Java向上转型和向下转型

 class Animal{
	public void eat(){
		System.out.println("eating...");
	}
}
class Cat extends Animal{	
	public void eat(){
		System.out.println("Cat eatting...");
	}	
	public void miao(){
		System.out.println("Cat miao~");
	}
} 

class Human {
	public void sleep() {
		System.out.println("sleep.");
	}
}
class Male extends Human{
	public void sleep() {
		System.out.println("Male sleep.");
	}
}
class Female extends Human {
	public void sleep(){
		System.out.println("Female sleep.");
	}
}

public class Main{
public static void main(String[] args) {

    //向上转型
	Animal cat = new Cat(); 
	cat.eat();     //输出Cat eatting...
	cat.miao();     //报错ClassCastException类型转换异常
    //b虽指向子类对象，但此时子类作为向上的代价丢失和父类不同的miao()方法

    //传入的参数是子类
	sleep(new Male());//输出Male sleep.
	sleep(new Female());//输出Female sleep.
}
	
public static void sleep(Human h){ //方法的参数是父类        
 	h.sleep();
}
}                        

class Fruit{
	public void myName(){
		System.out.println("Fruit...");
	}
}
 
class Apple extends Fruit{ 
	public void myName() { 
		System.out.println("Apple...");
	}
	public void myMore(){
		System.out.println("An apple a day keeps the doctor away.");
	}
}
 
public class Main{ 
public static void main(String[] args) { 
    //向上转型
	Fruit f=new Apple(); 
	f.myName();//输出Fruit...
		
    //向下转型
    //f指向子类的对象，子类的实例a也指向f,向下转型后因为都是指向子类对象，调用的全是子类的方法
	Apple a=(Apple)f; 
	a.myName();
	a.myMore();
		 
    //向下转型之前必须进行向上转型 
    //编译无错但会运行会出错ClassCastException，子类aa不能指向父类ff
	Fruit ff=new Fruit();
    //对象名A instanceof 类名B ，判断这个对象A是否是属于这个类B或是其子类 
    if(ff instanceof aa){
        Apple aa=(Apple)ff; 
  	    aa.myName();
  	    aa.myMore(); 
    }
    else {
        System.out.println("不能进行向下类型转换");
    }
}
}