| # JavaTM Deployment | Documentation Contents

Java Deployment includes the following topics:

- Applets and Java Plug-in
- Java Web Start for Deploying Applications
- Autodownload
- Java Update (1.4.2_01 and higher releases)
- Applet Compatibility
- Windows Installation (IFTW) and Java Update FAQ

## Applets and Java Plug-in

Applets are programs that extend the `java.applet.Applet` class. Applets run inside web browsers rather than running in their own windows or frames. See the Demonstration Applets and Applications page of the documentation for small example applets.

A Java virtual machine must be available to the browser for use in running applets. Many browsers come with their own version of the Java virtual machine built in. However, such built-in virtual machines are often based on the JDK 1.1 Java platform and therefore are not capable of running applets that make use of new features added to the Java platform since JDK 1.1.

To remedy this situation, the Java Plug-in provides an up-to-date Java virtual machine and runtime environment for "plugging in" to a browser. The browser can use this up-to-date Java virtual machine to run applets that use the latest functionality of the Java platform.

Applets can be posted on a network for running in web browsers, so they are obviously a powerful way for developers to deploy their programs. In addition, Java Plug-in provides technology that enables developers to specify which version of the Java platform is required to run their applet. If the specified version of the Java platform is not already installed on the client machine then the applet is accessed, an automatic download of the correct Java platform can be triggered (on Microsoft Windows). On the Solaris Operating Environment and on Linux, the developer can automatically take the user to a download page for the correct version of the Java platform.

On Microsoft Windows, Java Plug-in is automatically installed when the Java Runtime Environment or Java 2 SDK is installed. The Java Plug-in also comes with the Java 2 SDK and the Java Runtime Environment for Solaris and Linux, and it can be installed manually.

For more information on Java Plug-in, see Java Plug-in Documentation.

## Java Web Start for Deploying Applications

Applications written in the Java programming language can run in their own windows, unlike applets which run inside a web browser. Applications are usually larger and more full-featured than applets, and it is important that there be an effect and robust method to deploy them widely, while ensuring that the correct version of the Java platform is available to them. Java Web Start is designed for just this purpose.

With Java Web Start, a user launches an applications simply by clicking on a Web page link. If the application is not present on the client computer, Java Web Start automatically downloads all necessary files for the application, including a new version of the Java platform if needed. Java Web Start caches the application on client computer. On subsequent launches of the application, Java Web Start will check the network for an updated version of the application, and if there isn't an update, it will launch the cached version.

On Microsoft Windows, Java Web Start is automatically installed when the Java Runtime Environment or Java 2 SDK is installed. The Java Web Start also comes with the Java 2 SDK and the Java Runtime Environment for Solaris and Linux, and it can be installed manually.

For more information on Java Web Start, see Java Web Start.

## Autodownload

Both the Windows versions of Java Plug-in and Java Web Start make use of the `codebase` attribute of the `OBJECT` element to autodownload and install a particular version of the JRE. See:

- Java Plug-in in IE on Windows
- Creating an auto-install page

By specifying a particular `.cab` file in the `codebase`, a particular version of the JRE can be automatically downloaded and installed as required by an applet or application. For a list of the available `.cab` files, see Autodownload Files. Note that not every release of the JRE has an associated `.cab` file for autodownload.

## Java Update (1.4.2_01 and higher releases)

Installing the J2RE automatically installs the Java Update feature. Java Update can keep your computer up to date automatically with the latest J2RE releases. You no longer need to search for critical J2RE updates; Java Update delivers the latest version of the J2RE directly to your computer. Java Update recognizes when you are online and, using your Internet connection, searches for available updates from the Java Update web site. Whenever an update becomes available, an icon will appear in the status area of the taskbar.

You can specify how and when you want Java Update to update your computer. For example, you can set up Java Update to automatically download and install updates on a schedule that you specify. And you can choose to be notified before the download and the installation of the update occurs, or only before the installation of the update. You can also disable the option for automatic updates altogether and do them manually. It's your choice, and you can reset the options anytime you want.

For more detailed information, see Update Panel in Using the Java Plug-in Control Panel to Set Plug-in Behavior/Options.

## Applet Compatibility

For applet compatibility issues, see Applet Compatibility Guide—Microsoft vs Java 2 Virtual Machine.

## Windows Installation (IFTW) and Java Update FAQ

For questions on Windows Installation, which installs Java from the web while the user is online, and Java Update, see the Windows Installation (IFTW) and Java Update FAQ.

Copyright © 2002 Sun Microsystems, Inc. All Rights Reserved. Please send comments to: java-plugin-feedback@sun.com or javawebstart-feedback@sun.com | Java Software