?: is the "Elvis" operator.

That's pretty a hilarious name for it. Is this from the Groovy community?

The standard name is the "Null-coalescing" operator, see http://en.wikipedia.org/wiki/Null_coalescing_operator .

It's only called "Elvis" in Groovy. The name was announced one day by its Project Manager as part of a marketing campaign to make the name "G-String" mean a string on Elvis's guitar instead of a revealing item of clothing.