If you added it in the control panel while your command prompt was open, that won’t affect your current command prompt. You’ll need to exit and re-open or simply do:
set "path=%path%;c:\program files\java\jdk1.6.0_16\bin"
By way of checking, execute:
from your command prompt and let us know what it is.
Otherwise, make sure there is a javac in that directory by trying:
"c:\program files\java\jdk1.6.0_16\bin\javac.exe"
from the command prompt. You can also tell which executable (if any) is being used with the command:
for %i in (javac.exe) do @echo %~$PATH:i
This is a neat trick similar to the which and/or whence commands in some UNIX-type operating systems.