Where is File definition?

I am trying to convert printing Serial debug information into saving them to SD card. I thought that File might be derived from Stream but I can't find where File is defined. Can someone help me? Thanks.

/Applications/Arduino 1.0.1.app/Contents/Resources/Java/libraries/SD/SD.h

And, yes, it's derived from Stream:

    class File : public Stream {

Thanks John. I guess I would be able to do it then. Just need to replace all the Serial with a pointer. Not too hard.