Java Reference
In-Depth Information
items. The first menu item will create a new window, while the second menu item will
destroy all windows. The beauty of the design is that a single event source, the menu item
for close all windows, will have multiple event listeners that are associated with it. When
the close all menu item is selected, all windows will be closed. Here is the implementation.
import
java .awt .
∗
;
import
java .awt. event .
∗
;
import
java . util .
∗
;
import
javax . swing .
∗
;
public class
RandomWindows
{
public static void
main(String [] args)
{
MainFrame f =
new
MainFrame () ;
f . setVisible(
true
);
}
}
class
MainFrame
extends
JFrame
{
private static int
counter = 0;
public
MainFrame ()
{
setSize (200,200) ;
JMenuBar bar =
new
JMenuBar ( ) ;
setJMenuBar(bar ) ;
JMenu windowMenu =
new
JMenu(
"Window"
);
bar . add (windowMenu) ;
final
JMenuItem newWindow =
new
JMenuItem(
"New Window"
);
final
JMenuItem c l oseAl l =
new
JMenuItem(
"Close All"
);
windowMenu . add (newWindow) ;
windowMenu . add ( c l o s eA l l ) ;
newWindow. addActionListener(
new
ActionListener ()
{
public void
actionPerformed(ActionEvent e)
{
MyFrame f =
new
MyFrame( c l o s e A l l ) ;
f . setLocation((
int
) (Math . random ( )
∗
500) , (
int
) (Math . random ( )
∗
500)) ;
f . setSize (200,200) ;
f . setVisible(
true
);
}
}
);
}
}
class
MyFrame
extends
JFrame
{
public
MyFrame(
final
JMenuItem c l oseAl l )
{
closeAll . addActionListener(
new
ActionListener ()
{
public void
actionPerformed(ActionEvent e)
{
dispose() ;
}
}
);
}
}
Note that the position of every new window is chosen randomly. Figure 10.3 shows how
the three event listeners are registered with the same event source. When the
Close All
menu item is chosen, all three windows will be closed. Note that the menu item
closeAll
is part of the window constructor. Every time a window is created, an
ActionListener
is registered with the menu item
closeAll
. Therefore, if there are three windows, then
