Graphical User Interfaces - Java - page 557

b1 . addActionListener ( this this );

setSize ( 300 , 200 );

}

public public void void actionPerformed ( ActionEvent event ) {

System . out . println ( "Thanks for pushing my button!" );

}

public public static static void void main ( String [] unuxed ) {

new new ButtonDemo (). setVisible ( true true );

}

}

This version does not use an inner class to handle the events but does so itself by directly im-
plementing the ActionListener interface. This works for small programs, but as an applica-
tion grows, it quickly becomes unserviceable; how do you sort out which button was
pressed? To solve this problem, we normally use an inner class as the action handler and
have a different class for each button, or at least for each related set of actions. First, let's
write the previous code with two buttons so that you can see what I mean:

public public class class ButtonDemo2a ButtonDemo2a extends extends Applet implements implements ActionListener {

Button b1 , b2 ;

public public void void init () {

add ( b1 = new

new Button ( "A button" ));
b1 . addActionListener ( this

this );

add ( b2 = new new Button ( "Another button" ));

b2 . addActionListener ( this

this );

}

public public void void actionPerformed ( ActionEvent e ) {

iif ( e . getSource () == b1 )
showStatus ( "Thanks for pushing my first button!" );

else else

showStatus ( "Thanks for pushing my second button!" );

}

}

Now here is the same program written using a member inner class —that is, a class that is a
named part of its containing class: