UTC Flex Program Java Introduction January 9, 2002 Jeffrey L. Eppinger Senior Systems Scientist...

UTC Flex ProgramJava Introduction

January 9, 2002

Jeffrey L. EppingerSenior Systems Scientist

School of Computer Science

Outline

Survey

Introductions

Java Overview

The Survey

• It’s Optional

• It’s Ungraded

• It’s Anonymous– You can still put your name on the cover sheet

• Answer as much as you can– It’s intentionally far reaching so if you can’t get

too far…don’t worry (be happy :-)

Bonus Questions

Bonus questions (in my classes):• will NOT effect your grade,• but those who answer correctly will receive prized

potentially worth THOUSANDS of dollars!

(If you want to remain anonymous…rip off the back page of the survey and write your name on it.)

Bonus Question

• So…who is James Gosling?– Creator of Java

• Where did he get a Ph.D.?– From CMU (in Computer Science)

Outline

SurveyIntroductions

Java Overview

Introductions

• Raghu, you know

• Me

• You

• Course Home Page

• Goals

About Me

Jeff Eppinger (eppinger@cmu.edu, WeH 4620)Ph.D. Computer Science (CMU)Asst Professor of Computer Science (Stanford)Co-founder of Transarc Corp. (Bought by IBM)

• Transaction Processing Software• Distributed File Systems Software

IBM Faculty Loan to CMU eCommerce Inst. (99-00)Now an the faculty of the eCommerce InstituteMost Significant Qualification to Teach Java:

• James Gosling was my officemate in grad school

• 14 Students from United Technologies Corp

• How many know how to program?– In any language?– In Java?

The Course Home Page

Up to date info available on course homepage:http://euro.ecom.cmu.edu/program/courses/tcr753– Today:

• Copies of these slides

• Source code for all the examples

– Eventually:• Up to date information during the Core Java Mini

What should you expect to get from this class?Intuition about writing software for eCommerce

– What’s possible– What’s hard– How long it takes– Whom to hire– Who is giving you the run around

Ability to write moderately complex Java Programs– Ability to find what you need in Java– Ability to do programming in other MSEC classes

My Goals

What Are Your Goals?

• Pass the class

• Learn Java

• Have fun

• Learning to swear in Java

• Gadgets in Java

Outline

SurveyIntroductionsJava Overview

• Java is the coolest technology that you’ll learn about in the MSEC program.

• Here’s why:– Runs “everywhere”– Programming Language with the “Right Stuff”

Runs Everywhere

• You can run this stuff anywhere– On Windows, Mac, Linux, Unix, Mainframe, …– From MS-DOS Prompt– In Web Browsers

• Using Applets!

– In Web Servers• Using Servlets and EJBs

– In Smart Cards– In Integrated Development Environments

Examples

• First some quick examples from the MS-DOS Prompt (because these are the smallest programs)

HelloWorld.java AddYourNumber.javaPrintString.java IsEven.javaPrintNumber.java TimesTable.javaAddNumbers.java

• Next we’ll talk about other aspects of Java• Then I’ll show you examples of Java running

in other environments

HelloWorld.java

public class HelloWorld {

public static void main(String[] args) {

System.out.println("Hello World");

How does a program work?

• When you run a program, Java starts a little man running in the main method. The little man speaks only Java. He diligently does whatever the Java program says to do.

main(String args[]) { System.out.println("Hello…}

PrintString.java

public class PrintString {

System.out.println(args[0]);

PrintNumber.java

public class PrintNumber {

System.out.println(2);

AddNumbers.java

public class AddNumbers {

System.out.println(2+2);

AddYourNumber.java

public class AddYourNumber {

int yourNum = Integer.parseInt(args[0]);

System.out.println(2+yourNum);

IsEven.java

public class IsEven { public static void main(String[] args) { int yourNum = Integer.parseInt(args[0]); int halfYourNum = yourNum / 2; if (halfYourNum*2 == yourNum) System.out.println("Yes"); else System.out.println("No"); }}

TimesTable.java

public class TimesTable {

int yourNum = Integer.parseInt(args[0]);

int i=1;

while (i <= 10) {

System.out.println(i + " times "

+ yourNum + " is " + i*yourNum);

i=i+1;

Review

We saw:• a few examples of simple Java programs,• simple use of Strings• command line arguments• conversion of Strings to ints• if statements• a loop

I’ll show you more environments toward the end…

• Here’s why:√ Runs “everywhere”Programming Language with the “Right Stuff”

Right Stuff?

• Object-oriented

• Network-oriented (Security-oriented)

• Multithreaded

• Large class libraries

• High-performance

• Easy-to-use

Object-oriented

• The Data– Numbers, strings, etc, that represent the object

• The Methods– Operations you can perform on the data

• Concept– You don’t need to understand the data or the

implementation of the methods• In Java these are called classes• Examples of classes:

– String (or more formally java.lang.String)– StockQuote

Example Object: StockQuote

• Constructor:StockQuote(String ticker)

• Instance Methods:String currentQuote()

float getPrice()

String getName()

String getChange()

Let’s Try It: StockQuoteTest.java

public class StockQuoteTest {

public static void main(String args[]) {

StockQuote sq = new StockQuote(args[0]);

System.out.println(" " +

sq.getName() + " " +

sq.currentQuote() );

Network/Security Oriented

• Class Libraries to access the network• Portable: “write once, run anywhere”

– Interpreted byte codes

• Sandbox– Allows you to run untrusted code– Downloaded applets have restricted access

• Libraries to access security features– ACLs, Certificates, Encryption

• Example– java.net.URL

Selected Guts of StockQuote.javapublic class StockQuote … {

private URL url;

private final String urlHeader =

"http://quote.yahoo.com/d/quotes.csv?s=";

String urlString = urlHeader+ticker+urlTrailer;

url = new java.net.URL(urlString);

InputStream is = url.openStream();

Multithreaded

• Lets programs do multiple things at a time

• Your PC is “multithreaded”– Browser can run multiple windows

• Typical uses:– Separate threads to perform I/O and computing

• Example:– StockQuoteMTTest.java

Threads

• When you run a program the Java loader starts a thread running in the main method of the class you load (you know: java HelloWorld)

main(String args[]) { System.out.println("Hello…}

Making More Threads

• Use new Thread(obj) to create a new thread– This makes another little man

• Use start() method on the thread to run it– This starts the man in object’s run() method

main(String args[]) { StockQuote sq = new StockQuote(IBM); Thread t = new Thread(sq); t.start(); …}

Additional threads start in run()

public class StockQuote implements Runnab… public StockQuote(…ticker) { … }

public void run() { … }

MT StockQuote ExampleCode excerpt from StockQuoteMTTest.java:

System.out.println("Enter ticker:");

while (true) { char c = (char) isr.read(); if (c == '\n') { sq = new StockQuote(b.toString()); backgroundThread = new Thread(sq); backgroundThread.start(); b = new StringBuffer(); } else if (c != '\r') { if (sq != null) sq.stopRunning(); b.append(c); } }

Large Class Libraries

• Need a class that does something?– Chances are it’s already been written!

• The Java Foundation Classes– Packaged with Java– Provides everything from data structures to GUIs

• Examples– Vectors (implemented by java.util.Vector)– Swing GUIs (javax.swing)– Applets (e.g., java.swing.JApplet)

Example: java.util.Vector

(for those of you with programming background…)

• Implements an array of arbitrary size

• Incredibly handy

Selected Constructor:

Vector()

Selected Instance Methods:

add(obj)

insertElementAt(obj,pos)

Example: ToDoSwingGUI.javaCode excerpt from ToDoSwingGUI.java:

public class ToDoSwingGUI extends JFrame … { JButton topButton, bottomButton; JTextField textField; JTextArea textArea; java.util.Vector toDoList;

public ToDoSwingGUI() { … }

… public static void main(String[] args) { new ToDoSwingGUI(); }}

Example: ToDoApplet.java

Code excerpt from ToDoApplet.java:

public class ToDoApplet extends JApplet implement… { JButton topButton, bottomButton; JTextField textField; JTextArea textArea; java.util.Vector toDoList;

public void init() { … }}

Example: ToDo.html<html>

<head>

<title>HTML File to Launch ToDoApplet</title>

</head>

<body>

Your browser doesn't support Java!

</applet>

</body>

</html>

Example: StockQuoteSwingGUICode excerpt from StockQuoteSwingGUI.java:

public class StockQuoteSwingGUI extends JFrame … { private JButton button; private JTextField textField; private JTextArea textArea;

private java.util.Vector quoteHistory;

public StockQuoteSwingGUI() { … }

… public static void main(String[] args) { new StockQuoteSwingGUI(); }}

Example: TwoSwingGUIs.java

public class TwoSwingGUIs { public static void main(String[] args) { new ToDoSwingGUI(); new StockQuoteSwingGUI(); }}

High Performance

• High being a relative term:– Faster than PERL– (Slower than C or C++)

• Threading can improve throughput

• Many people working on optimization tools– JIT: Just-in-time compliation

• Your machine is fast, you can afford to run Java

Easy-to-use

• (Easy being a relative-term)

• Easier than other programming languages– No pointers– Automatic Garbage Collection

• Less cryptic than Perl

Right Stuff?

• Object-oriented

• Network-oriented (Security-oriented)

• Multithreaded

• Large class libraries

• High-performance

• Easy-to-use

Java Drawbacks

• Version skew– Newer versions not yet available in Web most web

browsers that are in use• Internet Explorer 5.0 offers Java 1.1.4• Netscape 4.7 offers Java 1.1.5• Netscape 6.1 offers Java 1.3.0_01

– I’m using Java.1.3.1• You can download an update for your browser, but…

– What’s on your machines?

• Time to download Java code for browser-based apps• Complexity of programming

Java Opportunities

• Server-side application programming– Consistent Environment– Need for faster development

• Ease of use (relative to older technologies…)• Availability of programmers

– Typical example: web applications

• Development of appliances– Smart cards, cellphones, printers, PDAs,

refrigerators, …– Same reasons as above

Integrated Development Environment• Source-code, syntax-directed editor• Incremental compiler• Repository-based environment for code• Project-based development• Integrated debugging• Support for team development• Tools to facilitate specific programming models

– Applets, Servlets, EJBs, Stored Procedures, XML, ...

Compile and Run

• Compile (This generates HelloWorld.class)

javac HelloWorld.java

• Run (This runs HelloWorld.class)

java HelloWorld

Many IDEs for Java

Being that I’m from IBM, I’ve been using:

• IBM’s WebSphere Visual Age for Java

Also, check out:

• JBuilder (Borland)

• JRun (Allaire)

Java in a DOS Window

java IsEven

IsEven.class

java.c

IsEven.class

Java in an IDE

Respository

IsEven.class

Java in an Applet

Browser HTTP Server

Operating System

HTTP Request

DataFiles

HTTP Request

ToDoApplet.classJVM

Java in Servlets

Browser HTTP Server

.classfiles

Operating System

HTTP Request

HTML ServletEngine

DataFiles

Power of Server Side Java

• No Java version mismatch– Just generate HTML (HTML mismatch easier problem)

• No long download problems– Many “real” apps have many big .class files

• Right way to access server data– Secure: Your program, running on your server– Fast: Your program, running on your server

Final Demo

• The IBM Visual Age IDE– With the WebSphere Unit Test Environment

• I’ll start up the server

• You start up your web browsers

MSEC Uses of Java

• Networking Programming Examples

• Java-based Web Servers– Servlets, Java Server Pages, JDBC, etc.

• Other programming assignments

Summary

• Here’s why:√ Runs “everywhere”√ Programming Language with the “Right Stuff”

UTC Flex Program Java Introduction January 9, 2002 Jeffrey L. Eppinger Senior Systems Scientist...

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