what is java??

 Upon looking around on my PC at documents and programs that I apparently downloaded, one of the ways that popped up to surf the net is “Java Sun”. I have no idea where that came from. I use explorer and Firefox. Is this “Java Sun” dangerous? Any idea how I got it on my PC?

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One clarification, it’s “Java”, produced by a company by the name of “Sun” Microsystems.
It’s not dangerous, in and of itself, but like any programming language or internet tool it can of course be used for good or evil.

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Second clarification: “Java” and “Javascript” are unrelated.
I’d call it a poor naming choice of “Microsoft-ean” proportions. Microsoft is known for it’s confusing names such as “Outlook” and “Outlook Express” (which have no relationship to each other), or the current mess that is “Hotmail”, “Windows Live Mail”, “Windows Live Hotmail” and “Windows Mail” (three different things with four different names).
The fact that Java and Javascript are unrelated and yet have similar names is unfortunate.
Java is a programming language. All that really means to most folks is simply that when you run an application, the developer who wrote it might have been using Java to create the program.

“… by virtue of having done some surfing on the web you may have downloaded and installed Java.”

Programs written in Java are transformed or “compiled” into an intermediate form that when run is interpreted by what’s called a “virtual machine” or VM. That intermediate form is not machine or platform specific – meaning that as long as there’s a Java virtual machine available for the platform you’re running on, a program written in Java may be able to run on it. In fact, one of Java’s mottos is “Write Once, Run Anywhere”. (Of course programmers certainly can still write Java programs that work on only specific platforms.) Java Virtual Machines are available for most popular platforms including Windows, Mac and Linux.
Because of its ability to be platform in ependent, Java is an occasionally popular language for web-based applications or “applets”. When you visit a web site that uses a Java applet, you may be prompted to download and install the Java VM, if you don’t already have it, and then the web application can run.
Visiting a web site that uses a Java applet is probably how you ended up with Java on your machine.
One of the items that occasionally surprises people is that Sun’s implementation of the Java VM will automatically update it self, much like Windows itself. Suddenly a Sun Java icon might appear in your taskbar’s notification area telling you that a new version is available, or that a new version has been downloaded and installed.
The bottom line is simply that by virtue of having done some surfing on the web you may have downloaded and installed Java. That’s typical, and nothing to be worried about. Similarly, if you periodically see update notifications for the Java VM, that too is to be expected.