Java Applets
Even if you don't know how to program in Java, you can
still employ Java applets that
someone else has already written.
Java Example: TickerTape Applet
Many applets let users perform a degree of customization using
only HTML commands. A nice example is the following ticker tape
display developed by an Egyptian company named ITS.
We've added this to our page using the following HTML:
<applet code=NavigatorTicker11.class width=300
height=28>
<param name=count value=2>
<param name=msg0 value=
"Welcome to Fred Fargle's Homepage.. Just Click
to Connect *** \\No Link">
<param name=msg1 value=
"Visit: ALCo -- Access LaPorte County
\\http://www.alco.org/">
<param name=speed value=8>
<param name=bgco value=50,0,200>
<param name=txtco value=250,250,0>
<param name=linkco value=180,25,21>
</applet>
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The actual Java program is in file NavigatorTicker11.class;
this is a compiled binary file, in a platform independent format
know as byte-code (compiled Java applets will generally have the
extension .class in their filenames; they are often termed class
files).
The CODE and CODEBASE Fields
Note that the Java code is not part of the HTML file but is only
referenced by the HTML. An HTML
applet tag is used to insert the applet on the page. The tag tells
the browser the name (and location) of the file containing the Java
code that is to be inserted on the page. The name is supplied through
the statement
code=NavigatorTicker11.class.
In this example, it is implied that this class file is located
in the same directory (folder) as this HTML document. You can also
place the Java code in a directory other than the one containing
the HTML file, but then you must specify the location of this new
directory (relative to the HTML file) by providing a value for codebase.
For example, if we were to add codebase=/Java/NavTicker inside
the applet tag,
<applet codebase=/Java/NavTicker
code=NavigatorTicker11.class width=300
height=28>
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we would indicate that the NavigatorTicker11.class file was in
a subdirectory named NavTicker of a directory named Java that was
itself a subdirectory of the directory containing the HTML file
for this page. This could be useful, for example, if we have used
the same applet in more than one document.
Specification of Applet Parameters
The other items in the above applet tag are specifications of parameters
that allow the user to customize the behavior of the applet (these
are the lines beginning with "param"). The meanings of the parameters
for the TickerTape applet are:
- count -- total number of messages (3 in the above example)
- msg0, msg1, ...individual messages; note that the count
starts with 0, not 1; each consists of the message text, followed
by two backslashes, followed by a URL (linking the message to
the URL)
- txtco -- color of message text, coded as a (Red, Green,
Blue) RGB triplet with the components separated by commas, and
each component a number in the range 0-255 indicating the amount
of red, green, and blue, respectively (for example, the triple
255, 255, 255 is white, 0, 0, 0 is black, and 0, 255, 0 is pure
green).
- bgco -- background color (denoted in the same format
as txtco)
- linkco -- active link color (same format as txtco)
- speed -- specifies the scrolling speed
Note that each displayed message can contain a hypertext
link. The URL for the link is
displayed at the bottom of the browser window when the cursor is
placed over that scrolling message. You can activate a link by clicking
on it as it scrolls by. If a message does not contain a link you
should still include two backslashes after the message text (followed
by optional text that will be displayed at the bottom of the browser
window when the cursor is placed over that message).
Add the TickerTape Applet to Your Page
You can add this ticker tape banner to your pages and have it display
whatever message(s) you desire. You only need to get the file NavigatorTicker11.class, add the above
section of HTML code to the desired spot on your page, and modify
the parameters to show the messages you want in the colors and speed
you like (remember to place the Java class file in the same directory
as your homepage file unless you add a codebase specification to
indicate which directory it is in). The applet
is free for you to use. The author only asks that you give credit
to its developer.
Customizing the Applet
Experiment with modifying the example:
- Change Fred's name to your own, to
make the banner a greeting to your homepage.
- Add a fourth message. (Don't forget
to update the value of the count parameter!)
- Change the background color to bright
red (255,0,0).
- Change the text color to cyan (0,255,255).
- Experiment with changing the scrolling
speed. What happens if you use values of the speed parameter greater
than 8? Less than 8?
- Now customize the banner to display
the messages that you would like for it to display and add it
to your homepage.
Note: In some cases the applet may not be reloaded with
the new parameters in effect if you simply reload the Web page.
You may have to exit your browser and restart it in order to see
the changes. Java is a rather new language on the Web and
there still are some bugs in its implementation for many browsers.
Some More Examples
If you would like to add more applets to your Web pages, check
out some additional examples at
- http://www.javasoft.com/applets/applets.html
Be sure to download the class file (or files) and a sample applet
tag showing what parameters can be set for any applets that you
want to add to your pages. In all cases, give credit where credit
is due if you are using someone else's applet.
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