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NOTE: This is a new version of an earlier article titled "Swinging Applets," which now resides in The Swing Connection Archive. The main difference between the two articles is that the sample program supplied with this article uses Swing's current set of package names, while the applet supplied with the old article used an older set of package names that were used prior to the introduction of Swing 1.1 Beta 3 and JDK^TM 1.2 RC1 (Java^TM 2).

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By Mark Andrews and Nancy Schorr

Yes, Virginia, you can write and run Swing applets in your Internet browser  right now, using the current version of Swing. And there are several ways  to do it.

Now that Java^TM Plug-in  software is available -- as reported in the "Plugging into Swing" article in this section --  you can use Sun's new Java Plug-in technology to write and distribute Swing applets that will run on any computer system using any browser. "Plugging into Swing" shows you how to use Java Plug-in to create and distribute your Swing applets.

But Java Plug-in, as powerful as it is, may not meet the needs of every  applet that you want to distribute. For one thing, Java Plug-in is designed  to be downloaded from a network, but some computers don't have network connections. And you might find it difficult to adapt Java Plug-in to certain combinations of browsers and operating systems that are sometimes found in multi-user corporate computer environments.

For situations such as these, several alternatives to using Java Plug-in are available. This article shows how to implement some of them. 

Is Your Browser Ready for Swing? 

Before we start exploring the topic of Swing-aware browsers, let's perform  a little test that will tell you whether the browser you're using now has a native JVM (Java^TM Virtual Machine) that works with Swing. If it does, it can run Swing applets without using Java Plug-in.

To see whether your browser's VM is currently Swing-ready, click the "Test My VM" button, below. A window will then open, and you'll see a little test that will show you whether your browser is configured to run Swing applets -- and, if your browser isn't Swing-ready, will advise you on what to do about it.

IMPORTANT: The sample applet used in this article was written and compiled using Swing 1.1.1 beta 1. You can run it by using Swing 1.1 beta 3 or later, or by downloading and using JDK 1.2 RC1 or later. But you can't use it with older versions of Swing or the JDK because because they used a set of Swing package names that are now outdated. If you'd like to examine an earlier version of the applet, which will run under older versions of Swing and the JDK, see the article titled "Swinging Applets " that now resides in The Swing Connection Archive.

Configuring Your Browser for Swing

The applet that you'll be implementing as you read this article is named SwingingApplet. There's a picture of it on the left. To run the SwingingApplet program -- or any other applet that uses Swing components  -- you can use either the techniques described in this article or those described in the article in this section titled "Plugging into Swing." If you choose to use the strategies described in the article you´re reading now, you'll need either a recent version of Microsoft Internet Explorer  (4.0 or later) or a recent version of the Netscape Navigator or Netscape Communicator browser.

When this article was last updated, the newest version of Netscape Navigator in general release was Version 4.5. For more details on the various versions of Netscape browsers and how they work with Swing, see the section headed "Versions of Netscape Browsers" farther down in this article.

Once you´re sure that you´re using a correct version of Netscape, you can add Swing support  to your Netscape browser's VM in two different ways. One way is to place the  pathnames of the Swing classes in your system's CLASSPATH variable. You  can do that by following the same instructions that are listed under the next blue subheading, "Setting Up Internet  Explorer for Swing." Because that technique works for Netscape browsers as well as for IE browsers, it might be the one you want to select if you have both kinds of browsers installed on the same computer system.

IMPORTANT: You don't have to set your system's CLASSPATH variable if you want to access Swing applets using Java Plug-in. Java Plug-in is not affected in any way by your system's CLASSPATH variable. You need to set it only if you plan to run applets without using Java Plug-in.

Configuring Navigator without Using CLASSPATH

There's also a way to configure the Navigator browser for Swing without using the  CLASSPATH variable. To that, follow these steps:

1. Navigate to the directory in which Swing is installed.
    
2. Copy swingall.jar and all of Swing's other JAR files into Netscape's Java\Classes subdirectory. By default, the target directory for  this copying operation is C:\Program Files\Netscape\Communicator\ Program\Java\Classes.

When you've completed those two steps, you're ready for action. Reload this page, and SwingingApplet should show up on your screen.

It's also easy to add Swing applet support to Internet Explorer 4.01's VM. To configure IE's CLASSPATH to run Swing applets, follow these steps:

On Windows NT:

1. Double-click the System icon inside the Control Panel. When the System Properties dialog box opens, place the following variables in the lower list box, which is labeled "User Variables." (Be careful not to change your system environment variables, which appear in the upper list box.)
   
   

   	JAVA_HOME	C:\JDK1.2.1
   	SWING_HOME	C:\swing-1.1.1beta2
   	CLASSPATH	.;%JAVA_HOME%\lib\classes.zip
   	PATH	%PATH%;%JAVA_HOME%\bin

   
   These settings assume that you have installed both the JDK and the Swing tool set on drive C. If either these toolkits has been installed on a different drive, substitute that drive's designator wherever it is appropriate.
   
   The settings also assume that you are using JDK 1.2.1 and Swing 1.1.1 beta 2. If you are using a different version of Swing, change the setting in Line 2 as appropriate.
   
   (It isn't always necessary to set the CLASSPATH environment variable, although a setting is shown in the preceding example. For example, you don't have to set the CLASSPATH variable if you're using Java Plug-in and JDK 1.2. For more details, see the article titled "Plugging into Swing.")
   
   (NOTE:  If you do use the CLASSPATH variable, be sure to enter the filenames of your Swing JAR files, as well as their pathnames, in the "Value" text field. Internet Explorer does not recognize CLASSPATH entries that don't include filenames.)
   
   (ANOTHER NOTE:  If you don't remember exactly how all the environment variables shown  in the System Properties dialog box work, you can refresh your memory by  reviewing the README.txt file that  comes with Swing.)
   
   
2. Click the Set button to apply your changes.
   
   
3. Close the System Properties dialog box by clicking the Close button.
   
   
4. If your browser still fails to run Swing applets, shut down and restart your system.

On Windows 95:

1. Start your computer's MS-DOS text editor or your favorite text editor.
   
   
2. Open your computer's AUTOEXEC.BAT file for editing.
   
   

3. Add both the pathnames and the filenames of your system's Swing JAR  files to the CLASSPATH environment variable that you set up in your AUTOEXEC.BAT file when you installed Swing.
   
   As you type in this entry, you can use any of the other environment variables that appear above it in your AUTOEXEC.BAT  file. For example, if your Swing JAR files reside in a directory that equates to an environment variable named %SWING_HOME%,  and if your JDK files reside in a directory that has been assigned the  variable %JAVA_HOME%,  you can add Swing support to your system by appending the following command to your AUTOEXEC.BAT file:
   
   SET CLASSPATH=%CLASSPATH%;%SWING_HOME%\swing.jar;
   %SWING_HOME%\windows.jar;%SWING_HOME%\motif.jar;
   
   (NOTE: Be sure  to enter the filenames of your Swing JAR files, as well as their pathnames, in your SET CLASSPATH command. Internet Explorer does not recognize CLASSPATH entries that don't include filenames.)
   
   (ANOTHER NOTE:  If you don't remember exactly how all the variables shown in your AUTOEXEC.BAT file work, you can refresh your memory by reviewing the README.txt file that came with Swing.)
   
   If your browser still doesn't run Swing applets, shut down and restart your system.

The techniques outlined in the preceding subsections are not the only strategies for adding Swing support to the IE browser. If you're familiar with the Windows system registry and know how to use the Windows registry editor (named regedit), you can add Swing support to Internet Explorer by modifying a registry key named Java VM | Classpath.  

CAUTION: If you decide to add Swing support to your IE browser using the regedit method, remember that regedit can be dangerous; corrupting the Windows registry can cause your system to fail. So before you start changing  registry keys using regedit, don't forget to save your current registry settings by executing regedit's Registry | Export Registry Files menu  command.

 Starting regedit

To start regedit, follow these two steps:

1. From the Windows Start | Programs menu, open an MS-DOS style console  (command-prompt) window.
    
2. Open regedit by executing the command
   
   > regedit
   
   Windows then opens its registry window, which looks like this:
   
    

Using regedit

As you can see, the registry editor window has two panes. The left-hand pane contains a tree display that represents registry keys, and the right-hand pane contains icons that represent key values. To modify the Java VM Classpath entry in the system registry, these are the steps to follow:

1. In the left-hand pane, expand the HKEY_LOCAL_MACHINE tree  node followed by SOFTWARE, followed by Microsoft.  Then choose Java VM. Your regedit window now resembles the one shown in the preceding picture.
    
2. Confirm that the status line at the bottom of the window shows the entries that you have typed in, as shown in the illustration.
    
3. In the right-hand pane of the regedit window, double-click the Classpath  icon.
   
   Windows responds by opening an Edit String dialog box like the one shown below. If a Java virtual machine is running on your system,  the Value name text field in the Edit String dialog already contains some information about the Java classes used by the Windows  Java VM. The Java VM needs this information to run, so just leave it there.
   
    
   
   

4. Without disturbing the text already shown in the Value data  text field, type a semicolon after it and then add the pathnames and  filenames of your Swing JAR files. For example, if you have installed  Swing on your C drive in a directory named swing-1.1.1beta2, append  this information to the text already shown in the "Value data"  text field.
   

   C:\WINNT\java\classes;.;
   C:\swing-1.1.1beta2\swing.jar;
   C:\swing-1.1.1beta2\windows.jar;
   C:\swing-1.1.1beta2\motif.jar;

5. Click OK twice to exit from the Edit String dialog and the registry editor.
   
   
6. Reload this page, wait for SwingingApplet to load, and then click the "Your  browser swings!" button to test the applet.  

Versions of Netscape Browsers 

When this article was last updated, the latest official release of Netscape was Netscape 4.5, which comes ready to run JDK 1.2 and Swing. When you use Java Plug-in (see "Plugging into Swing"), it doesn't really matter what Netscape JDK version you have, because Java Plug-in always uses the version of JDK that the Plug-in is pointing to. However, in general, it's always best to use the latest versions of the browsers for other tasks related to the Java programming language that the browser may need to perform.

You can tell what version of Java your browser is running by choosing the Communicator|Java Console menu item to bring up the Netscape Java Console window. Don't close the Netscape Java Console window after you've looked at it, because you won't be able to display it again unless you restart Netscape.When you´re using Java Plug-in, you can tell which version of Java is running by consulting the Java Plug-in Console window. You can open that window from the Windows Start|Programs menu.

The best way to get the latest version of Netscape is to visit Netscape´s Download site, which is at

http://home.netscape.com/download/index.html

Possible Problems 

Even after you've upgraded your browser to use Swing, you still may encounter a few problems that haven't been quite ironed out yet. For example:When there are multiple archive files, Netscape Communicator loads only the first one. So, when Netscape has unarchived the swing.jar file, it may ignore the look-and-feel JAR files, blocking their use in applets.

Although Internet Explorer recognizes both class files and archive (JAR)  files when you specify both types in an APPLET tag definition, it refuses to use both kinds of files at the same time. To work around this problem, use the jar command to  convert any class commands that you use in your applets to JAR files.  Then you can list the names of both Swing's JAR files and your own JAR  files in the same APPLET tag definition.

Both Netscape Navigator and Internet Explorer have some mini-bugs that  can cause them to miss repainting operations in Swing applets. Currently, there are only a couple of ways to solve these problems: You can either move the mouse around  just right or minimize frames that haven't been repainted  properly and then repaint them. We're working on more satisfactory workarounds.

Internet Explorer doesn't call the Class.getResource() method to get JAR files. As a result, you may encounter missing text and graphics files in the SwingSet sample applet and in other applets that use Swing.