java -version

[Avi Greenbury]

I'm not sure of any definitive guides, but it'd be help to have an idea
of how Java works from a high-level - to be familiar with what the JRE
and JVM are, for example, and how Java runs portable bytecode.

http://en.wikipedia.org/wiki/Java_%28software_platform%29

is probably a good place to start, but I'll admit I've not read it.
Either way, searching the net for any phrases in my attempted
explanations might help:

Kaushal Shriyan wrote:
> $java -version
> java version "1.6.0_24"
Your Java Runtime Environment (JRE) is version 1.6.0_24

> Java(TM) SE Runtime Environment (build 1.6.0_24-b07)
You are running build 07 of version 1.6.0_24 of that JRE

> Java HotSpot(TM) 64-Bit Server VM (build 19.1-b02, mixed mode)
Your Java Virtual Machine is HotSpot, it is compiled for a 64-bit
system and it is running in 'server' mode. Server-mode refers to the
sorts of optimisations made - it assumes a long-running JRE instance.
You are running Hotspot version 19.1-b02 in mixed-mode. Mixed-mode
means that it will sometimes compile Java bytecode down into native
code.

-- 
Avi