abstract class Animal {
  String name;   // The human name for the animal, not some secret animal name.
  String sound;  // What sound does it vocalize?
  int age;
  
  /** Constructor.
   * @param _name the name of the animal.
   * @param _sound what sound the animal makes.   
   */
  Animal( String _name, String _sound ) {
    name  = _name;
    sound = _sound;
    age = 0;
    }

  public int  getAge() { return this.age; }
  public void setAge( int _age ) { this.age = _age; }
  
  public String toString() {
    return this.name + " says " + this.sound;
    }
    
  /** When the animal wants to bug a human, it says...
   * @return The sound of the animal, bugging its owner.
   */
  public String speak() {
    return name + ": " + sound + ", " + sound + ".";
    }


  /** Test: overriding "speak".
   */
  public static void test2() {
    System.out.println( "====" );
    System.out.println( "Testing Inheritance:" );

    System.out.println( new Cat("Bartok").speak() );
    System.out.println( new Dog("Beethoven").wagTail() );
    System.out.println( new Dog("Phydeaux").speak() );
    System.out.println( new Python().speak() );
    }

  /** Test: polymorphism.
   */
  public static void test4() {
    System.out.println( "====" );
    System.out.println( "Testing polymorphism (w/ small dogs): " );

    Animal[] zoo = { new Cat("Bartok"),
                     new Dog("Beethoven"),
                     new SmallDog("Phydeaux"),
                     new Python()
                   };

    // Demonstrate polymorphism:
    // In the loop, "critter" is of (declared) type Animal,
    // yet Dog's specialized speak() is still getting used.
    //
    System.out.println( "Polymorphism:" );
    for ( Animal critter : zoo ) {
      System.out.println( critter.speak() );
      }

    }

  }