I've been dabbling in this for a year or so for fun...so take this with a pinch of NaCl.
I'd take the Java course, but definitely get yourself a couple of straightforward books on C (and maybe even C++) books to read on the side - I think they would shed additional light and insight on what's going on in your Java course. C can be a heck of a large mountain to climb, with many base camps to pass through before you reach the tree-line, but a grasp of the fundamentals of it I think very useful in Java.
It's not really that much of a stretch to check out two languages at the same time - especially when they are as closely related as the C/C++ family and Java.
Kinda like athletic cross training. You see the same concept from a different perspective and suddenly the light goes on in your mind and learning is reinforced.