Applets and HTML

1
Applets and HTML

• Chapter 13

2
Reminders

• Project 8 due Dec 8 _at_ 1030 pm
• Project 6 regrades due by midnight tonight
• Submit all files (including your exception
  classes)
• Nothing scheduled for CS180 next week
• No lectures
• No labs
• No recitations
• No discussion groups

3
Introduction

• Applets are simply Java programs designed to run
  from a document (page) on the World Wide Web.
• HyperText Markup Language (HTML) is the language
  used to create Web documents.

4
Introduction to Applets

• An applet is a small application or a little
  Java program.
• Applets are Java programs that are typically
  displayed on a Website and viewed over the
  Internet.
• An applet can also be run as a stand-alone
  program on a computer which is not connected to
  the Internet.

5
Applet Basics

• An applet is a derived class of class JApplet
  which is a class in the Swing library.
• When writing an applet, it is a good idea to
  include all of the following
• import javax.swing.
• import java.awt.
• import java.awt.event.

6
Adding Icons to an Applet

• An icon typically is a small picture.
• By placing the icon in a JLabel, the icon is
  displayed.
• A JLabel can consist of text, an icon, or both.
• A JButton or JMenuItem can also have an icon.

7
Adding Icons to an Applet, cont.

• class DukeApplet

8
Adding Icons to an Applet, cont.
9
Introduction to HTML

• Documents to be read on the Web or using a Web
  browser typically are expressed in a language
  called HTML.
• HTML stands for HyperText Markup Language.
• Hypertext contains links (or hyperlinks) which
  permit you to go to other documents.
• Intro to HTML http//archive.ncsa.uiuc.edu/Genera
  l/Internet/WWW/HTMLPrimer.html

10
HTML Basics, cont.

• HTML is not case sensitive. lttablegt, ltTablegt,
  ltTABLEgt, lttAbLegt are all the same
• An HTML file is a regular text file that you
  create and edit with a text editor.
• HTML files should end with .html or .htm
• Commands such as lttablegt and lt/tablegt form a
  container (in this case a table container).

11
HTML Basics, cont.
12
Displaying the Most Current Version of a Document

• While you are developing an HTML page, you can
  display the most recent version of the page by
  clicking the button labeled Reload (or perhaps
  Refresh).
• Otherwise, for efficiency, the browser may access
  an earlier copy of the page.

13
Displaying a Picture

• A picture can be inserted into an HTML document
  using
• ltimg srcFile_with_Picturegt
• example
• ltimg srcimages/mypicture.jpggt
• The picture can be in any directory, but the path
  name, either full or relative, leading to the
  picture must be provided.

14
Placing an Applet in an HTML Document

• To display the adder window created by class
  AdderApplet, place the following command in an
  HTML document
• ltapplet codeAdderApplet.class width400
  height200gt
• lt/appletgt
• (Actually .class is optional.
  codeAdderApplet works just as well)

15
Placing an Applet in an HTML Document, cont.

• This command assumes that the HTML file and the
  file AdderApplet.class are in the same directory.
• Otherwise, a relative or absolute path name to
  AdderApplet.class is needed.

16
Applet in an HTML Document,
17
Placing an Applet in an HTML Document, cont.
18
Using an Old Web Browser

• A Web browser must be set up to run applets.
• Web browsers do not use the same Java interpreter
  used to run Java applications.
• Older Web browsers (yours or someone elses who
  may want to view your HTML document) may not be
  able to run applets from an HTML document.

19
Using an Old Web Browser, cont.

• Furthermore, Java updates for browsers typically
  lag core Java language updates.
• Using the older Applet class sometimes can remedy
  the problem.
• These problems do not exist if you are running
  applets from the applet viewer using a recent
  version of Java.

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The Older Applet Class

• To use the older Applet class instead of the
  JApplet class
• remove the Js from JApplet, JButton, JLabel, etc.
  (that is, use Applet, Button, Label)
• use the following import statements
• import java.awt.
• import java.awt.event.
• import java.applet.

21
The Older Applet Class, cont.

• you do not need
• import javax.swing.
• add components to the applet to itself rather
  than using a content pane (whatever was done to
  the content pane of a JApplet should be done
  directly to the Applet).

22
The Older Applet Class, cont.

• example
• substitute
• add(friendlyLabel)
• for
• getContentPane().add(friendlyLabel)
• Furthermore, class Applet cannot accommodate
  icons easily.

23
Applets and Security

• Your applet is a program that may be run on
  someone elses computer.
• Worse, someone elses applet might be run on your
  computer!
• Furthermore, you dont know that an HTML page
  contains an applet until you load it into your
  browser, and then it is too late to reject the
  applet it is already stored on your computer.

24
Applets and Security, cont.

• Someone elses program running on your computer
  creates serious security concerns.
• Will it leave a virus?
• Will it alter your files or read confidential
  information?
• Will it corrupt your operating system?
• Applets cannot do any of these things (at least
  not easily).

25
Applets and Security, cont.

• Applets cannot run your programs, nor can they
  read from or write to files on your computer
  (unless the applet originated on your computer).

26
Summary

• You have learned how to write applets.
• You have learned to write a simple HTML document.
• You have learned how to embed an applet in an
  HTML document.