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"Variables Have Types, Objects Have Classes"
Vol. 2, Issue 4, p. 29

	

Listing 1

public abstract class Animal
{
   public abstract String movement();
}


public class Fish extends Animal
             implements WaterDweller
{
   public String movement()
   {   return "swim";
   }
}


public class Salmon extends Fish
{
   public void jump()
   {   System.out.println( "Jump" );
   }
}


public class GoldFish extends Fish
             implements FreshWaterDweller
{
}


public class Mammal extends Animal
{
   public String movement()
   {   return "quadraped";
   }
}


public class Dog extends Mammal
{
}


public class Whale extends Mammal
             implements SaltWaterDweller
{
   public String movement()
   {   return "swim";
   }
}

Listing 2

public interface WaterDweller
{
}


public interface FreshWaterDweller
       extends WaterDweller
{
}


public interface SaltWaterDweller
       extends WaterDweller
{
}


 

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