Where does a class reside?

I confess, I'm new. I'm trying to learn Java progrmming and in the book "Teach Yourself Java in 21 Days" it says that an instance can reference and update class variables. Where are these class variables? Okay, they reside on a hard drive somewhere but does an instance have update authorization to the hard drive? or is the class held in memory somewhere and when and instance updates the class it is only in memory? It would not make sence if you are creating a dozen instances of the same class to keep going out to the hard drive for the creation of every instance.
I'd appreciate any light you can shed on the subject.
Thanks,
Byron in Seattle

You hit the nail on the head; it would be way too costly to run java having to read class file definitions from the hard drive every time you use one.
Here's how it works:
When you start java, all of the classes in the java software version you are using (1.3, 1.4, etc) are automatically loaded into memory along with the Java Virtual Machine (JVM)
Next, everything in your classpath (well, not everything, but all .class files) will be loaded into memory.
After that, classes can be 'bootstrapped' by using Class.forName(...)

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