If you were asked that in an interview and do not have the answer and cannot figure out how to find that answer, you really should not have the job. A working programmer should know how to find answers to such things on their own through the documentation or other available resources.
I don't say that to be mean. It's just something you need to learn to do if you expect to hold a job programming and the sooner you get used to it the better.
Take a look at the source code of the Vector class and things will become a bit more clear for you. Just don't be attracted by the 'synchronized data structure' thing, hand craft your synchronization code. It would save you a lot of trouble.