jdsullivan

The more important and general wisdom: know your audience. You will sometimes have clients with deep technical backgrounds that expect a sufficient level of detail to have any faith or trust in your solutions. You need to be able to tailor your communication based on the situation and the expectations of the audience in question. This is never binary and can be especially challenging when you need to communicate to multiple people at the same time that each require different levels of detail.

This is a durability metric, not an availability one. This typically tells you the likelihood of losing a given object in a year. (5 9's would be quite poor for this, implying a loss of 1 object out of 100,000 every year)

Not quite: "On strings, numbers and collection classes, hashCode() always returns a consistent value, apparently even across different JVM vendors. It’s like that despite the documentation for hashCode() explicitly not guaranteeing consistency across different processes"

String.hashCode explicitly guarantees consistency across processes by specifying how the hash code is computed, this is something that can be safely relied upon. (Same for Integer, Long, Float and Double)