The Java TM Tutorial

| Start of Tutorial > Start of Trail > Start of Lesson | Search

Trail: Writing Applets
Lesson: 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.
> >             }
> >         }

| Start of Tutorial > Start of Trail > Start of Lesson | Search