//
// another example of the Java AWT, showing use of adapter classes.
//      (here, they're implemented as anonymous inner classes.)
// see class definition for details.
//
import java.awt.* ;
import java.awt.event.* ;

//
// a PowerOf2 object represents an integer power of 2.
//
class PowerOf2 {

        int p = 0 ;

        void doubleIt() {
                p++ ;
        }

        void halveIt() {
                p-- ;
        }

        double val() {
                return Math.pow(2.0, (double) p) ;
        }

}

//
// a PowerOf2GUIAlt object is a CloseableFrame with GUIs for two
//      PowerOf2 objects, each GUI consisting of two buttons to
//      invoke the doubleIt() and halveIt() methods and a display
//      area.
//
class PowerOf2GUIAlt extends CloseableFrame {

        PowerOf2GUIAlt() {

                super("PowerOf2GUIAlt") ;

                int num = 2 ;           // number of PowerOf2 objects

                setLayout(new GridLayout(num, 3, 20, 20) ) ;

                for (int i = 0 ; i < num ; i++) {
        
                        // create a PowerOf2 object together with
                        //      associated buttons and label, and
                        //      add to frame.
                        p2PlusGUI() ;
                }

                // set minimum size needed to hold everything, and
                //      display.
                pack() ;
                show() ;
        }

        // create a PowerOf2 object together with associated buttons
        //       and label, and add to container.
        // this code is a separate method rather than being included
        //      in main() because anonymous inner classes can access
        //      only final variables.
        void p2PlusGUI() {

                final PowerOf2 o = new PowerOf2() ;

                Button h = new Button("halve it") ;
                add(h) ;

                Button d = new Button("double it") ;
                add(d) ;

                final Label l = new Label(
                        Double.toString(o.val()), Label.RIGHT) ;
                add(l) ;

                h.addActionListener(new ActionListener() {
                          public void actionPerformed(ActionEvent e) {
                                o.halveIt() ;
                                l.setText(Double.toString(o.val())) ;
                          }
                } ) ;

                d.addActionListener(new ActionListener() {
                          public void actionPerformed(ActionEvent e) {
                                o.doubleIt() ;
                                l.setText(Double.toString(o.val())) ;
                          }
                } ) ;
        }

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

                PowerOf2GUIAlt f = new PowerOf2GUIAlt() ;
        }

}