Java in Sudoku boards

I am currently in need of some help on a java based Sudoku board. There
are a couple of questions I have.
1. How would I go about generating random boards for people to solve
rather than a select few that have already been completed and when the
inputer is completed with the board and hits the solve jbutton the
board is just checked against the already completed board. I would like
to know how I can get something that when the jcombobox has been
selected say medium and then the user clicks the newpuzzle jbutton it
would randomly generate a medium level of difficulty sudoku board. (I
am working with a jtextfields rather than a 2d array for a board.)
2.I would like to implement a timer that when the user is complete
would save the time it took to solve and then put it into a
JTextfieldbox and would continue to keep all of the times from that
session.
Thanks for any and all help that is given.

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