Applets are embedded in web pages using the <APPLET> and </APPLET> tags. The
APPLET element is similar to the IMG element. Like IMG APPLET references a source file that is not part of
the HTML page on which it is embedded. IMG elements do
this with the SRC attribute. APPLET
elements do this with the CODE attribute. The CODE attribute tells the browser where to look for the
compiled .class file. It is relative to the location of the source
document. Thus if you're browsing
http://www.ibiblio.org/javafaq/index.html and that page references
an applet with CODE="Animation", then the file
Animation.class should be at the URL
http://www.ibiblio.org/javafaq/Animation.class.
If
the applet resides somewhere other than the same directory as the
page it lives on, you don't just give a URL to its location. Rather
you point at the CODEBASE. The CODEBASE
attribute contains a URL that points at the directory where the .class
file is. The CODE attribute is the name of the .class
file itself. For instance if on the HTML page of the previous
section you had written
<applet code="HelloWorldApplet" codebase="classes"
width="200" height="200">
</applet>
then the browser would have tried to find HelloWorldApplet.class in the classes directory in the same directory as the HTML page that included the applet. On the other hand if you had written
<applet code="HelloWorldApplet"
codebase="http://www.foo.bar.com/classes" width="200" height="200">
</applet>then the browser would try to retrieve the applet from http://www.foo.bar.com/classes/HelloWorldApplet.class regardless of where the HTML page was.
In short the applet viewer will try to retrieve the applet from the URL given by the formula (CODEBASE + "/" + code). Once this URL is formed all the usual rules about relative and absolute URLs apply.
If the applet is in a non-default package, then the full package qualified name must be used. For example,
<applet code="com.macfaq.greeting.HelloWorldApplet"
codebase="http://www.example.com/classes" width="200" height="200">
</applet>
In this case the browser will look for http://www.example.com/classes/com/macfaq/greeting/HelloWorldApplet.class so the directory structure on the server should also mirror the package hierarchy.
The HEIGHT and WIDTH attributes work
exactly as they do with IMG, specifying how big a
rectangle the browser should set aside for the applet. These
numbers are specified in pixels and are required.