Not long ago, Sun Microsystems introduced us to Java, a
platform-independent, object-oriented programming language well-suited to Web
application development. Shortly thereafter, Microsoft countered with ActiveX, a
component-oriented application development solution for Windows NT 4.0 and
Windows 95. Now Microsoft gives us Visual J++ (VJ++), a combination of ActiveX
and Java for Windows NT 4.0 and Windows 95.
VJ++ lets you quickly build applets on NT 4.0 with the powerful and
consistent IDE of Microsoft's Developer Studio--the same IDE that Visual C++
(VC++) 4.x products use. With VJ++, you can do almost everything you can do with
VC++, from creating a Windows-like GUI for a Java Internet-centric application
to incorporating ActiveX Controls into a Java applet. In this article, I'll
explain how to create a Java applet using the VJ++ Java Applet Wizard. The
resulting Java applet demonstrates the simple power of VJ++.
Java Applet Wizardry
The VJ++ Java Applet Wizard walks you through a set of option pages to
create the classes and code for a Java applet and provides a sample HTML file
for browsing the applet. The framework for the Wizard-created applet supports
multithreading, image animation, mouse event handling, and parameters read from
the HTML. After the Wizard is finished and you compile the applet, you can test
it with Internet Explorer (IE) 3.0 or later, with other browsers that support
Java, or with VJ++'s standalone interpreter, jview.exe. In the current version
of VJ++, IE is the only browser you can use for debugging. (Before you can
install VJ++ from http://www.
microsoft.com/visualj, you must install IE
3.0 from http://www.microsoft.com/ie.)
When you first run VJ++, you will see menu bars typical of those in VC++
and a project workspace window with InfoView (a powerful integrated Help
system). To begin the Java Applet Wizard, select the File menu and click New.
Double-click the Project Workspace option to display the New Project Workspace
dialog box, as shown in Screen 1 on page 120. In the Type list, select Java
Applet Wizard. Enter a name for your project in the Name text box (I used
boingi, short for "boing image") and click Create. The Java Applet
Wizard - Step 1 of 5 dialog box appears, as in Screen 2. Select As an applet
only for how you want to run your program. (If you plan to use jview.exe to
test your applet, you must choose As an applet and as an application.)
Click Next, and the Java Applet Wizard - Step 2 of 5 dialog box appears, as in
Screen 3. Selecting Yes, please to Would you like a sample HTML
file? creates the HTML file for debugging. The initial size fields (Width,
Height) let you change the size of the applet. Click Next, and the Java Applet
Wizard - Step 3 of 5 dialog box appears. Our example includes animation, so keep
the default option, Yes, please, for both multithreading and animation
support, as shown in Screen 4. Click Next, and the Java Applet Wizard - Step 4
of 5 dialog box appears, as in Screen 5. Enter the applet parameters from Table 1 on this screen.
Click Next, and the Java Applet Wizard - Step 5 of 5 dialog box appears, as
in Screen 6. This dialog box shows the information the applet will return to the
browser. Click Finish, and the New Project Information dialog box displays a
summary of specifications for the project. Click OK to complete the Wizard and
return to the main VJ++ window.
From the Build menu, select Build boingi to build the project. To run it,
select Debug from the Build menu and Go from the Debug submenu (or simply press
F5). If you are asked to specify the path to a browser, I recommend you use IE
3.0 or later, but the applet will run properly with Netscape and other browsers
that support Java. The applet the Wizard will create animates a series of .gif
files as a spinning globe.
Applet with Attitude
The spinning globe example the Wizard creates is OK, but let's extend the
example by bouncing the globe around, changing its direction and speed whenever
it hits the applet's boundary. Let's jump right into the code by opening the
boingi.java file (part of which is in Listing 1) that the Wizard generated. At
callout A in Listing 1, add the instance data shown in Listing 2. The program
uses this instance data to keep track of the previous position and to calculate
the next position of the image as it moves across the applet.
Next, at the end of the public void init() method (in Listing 3), comment
out (// signals a comment line) the call to resize() and save the range of the
applet in m_rng, as follows:
// resize(320,240);
// save the applet's range
m_rng = size();
Now move down two more methods in the boingi.java file to the private void
displayImage(Graphics g) method. Modify the code to appear as in Listing 4, and
you're ready to compile and test the new Java code.
The displayImage() method in Listing 4 first clears the previous image.
Then the method displays a new image at the current position (m_nImgX, m_nImgY).
Finally, the method calls the travelImage() method to calculate a new position
to display the next image. The Wizard-generated code (commented out in Listing
4) displays the image in the center of the applet; the new code moves the image
on each call to the displayImage() method.
The travelImage() method saves the previous image coordinates and calls the
checkForTurnaround() method to calculate a new vector (m_incX, m_incY) when the
image is about to hit the applet's boundary. The checkForTurnaround() method
checks whether the image is out-of-bounds; if so, it calculates a new speed in
the opposite direction.
Surf the Java
To compile the extended project, select Build boingi from the Build menu.
This command processes the revised boingi.java file and generates a file called
boingi.class.
The HTML file that the Wizard creates is called boingi.html. The applet tag
in this HTML is in Listing 5. The line code=boingi.class specifies the name of
the boingi class file that is the compiled applet. The two parameters minSpeed
and maxSpeed specify to the boingi applet the minimum and maximum pixels to
move.
Run the extended project by choosing Execute from the Build menu or by
pressing F5. IE is the default application, but you can change the default by
choosing Settings from the Build menu and selecting the Debug tab. In the
Broswer field, enter the path to your favorite browser.
Where to Now?
Where do you go from here? Investigate the Test Drive topics in the VJ++
InfoView to learn more about the Java capabilities that VJ++ lets you tap. Also,
visit the VJ++ site at Microsoft (http://
www.microsoft.com/visualj) for
updates and more information about VJ++. These resources can help you take what
you have learned and quickly develop Internet-centric NT 4.0 applets.
With the addition of VJ++ (and ActiveX) to Windows NT 4.0, you can easily
argue that NT, which originally stood for New Technology, now stands for Net
Technology. VJ++, the combination of Java and ActiveX on NT, will likely be to
the late '90s what C++ was to the late '80s.
End of Article
