I've become more and more comfortable programming in Java than with C++ or C. I am hoping to get a sense of the performance hit incurred using a JVM interpreter, as opposed to executing the same "project" natively. I realize that there is some level of subjectivity here; the quality of the program will depend highly on a good implementation. I'm interested in the following aspects in a general sense:
There must be some baseline for overhead when using an interpreter. Is there some general rule of thumb to remember? 10% 15%? (I pulled these numbers out of thin air) I have read the occasional blog stating that Java code is nearly as fast as native code, but I think that may have been biased.
Does the JVM garbage collector add significant overhead to runtime performance? I know Cocoa applications have begun to use a garbage collection model, and i agree that it makes programming a lot simpler, but at what cost?
What is the overhead of making system calls from Java? For example creating a Socket object as opposed to the C socket API.
Finally, I recall reading somewhere that the JVM implementation is single threaded. If this is true (which i am skeptical about), does that mean that Java threads really aren't true threads? Does a java thread, in general, correspond to an underlying kernel-provided thread? Does a Java application benefit in the same way a native application would from multiple cores / multiple cpu's?
Any advice from developer who understands the intricacies of JVM and java program performance would be much appreciated. Thanks.