Is there any way to extract java code from a jar file?

Well me and my partner are in very a sticky situation. We have a project due sometime soon and we were finished quite early. It took forever to write up but we were able to get it done with 100% functionality. But yesterday my partner's computer crashed and that's where we had all our stuff. when he told me this, i said it was ok because we always saved our work on his usb when we were finished coding. But it turns out that we have very bad luck. he's tried taking files off it on all 3 of the other computers in his house but every time it says error, file not found. The only ray of hope left is that jar file that he made and sent to my email after he cleaned up the program with some finishing touches. I've told my prof but he says that he cannot mark our work with only a jar file. We need to have the java file too. Is there some way that the java file can be extracted from the jar executable? It's the only chance we have to finish this project because we don't have nearly enough time to re-write the entire program again. Please, Help if you can...