public class Animals
{
  public static void main(String args[])
  {
    Pet myPets[] = new Pet[4];
    myPets[0] = new Duck();
    myPets[1] = new Cat();
    myPets[2] = new Duck();
    myPets[3] = new Dog();

    for (int index=0; index<4; index++)
      myPets[index].speak();
  }
}