Within the J2SE -- again, this is the platform most people are referring to when they talk about Java software, unless they specifically mention J2EE -- there are a few things to know about version numbers. First, the Java language and the J2SE platform share a version number, so to say "Java 1.3" is to say "J2SE 1.3." Technically, one is the language and one is the platform, but they move in synchronization.

Of course the "2" in "J2SE" looks like a version number of sorts, but it mostly confuses the issue of what "version of Java" one is working with or wants. The primary version numbering has historically run from Java 1.0 (released in 1996) up through 1.1, 1.2, and 1.3, to the currently dominant Java 1.4; there have been minor upgrades to each platform along the way and so, for instance, many companies are currently using Java 1.4.2. As of Java 1.2, Sun defined the three-platform architecture and developed the "Java 2" platform as a brand of sorts. Thus -- sadly -- "Java 2" overlaps "Java 1.2," All versions since Java 1.2 have been versions of the "Java 2 Platform."

Most recently, Java 1.5 was released -- "Tiger" by its code name. At this point the version-numbering scheme was also revised, with the aim of making the first digit in the number more meaningful: we'll start talking about version X, not version 1.X. So Java 1.5 is also Java 5.0! Fantastic. Either number is valid, but Sun generally favors 5.0 for the current version (and so does Wintrac). Future revisions will just be labeled 6.0, 7.0, etc., with minor upgrades appearing as 5.1, 6.2, and so on.

So these three overlapping schemes lay out like this:

J2SE releases are backward-compatible, for the most part. However there is less forward compatibility. By "backward-compatible," we mean that old code will run on a new version of the platform; and by "forward-compatible," that code written on a new version of the platform will run on an old version of the platform. Especially with the new release of Java 5.0, there is no such forward-compatibility: this version uses a new format for its binary files (class files), which cannot be understood by an old (1.4 or earlier) runtime.

Wintrac offers multiple versions of many of its Java courses, but which version should you choose for training? It can be critical to get this right, as the language changed significantly between 1.4 and 5.0. If you are not sure, the first, best option is to contact someone in your company or at your client's site who knows. Typically there is either a Java infrastructure in place, or one is forming, or there is a specific product with specific requirements including a Java version.

If you have a mixed classroom (perhaps a public offering) or simply don't know what the participants will want, here are a few guidelines and tips:

• 1.4 is right now the dominant version.
• Early adopters are jumping on 5.0 with some gusto, because it introduces a number of new features that strengthen the language and make it easier to write code.
• Remember that we're talking about Java or J2SE versions! Many companies have investments in J2EE, and right now there are no J2EE products that fully support the 5.0 J2SE runtime. This is probably the major brake on adoption of J2SE 5.0: no one wants to be stuck writing one version of the language for some applications and an older version for J2EE components. J2EE 5.0 is due out later this year, and will synch up with J2SE 5.0 for a seamless architecture.