# Overview—What Is Java Plug-in? What Does It Support?

This chapter includes the following topics:

- What Is Java Plug-in?
- Supported Operating Systems and Browsers

## What Is Java Plug-in?

Java Plug-in extends the functionality of a web browser, allowing applets or Java Beans to be run under Sun's Java 2 runtime environment (JRE) rather than the Java runtime environment that comes with the web browser. Java Plug-in is part of Sun's JRE and is installed with it when the JRE is installed on a computer. It works with both Netscape and Internet Explorer.

This functionality can be achieved in two different ways:

1. By using the conventional `APPLET` tag in a web page.
2. By replacing the `APPLET` tag with the `OBJECT` tag for Internet Explorer; by replacing the `APPLET` tag with the `EMBED` tag for Netscape 4. Note, however, that the `OBJECT` and `EMBED` tags must conform to a special format as described in the next chapter, Using OBJECT, EMBED and APPLET Tags in Java Plug-in.

## Note: Currently the `OBJECT` and `EMBED` tags do not work with Netscape 6 with Java Plug-in. You must use the `APPLET` tag with Netscape 6.

`OBJECT` and `EMBED` tags may be manually updated in web pages, but to facilitate updating web pages to this special format, an HTML Converter is provided. It is described in the section called Using the HTML Converter to Convert Applet Tags for Java Plug-in.

While the above constitutes the heart of Java Plug-in, there are many other related topics that you may want to understand. For instance, you may want to know how proxy configuration works in Java Plug-in, you may want to know what protocols Java Plug-in supports, or you may want to know about cookie support and caching. Such topics are included in Part I: Java Plug-in Basics.

You can determine some of the behavior of Java Plug-in and set options via the Java Plug-in Control Panel. How you do this is also discussed in Part I in the chapter called Using the Java Plug-in Control Panel to Set Plug-in Behavior/Options.

Java Plug-in may be deployed in various ways—on the Internet, within an intranet, via Java Server Pages, etc. The various types and methods of deployments are discussed in the Part II: Deployment Schemes.

Applets must be run in a secure environment, and various security topics are discussed in the Part III: Security, including RSA signed applet verification. As signing applets can be a difficult topic for novice applet developers, this guide provides step-by-step instructions for signing applets in the chapter called How to Sign Applets Using RSA-Signed Certificates.

Java Plug-in provides various kinds of debugging support for applets, and Part IV: Debugging Support describes them. Java Debugger support is discussed. So is the Java Plug-in Console, which includes various options that may be set for debugging, including ones for tracing and logging.

Part V: Advanced Topics discusses more esoteric matters such as supporting multiple JREs in the same environment, Java-toJavaScript communication, how to persist applets across browser sessions, special applet attributes for changing the applet window background color, etc.

Finally, there are Appendices that information about Netscape 6; a FAQ; additional information about the HTML Converter; and Microsoft VM versus Java 2 compatibility issues.

## Supported Operating Systems and Browsers

For supported operating system and browsers, see Supported System Configurations.