When I interviewed for my current job using Java, I had been programming in Ruby and JS for the better part of a decade and had to refresh my Java syntax fairly quickly. I know I made some dumb syntax mistakes in my phone interview, like instantiating collections totally incorrectly. I distinctly remember one of my in-person interviewers saying "well, in Java it's boolean, not bool, but sure...". More semantically, I may very well have messed up mutability of collections and primitive conversions and boxing and such.

Enough of my interviewers saw through all of this that I got the job. Now people on my team come to me and say, "hey you're a java guy right?" and ask me questions about this stuff. I wasn't a java expert when I interviewed, but now I am, because that's what my job required, so I learned it. That's what my interviewers were looking for, to the company's benefit.