I understand that there is quite a number of people here who works/has worked for Google or Facebook. So, my question is. How do you get into those companies when no one (or a very little number of other companies) use their technologies?

Let's consider Facebook for example. I want to be a backend software engineer at Facebook. But how do I get that job and relevant work experience? Like no one uses HHVM or hack language and there's no way to get experience in it, I work for a company doing backend stuff with java spring, but none of these cool companies use it. I understand that I can learn android development and it'll be easier to get a job that way, but I am not really passionate about it. Looks like Microsoft is the only company who's tech is widely used everywhere...

I guess Facebook and Google mostly hire interns for these positions then, because they will have to teach them from scratch anyways, rather than experienced developers who are expected to know everything in the interview? Or do these companies look at general and not library specific knowledge and can invest in you and teach you their specific stuff?