I did courses at two universities (I transferred) and in either case one would need to compile the assignment source code in order to actually do the homework.

I did courses at two universities (I transferred) and in either case one would need to compile the assignment source code in order to actually do the homework. I think that a compiler, especially javac, would catch almost all of these and warn about some of the others. Moreover, good syntax highlighting or an IDE with some static analysis in it would help a lot too. I think that might be a useful thing to put in intro programming classes. Eclipse is free right? I use IDEA-based editors for most of my work, but even the syntax highlighting in, say, emacs without installing packages (at least on the OS/distros I'm familiar with) would go some fair distance to this goal. I assume the same would be true of vi.