Use a cell renderer which does that. I think that having it return a JPasswordField would work. You didn't say whether the table was editable, but if it is then you're going to have to do the same with your cell editor.
(I'm guessing you have never heard of those things, based on the incorrect things you said about JTable in your post. I would suggest going through Oracle's JTable tutorial starting from the beginning and continuing until you get to the part where cell renderers and editors are covered.)