Hotspot is a complete VM, not an add-on to an existing VM. Therefore, if Visual Cafe doesn't offer the Hotspot VM, you're out of luck, assuming you use that tool.
How much performance will increase with Hotspot vs. a JIT depends on many factors: The quality of the JIT and Hotspot and the code it is optimizing, to name two. Some people report great performance improvements with Hotspot vs. JIT, others report the opposite. I'd advise that if you are having performance problems to try Hotspot to see if you get any benefit. If not, it may be time to try another JIT VM, or better yet, run your code throug a profiler and find out where it is spending its time. Then look at your design, data structures and algorithms to make improvments.
Peter Haggar
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Senior Software Engineer, IBM
author of:
Practical Java