I find it hard to believe you could really deep grasp anything after a week of training. You can learn a bunch of tricks and gotchas!
Does your career let you dive into a C++ job for a year or two? Nothing will give you more C++ exposure than doing it for a job, and being good lets you do cool tricks in Java (looking at you sun.misc.Unsafe)
On the second point I have to disagree. I worked with plenty of C++ who have been programming for years but never read a C++ book. Many of them are stuck doing hacky "C with classes" programming, much like they did from day one. The attitude is if it ain't broken, don't fix it.
I was one of those programmers. Then I picked up "Effective C++" by accident. It was a mind shift. I started coding differently after all these years. I got hooked and read every popular non beginner C++ book out there (I would guess around 50 of them).
So I think reading books, is a better way of learning to program than just blindly going your own way, or the blind leading the blind.
Most of the time, "C with classes" is exactly what the problem calls for. I cringe every time I see classes whose functionality can be replaced by a simple function. Those shouldn't even be classes. They should be free functions. And this happens quite often.
What I mean by "C with classes" is the worst side of both languages. Type-unsafe C coding (pointers, casts., manual memory allocations, etc), with OOP (highly coupled complex class hierarchies, virtual calls, etc).
The modern C++ way is to use RAII, value semantics, and STL everywhere.
Does your career let you dive into a C++ job for a year or two? Nothing will give you more C++ exposure than doing it for a job, and being good lets you do cool tricks in Java (looking at you sun.misc.Unsafe)