JVM garbage collection: What is the difference between "survivor 1" and "survivor 2"?

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http://serverfault.com – In Oracle's Java Virtual Machine's Garbage Collector, what are the respective roles of "survivor 1" and "survivor 2" ? Are the objects always moving like: Eden → Survivor 1 → Survivor 2 Or can an object jump directly from Eden to Survivor 2? Would a "Survivor 3" make no sense, or it could be OK but it was deemed that two are enough? (HowTos)