Over 9M according to this blog post. I first looked at Java back in 1996. An engineer at Alcatel brought the first copy of "Java in a Nutshell" and said: "This is the future".The author of the blog says that at the time of Java's open sourcing in 2007, there were 6 million Java developers and the number of Java developers had been rising at an average of 0.75 million per year during the previous two years. After Java was open sourced, that number shot up to 1 million per year.
Why the success?
From a technical point of view, "Write Once, Run Anywhere" and a solid set of APIs would do the trick.
From a business point of view, Free and a "transparent" Java Community Process would work, but a solid evangelist like Sun Microsystems is also needed.
As the back-end is moving to the cloud and the front-end is moving to mobile devices, Google and Apple are in control of the user experience. Java is still very relevant (through Android for the front-end).
