'TheJVM'

From Jmri

[edit] Do I have Java? What version is needed?

Most systems already have a suitable Java Virtual Machine (JVM) installed. In general, if you're planning to run on a pretty modern machine, a good start would be to ensure that you have the latest version [1.5] installed. However, any version from 1.1 onwards should work and earlier versions, being smaller, tend to load faster than the behemoth that is version 1.5 :-)

[As an example, on a Pentium 166 with 128mb ram, startup time for DecoderPro went from over 30seconds before the logo appeared to less than 10 when comparing Java 1.5 to 1.3. Of course, ymmv and a discussion on this topic is hopefully taking place on the 'discussion' page above!]

[edit] Determining which Java is installed

• Windows98: Go to 'run' -> 'Command' and enter 'cmd' at the prompt. This will open a new window with a prompt something like: 'C:>'. Enter (no quotes) "java -version" and it should return the version number of your installation. If some kind of error message comes back you're going to need to download Java from Sun.
• Other Windows - Help!
• Apple Mac OS X: Every version of MacOS X has a suitable version of Java already installed, so you don't need to do anything
• Apple Macintosh "Classic": Check for an "MRJ Libraries" folder in the Extensions folder in the System Folder. If not present, you need to download Java from Apple.
• Linux - If you're running Linux you know how to do this! :-)

[edit] Do I need the Java development kit? (The 'Java SDK')?

Only the virtual machine (JVM, sometimes referred to as the JRE, for 'Java Runtime Environment') is needed to run the JMRI programs.

The Software Development Kit lets you recompile and debug Java code. If you'd like to work on the JMRI program itself, or write your own Java program that uses it, you'll eventually want to download the SDK. Until then, you don't need it.