Identify shareable state (intrinsic) and non-shareable state (extrinsic)
Create a Factory that can return an existing object or a new object
The client must use the Factory instead of "new" to request objects
The client (or a third party) must provide/compute the extrinsic state
class FlyweightFactory {
private static Map treeMap = new TreeMap();
private static int sharedButtons = 0;
private static ButtonListener listener = new ButtonListener();
public static Button makeButton(String num) {
Button button;
if (treeMap.containsKey(num)) {
// 1. Identify intrinsic state (Button label)
// 2. Return an existing object [The same Button cannot be added
// multiple times to a container, and, Buttons cannot be cloned.
// So - this is only simulating the sharing that the Flyweight
// pattern provides.]
button = new Button(((Button) treeMap.get(num)).getLabel());
sharedButtons++;
} else {
// 2. Return a new object
button = new Button(num);
treeMap.put(num, button);
}
button.addActionListener(listener);
return button;
}
public static void report() {
System.out.print("new Buttons - " + treeMap.size()
+ ", \"shared\" Buttons - " + sharedButtons + ", ");
for (Object o : treeMap.keySet()) {
System.out.print(o + " ");
}
System.out.println();
} }
class ButtonListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
Button button = (Button)e.getSource();
Component[] buttons = button.getParent().getComponents();
int i = 0;
for ( ; i < buttons.length; i++) {
if (button == buttons[i]) {
break;
}
}
// 4. A third party must compute the extrinsic state (x and y)
// (the Button label is intrinsic state)
System.out.println("label-" + e.getActionCommand()
+ " x-" + i/10 + " y-" + i%10);
}
}
public class FlyweightDemo {
public static void main( String[] args ) {
Random rn = new Random();
Frame frame = new Frame("Flyweight Demo");
frame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
frame.setLayout(new GridLayout(10, 10));
// 1. Identify shareable and non-shareable state
// shareable - Button label, non-shareable - Button location
for (int i=0; i < 10; i++)
for (int j=0; j < 10; j++)
// 3. The client must use the Factory to request objects
frame.add(FlyweightFactory.makeButton(
Integer.toString(rn.nextInt(15))));
frame.pack();
frame.setVisible( true );
FlyweightFactory.report();
}
}
