What the Signature Says, and What It Costs

Five things this topic established, and where each one was.

What the topic established, and which card it was on
The thing	Where
`Optional` puts "there might be nothing" into the signature	A Return Type That Says There Might Be Nothing Here
`orElse` for a value in hand, `orElseGet` for anything that costs	orElse, orElseGet and orElseThrow
`orElse`'s argument is evaluated whether or not it is needed	Why orElse Ran Your Fallback
`get()` without a check throws, exactly as the null would have	Why get() Without a Check
A return type, never a field, a parameter or an element	Where Optional Does Not Belong

The one worth carrying: Optional makes absence visible and does not make anybody handle it. Everything that goes wrong with it is a caller unwrapping it immediately, which puts the original problem back with a longer name.

Java
Java Streams