David Sosnowski |
David Sosnowski is the
webmaster of CodeBrain.com Free Java . He is also the creator of
CodeBrain.com's many freeware and commercial applets, kits, JavaScripts, and
Perl scripts. |
David Sosnowski
has written 1 tutorials for JavaScriptSearch. |
View all tutorials by David Sosnowski... |
INTRODUCTION
Setting up JAVA
applets, though perhaps daunting the first time you do it, is really quite
simple. Today we're going to walk you through the basics; and believe it or not,
you can get all this sorted out in under ten minutes. Let's just dive in and do
it!
JAVA applets use
only two types of HTML tags -- both easy to deal with.
The <APPLET>
tag basically just tells the browser what applet.class file to use, and how wide
and high the applet should be.
There are
additional (optional) attributes you can set up, too; but in simplest use,
that's all there is to this tag, and usually all you will need.
The <PARAM>
tag is likewise simple -- it NAMES a parameter the JAVA applet needs to run, and
provides a VALUE for that parameter.
Though a given
applet may have anywhere from no PARAM tags to dozens, still, every PARAM tag
takes the very same simple form: just a NAME, and a VALUE.
Let's have a look
at those two tags in greater detail. And please, remember the www.CodeBrain.com
maxim: "This is simple -- don't make it complicated!"
THE
<APPLET> TAG
Here's the
framework of a simple HTML tag set for putting an applet into your page:
<APPLET
CODE="filename.class" WIDTH="400" HEIGHT="200"> . . (parameters
go here - more about them presently) . . < /APPLET>
The
CODE="filename.class" contains the name of the applet's class file. The class
file is a small executable which does the real work of the applet.
For newcomers to
JAVA, there are two important things to remember about the class file: Put the
class file in the same place on your server as the HTML page calling it; and
make certain you send the class file up in binary format -- never ASCII!
Forgetting to send
the class file up or sending it up in the wrong format is responsible for
about 90% of all problems encountered while setting up applets.
Next, let's look at
how to set the applet size on the page. WIDTH="400" and HEIGHT="200" would cause
the applet to appear 400 pixels wide and 200 pixels high on your page. If you
want the applet to be a different size, change these values, just like you would
for an image.
Following the
<APPLET> tag you will then insert the <PARAM> tags, and -- don't
forget! -- close off this tag set with a mating </APPLET> tag.
THE
<PARAM> TAG
As we said, the
<PARAM> tags go between the <APPLET> and </APPLET> tags, as in
this sample code:
<APPLET
CODE="filename.class" WIDTH="400" HEIGHT="200"> < PARAM NAME="SPEED"
VALUE="100"> < PARAM NAME="IMAGE1" VALUE="thisimage.gif"> <
PARAM NAME="IMAGE2" VALUE="thatimage.jpg"> < /APPLET>
The very first
thing you will notice is that <PARAM> tags absolutely do not, ever, have a
mating end tag. <PARAM> tags are among the few HTML tags that do not.
As for what they
do, parameter tags tell the applet how it is to behave and what resources it
will use (for instance, in this example, how fast the applet will run, and what
image files it will use).
A key point for
newcomers to remember is that, unlike HTML tags and JavaScript methods or
properties, a parameter's NAME is absolutely not standard. The person who builds
the applet decides what the parameter names will be, so study the applet's
documentation carefully.
However, the syntax
and use of <PARAM> tags is regular, and very simple.
The NAME="whatever"
specifies the parameter to be set, and its corresponding VALUE="whatever" says
what its value is to be.
In the example
above, the SPEED parameter is being set to a value of 100 (probably in
milliseconds, but you would check the applet documentation to find out).
Likewise, the IMAGE1 and IMAGE2 parameters would tell this applet to use
"thisimage.gif" and "thatimage.jpg" respectively for its image resources.
And that's it for
the parameters! No matter how many parameters, they'll all follow the same
simple pattern.
PUTTING THE
APPLET CODE INTO YOUR HTML PAGE
Now comes the
easiest part. To insert applet code into an HTML page, you simply copy
everything from <APPLET> through </APPLET> into the <BODY>
area of your page HTML, wherever you would like the applet to appear.
To make this
clearer, you can think of everything from <APPLET> to </APPLET> as
one block, and insert the whole block into your page just like you would, say,
an image <IMG> tag.
For layout control,
note that you can put the entire <APPLET> ... </APPLET> block into
an individual cell in a table; as in this example, which would show a 5-pixel
red border around the applet:
<table
cellpadding="5" bgcolor="#FF0000"> < tr> < td> <
APPLET CODE="filename.class" WIDTH="400" HEIGHT="200"> < PARAM
NAME="SPEED" VALUE="100"> < PARAM NAME="IMAGE1"
VALUE="thisimage.gif"> < PARAM NAME="IMAGE2"
VALUE="thatimage.jpg"> < /APPLET></td> < /tr>
< /table>
Tip: Note how we
pulled the </td> tag right against the </APPLET> tag, by the way --
that solves a shortcoming of Netscape when it comes to proper centering.
GETTING IT ALL
TO YOUR SERVER
For newcomers to
JAVA, always put everything related to the JAVA applet in the same place
(directory) on your server.
What has to go up?
Your HTML page, of course. But also be sure any image files or other resources
the applet uses are properly sent up. If they aren't there, most applets will be
unable to start.
Finally, and of
special note, the applet class file must be sent up. We can't say it often
enough: Make sure the class file is on the server, where it should be, and make
certain you sent it up in binary format.
A QUICK TAKE ON
TROUBLESHOOTING
The single most
common cause for problems with JAVA applets is either neglecting to send up the
class file, or sending it up in ASCII (text) format, instead of binary.
If you see an error
in the browser status bar like "class whatever.class not found" or "class
whatever.class could not be loaded", send the class file up again, and watch
your FTP client to be sure it goes up in binary.
The second most
common problem is forgetting to send up resources the applet needs, such as
image files or text files. Obviously, make sure they're on the server, in the
right place, and sent in the appropriate formats.
The third most
common problem is, you didn't proofread your code! Remember, check it three
times, and when you're absolutely sure it's right? Check it again.
LAST WORDS...
There is a truly
stunning array of JAVA applets available, thousands upon thousands of them, that
perform myriad tasks and functions -- from basic text scrollers to striking
display applets and powerful animation tools.
Once you get the
basic dance steps down, JAVA applets are straightforward installations, and a
great way to add interest, functionality, and versatility to your pages.
Even better, many
JAVA applets are absolutely free for the taking, so don't miss a great
opportunity to add some flash for zero cash! - |