Java Applets #1
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Published on: Friday 6th March 1998 By: Tarique Sani
Introduction
Starting this week I will be presenting a series of articles
on JAVA and how to use it to enhance your pages, for material I
am relying heavily on my own experiences in page designing and
how I graduated from plain HTML to JavaScript to Java. Hence my
dig at not so poor Bill!
Those of you who are impatient or in a hurry to plug in a zany
navigational applet on to your page, without wanting to learn
much can download one now
& those of you want to be sure that I am not wasting your time can
see a working example
The trustworthy and the trusting please read on....
A Simple Applet tag
The very basic pre-requisite to having an applet in your page
is to have an <APPLET> tag - This is what I will discuss,
but first an example:
<APPLET
CODE="tarique.class" WIDTH=200 HEIGHT=40>
</APPLET> |
Honest! this is a perfectly valid <APPLET> declaration,
but as you might have guessed good things are not that simple
(always!?)
Complete Applet Syntax
Here is the complete syntax of the applet tag:
<APPLET
[CODEBASE=codebaseURL]
CODE=appletFile
[ALT=aternateText]
[NAME=appletInstanceName]
WIDTH=pixels HEIGHT=pixels
[ALIGN=alignment]
[VSPACE=pixels] [HSPACE=pixels]
>
[< PARAM NAME=attributeName VALUE=attributeValue >]
[< PARAM NAME=attributeName2 VALUE=attributeValue2 >]
.. .. ..
</APPLET>
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Don't be scared - Its not as complex as it seems - Lets take one keyword at a time.
CODEBASE=codebaseURL
CODEBASE is an optional attribute that specifies the
base URL of the applet code, which is the directory that will be
searched for the applets executable class file (specified with
the CODE tag). The HTML document's URL directory is used as the
CODEBASE if this attribute is not specified. The CODEBASE does
not have to be on the host that the HTML document was read from,
i.e. you can use applets from my site for your pages without
keeping the class file with you!
CODE=appletFile
CODE is a required attribute that gives the name of the
file that contains your applet's class file. This file is
relative to the code URL.
ALT=aternateText
ALT is an optional attribute which specifies a short
text message that should be displayed if the browser understands
the APPLET tag but can't currently run java applets.
NAME=appletInstanceName
NAME is an optional attribute used to specify a name for
the applet instance. Applets must be named for other applets on
the same page to find them by name and communicate.
WIDTH=pixels HEIGHT=pixels
WIDTH and HEIGHT are required attributes that give the initial
size (in pixels) of the applet display area.
ALIGN=alignment
ALIGN is an optional attribute that specifies the
alignment of the applet. This attribute is treated the same as
the HTML IMG tag.
VSPACE=pixels HSPACE=pixels
These are optional attributes specifying the space in
pixels above and below the applet. It is again the same a IMG
VSPACE & HSPACE attributes.
PARAM NAME=attributeName VALUE=value
The PARAM tag is how you pass applet specific arguments to Java from HTML.
Sample ktn Applet
Lets see the <APPLET> tag for the ktn applet
demonstrated above (If you trusted me -
please have a look now! )
<APPLET CODE="ktn" WIDTH=450 HEIGHT=100>
<PARAM NAME=item0 VALUE="Welcome+main.html+Welcome from Dr. Tarique Sani+splash">
<PARAM NAME=item1 VALUE="<applet> tag+tag.html+See the Applet tag for this applet+splash">
<PARAM NAME=item2 VALUE="Source Code+source.html+Obviously the source code for ktn.java+splash">
<PARAM NAME=item3 VALUE="Download+download.html+Download Applet+splash">
<PARAM NAME=welcome VALUE=" Dr Tarique Sani welcomes you, please wait ...">
<PARAM NAME=delay VALUE=2>
</APPLET>
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OK! that was real easy stuff. When I had first designed and
pasted this applet on to a friends site, before I could pat
myself on the back - the phone rang! It was my friend he angrily
retorted "What a lousy site, it has just one page", I
said "Click on the applet", "Applet what applet? - There's just a blank area!"
Perplexed, I tested and retested the applet code before
realising that the browser on my friends machine had JAVA turned
off - hence he could not see the applet nor could he navigate!
Browsers without Java Support
What does one do in such a situation? Of Course - one can be
elitist and say "JAVA compatible browser required", or, reconsider
coding as follows.
<APPLET CODE="ktn" WIDTH=450 HEIGHT=100>
<PARAM NAME=item0 VALUE="Welcome+main.html+Welcome from Dr. Tarique Sani+splash">
<PARAM NAME=item1 VALUE="<applet> tag+tag.html+See the Applet tag for this applet+splash">
<PARAM NAME=item2 VALUE="Source Code+source.html+Obviously the source code for ktn.java+splash">
<PARAM NAME=item3 VALUE="Download+download.html+Download Applet+splash">
<PARAM NAME=welcome VALUE=" Dr Tarique Sani welcomes you, please wait ...">
<PARAM NAME=delay VALUE=2>
<TABLE BORDER="0" CELLSPACING="4">
<TR>
<TD COLSPAN="3" BGCOLOR="#C00000"><FONT COLOR="#FFFFFF" SIZE="3" FACE="helvetica"><B>Kalptaru Net</B> - <I>JAVA applet at a glance... </I></FONT></TD>
</TR>
<TR>
<TD BGCOLOR="#008000"><A HREF="main.html" TARGET="splash"><FONT COLOR="#FFFFFF">Welcome</FONT></A></TD>
<TD BGCOLOR="#007000"><A HREF="tag.html" TARGET="splash"><FONT COLOR="#FFFFFF">Applet Tag</FONT></A></TD>
<TD BGCOLOR="#005000"><A HREF="source.html" TARGET="splash"><FONT COLOR="#FFFFFF">Source Code</FONT></A></TD>
</TR>
<TR>
<TD BGCOLOR="#007000"><FONT COLOR="#FFFFFF">Some</FONT></TD>
<TD BGCOLOR="#006000"><FONT COLOR="#FFFFFF">More</FONT></TD>
<TD BGCOLOR="#004000"><FONT COLOR="#FFFFFF">Options</FONT></TD>
</TR>
</TABLE>
</APPLET>
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The browsers that don't support Java will see it as:
As the HTML'ers amongst you must have figured out - you just stick
the HTML code before the </APPLET> tag, remembering to keep the
HTML code such that it fits in the WIDTH and HEIGHT of the
applet, so that it does not upset the layout of your page.
I personally prefer to use a table with one link in each cell.
Java Resources
That's almost all there is to the <applet> tag.
You can see lots of nifty applets at
http://www.javasoft.com/java.sun.com/applets/applets.html
There's a fabulous Java programming tutorial at
http://sunsite.unc.edu/javafaq/javatutorial.html
but be warned its a huge download (it was 4Mb last I saw it!)
The faithful should be patient until the next Java Applets article, when I will start the dissection of an applet.
View the profile on Tarique Sani and the list of other Articles by Tarique Sani.
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