Java in 4 hours - Seton Hall University

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Transcript Java in 4 hours - Seton Hall University

Java
Quick & Dirty
By Bert Wachsmuth
Overview
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We will cover:
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We will need:
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What is Java
Using and Writing Java applets
Getting more information
Knowledge of HTML and web page creation
We will get:
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Basic understanding of Java but we will
NOT become the world’s foremost Java
programmer
What is
Java
 Java
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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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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
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To use Java applets, you:
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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
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TickerTape
codebase: http://pirate.shu.edu/~wachsmut/Ticker
code: TickerApplet.class
width: 300, height=30
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3D Surface
codebase: http://pirate.shu.edu/~wachsmut/Surface
code: surface.class
width: 500, height=550
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Missile Defense
codebase: http://www.csd.uu.se/~d95vil/missile/classes
code: MissileCommand.class
width: 320, height: 200
Configurable
Applets
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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
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TickerTape
codebase: http://pirate.shu.edu/~wachsmut/Ticker
code: TickerApplet.class
width: 300, height=30
param: msg, delay, foreground, background
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Chatterbox
codebase: http://sciris.shu.edu/Java/Chat
code: ChatterBoxlet.class
width: 200, height=50
param: host (use sciris.shu.edu), port (use 1234)
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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
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or
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An “Integrated Developing Environment” (IDE)
Tools for Writing
Java Applets
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Java API -> essential resource
http://mathcs.shu.edu/Resources/Java/API/
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Editor ->Programmer’s File Editor
http://www.lancs.ac.uk/people/cpaap/pfe/
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Compiler -> SUN’s Java compiler
http://www.javasoft.com/
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IDE -> BlueJ version 1.1
http://bluej.monash.edu/
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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”
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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
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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
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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.
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Questions:
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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
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What’s happening?
What’s the delay?
Pick a new <param> tag!
Does paint method change?
A Professional
Applet
 To
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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:
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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:
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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:
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Think about the objects to be used
Download the files from the web site
Compile, execute, test, and IMPROVE
Some “less-good” News
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Java has “version problems” with applets:
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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…)
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More Information
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Sun’s Website & Online Tutorials
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JARS Resources
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CSAS1111, CSAS1112, etc
Java by Definition
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http://www.jars.com/
Seton Hall Classes
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http://www.javasoft.com/
http://pirate.shu.edu/~wachsmut/jbd/
Books
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See Barnes & Nobles or Amazon.com
The End …
What is
JavaScript
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JavaScript is a programming language that:
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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>