Transcript Java in 4 hours - Seton Hall University
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
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3.
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
Using Java Applets
To
use
Java applets, you:
Locate appropriate class file(s) Learn how to configure applet Embed the Applet into web page // 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
1.
2.
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
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
1.
2.
3.
4.
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7.
Steps
Open editor Type this source code Save as “Junk.java” Compile into “Junk.class” Create HTML document Add proper
Writing Applets – Example 2
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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
Enhancing Applet 2 Steps
1.
2.
3.
4.
Modify previous source code Save and compile
Add proper 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?
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 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
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: members Regulate access to class 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 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
JavaScript-aware web browser inside a Code is embedded directly in a web page Is
a lot
easier than Java JavaScript Example: