Linux is free, Linux is maintained by the open source community, and Linux simply isn't Windows.
Many see Linux as being more stable than windows OS, although I do find the more junt you install on Linux, the more unstable it becomes.
Most major programs you use in Windows, you can find open source equivalents in the Windows community.
OpenSuse is my favorite Linux distribution. On a major brand of hardware, like a Dell desktop, installation typically is seemless.
On the other hand, there are alot of people that still don't know Linux, and are afraid of it. It's alot easier finding administrators that have an MCSE or MCP designation, than it is to find certified Linux professionals. On the other hand, Linux knowledge always looks great on a resume, especially in the Java/Sun/IBM community.
There's no shortage of information on the web about Linux. You can download a bootable cd and get started playing around without installing anything. Other options include Cygwin, a windows port of many Unix tools, and vmware, which allows you to run other OS's without leaving your familiar Windows desktop (VMWare Player is a $0 product).
How is Linux different from Windows? - besides the already mentioned differences it will make you think and if you like freedom and feel good when you accomplish something on your own or with little assistance you will be happy with Linux. You will feel that you can talk to your computer not the computer said "An error occurred!" and I pressed OK, but "An error occurred! Check the configuration file and contact us at this forum and we will answer for FREE with a fix".
Linux is more stable than Windows, but like Windows it is just an operating system so yes you can crash it and it can misbehave when things are not going well and you may pull your hair but at the end you can say big deal at least I did not pay for the software the support call and the program I installed and could not get to work contrary to the statement of the sales person and the package.
GNU/Linux which is Linux plus a massive array of open source free programs are the absolute best from functionality and endless configurability (that must be a new word) Linux can do thing Windows cannot even dream of dreaming about.
Linux can run for years without crashing is much harder to break in than windows and is multiuser from the outset.
Last I remember 7 out of the 10 biggest supper computers run Linux the other 3 Unix and none Windows.....
If you wish to do Java development there are tools for Linux and many other languages. I have been doing Java development for 3 years and only had to switch to Windows when I was preparing for the SCJP exam as the book came with Windows software that was a funny moment .
Linux doesn't have Drive-Letters like A: B: C: ... Z: but mounts devices to a rootfilesystem '/' where you like. Linux was a multitasking/ multiuser-system ever. Linux was a networking system from the beginning. Linux doesn't have a central, cryptic registry, but most configurations are written in plain config files. Linux has symbolic Links. Linux has package-managers. You don't need a graphical user interface to run programs, but if you like (nearly everybody does) you may choose between a few dozen - the most populars are KDE and Gnome. You may configure everything. You may change everything. Even the kernel. Make your own distribution (Sivarajlinux). 3D-Desktop? We got it. Half a dozen or even more filesystems to choose. Half a dozen or even more shells to choose. ... Last but not least, we have a nice looking penguin mascot.