An example to demonstrate animal classification system in Java 1.8.x.

AnimalClassfication.java

class Animal { }

class Reptile extends Animal { }
class Bird extends Animal { }

interface MobileLife {
  // Every classes derived from this interface should implement common features on it.
  void move(double displacement);

  double getDistance();
};

interface Swimmer extends MobileLife {
  default void swim() {
    move(getSwimDistance());
  }

  double getSwimDistance();
};

interface Walker extends MobileLife {
  default void walk() {
    move(getWalkDistance());
  }

  double getWalkDistance();
}

class Duck extends Bird implements Swimmer, Walker {
  /// {{{ Duplicate code could be found in class Turtle
  private double distance = 0.0d;

  @Override
  public void move(double displacement) {
    distance += displacement;
    System.out.println("I moved " + distance + " metres.");
  }

  public double getDistance() {
    return distance;
  }
  /// }}}

  @Override
  public double getWalkDistance() {
    return 0.05D;
  }

  @Override
  public double getSwimDistance() {
    return 0.1D;
  }
}

class Turtle extends Reptile implements Swimmer, Walker {
  /// {{{ Duplicate code could be found in class Duck
  private double distance = 0.0d;

  @Override
  public void move(double displacement) {
    distance += displacement;
    System.out.println("I moved " + distance + " metres.");
  }

  public double getDistance() {
    return distance;
  }
  /// }}}
  
  private int walkedTimes = 0;

  @Override
  public double getWalkDistance() {
    walkTimes++;
    if (walkedTimes % 10 == 0) {
      return 0.001D;
    } else {
      return 0.0D;
    }
  }

  @Override
  public double getSwimDistance() {
    return 0.5D;
  }
};

class Main {
  public static void main(String[] args) {
    final Duck duck = new Duck();
    duck.walk();
    duck.swim();
  
    final Turtle turtle = new Turtle();
    turtle.swim();
    for(int i = 0; i < 10; i++) {
      turtle.walk();
    }
  }
}

/*
 * Result:
 * Duck says:
 * 
 * I moved 0.05 metres.
 * I moved 0.15000000000000002 metres.
 *
 * Turtle says:
 * I moved 0.5 metres.
 * I moved 0.5 metres.
 * I moved 0.5 metres.
 * I moved 0.5 metres.
 * I moved 0.5 metres.
 * I moved 0.5 metres.
 * I moved 0.5 metres.
 * I moved 0.5 metres.
 * I moved 0.5 metres.
 * I moved 0.5 metres.
 * I moved 0.501 metres.
 * I moved 0.501 metres.
*/