Java has had seven major releases in its 15 year history, and an 8th is soon to arrive (will there be significant JDK 1.7 news at Java One? There's been quite a lot of recent activity.). Here's a nice page that summarizes things. For much of this century, Java releases arrived reliably every two years, and for much of Java's lifetime, adoption of the new releases was quite rapid.
However, that adoption rate has slowed, and recent Java releases are taking much longer to achieve high penetration rates. In my experience, it's quite common to find that JDK 1.4 is still the deployed release in a certain environment.
I find this rather surprising, as 1.5 and 1.6 offer substantial benefits. In my own development work, I try to use Java 1.6 as much as possible, not only for its higher performance, but in large part because of the great work on supportability and diagnosis. Many of the problems that I study at work only arise in situations where I can't pre-configure a specially-enabled JVM, so the ability to attach to an existing JVM and get heap dumps, thread dumps, performance information, etc. is extremely valuable.
But there's no denying that JDK 1.4 remains highly common in deployment. I'm not the only one to notice this, for example see the commenters in this article. So why is this? I think that the contributing factors include at least the following:
- In the enterprise software world, where I spend much of my time, application servers drive adoption. These are systems such as WebSphere, Weblogic, JBoss, Netweaver, Oracle AppSvr, etc. The vendors that provide these systems tend to be conservative and upgrade their base JDK level slowly, and the users of these systems tend to be even more conservative and upgrade their installed applications slowly. So even though IBM has introduced a new WebSphere version which supports JDK 1.6, most IBM customers are still in the process of upgrading from WebSphere version 5 (which supported JDK 1.3) to WebSphere version 6.0/6.1 (which support JDK 1.4 and JDK 1.5)
- JDK 1.4 was "good enough" for many things. Although there continue to be major improvements in Java, JDK 1.4 was a very impressive release, and for an enormous class of applications, it has everything you need. So since it exists, and it's stable and reliable and widely available, it has seen wide and stable adoption, with little pressure to upgrade.
- Slow delivery of 1.5 and 1.6 on Mac OS X, Linux, etc. Java releases on platforms other than Windows and Solaris have lagged, sometimes substantially. It will be quite interesting to see if the open source treatment of Java 7 changes this platform coverage experience, but in the past it was certainly true that platforms were rolled out unevenly. For example, I believe there is still no version of Java FX for Linux, well more than a year after it was released for Windows and Solaris.
- Generics are intimidating. Moving past JDK 1.5 means dealing with the world of Generics, which, although extremely powerful, mean a lot of new syntax, behavior, error messages, and the like. I think Generics are a very good feature, but the "in your face" nature of generics means that many will prefer to procrastinate and stay with JDK 1.4.
- Java update isn't pushy enough. Sun generally doesn't force Java updates on their users. They have been very good about sustaining older releases, and have not pushed very hard on their user base to upgrade.
So just because the world is stuck at JDK 1.4, don't feel like you have to stay there.