Design Patterns : Flyweight pattern

• An application uses a large number of objects
• Storage costs are high because of the sheer quantity of objects

Note: Flyweights are not frequently used at the application level in Java. They are more of a system resource management technique, used at a lower level than Java.

Diagram

Code Sample

public abstract class TeaOrder {

    public abstract void serveTea(TeaOrderContext teaOrderContext);

}

Concrete Flyweight

public class TeaFlavor extends TeaOrder {

    String teaFlavor;

    TeaFlavor(String teaFlavor) {

        this.teaFlavor = teaFlavor;

    }

    public String getFlavor() {

        return this.teaFlavor;

    }

    public void serveTea(TeaOrderContext teaOrderContext) {

        System.out.println("Serving tea flavor " + teaFlavor +

                           " to table number " +

                             teaOrderContext.getTable());

    }

}

Context // This class is only in the context of this example

public class TeaOrderContext {

   int tableNumber;

   TeaOrderContext(int tableNumber) {

       this.tableNumber = tableNumber;

   }

   public int getTable() {

       return this.tableNumber;

   }

}

The Factory

public class TeaFlavorFactory {

   TeaFlavor[] flavors = new TeaFlavor[10];

     //no more than 10 flavors can be made

   int teasMade = 0;

   public TeaFlavor getTeaFlavor(String flavorToGet) {

       if (teasMade > 0) {

           for (int i = 0; i < teasMade; i++) {

               if (flavorToGet.equals((flavors[i]).getFlavor())) {

                   return flavors[i];

               }

           }

       }

       flavors[teasMade] = new TeaFlavor(flavorToGet);

       return flavors[teasMade++];

   }

   public int getTotalTeaFlavorsMade() {return teasMade;}

}

The Client

class TestFlyweight {

   static TeaFlavor[] flavors =

     new TeaFlavor[100];

     //the flavors ordered

   static TeaOrderContext[] tables =

     new TeaOrderContext[100];

     //the tables for the orders

   static int ordersMade = 0;

   static TeaFlavorFactory teaFlavorFactory;

   static void takeOrders(String flavorIn, int table) {

       flavors[ordersMade] =

         teaFlavorFactory.getTeaFlavor(flavorIn);

       tables[ordersMade++] =

         new TeaOrderContext(table);

   }

   public static void main(String[] args) {

       teaFlavorFactory = new TeaFlavorFactory();

       takeOrders("chai", 2);

       takeOrders("chai", 2);

       takeOrders("camomile", 1);

       takeOrders("camomile", 1);

       takeOrders("earl grey", 1);

       takeOrders("camomile", 897);

       takeOrders("chai", 97);

       takeOrders("chai", 97);

       takeOrders("camomile", 3);

       takeOrders("earl grey", 3);

       takeOrders("chai", 3);

       takeOrders("earl grey", 96);

       takeOrders("camomile", 552);

       takeOrders("chai", 121);

       takeOrders("earl grey", 121);

       for (int i = 0; i < ordersMade; i++) {

           flavors[i].serveTea(tables[i]);

       }

       System.out.println(" ");

       System.out.println("total teaFlavor objects made: " +

                           teaFlavorFactory.getTotalTeaFlavorsMade());

   }

}