Errore di compilazione Actionscript 3.0

[Razorblade]

Ciao,
questo è l'errore che viene fuori sia in flax che flash durante la compilazione di un file .as

A file found in a source-path can not have more than one externally visible definition.

Che vuol dire?
Questo è il codice che ho cercato di compilare

 
  
  // VirtualZoo class
  package
  {
    import flash.display.Sprite;
    import zoo.*;
    public class VirtualZoo extends Sprite
    {
      private var pet;
      
      public function VirtualZoo() 
      {
        this.pet = new VirtualPet("Stan");
        
        pet.eat(new Apple());  // Feed Stan an apple
        pet.eat(new Sushi());  // Feed Stan some sushi
        // Assign the pet's old name to the local variable oldName
        //var oldName = pet.getName();
        // Give the pet a new name
        //pet.setName("Marcos");
      }
    }
  }
  
  
  // VirtualPet class
  package zoo 
  {
    import flash.utils.setInterval;
    import flash.utils.clearInterval;
    
    public class VirtualPet 
    {
      internal var petName;
      private var currentCalories = 1000;
      private var creationTime;
      private static var maxNameLength = 20;
      private static var maxCalories = 2000;
      // Le calorie che consuma durante la digestione
      private static var caloriesPerSecond = 100;
      // Id del set interval per la digestione
      private var digestIntervalID;
      
      public function VirtualPet(name) 
      {
        this.creationTime = new Date();
        this.petName = name;
        digestIntervalID = setInterval(digest, 1000);
      }
      
      
      
      private function digest () 
      {
        // If digesting more calories would leave the pet's currentCalories at
        // 0 or less...
        if (currentCalories - VirtualPet.caloriesPerSecond <= 0) 
        {
          // ...stop the interval from calling digest()
          clearInterval(digestIntervalID);
          // Then give the pet an empty stomach
          currentCalories = 0;
          // And report the pet's death
          trace(getName() + " has died.");
        }
        else 
        {
          currentCalories -= VirtualPet.caloriesPerSecond;
          trace(getName() + " digested some food. It now has " + currentCalories + " calories remaining.");
        }
      }
      
      public function setName (newName) 
      {
        if (newName.length > VirtualPet.maxNameLength) 
        {
          newName = newName.substr(0, VirtualPet.maxNameLength);
        } 
        else if (newName == "") 
        {
          return;
        }
        petName = newName;
      }
      
      public function getName() 
      {
        return petName;
      }
      
      // setter method AKA mutator method, from AS3.0 modifier method
      public function eat(foodItem) 
      {
        // If this pet is dead...
        if (currentCalories == 0) 
        {
          // ...quit this method without modifying currentCalories
          trace(getName() + " is dead. You can't feed it.");
          return;
        }
        
        if (foodItem is Apple) 
        {
          if (foodItem.hasWorm())
          {
            trace("The " + foodItem.getName() + " had a worm. " + getName()
                  + " didn't eat it.");
            return;
          }
        }
        
        var newCurrentCalories = currentCalories + foodItem.getCalories();
        if (newCurrentCalories > VirtualPet.maxCalories) 
        {
          currentCalories = VirtualPet.maxCalories;
        } 
        else 
        {
          currentCalories = newCurrentCalories;
        }
        
        trace(getName() + " ate some " + foodItem.getName() + ". It now has " + currentCalories + " calories remaining.");
      }
      
      // getter method AKA accesser method, from AS3.0 retriever method
      public function getHunger() 
      {
        return currentCalories / VirtualPet.maxCalories;
      }
      
      public function getAge() 
      {
        var currentTime = new Date();
        var age = currentTime.time - this.creationTime.time;
        return age;
      }
    }
  }
  
  // Food class
  package zoo 
  {
    public class Food 
    {
      private var calories;
      private var name;
      
      public function Food (initialCalories) 
      {
        setCalories(initialCalories);
      }
      
      public function getCalories ()
      {
        return calories;
      }
        
      public function setCalories (newCalories)
      {
        calories = newCalories;
      }
        
      public function getName ()
      {
        return name;
      }
        
      public function setName (newName)
      {
        name = newName;
      }
    }
  }
  
  // Apple class
  package zoo 
  {
    public class Apple extends Food 
    {
      // Set the default number of calories for an Apple object to 100
      private static var DEFAULT_CALORIES = 100;
      private var wormInApple;
      
      public function Apple (initialCalories = 0) 
      {
        // If no calorie value or a negative calorie value was specified
        // for this particular object...
        if (initialCalories <= 0) 
        {
          // ...use the default value
          initialCalories = Apple.DEFAULT_CALORIES;
        }
        
        super(initialCalories);
        
        wormInApple = Math.random() >= .5;
        
        // Set the food name for all Apple objects
        setName("Apple");
      }
      
      public function hasWorm ()
      {
        return wormInApple;
      }
    }
  }
  
  // Sushi class
  package zoo 
  {
    public class Sushi extends Food 
    {
      private static var DEFAULT_CALORIES = 500;
      
      public function Sushi (initialCalories = 0) 
      {
        if (initialCalories <= 0) 
        {
          initialCalories = Sushi.DEFAULT_CALORIES;
        }
        
        super(initialCalories);
        
        setName("Sushi");
      }
    }
  } 

Grazie