//
// "hint" program for homework #4 -- provide GUI for a very simple
//      "adding machine".
//
// see class definitions for additional info.
//
import java.awt.* ;
import java.awt.event.* ;

//
// an AddMachine object represents a very primitive adding machine
//      (supporting only "add" and "clear" functions).
//
class AddMachine {

        private int balance = 0 ;

        int getBalance() { return balance ; }

        void clear() { balance = 0 ; }

        void add(int i) { balance += i ; }
}

//
// an AddMachineGUI object provides a GUI for an AddMachine object,
//      consisting of a Label to display the current balance (also
//      used to display error messages), a TextField for entering
//      data, and the following Buttons:
// "Clear" clears the AddMachine's balance to 0.
// "Show" redisplays the balance (useful after an error message).
// "Add" adds to the balance the number represented by the contents
//      of the TextField (if not numeric, an error message replaces
//      is shown in the balance-display area).
// the object also disposes of itself and ends the program when
//      its window is closed.
//
class AddMachineGUI extends Frame implements ActionListener {

        AddMachine adder ;
        Label display ;
        TextField tf ;

        AddMachineGUI(AddMachine adder) {

                super("AddMachineGUI") ;
                this.adder = adder ;
                setLayout(new GridLayout(0, 1)) ;

                // add a window listener to respond to window-closing
                //      events.
                addWindowListener(
                        new WindowAdapter() {
                                public void 
                                  windowClosing(WindowEvent e) {
                                        dispose() ;
                                        System.exit(0) ;
                                }
                        } ) ;

                // display area
                display = new Label("", Label.CENTER) ;
                add(display) ;
                showBalance() ;

                // text field for entering number, in a Panel with
                //      FlowLayout so it keeps its original size if 
                //      the window is resized.
                tf = new TextField(20) ;
                Panel p1 = new Panel(new FlowLayout()) ;
                p1.add(tf) ;
                add(p1) ;

                // buttons, grouped as a Panel with FlowLayout so
                //      they keep their size.
                Panel p2 = new Panel(new FlowLayout()) ;
                p2.add(makeButton("Clear", "clear", this)) ;
                p2.add(makeButton("Show balance", "show", this)) ;
                p2.add(makeButton("Add", "add", this)) ;
                add(p2) ;

                pack() ;
                show() ;
        }

        // return a button with the specified label and action command
        //      an an ActionListener of "this".
        Button makeButton(String label, String command, 
                        ActionListener l) {
                Button b = new Button(label) ;
                b.setActionCommand(command) ;
                b.addActionListener(l) ;
                return b ;
        }

        // handle ActionEvent (button press).
        public void actionPerformed(ActionEvent e) {
                String cmd = e.getActionCommand() ;
                if (cmd.equals("clear")) 
                        doClear() ;
                else if (cmd.equals("show")) 
                        doShow() ;
                else if (cmd.equals("add")) 
                        doAdd() ;
                else 
                        System.out.println("Something odd happened!") ;
        }

        void doClear() {
                adder.clear() ;
                showBalance() ;
        }

        void doShow() {
                showBalance() ;
        }

        void doAdd() {
                try {
                        int num = Integer.parseInt(tf.getText()) ;
                        adder.add(num) ;
                        showBalance() ;
                } catch (NumberFormatException e) {
                        showError("Input text is not a number") ;
                }
        }

        void showBalance() {
                display.setText("Balance = " + adder.getBalance()) ;
        }

        void showError(String s) {
                display.setText(s) ;
        }

        //
        // ---- main method --------------------------------------------
        //
        // no command-line arguments.
        //
        public static void main(String[] args) {

                AddMachine adder = new AddMachine() ;

                AddMachineGUI gui = new AddMachineGUI(adder) ;
        }

}