Chances are, there is a copy of Java on any computer you walk up to. According to Sun Microsystems, the company behind Java, it has been installed on more than 800 million computers. There are versions of Java for many operating systems, including Windows, OS X, Linux, and Solaris, just to name a few. You can see if Java is installed on a computer by visiting Javatester.org.
If there is a copy of Java on a computer you own or maintain, it may be old. JavaTester.org not only reports the installed version but gives you some idea of how old that version is, by listing the most recent versions and when they were released.
Multiple versions of Java can, and often do, coexist on a single computer. This is because installing newer versions of Java has never removed older versions. Windows users will see any old versions in the usual Add/Remove Programs list in the Control Panel.
Do you need Java at all? Maybe, maybe not.
Many people use Java without realizing it. Ithe Secunia Online Software Inspector, a great online service for reporting old, dangerously buggy software that's installed on Windows computers. It requires Java. If you have a Box.net account and use their drag-and-drop multiple file uploader, you're using Java.
What follows are step-by-step instructions for installing the latest versions of Java on a Windows computer.
Sun, the company behind Java, just released a new version known as Java 6 Update 10 (among other names). As, there's no compelling reason to install this latest version, in fact, a case can be made that the prior version, Java 6 Update 7, is the better way to go. The steps involved in installing either version are the same.
In theory, the first time you try to use a Web page that requires Java it should be automatically installed. In reality, this rarely works. I just tested it under Windows XP with Firefox versions 2 and 3 and with Internet Explorer versions 6 and 7. Not once did Java auto-install (see above).
No matter, the manual installation is fairly simple. And unlike Flash, Windows users only have to install Java once.
Technically, what you download is the Java Runtime Environment (JRE). The latest JRE version is always available at www.java.com/en/download/manual.jsp. Go for the "offline" version. The prior Java version (Java 6 Update 7) is available at java.sun.com/products/archive/j2se/6u7/index.html. Click on the "Download JRE" link at the bottom of the page.
For both versions, when you run the downloaded EXE file, the installation starts with the usual license agreement.
Then you may be given the chance to download additional software. When I installed Java 6 Update 7, there was no additional software. But when I installed the latest version, it defaulted to also installing the Yahoo Toolbar for Firefox. No one needs the Yahoo Toolbar, so I suggest not installing it. Defensive computing means installing only the software you really need. The less software installed, the less of a bug magnet your computer is.
As the software is being installed, you'll see a standard progress bar.
When it's all done, this too is clearly shown.
What to do with older versions of Java that may be on your computer is debatable.
My preference is to delete old software, so that malicious software can't exploit any known bugs. Others may argue to let sleeping dogs lie because there may be some software that specifically requires an old version of Java. I'll take that chance. In the worst case, you can always download an old version of Java at java.sun.com/products/archive/.
On Windows, Java uninstalls in the normal, standard manner.
This latest version of Java (6 Update 10) is going to complicate things in the future. Newer versions of Java 6 may install themselves over this version or they may not. Java can now be installed in two ways: patch-in-place and static.
If your copy of Java 6 Update 10 is "patch-in-place" then a newer version of Java 6 will remove Update 10 when it's installed. However, if your copy of Java 6 Update 10 is "static," then newer versions of Java 6 will not replace Update 10.
Either way, newer versions of Java 6 will not remove versions of Java 6 prior to Update 10. Also, when Sun gets up to Java version 7 Update 1, that will not remove any copies of Java 6 that may exist.
I don't make these decisions, I only report them.