public class Student {

   public String name; // 直接暴露属性

   public void study() { ... }

}

class Animal {

   void sound() { System.out.println("Animal sound"); }

}

class Dog extends Animal {

   void sound() { System.out.println("Bark"); }

}

public class Test {

   public static void main(String[] args) {

       Animal a = new Dog();

       a.sound();

   }

}

class Animal {

   void sound() { System.out.println("Animal sound"); }

}

class Dog extends Animal {

   void sound() { System.out.println("Bark"); }

}

public class Test {

   public static void main(String[] args) {

       Animal a = new Dog();

       a.sound();

   }

}