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I guess what happened is you created a file and wrote to it. Then in the closeF() method you created a new file with the same name and wrote nothing to it destroying the first version.

I got output (1 byte) when I ran your code (except I moved the close to the outputF() method).

The f object in the close method is NOT the same as the f object in the write method.
Close the output file after writing to it or have a reference to the object that was written to when closing...