american well questions

list^set difference?
how do u prevent duplicates in a set?
why we need both equals() and hashcode()? (within separate-chaining ...)
php caching?
ejb advantage over spring?
why not host biz logic components in the same jvm as web components?
jpa can employ hibernate?

fail-over with pairing cluster, where one a pair of nodes share state data. hot copy
spring XA? a container is needed
ejb3: annotation-based security and tx
ejb: usually generated. easy to make mistakes