You can check here how to get user input with JOptionPane.
But first I would suggest you reconsider the existing solution. First of all, it's never a good approach to mix GUI with console input/output, which is what you did. You could also check the design of your class, not everything should be in the main method. Declaring 12 variables of type int could probably be replaced with one int array of size 12. Math.random() returns double value (did you check the results you get?), so you should consider using Random class that contains method for generating int values that would be more appropriate for dices. That switch also doesn't make sense to me; first, you have no break statements, which means all of subsequent cases are always executed (maybe that was what you want, but it doesn't seem to me). And also, what's the point of putting case 1: when it's not possible to have the sum of two dice result equal to 1 (the least is 2, I guess)?
Edit: And please put the code inside code tags, and remove those extra blank lines you have so it will be easier to read. Check UseCodeTags (<- click).
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