多态

父类的引用指向子类的对象

方法只能使用父类的

public class Exec{
  public static void main(String[] args){
    Animal ani = new Dog( );
    // ani 只能调用方法sound 和 run
    ani.sound( );
    ani.run( );
  }
}

class Animal{
  void sound( ){
    System.out.println("Sound");
  }
  
  void run( ){
    System.out.println("Run");
  }
}

class Dog{
  void sound( ){
    System.out.println("Barf");
  }
  
  void eat( ){
    System.out.println("Bone");
  }
}

如果想调用子类的方法,则需要强制转换类型

public class Exec{
  public static void main(String[] args){
    Animal ani = new Dog( );
    // ani.sound( ) 输出打印Barf而不是Sound
    ani.sound( );
  }
}

class Animal{
  void sound( ){
    System.out.println("Sound");
  }
  
  void run( ){
    System.out.println("Run");
  }
}

class Dog{
  void sound( ){
    System.out.println("Barf");
  }
  
  void eat( ){
    System.out.println("Bone");
  }
}

如果子类重写了父类的方法, 则执行子类的方法

public class Exec{
  public static void main(String[] args){
    Animal ani = new Dog( );
    // ani 如果想调用eat,则需要首先强制类型转换策成Dog类
    (Dog)ani.eat( );
  }
}

class Animal{
  void sound( ){
    System.out.println("Sound");
  }
  
  void run( ){
    System.out.println("Run");
  }
}

class Dog{
  void sound( ){
    System.out.println("Barf");
  }
  
  void eat( ){
    System.out.println("Bone");
  }
}