Java™ Application Development on Linux - Dator

372Chapter 16Getting in the Swing of Things: Designing a GUI for BudgetProFigure 16.5 Dialog for creating a new subaccountthan once. We could throw away the dialog (or let it get garbage-collected) bydeclaring it internal to the actionPerformed() method. Then on each buttonpress the dialog would need to be recreated. Well, it’s slower to do it that way,and for a button click we want quick response—so we keep it around from oneuse to the next. When the user closes the dialog, all that really does is makes itinvisible; to reuse it, we make it visible again.Notice, too, that in either case—creating the dialog or making it visible—controldoes not return to our method until the user has dismissed thedialog. That’s because it’s a modal dialog, one that allows no other interactionwith the application until the user has responded to this dialog.The dialog is dismissed (finished, ended, put away) simply by making itno longer visible. For example:73 dialog.setVisible(false); // go awayNew to our application, in AcctDialog, is the JTextField. On lines 22and 23 we declare two of them, one for the account name and the other for theamount.22 nameField = new JTextField(25);23 amntField = new JTextField(9);The size that we pass in to the constructor is the number of characters; itsets a maximum for that field, but also gives a clue to some layout managers asto how big the field needs to be.Speaking of layout managers, we use a few here, including a BoxLayout,to format the buttons relative to each other; a BorderLayout, to hold theoverall dialog; and a newer layout manager, the SpringLayout, which is newas of Java 1.4. The Swing Tutorial provides a handy utility class for dealing