The Java Boutique: Introduction to Java Part 6: Building Your First Application

Applet HTML

After creating the Java code for an applet, you will need to compile it to create a Java .class files used to run the program. If you are using the JDK, the following command can be used to compile the applet (as you can see, it is just the same as for applications):

> javac Hello.java

Make sure that you are in the same directory as the .java file you are compiling and make sure that you are careful to type the name of the .java file correctly.

When you compile the .java file, you should have a Hello.class file in the same directory as the .java file.

Now, you are ready to distribute your applet over the web. To do so, you must create an HTML page that displays the applet using the <APPLET></APPLET> HTML tag to define an applet which you would like the browser to run.

When a web browser interprets an HTML page sent to it from a web server, it begins decoding it right away. In other words, each tag that the browser encounters is read and interpreted. When the browser reaches the <APPLET> tag, it either ignores it if it does not understand Java, or it sends a request to the server to retrieve the applet code in the location specified by the tag.

For example, the following code provides an example of what an <APPLET> tag might look like in the body of an HTML page:

<HTML> <HEAD> <TITLE>My Applet!</TITLE> </HEAD> <BODY> <APPLET CODEBASE = "http://www.x.com/MyApplet/" CODE = "MyApplet.class" ALT = "My Applet" NAME = "MyApplet" WIDTH = "100" HEIGHT = "100" ALIGN = "LEFT" VSPACE = "5" HSPACE = "5"> <PARAM NAME = "phrase" VALUE = "Hello World!"> . . . Here is some text which can be displayed if the browser does not support Java. </APPLET> </BODY> </HTML>

The following table goes over the attributes in the APPLET tag.

Attribute	Description
CODE	Specifies the name of the class file which starts your applet.
CODEBASE	Specifies the base directory on the web server where your class files are stored.
ALT	Specifies the text which should be displayed if the browser is capable of running Java applets but is unable to run your applet.
NAME	Specifies the name of your aplet within the context of the HTML page and other applets which might be running on the same page.
WIDTH and HEIGHT	Specifies the amount of space given for your applet in pixels.
ALIGN	Specifies how your applet will be aligned within the browser window. You can pass the following values along with this attribute: TOP, BOTTOM, LEFT, RIGHT, TEXTTOP, MIDDLE, ABSMIDDLE, BASELINE, BOTTOM. These values are standard HTML values such as those for images. If you need an explanation check out an HTMl reference guide.
VSPACE and HSPACE	Specifiy how much of a margin to give the applet in pixels.

Selena Sol contributes to the JavaBoutique's Introduction to Java. Selena curently works for Barclays Capital in London, one of the leading global investment banks in Europe and has worked as a software developer for the National Center for Human Genome research, Microline Software, Neuron Data, and Electric Eye in Singapore. Selena is perhaps best-known for creating the Public Domain Web Script Archive (Extropia) and writing several books on Web Programming (Perl, CGI, Java).
Email: selena@extropia.com