Minecraft was either coded entirely in C#, or Java, and my guess, its more likely to be entirely coded in Java.
The problem with Java, is... Its only a semi-stand alone encoder... It still requires other sources and certain computer permissions to perform certain actions (for example, "saving").
Anyway, yes, for a game like Minecraft, I would imagine that you would infact need Java.
Java is not a virus, but there are many producers who have either made a virus into the installation, or have you pass through unsecured sites & information fields, which contain viruses on their own.
I would suggest ONLY getting any legit product from the legit manufacturers. "Oracle" created Java.
Go here to download Java, from the real source, this one is not a virus, seeing as "Oracle" created this copy. http://www.java.com/en/download/manual.jsp
I also imagine, because the developers behind Minecraft is such a small company, they would do a "x-day Money Back" deal. I think in most cases, x would be 10. Im not sure though.
I would however suggest getting the demo version, and getting that to work with your Java plugin before purchasing the product in case you happen to find that you run into more problems then this. Otherwise, you would then have to contact Customer Support for Minecraft.