Biggest concern: Java has memory management. C and C++ do not, you do that on your own. If the Java developer has never had to be concerned with memory management they will create a program that will leak memory and program will run for some time then it will fail, especially in embedded world. I came from assembly, C / C++. Then I learned Java and thought, wow that is nice, memory is managed for me. Going from Java to system level programming language like C will be a big learning curve.