Need help writing an application?

I am required to write GUI application which acquires data and reports to the computer screen. It is more of like a simulation of the real world data acquisition systems. I know C language and nothing else (not even c++). Would it be beneficial if I learn Java and write gui or continue with C or GTK+(I have to learn GTK+ too) considering the fact that I still have 5 months to do so? Please let me know, thank you very much!