sap abap program for Change Text Into Password

I had a doubt for creating a password.

How can I change text into password(*******) in a text box?
eg: I will give some password in a text field. But it must appear in ******* like that..

To set it as password field, add the below code in the PBO of the screen:

loop at screen.
if screen-name = 'text box name'.
screen-invisible = '1'.
modify screen.
endif.
endloop.

and it must in selection-screen output.