Well,"fat" is an unprecise term anyway, but the main concern when evaluating languages like that is mandatory overhead. What exactly constitutes overhead is de

Well,"fat" is an unprecise term anyway, but the main concern when evaluating languages like that is mandatory overhead. What exactly constitutes overhead is debatable, but generally anything that is not strictly necessary for the functionality is considered as such... Even if it has useful tradeoffs. Examples from Java are the GC, compound types need to be objects and thus are wasting space with type and vtable pointers, and the jvm is actually an interpreter (one with only stack semantics at that). Since C++ has none of that, it is quite natural to say that it is more lightweight than Java. But that in itself is not necessarily a judgement about execution speed, although it is heavily implied. If you write Java in a way that it is heavily jitable and doesn't stress the GC, you can end up with a faster program than a naive C++ version would achieve. But all else being equal, the C++ version will be ever so slightly fester, because less stuff to do means more stuff done.