GiftBasket.java

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// GiftBasket.java - A demonstration of interfaces.  This program could be the basis
// of a simplified "point of sale" (POS) system:  Imagine each item is scanned
// when added to the gift basket, and the scanner reads a bar-code that identifies
// the item.  The program might then print the items description and price on the
// receipt, update the inventory records, etc.  The Sellable interface defines the
// guarantee that any Sellable item can have its description printed and its cost
// calculated.
//
// The gift basket doesn't contain fruit alone, but several different types of items.
// Classes Fruit and Bouquet are unrealistic here to keep the example simpler.
// This slightly more complex example correctly uses abstract classes to define
// the generalization of fruits and flowers.  Also notice the constructor details
// in class Bouquet: "type" has a reasonable default value so no constructor argument
// is needed, but may be supplied.  Overloaded constructors and methods are a common
// way to deal with optional arguments.
//
// Written 2002 by Wayne Pollock, Tampa FL USA.  All Rights Reserved.

import java.text.NumberFormat;

interface Sellable
{
   float cost();
   void describe ();
}

abstract class Fruit
{
   String color;
   float weight;

   public Fruit ( String color, float weight )
   {  this.color = color;
      this.weight = weight;
   }

   public void describe ()
   {
      System.out.println( "I am " + color +
         " and I weigh " + weight + " pounds." );
   }
}

class Mango extends Fruit implements Sellable
{
   public Mango ( String color, float weight )
   {  super( color, weight );  }

   public void describe ()
   {  System.out.println( "A juicy " + color + " " + weight + " lb. mango." );  }

   public float cost ()
   {  return 0.88f * weight;  }
}

class Banana extends Fruit implements Sellable
{
   public Banana ( String color, float weight )
   {  super( color, weight );  }

   public void describe ()
   {  System.out.println( "A " + color + " " + weight + " lb. bunch of bananas." );  }

   public float cost ()
   {  return 0.88f * weight;  }
}

class Orange extends Fruit
{
   public Orange ( String color, float weight )
   {  super( color, weight );  }

   public void describe ()
   {  System.out.println( "A ripe " + color + " " + weight + " lb. Orange." );  }

   public float cost ()
   {  return 0.39f * weight;  }
}

class Marmalade implements Sellable
{
   String type;

   public Marmalade ( String type )
   {  this.type = type;  }

   public void describe ()
   {  System.out.println( "A tasty jar of " + type + " marmalade." );  }

   public float cost ()
   {  return 1.99f;  }
}

abstract class Bouquet implements Sellable
{
   int numOfFlowers;
   float priceEach;
   String type;

   public Bouquet ( int numOfFlowers, float priceEach )
   {  this( numOfFlowers, priceEach, "flowers" );  }

   public Bouquet ( int numOfFlowers, float priceEach, String type )
   {  this.numOfFlowers = numOfFlowers;
      this.priceEach = priceEach;
      this.type = type;
   }

   public void describe ()
   {  System.out.println( "A fragrent bouquet of " + numOfFlowers + " " + type + "." );
   }

   abstract public float cost ();
}

class RoseBouquet extends Bouquet
{
   public RoseBouquet ( int numOfFlowers )
   {  super( numOfFlowers, 1.25f );
      type = "Roses";
   }

   public float cost ()
   {  float price = numOfFlowers * priceEach;
      if ( numOfFlowers > 12 )
         return 0.90f * price;  // a 10% discount
      else
         return price;
   }
}

public class GiftBasket
{
   public static void main ( String [] args )
   {
      int numItems = 0;
      Sellable [] giftBasket = new Sellable[10];  // An array of 10 "Sellable" items.

      giftBasket[numItems++] = new Mango( "red", .25f );
      giftBasket[numItems++] = new Banana( "yellow", 2.15f );
//    giftBasket[numItems++] = new Orange( "orange", 0.12f );  // This won't work!
      giftBasket[numItems++] = new Marmalade( "Lemon" );
      giftBasket[numItems++] = new Mango( "red", .18f );
      giftBasket[numItems++] = new RoseBouquet( 6 );

      float totalCost = 0;
      System.out.println( "\nYour gift basket contains the following items:\n" );
      for ( int i = 0; i < numItems; ++i )
      {
         giftBasket[i].describe();
         totalCost += giftBasket[i].cost();
      }
      NumberFormat nf = NumberFormat.getCurrencyInstance();
      System.out.println( "\nThe total cost is " + nf.format( totalCost ) + "." );
   }
}

Send comments and questions to pollock@acm.org.
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