ION Java User's Guide: Using ION's Pre-Built Applets

The <APPLET> Tag

The HTML <APPLET> tag is used to include Java applets in your HTML code. For more information on embedding applets into a web page, consult an HTML manual The syntax of the <APPLET> tag is as follows:

<APPLET
[ALIGN={"left" | "right" |"top" | "middle" | "bottom"}]
[ALT="alternate text"]
[ARCHIVE="zip or jar file"]
CODE="class file"
[CODEBASE="path or URL"]
HEIGHT="height"
[HSPACE="pixels"]
[NAME="name"]
[VSPACE="pixels"]
WIDTH="width" >
</APPLET>

Attributes

The <APPLET> tag takes the following attributes:

ALIGN

ALIGN specifies either the position of the applet in relation to the left and right borders of the browser, or the alignment of text in relation to the applet:

ALT

The ALT attribute specifies a text string to be displayed if for some reason the applet cannot be loaded. The ALT attribute is not required, but consider adding something like the following to your applet description to enhance the user-friendliness of your HTML page:

ALT="ION Applet failed to load. Is Java enabled in your browser?"  

ARCHIVE

The ARCHIVE attribute is not required. However, it is recommended that you download all of the ION classes as a single package. See Supporting Java Archive Files for a discussion of Java archive files.

CODE

A string specifying the name of the applet class. The CODE attribute should specify the fully-qualified class name relative to the directory in which the HTML file is located. If the CODEBASE attribute is included, the class name specified in the CODE attribute should be relative to the directory specified by CODEBASE.

For example, if you were to place an HTML file that used the IONPlotApplet in an html subdirectory of the ION directory, the CODE, CODEBASE and ARCHIVE attributes would be:

CODE=com.itt.ion.IONPlotApplet.class  
CODEBASE="../classes"  
ARCHIVE="ion_64.jar"  

because the IONPlotApplet.class file is located in the com/itt/ion subdirectory within the ION .jar file. Similarly, if you were to place all of the Java class files necessary for your applet in the directory containing your HTML files, you could omit the CODEBASE attribute and use something like the following:

CODE=MyApplet.class  

The CODE attribute is required for all ION applets.

CODEBASE

The CODEBASE attribute is not strictly required, but is often useful. The Java class loader searches for the contents of the classes directory in current directory — that is, the directory from which the HTML page containing the <APPLET> tag was loaded. If you locate the HTML page somewhere other than the IONJava/classes directory, you will need to set the CODEBASE attribute to the relative path from the page location to the classes directory, or to a URL that specifies the location.

For example, if your HTML page is located in a directory called /ITT/IDL63/products/ION63/ion_java/html, you would set the CODEBASE attribute as follows:

CODEBASE="../classes"  

HEIGHT

The height of the applet in pixels. ION uses the HEIGHT attribute when creating the drawing area. This attribute is required for all ION applets.

HSPACE

The amount of white space to the left and right of the applet, in pixels.

NAME

A string containing a unique name for the applet. The string should be enclosed in double quotes marks. This attribute is required for all ION applets.

WIDTH

The width of the applet in pixels. ION uses the WIDTH attribute when creating the drawing area. This attribute is required for all ION applets.

VSPACE

The amount of white space on the top and bottom of the applet, in pixels.

Example

The following <APPLET> tag creates an applet of the IONGraphicApplet class, with a drawing area 100 pixels by 100 pixels, with the name "MyApplet." The HTML page containing the applet code is assumed to be located in the directory /ITT/IDL63/products/ION63/classes, so no CODEBASE attribute is included.

<APPLET NAME="MyApplet" WIDTH=100 HEIGHT=100  
    CODE=com.itt.ion.IONGraphicApplet.class  
<!- Other applet code >  
</APPLET>  

<APPLET attributes>  
   <!-- Applet code -->  
   <B>Java virtual machine failed to start.   
   Is Java enabled in your browser? </B>  
</APPLET>