[brudgers]

An intern is not expected to perform like a person with years of experience. An intern is at the start of their career and is expected to learn.

The list of Java topics is long enough that even someone with many years of experience may have only passing familiarity with some of them.

Finally, if a company has unrealistic expectations there is nothing you can do about it. On the other hand, realistic expectations regarding your own knowledge might be possible; http://norvig.com/21-days.html

Good luck.