Probably you meant "blank .txt file manually" instead of "black .txt file"
You can create new files as follows:
File file = new File(fileName);
So if the filename "blank.txt" then the code snippet above creates an empty file named "blank.txt" in the current folder. (normally application folder)
And if you want to make sure that its directories exist before saving the file:
File dir = new File(dirName);