Java Quick & Dirty By Bert Wachsmuth

Overview  We will cover: What is Java Using and Writing Java applets Getting more information  We will need: Knowledge of HTML and web page creation  We will get: Basic understanding of Java but we will NOT become the world’s foremost Java programmer

What is Java  Java is a programming language that: Is exclusively object oriented Has full GUI support Has full network support Is platform independent Executes stand-alone or “on-demand” in web browser as applets

Simple Example Web page with Java applet HTML code for above web page

Simple Example Java code for TickerApplet

Example Summary  To create a web page with an Applet you need: 1. A Java-aware web browser (usually beyond your control) 2. A web page including a special HTML tag called tag 3. One or more Java class files (produced separately from Java source code)

Using Java Applets  To use Java applets, you: Locate appropriate class file(s) Learn how to configure applet Embed the Applet into web page <applet codebase=“base_url” // if different from current directory code=“AppletName.class” // name of class file width=“###” // width of applet area height=“###”> // height of applet area // do not forget this

Simple Applets  TickerTape codebase: code: TickerApplet.class width: 300, height=30  3D Surface codebase: code: surface.class width: 500, height=550  Missile Defense codebase: code: MissileCommand.class width: 320, height: 200

Configurable Applets  Many applets can be configured using “param” tags: 1. Inquire about name and meaning of “param” tags for the applet 2. Add “param” tags to HTML as needed <applet codebase=“base_url” code=“AppletName.class” width=“###” height=“###”>...

Configurable Applet Examples  TickerTape codebase: code: TickerApplet.class width: 300, height=30 param: msg, delay, foreground, background  Chatterbox codebase: code: ChatterBoxlet.class width: 200, height=50 param: host (use sciris.shu.edu), port (use 1234)  Note: Applets can be embedded easily with FrontPage or Notes (LearningSpace)

Writing Java Applets To create Java Applets, you need: Knowledge and a good Java book Good ideas, patience, and persistence and A text editor & Java compiler or An “Integrated Developing Environment” (IDE)

Tools for Writing Java Applets Java API -> essential resource Editor ->Programmer’s File Editor Compiler -> SUN’s Java compiler IDE -> BlueJ version IDE -> Microsoft Visual J Available from SHU but not recommended

Writing Applets - Intro  Java Applets are saved as “Name.java”  They must be compiled into “Name.class”  They require HTML page to run  They have “fields” and “methods” fields are used to store data methods are used to perform action  They inherit *lots* of fields and methods from “parent” classes

Writing Applets - Framework import java.awt.*; import java.awt.event.*; import java.applet.Applet; public class Name extends Applet implement ActionListener { private type aField = new type(“foo”); public void init() { /* code here when applet is initialized */ } public void start() { /* code here to execute when page is visited */ } public void stop() { /* code here to execute when page is left */ } public void paint(Graphics g) { /* drawing code goes here */} public void actionPerformed(ActionEvent ae) { /* code to react to action events here */ } }

Writing Applets – Example 1 1.Open editor 2.Type this source code 3.Save as “Junk.java” 4.Compile into “Junk.class” 5.Create HTML document 6.Add proper tag 7.View in web browser Steps

Writing Applets – Example 2 1.Need two pictures named “picture1.jpg” and picture2.jpg” 2.Open editor 3.Type this source code 4.Save as “Slide.java” 5.Compile into “SSlide.class” 6.Create HTML document 7.Add proper tag 8.View in web browser Steps

Enhancing Applet 2 1.Modify previous source code 2.Save and compile 3.Add proper tag(s) to previous HTML document 4.View new applet in web browser (quit and restart) Steps What parameter tag(s) to use? What must image names be? How many images can be loaded? Questions :

Self-running Applet 1.Modify previous source code 2.Save and compile 3.View new applet in web browser (quit and restart) Steps What’s happening? What’s the delay? Pick a new tag! Does paint method change? Questions

A Professional Applet  To create a professional Applet: small, fast loading, preloading resources completely fool-proof completely configurable utilizes reusable components (objects) cool and new  Too much for this course

What’s the Object of Object- Oriented Programming? OOP revolves around 6 principles: Classes: Fundamental structure of every Java program (fields and methods) Objects: Are constructed from class blueprints Encapsulation: Regulate access to class members Overloading: Multiple definitions for methods Inheritance: Relationships between classes Polymorphism: To deal with related classes based on common features

OOP Example Our Task: Create a unit conversion applet that converts between feet and meter The program should execute in a separate window The program should have one menu item to exit Steps: Think about the objects to be used Download the files from the web site Compile, execute, test, and IMPROVE

Some “less-good” News  Java has “version problems” with applets: 1.0: Netscape 3, IE 3 1.1: Netscape < 4.5, IE 4 1.2: Netscape > 4.5, IE 4 1.3: Netscape 6 or “Java plugin”  Platform independent questionable (<1.3)  C++ “native” code is faster  No access to system-level programming  Large Programs need long download times  Applets have Security Restrictions (no saving…)

More Information  Sun’s Website & Online Tutorials  JARS Resources  Seton Hall Classes CSAS1111, CSAS1112, etc  Java by Definition  Books See Barnes & Nobles or Amazon.comAmazon.com

The End …

What is JavaScript  JavaScript is a programming language that: Is object-oriented but “loosely typed” Has no GUI support but supports most web page elements Is somewhat standardized and runs only inside a JavaScript-aware web browser Code is embedded directly in a web page Is a lot easier than Java  JavaScript Example: document.writeln(“Today is ” + (new Date()));