Flyweight in Java

import java.awt.*;

import java.awt.event.*;

 

class FlyweightFactory {

   private static java.util.Map  ht = new java.util.TreeMap();

   private static int            sharedButtons = 0;

   private static ButtonListener bl = new ButtonListener();

   public static Button makeButton( String num ) {

      Button btn;

      if (ht.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.]

         btn = new Button( ((Button)ht.get(num)).getLabel() );

         sharedButtons++;

      } else {

         // 2. Return a new object

         btn = new Button( num );

         ht.put( num, btn );

      }

      btn.addActionListener( bl );

      return btn;

   }

   public static void report() {

      System.out.print( "new Buttons - " + ht.size()

         + ", \"shared\" Buttons - " + sharedButtons + ", " );

      for (java.util.Iterator it = ht.keySet().iterator(); it.hasNext(); )

         System.out.print( it.next() + " " );

      System.out.println();

}  }

 

class ButtonListener implements ActionListener {

   public void actionPerformed( ActionEvent e) {

      Button      btn  = (Button) e.getSource();

      java.awt.Component[] btns = btn.getParent().getComponents();

      int i = 0;

      for ( ; i < btns.length; i++)

         if (btn == btns[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 );  // 1. Identify extrinsic state

}  }                                           //    (Button location)

 

public class FlyweightDemo {

   public static void main( String[] args ) {

      java.util.Random rn = new java.util.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();

}  }