences.

We recognize words in a sentence as tokens.

StringTokenizer st; st = new StringTokenizer("this is a test");

while (st.hasMoreTokens()) { System.out.println(st.nextToken());

}


1. What does count++ mean?2. What does x += 3 mean?3. What is the difference between

== and = ?4. What keywords in Java are used for

exception handling?5. In the for loop, what are the three parts

(names not important, just purpose)? for (a; b; c)

LabLab

StringTokenizer

Topics:StringTokenizerLoopsUsing the Doc set


A subclass is a class that inherits from another class

Using Using extendsextends

The extends keyword follows the class name

Example: class Employee extends Person

This example allows Employee to use all of the properties and methods of Person


All public methods of inherited class can be called by the subclass (the inheritor)

All public properties of the inherited class can be referred to by the subclass (the inheritor)

public class Pawn extends ChessPiecepublic class BigFinnedRocket extends Rocket

Method OverridingMethod Overriding

Like blotting-out the parent’s method with a new method.

Replacing an inherited method.New method must have the same

argumentsNew method must have the same return

data type.


1. What does extends mean?2. What is the difference between

overloading and overriding?3. Why does the main method of a class

that you want to run from the command line (when loading the JVM) need to be static?

LabLab

Vegetables

Topics:InstantiationInheritanceOverriding

staticstatic

Static is a modifier of both methods and properites

It means:– “There is only one of these.”– “This exists always.”

staticstatic Our main methods so far:

public class Vegetable {

static void main (String[] args) {do stuff

}}

The line we’ve had you erase:

public class Vegetable {

static void main (String[] args) {Vegetable vegetable1 = new Vegetable();

do stuff

}}

Databases and JDBCDatabases and JDBC

Java Database ConnectivityJDBC is a database neutral library for

accessing information from SQL-92 compliant databases that have JDBC package.

To use JDBC you need to import java.sql.*Need to handle SQLException in most

cases.

JDBC classesJDBC classes

Connection– Link to a database

Statement– sql statements (select, update, delete)

ResultSet– holder for returned data

ConnectionConnection

A class that maintains a session with a specified database.

First, load the appropriate JDBC driverSecond, create a new Connection object

with the DriverManager:

Class.forName(jdbcDriver); //load the driver

Connection conn = DriverManager.getConnection(url, “user”, “pw”);

StatementStatement

Statement – SQL commands that are sent to the database

PreparedStatement – Same – but better!SQL commands that are precompiled and therefore more efficient than Statement

CallableStatement - used to execute SQL stored procedures.

PreparedStatement stmt;stmt = conn.prepareStatement(“select…..”);

ResultSetResultSet

Structure that maintains the rows of data returned from a SQL command.

Product of a Statement executionAllows simple navigation of the rows.

StatementStatement.executeQuery().executeQuery()

A method of Statement that executes a an SQL command and returns a ResultSet

Used mostly with SQL statements that use the SELECT command

Returns a ResultSet

ResultSet rs;rs = stmt.executeQuery();

StatementStatement.executeUpdate().executeUpdate()

A method of Statement that is used to execute SQL statements that utilize UPDATE, INSERT, and DELETE.


1. What is the jdbc Connection used for?2. What is the difference between the

Statement’s executeQuery() and executeUpdate() methods?

3. What is the difference between Statement and PreparedStatement?

Setup ODBC link now.Setup ODBC link now.

Control PanelData Sources odcbNew System datasourceAdd new reference to JavaLesson on

seg01Username: StudentPassword: learning

Windows ODBC driverWindows ODBC driver

You have now created a windows ODBC link to the JavaLesson database.

You can now refer to this database from:– Excel, Word, Visual Basic, Java, etc…

Java has a JDBC / ODBC driver.This is the driver we’re going to use.

Lab 8Lab 8

Who Stole My Cookie – jdbc VersionPurpose:JdbcConnectionPreparedStatementResultSet

Object Oriented DevelopmentObject Oriented DevelopmentJava

Part II

Web ServersWeb Servers

Fancy File Servers

BrowserBrowser

An application which allows you to view html files.

http://bgcc.globe.com/hello.html

Means: Display the file hello.html which is available from the web server bgcc.globe.com

Hypertext Markup LanguageHypertext Markup Language(HTML)(HTML)Widely used to generate web pagesAllows for simple formattingSmall vocabulary of tags

HTMLHTML

Begin Tags and End TagsFormat: <tag> stuff </tag>Every html document begins with

<html>

Every html document ends with

</html>

<body><body>

Separates the <head> from the <body>

<html>special header stuff

<body>viewable content

</body></html>

TagsTags

Things tags are used for:– Format text– Insert Graphics– Colors– Display data in table format– Link to other pages– Insert sounds

CommentsComments

Format:

<h1> <h2> <h3><h1> <h2> <h3>

Header lines. Like Headers in Microsoft Word.

<h1>Information Technology</h1><h2>Employee List</h2><h3>Lower Level</h3>

Information TechnologyEmployee ListLower Level

<p><p>

Paragraph. Used because carriage returns and line-feeds in

source document are ignored.

<p>The cow went to the stream. The water was cold.</p><p>Hello</p>

The cow went to the stream. The water was cold.

Hello

<br/><br/>

Break line. Used because carriage returns and line-feeds in

source document are ignored.

<p>The cow went to the<br/> stream. The water was cold.</p><p>Hello</p>

The cow went to the stream. The water was cold.

Hello

<b> <i><b> <i>

<b> is bold<i> is italics.

<b>Notice:</b> Don’t <i>drink</i> the water.

Notice: Don’t drink the water.

TableTableUsed whenever you need to line up

columns<table> <tr> <th><td>

<table> <tr> <th>First Name</th> <th>Last Name </th></tr> <tr> <td>John</td> <td>Adams</td> </tr> <tr> <td>Abraham</td> <td>Lincoln</td> </tr> <tr> <td>George</td> <td>Bush</td> </tr></table>

ListListUnordered List <ul> <li>

<html><body>

Before you go, pick up:<ul><li>Food packs</li><li>Compass</li><li>Map</li></ul>

</body></html>

ListsListsOrdered List <ol> <li>

<html><body>

Follow these steps:<ol><li>Check your parachute</li><li>Move to the door</li><li>Jump</li></ol>

</body></html>

AttributesAttributes

Many tags have attributes.

Format:<tag attribute1=setting attribute2=setting> stuff </tag>

<table<table border border=#>=#>

<table border=1> <tr> <th>First Name</th> <th>Last Name </th></tr> <tr> <td>John</td> <td>Adams</td> </tr> <tr> <td>Abraham</td> <td>Lincoln</td> </tr> <tr> <td>George</td> <td>Bush</td> </tr></table>

bgcolorbgcolorSet the background color.

<html>

<body bgcolor="green"><b>The grass is always greener on the other side

of the fence.</b>

</body></html>

bgcolor in Tablesbgcolor in Tables <table border=1> <tr bgcolor="yellow">

<th>First Name</th> <th>Last Name </th> </tr>

<tr> <td>John</td> <td>Adams</td> </tr> <tr> <td>Abraham</td> <td bgcolor="lightblue">Lincoln</td> </tr> <tr> <td>George</td> <td>Bush</td> </tr> </table>

Color Codes in Hex FormatColor Codes in Hex Format

Anchor / HyperLinkAnchor / HyperLink

A link to another location.<a href=“location”> stuff </a>

<html> <body> <h1>Hello world</h1> <p>Welcome to my town.</p> <p>Now please<a

href=“http://bgcc.globe.com”>go home</a>! </body> </html>

<font><font><html>

<body>The grass is <font size=+2>always</font><font color="green" face="script"

size=+5>greener</font> on the <font face="junius">other side</font> of the

fence.</b>

</body></html>

<img><img>

<img src=“filename”/>

<html><body bgcolor="000000" text="FFFFFF"><h1>Hello world</h1><img src="c:\pics\60gunner.gif"></body></html>

Lab 12Lab 12

Hello World Web Page

Lab tagsLab tags

<h1>…</h1> <p>…</p> <font color=“xxxxxx”>…</font> <img src=“…”/> <table> <tr> <th> <td> Bgcolor border <a href=“…”>….</a> <center>…</center> <hr/> <i>…</i> <b>….</b>

HTML FormsHTML Forms

<form><input><select>

– <option>

<select><select>

<select name=name><option selected value=value1>Stuff1<option value=value2>More Stuff<option value=value3>Yet More Stuff<option value=value4>Yet Still More

Stuff</select>

Get and PostGet and Post

Both send the variable names and their values back to the web server.

Get– Shows them in the URL line.– Whenever the URL is typed in, it is a “get”.

Post does it behind the scenes.– Can only be done from submits of forms.– Better when sending a lot of data because it

looks cleaner – no other reason.

GetGet

Web ServersWeb Servers User web browser requests a file from web server. Server loads the file and sends it back to the

browser. With a plug-in, the web server is able to send back

files that are created on demand. Sort of like going the drive-up window of a burger

joint. When you order (you are the browser, clerk is the server), you don’t know, whether your burger is created “on the spot” or was “prepared in advance.” If it is prepared on the spot for you, you’ll be able to add qualifications and change the burger to fit your specific needs.

ServletsServlets

Servlets allow web surfers to see “live” data instead of a previously prepared page.

Often, previously prepared pages are referred to as “static” pages.

Servlets allow you to produce “dynamic” pages. User’s web browser does know that the returned

page was created on the spot. To the browser, it looks no different than a regular page.

ServletsServlets

Web server plug-ins allow the web server to call a “servlet” which will create a page “on-the-fly” and pass this page back to the browser.

You can write java classes which write their output to a web server.(instead of the console: System.out.println).

ServletsServlets

If you were to write a servlet from scratch, it would be painful.

With Object Oriented Technology and inheritance,you can inherit all the necessary properties and methods and merely extend them to meet your specific needs.

ServletsServlets

You will need to import the following:– import javax.servlet.*;– import javax.servlet.http.*;

If you plan to access a database,don’t forget to import:– import java.sql.*;

Extending HttpServletExtending HttpServlet

You class needs to extend HttpServlet

public class WebReport extends HttpServlet {

}

Requests and ReponsesRequests and Reponses

An object of the Request class will hold information regarding what data the user browser is requesting from your servlet.

An object of the Response class will enable your servlet to send a response to the user browser.

doGet() doGet() The web server that will call your servlet will specifically call

your doGet() method so you better have one… and it better look like this…

public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException {

your stuff here…

}

because that’s the signature of the doGet() method that the web server is going to call…

because that’s how programmers who created the web server wrote it!

HttpServletRequestHttpServletRequest

getParameter() method of HttpServletRequest

String eDate = req.getParameter("eDate");String runCode = req.getParameter("runCode");String pCode = req.getParameter("productCode");

HttpServletResponseHttpServletResponse

PrintWriter out;out = res.getWriter();res.setContentType("text/html");out.println("<html>”);out.println(“<head>”);out.println(“<body>”);out.println(“<h1>Hello World</h1>”);out.println("</body>");out.println("</html>");

Reading from the Web ServerReading from the Web Server

Printing to the Web ServerPrinting to the Web Server

Lab 13Lab 13

Hello World Servlet

Lab 14Lab 14

Database Servlet

Arrays and VectorsArrays and Vectors

ArraysArrays

An array is a fixed-length structure that stores multiple values of the same type.

Car c = new Car[10];Car[] c = null;

VectorsVectors

A vector is a variable-length structure that can store values of many data types.

Vector vCar = new Vector(10);

Using the Using the instanceofinstanceof operator operator

Binary operator that determines whether the object on the left is a member of the class on the right.

if (c instanceof Car)


1. What is one restriction that an array has the a Vector does not?

LabLab

Missile Arrays and Family FunArraysVectors

Using Using implementsimplements

The implements keyword follows the class name

Example:class Employee implements Comparable

This means that Employee must contain the methods defined in the Comparable interface.


1. What does extend mean?2. What is the difference between

overloading and overriding?3. What is the difference between extends

and implements?

File I/OFile I/O

Every file is seen by Java as a byte stream.To use file, one must use the java.io.*

packageNeed to handle IOException in most cases

FileInputStream & FileInputStream & FileOutputStreamFileOutputStreamClasses used to access the contents of a

fileSends and receive the data as byte streams

InputStreamReaderInputStreamReader

Readers view the data as character streams.

BufferedReaderBufferedReader

Buffers allow for data to be collected before an action takes place

BufferedReaders use buffers to read character based streams.


1. How do you know when to use BufferedReader versus other readers?

LabLab

Who Stole My Cookie – File Version

Topics:File I/O

NetworksNetworks

A collection of computers that have some medium of communication

Networks are passive entities that can’t interpret any of the data being transmitted.

One of Java’s strengths is its robust handling of network programming

TCP/IPTCP/IP

A protocol that maintains the order of data transmitted over a network.

TCP/IP is reliable because it reports an error if any of the data is not transmitted properly.

IP addresses are unique identifiers of computers in a network.

PortsPorts

A 16 bit number that is used by TCP/IP to deliver data to an application on a server

An analogy:– A telephone number is to an IP address as an

extension number is to a port.

ProtocolsProtocols

Rules that determine how the server and client applications communicate with each other.

Examples:HTTPFTPTELNETTIME

SocketsSockets

A Java Class that provides an input and output stream to a named port.

Similar to File I/OTo use the Socket class: import java.net.*;


1. What is a port?2. What is a socket?

Lab 9Lab 9

Echo & Pig Latin ServerSockets

ThreadsThreads

Threads allow for multi-tasking. Threads eliminate unnecessary idle time.To use threads, you may make a subclass

of Thread.

SleepSleep

Threads can be placed in a state of sleep. They will remain dormant for a pre-determined time.

Threads will only leave the sleep state when an interrupt is called or the predetermined time expires.

When a process halts, all its child threads stop functioning.

Using synchronizedUsing synchronized

The synchronized keyword is used to lock methods or code blocks.

Locking a method or code block queues other threads attempting to access the method or code block.

wait / notify / notifyAllwait / notify / notifyAll

The wait method places the thread in a dormant state for either a specified time or until the notify method is called.

notifyAll sends a message to all threads to attempt to run


1. What are two ways to make a thread hibernate?

Lab 10Lab 10

Pig Latin Server Goes Berserk

Topics:Threads

ServersServers

An application that waits for other applications or instances to connect to it.

ServerSocketServerSocket

Need to import java.net.* and java.io.*Primary function is to wait and accept

socket connections.Example:

Socket clientSocket = null;ServerSocket serverSocket = null;serverSocket = new ServerSocket(4004); // 4004 is the porttry{

clientSocket = serverSocket.accept();}catch(IOException){

//handle the socket error}


1. What is the difference between Socket and a ServerSocket?

Lab 11Lab 11

Instant Messenger

Topics:ServerSocket

ReferencesReferences

The Java Programming Language, by Ken Arnold and James Gosling, Addison-Wesley, 1999, ISBN 0-201-31006-6

Java: An Introduction to Computer Science Programming, Walter Savitch, Prentice-Hall, 2001, ISBN 0-13-031697-0

Java: How to Program, H.M Deitel and P.J. Deitel, Prentice-Hall, 2002, ISBN 0-13-034151-7

Object Oriented Development Java Objectives Develop a basic understanding of: OO Concepts Networking...

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