Check out this tutorial on swing in case you want to get your GUI up and running and then you might want do some validations on the username and password either in the database (then you might want to look here for jdbc) or want to use Files instead.
Now the next logical step would be you want to validate the user.
What you could do is store a username and a password in either a File or a table in a database for ex: MS Access (or Apache Derby which ships with the JDK I assume.)
And whenever anyone clicks on say the "Login" or "Submit" button you would have to first validate whether the user has actually entered a value in the Password and UserName fields (if not you could show him an error message using the dialog boxes of JOptionPane) but if a proper value is found in both the fields you validate the user against the values (for username and password) present in the File or the database.
If the username and password combination specified in the form fields matches what you have in the File (or a the database table), you could display a success message (using JOptionPane once again) and stop there itself or take him a new form where you might want to do some more processing.
ok, i will try it. Thanks for giving advise.:)....actually i need to implement a motor plate recognition system by using java language.Anyone have any idea? I just got 2 more months to develop this system.