The HTML APPLET Tag

The HTML APPLET Tag

As mentioned earlier, at the time of this writing, Oracle recommends that the APPLET tag be used to manually start an applet when JNLP is not used. An applet viewer will execute each APPLET tag that it finds in a separate window, while web browsers will allow many applets on a single page. So far, we have been using only a simplified form of the APPLET tag. Now it is time to take a closer look at it.

The syntax for a fuller form of the APPLET tag is shown here. Bracketed items are optional.

< APPLET

[CODEBASE = codebaseURL] CODE = appletFile

[ALT = alternateText]

[NAME = appletInstanceName] WIDTH = pixels HEIGHT = pixels

[ALIGN = alignment ]

[VSPACE = pixels] [HSPACE = pixels]

> 

[< PARAM NAME = AttributeName VALUE = AttributeValue>] [< PARAM NAME = AttributeName2 VALUE = AttributeValue>]

. . .

[HTML Displayed in the absence of Java] </APPLET>

Let’s take a look at each part now.

CODEBASE  CODEBASE is an optional attribute that specifies the base URL of the applet code, which is the directory that will be searched for the applet’s executable class file (specified by the CODE tag). The HTML document’s URL directory is used as the CODEBASE if this attribute is not specified.

CODE  CODE is a required attribute that gives the name of the file containing your applet’s compiled .class file. This file is relative to the code base URL of the applet, which is the directory that the HTML file was in or the directory indicated by CODEBASE if set.

ALT  The ALT tag is an optional attribute used to specify a short text message that should be displayed if the browser recognizes the APPLET tag but can’t currently run Java applets. This is distinct from the alternate HTML you provide for browsers that don’t support applets.

NAME  NAME is an optional attribute used to specify a name for the applet instance. Applets must be named in order for other applets on the same page to find them by name and communicate with them. To obtain an applet by name, use getApplet( ), which is defined by the AppletContext interface.

WIDTH and HEIGHT  WIDTH and HEIGHT are required attributes that give the size (in pixels) of the applet display area.

ALIGN  ALIGN is an optional attribute that specifies the alignment of the applet. This attribute is treated the same as the HTML IMG tag with these possible values: LEFT, RIGHT, TOP, BOTTOM, MIDDLE, BASELINE, TEXTTOP, ABSMIDDLE, and ABSBOTTOM.

VSPACE and HSPACE  These attributes are optional. VSPACE specifies the space, in pixels, above and below the applet. HSPACE specifies the space, in pixels, on each side of the applet. They’re treated the same as the IMG tag’s VSPACE and HSPACE attributes.

PARAM NAME and VALUE  The PARAM tag allows you to specify applet-specific arguments. Applets access their attributes with the getParameter( ) method.

Other valid APPLET attributes include ARCHIVE, which lets you specify one or more archive files, and OBJECT, which specifies a saved version of the applet. In general, an APPLET tag should include only a CODE or an OBJECT attribute, but not both.