I have C++ code from 1997 that I occasionally compile. So far it runs. 10 yeas ago compiling with -Wall exposed an inconsequential bug and that was it. I suspect when it stops to compile it will be from an absence of a particular X11 library that I used to parse a config in otherwise command-line utility.

Which also points to another thing where Java compatibility shines. One can have a GUI application that is from nineties and it still runs. It can be very ugly especially on a high DPI screen, but still one can use it.