JavaQuick & 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 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

Simple Example Web page withJava 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 <APPLET> tag

3. One or more Java class files (produced separately from Java source code)

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

Simple Applets TickerTape

codebase: http://pirate.shu.edu/~wachsmut/Tickercode: TickerApplet.classwidth: 300, height=30

3D Surfacecodebase: http://pirate.shu.edu/~wachsmut/Surfacecode: surface.classwidth: 500, height=550

Missile Defensecodebase: http://www.csd.uu.se/~d95vil/missile/classescode: MissileCommand.classwidth: 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=“###”>

<param name=“Name” value=“Value”> <param name=“Name2” value=“Value2”> ...</applet>

Configurable Applet Examples

TickerTapecodebase: http://pirate.shu.edu/~wachsmut/Tickercode: TickerApplet.classwidth: 300, height=30param: msg, delay, foreground, background

Chatterboxcodebase: 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)

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)

Tools for WritingJava Applets

Java API -> essential resourcehttp://mathcs.shu.edu/Resources/Java/API/

Editor ->Programmer’s File Editorhttp://www.lancs.ac.uk/people/cpaap/pfe/

Compiler -> SUN’s Java compilerhttp://www.javasoft.com/

IDE -> BlueJ version 1.1http://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

1. Open editor2. Type this source code3. Save as “Junk.java”4. Compile into “Junk.class”5. Create HTML document6. Add proper <applet> tag7. View in web browser

Steps

Writing Applets – Example 2

1. Need two pictures named“picture1.jpg” and picture2.jpg”

2. Open editor3. Type this source code4. Save as “Slide.java”5. Compile into “SSlide.class”6. Create HTML document7. Add proper <applet> tag8. View in web browser

Steps

Enhancing Applet 2

1. Modify previous source code

2. Save and compile3. Add proper <param>

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-runningApplet

1. Modify previous source code

2. Save and compile3. View new applet in web

browser (quit and restart)

Steps

• What’s happening?• What’s the delay?• Pick a new <param> tag!• Does paint method change?

Questions

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

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

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

The End …

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>