public class Animal {

     public void eat(){

          System.out.println("animal eatting...");

     }

}

class Bird extends Animal{

     public void eat(){

          System.out.println("bird eatting...");

     }

     public void fly(){

          System.out.println("bird flying...");

     }

}

class Main{   

     public static void main(String[] args) {

          Animal b=new Bird(); //向上转型

          b.eat();

     b.fly(); //此处提示在Animal中没有定义fly方法。

｝

public class Girl {

     public void smile(){

          System.out.println("girl smile()...");

     }

}

class MMGirl extends Girl{

          @Override

     public void smile() {

                   System.out.println("MMirl smile sounds sweet...");

     }

     public void c(){

          System.out.println("MMirl c()...");

     }

}

class main{

          public static void main(String[] args) {

          Girl g1=new MMGirl(); //向上转型

          g1.smile();

          MMGirl mmg=(MMGirl)g1;  //向下转型,编译和运行皆不会出错

          mmg.smile();

          mmg.c();

          Girl g2=new Girl();

      //MMGirl mmg1=(MMGirl)g2; //不安全的向下转型,编译无错但会运行会出错

      //mmg1.smile();

      //mmg1.c();

          if(g2 instanceof MMGirl){

              MMGirl mmg1=(MMGirl)g2;

              mmg1.smile();

              mmg1.c();

          }

     }