Using Ubuntu for commercial software development

if I develop a program using C++/Java and compile it using GCC compiler or OpenJDK's compiler, can I sell it without having to place my program under GPL as well?

Yes. The GPL specifically excludes the output of running the program:

the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program).

which means that if you include bits of GCC or something else GPLed in your program, then yes it would have to be GPLed, otherwise no - the fact that its object code was produced by a GPLed compiler is not relevant to whether it should be GPLed.

All the standard language libraries you would link to are either not GPLed, or are GPLed but have a special exception to allow your proprietary software to link to them, if you do not modify them. In the case of C++ I mean libgcc, glibc and libstdc++; in the case of Java I mean all the libraries included in the JRE.

Technically, you can legally sell GPL software anyway, but almost no-one makes any money out of doing so.

The text of the license specifically covers translations, so no, you wouldn't be able to relicense it.

The "Program", below, refers to any such program or work, and a "work based on the Program" means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language.