Java failed to be what JavaScript became for a number of reasons, but I think the primary was the fact that it never integrated with HTML as cleanly as JS.
It could have been JS, but it was strangled to death by Sun (on the client).
Java also has the problem of long startup times while the JIT is doing its thing. Javascript has always just started executing right away. Waiting a minute or two for a Java loading bar wasn't fun.
JavaScript hasn't always worked that way. My guess is that if Java had become the tool for this, then it's startup times would have been fixed. Pure speculation of course.
If Sun had not killed Hotjava and continued to develop and market it, Java instead of JS might have been the frontend web programming language today. There were millions of Java applets written in a very short time and a Java browser would have been a first class citizen for hosting those apps.
Not the intention, but I see that interpretation. It's not hard to imagine oracle making a netbeans plugin for free and an expensive enterprise version that's faster. Selling point is leveraging existing back end skills.
