Taking Advantage of the Applet API

Writing the Code to Support Parameters

Applets use the Applet getParameter method to get user-specified values for applet parameters. The getParameter method is defined as follows:

public String getParameter(String name)

Your applet might need to convert the string that getParameter returns into another form, such as an integer. The java.lang package provides classes such as Integer that you can use to help with converting strings to primitive types. Here's an example from the AppletButton class of converting a parameter's value into an integer:

int requestedWidth = 0;
. . .
String windowWidthString = getParameter("WINDOWWIDTH");
if (windowWidthString != null) {
    try {
        requestedWidth = Integer.parseInt(windowWidthString);
    } catch (NumberFormatException e) {
        //Use default width.
    }
}

Note that if the user doesn't specify a value for the WINDOWWIDTH parameter, the above code uses a default value of 0, which the applet interprets as "use the window's natural size." It's important that you supply default values wherever possible.

Besides using the getParameter method to get values of applet-specific parameters, you can also use getParameter to get the values of attributes of the applet's <APPLET> tag. See The <APPLET> Tag for a list of <APPLET> tag attributes.

An Example: AppletButton

Below is the AppletButton code that gets the applet's parameters. For more information on AppletButton, see the previous page.

String windowClass;
String buttonText;
String windowTitle;
int requestedWidth = 0;
int requestedHeight = 0;
. . .
public void init() {
    windowClass = getParameter("WINDOWCLASS");
    if (windowClass == null) {
        windowClass = "TestWindow";
    }

    buttonText = getParameter("BUTTONTEXT");
    if (buttonText == null) {
        buttonText = "Click here to bring up a " + windowClass;
    }

    windowTitle = getParameter("WINDOWTITLE");
    if (windowTitle == null) {
        windowTitle = windowClass;
    }

    String windowWidthString = getParameter("WINDOWWIDTH");
    if (windowWidthString != null) {
        try {
            requestedWidth = Integer.parseInt(windowWidthString);
        } catch (NumberFormatException e) {
            //Use default width.
        }
    }
 
    String windowHeightString = getParameter("WINDOWHEIGHT");
    if (windowHeightString != null) {
        try {
            requestedHeight = Integer.parseInt(windowHeightString);
        } catch (NumberFormatException e) {
            //Use default height.
        }
    }

Taking Advantage of the Applet API