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Java Quick & Dirty

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.

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Java Quick & Dirty

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  1. JavaQuick & Dirty By Bert Wachsmuth

  2. 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 willNOT become the world’s foremost Java programmer

  3. What isJava • 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

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

  5. Simple Example Java code for TickerApplet

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

  7. Using JavaApplets • 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 </applet> // do not forget this

  8. Simple Applets • TickerTape codebase: http://pirate.shu.edu/~wachsmut/Tickercode: TickerApplet.classwidth: 300, height=30 • 3D Surface codebase: http://pirate.shu.edu/~wachsmut/Surfacecode: surface.classwidth: 500, height=550 • Missile Defense codebase: http://www.csd.uu.se/~d95vil/missile/classescode: MissileCommand.classwidth: 320, height: 200

  9. Configurable Applets • Many applets can be configured using “param” tags: • 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>

  10. Configurable Applet Examples • TickerTape codebase: http://pirate.shu.edu/~wachsmut/Tickercode: TickerApplet.classwidth: 300, height=30param: msg, delay, foreground, background • Chatterbox codebase: http://sciris.shu.edu/Java/Chatcode: ChatterBoxlet.classwidth: 200, height=50param: host (use sciris.shu.edu), port (use 1234) • Note: Applets can be embedded easily with FrontPage or Notes (LearningSpace)

  11. WritingJava 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)

  12. Tools for WritingJava 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

  13. 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

  14. 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 */ } }

  15. Writing Applets – Example 1 Steps • 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

  16. Writing Applets – Example 2 Steps • 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

  17. Enhancing Applet 2 Steps • 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) Questions: • What parameter tag(s) to use? • What must image names be? • How many images can be loaded?

  18. Self-runningApplet Steps • 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?

  19. A ProfessionalApplet • 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

  20. 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

  21. 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

  22. 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…)

  23. More Information • Sun’s Website & Online Tutorials • http://www.javasoft.com/ • JARS Resources • http://www.jars.com/ • Seton Hall Classes • CSAS1111, CSAS1112, etc • Java by Definition • http://pirate.shu.edu/~wachsmut/jbd/ • Books • See Barnes & Nobles or Amazon.com

  24. The End …

  25. What isJavaScript • 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>

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