If you learned how to *program* and not just Java, then I would say it's sufficient.
To make my statement a bit clearer: the basic concepts of programming are more or less the same. A simple example: If you want to print a
string ten times on the screen and you think about, how to achieve this task, you will come up with a for-loop. If
you should write this little program in a language that you never used before, you look up the syntax and that's it.
Another example: you want to sort an array. If your only idea is to call the sort() method, but you have no clue how to achieve this *manually* then you might have learned "only Java", but not really "programming". If you say: "hey that's easy, I might use BubbleSort because it's only a few values that needs to be sorted and if the speed is not sufficient I will implement a QuickSort" then it doesn't really matter if you programmed so far only in one language.
I hope my point is clear. If I would be in charge of hiring programmers, I'm not interested how many different syntax the person ever learned, but if (s)he is able to produce solutions. If the basic concepts are understood languages are only tools which will be learned in a very short amount of time.
PS: I know, I didn't take other paradigmas, like functional or logic programming, into account, neither the possibility of needing another language which needs e.g. manual memory management, which might be harder to grasp / make it right in the beginning, if you never had a reason to deal with that before.
PPS: Quick anecdote: for my first job I was hired as a Delphi developer. My first task? A JavaScript which needed to be finished at the end of the day. Only help I had: a book they gave me. I never ever even saw JavaScript in my life before. But it worked.
Hope that helps a bit.