A Simple Java Applet

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A Simple Java Applet

• Cmput 114 Section A3 Fall 2005
• Lecture 2
• Department of Computing Science
• University of Alberta

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About This Lecture

• In this lecture we will create and run a simple
  Java applet.
• We wont try to understand any of the code.
• Instead we will simply concentrate on the
  mechanics of using the programming environment to
  create and run the applet.

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Outline

• Kinds of Java programs
• Applet template
• A simple applet Applet0
• Running applets from a Browser
• Eclipse applet demonstration

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Kinds of Java Programs

• Recall the three kinds of Java programs
• Applications
• Applets
• Libraries
• An application is a Java program that is run by
  using a Java interpreter program.
• An applet is a Java program that is run by a
  Java-enabled web browser.
• A library is a set of Java classes that can be
  used by another Java program.

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Java Applet Template

• import java.awt.
• import java.applet.
• public class AppletName extends Applet
• /
• Applet description.
• /
• public void paint(Graphics graphics)
• / applet display statements go here. /

put display statements here
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Applet Applet0

• import java.awt.
• import java.applet.
• public class Applet0 extends Applet
• /
• This is our first applet.
• /
• public void paint(Graphics graphics)
• / Display myself on the given Graphics /
• graphics.drawString(This is an applet., 10,
  50)

x and y coordinates of upper left corner of the
String
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Applet0 Output in Applet Viewer
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HTML Documents

• A web browser runs an Applet by first loading a
  document written in a language called HTML
  (HyperText Markup Language).
• HTML defines the meanings of tags that are added
  to document text, which specify the format of the
  document and links to other documents.
• One of the tags in the HTML file tells the
  browser to load an applet.

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Applet0.html
start of html

• ltHTMLgt
• ltHEADgt
• ltTITLEgtApplet0lt/TITLEgt
• lt/HEADgt
• ltBODYgt
• ltHRgt
• ltAPPLET
• CODEApplet0.class
• WIDTH300 HEIGHT60gt
• lt/APPLETgt
• ltHRgt
• lt/BODYgt
• lt/HTMLgt

start of header information
the web page title
start of web page content
a horizontal line (rule)
load an applet
from this file
in a box this big
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Applet0 Output in a Browser
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Demonstration Applet

• Start Eclipse.
• Create a new project called Applet0.
• Create a class called Applet, setting superclass
  to java.applet.Applet.
• Edit the code.
• Save the source file as Applet0.java.
• Compile (Build) to create Applet0.class file.
• Run from Eclipse.
• Edit HTML file - Applet0.html.
• Load html file from Browser.