Sending Parameters from a Web Page

The functionality of an applet can be customized with the use of parameters, settings stored in HTML markup that serve the same purpose as command-line arguments in applications.

Parameters are stored as part of the web page that contains an applet. They’re created using the HTML tag param and its two attributes: name and value. You can have more than one param tag with an applet, but all must be placed between the opening <applet> and closing </applet> tags. Here’s an applet tag that includes several parameters:

<applet code="ScrollingHeadline" height="50" width="400">
    <param name="headline1" value="Dewey defeats Truman">
    <param name="headline2" value="Stix nix hix pix">
    <param name="headline3" value="Man bites dog">
</applet>

This markup could be used with an applet that scrolls news headlines across a web page. Because news changes all the time, the only way to design a program like that is through the use of parameters.

The name attribute give a parameter a name and value assigns it a value.

Receiving Parameters in the Applet

You access parameters in an applet by. calling the getParameter(String) method of the applet—inherited from JApplet—with its name as the argument, as in this statement:

String display1 = getParameter("headline1");

The getParameter() method returns parameter values as strings, so they must be converted to other types as needed. If you want to use a parameter as an integer, you could use statements such as the following:

int speed;
String speedParam = getParameter("speed");
if (speedParam != null) {
    speed = Integer.parseInt(speedParam);
}

This example sets the speed integer variable by using the speedParam string. When you try to retrieve a parameter with getParameter() that was not included on a web page with the param tag, it is sent as null, which is the value of an empty string.