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Java Quick & Dirty By Bert Wachsmuth Overview We will cover: We will need: What is Java Using and Writing Java applets Getting more information 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. 3. A web page including a special HTML tag called <APPLET> tag 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” code=“AppletName.class” width=“###” height=“###”> </applet> // if different from current directory // name of class file // width of applet area // height of applet area // do not forget this Simple Applets TickerTape codebase: http://pirate.shu.edu/~wachsmut/Ticker code: TickerApplet.class width: 300, height=30 3D Surface codebase: http://pirate.shu.edu/~wachsmut/Surface code: surface.class width: 500, height=550 Missile Defense codebase: http://www.csd.uu.se/~d95vil/missile/classes code: MissileCommand.class width: 320, height: 200 Configurable Applets Many applets can be configured using “param” tags: 1. 2. Inquire about name and meaning of “param” tags for the applet Add “param” tags to HTML as needed <applet codebase=“base_url” code=“AppletName.class” width=“###” height=“###”> <param name=“Name” value=“Value”> <param name=“Name2” value=“Value2”> ... </applet> Configurable Applet Examples TickerTape codebase: http://pirate.shu.edu/~wachsmut/Ticker code: TickerApplet.class width: 300, height=30 param: msg, delay, foreground, background Chatterbox codebase: http://sciris.shu.edu/Java/Chat 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 http://mathcs.shu.edu/Resources/Java/API/ Editor ->Programmer’s File Editor http://www.lancs.ac.uk/people/cpaap/pfe/ Compiler -> SUN’s Java compiler http://www.javasoft.com/ IDE -> BlueJ version 1.1 http://bluej.monash.edu/ IDE -> Microsoft Visual J++ 6.0 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 Steps 1. 2. 3. 4. 5. 6. 7. Open editor Type this source code Save as “Junk.java” Compile into “Junk.class” Create HTML document Add proper <applet> tag View in web browser Writing Applets – Example 2 Steps 1. 2. 3. 4. 5. 6. 7. 8. Need two pictures named “picture1.jpg” and picture2.jpg” Open editor Type this source code Save as “Slide.java” Compile into “SSlide.class” Create HTML document Add proper <applet> tag View in web browser Enhancing Applet 2 Steps 1. 2. 3. 4. Questions: • • • What parameter tag(s) to use? What must image names be? How many images can be loaded? Modify previous source code Save and compile Add proper <param> tag(s) to previous HTML document View new applet in web browser (quit and restart) Self-running Applet Steps 1. 2. 3. Modify previous source code Save and compile View new applet in web browser (quit and restart) Questions • • • • What’s happening? What’s the delay? Pick a new <param> tag! Does paint method change? 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 ObjectOriented 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 CSAS1111, CSAS1112, etc Java by Definition http://www.jars.com/ Seton Hall Classes http://www.javasoft.com/ http://pirate.shu.edu/~wachsmut/jbd/ Books See Barnes & Nobles or Amazon.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: <script language=“JavaScript”> document.writeln(“Today is ” + (new Date())); </script>