面向对象之多态

abstract class Animal {
    public abstract void eat();
}
class Cat extends Animal {
    public void eat() {
        System.out.println("吃鱼");
    }
    public void catchMouse() {
        System.out.println("抓老鼠");
    }
}
class Dog extends Animal {
    public void eat() {
        System.out.println("吃骨头");
    }
    public void KanJia() {
        System.out.println("看家");
    }
}
class Pig extends Animal {
    public void eat() {
        System.out.println("饲料");
    }
    public void gongDi() {
        System.out.println("拱地");
    }
}
//-----------------------------------------------------------
public class PolDemo {

    public static void main(String[] args) {
//        Cat c = new Cat();
//        c.eat();
//        
//        Dog d = new Dog();
//        d.eat();
//        Cat c = new Cat();
//        function(c);
//        
//        function(new Dog());
//        
//        function(new Pig());
        
//        Animal c = new Cat();
//        c.eat();
        
        Animal a = new Cat();//类型提升。向上转型
        a.eat();
        
        //如果想要调用猫的特有方法时，如何操作？
        //强制将父类的引用转成子类类型，向下转型
        Cat c = (Cat)a;
        c.catchMouse();
        
        /*
         * 千万不要出现这样的操作，就是将父类对象转成子类类型
         * 我们能转换的是父类引用指向了自己的子类对象时，该引用可以被提升，也可以被强制转换
         * 多态自始至终都是子类对象在做着变化
         * Animal a = new Animal();
         * Cat c = (Cat)a;
         * 
         */
//        function(new Cat());
//        function(new Dog());
//        function(new Pig());
        
    }
    
    public static void function(Animal a) { //Animal a = new Cat();
        a.eat();
//        a.catchMouse();
        /*if(a instanceof Animal) {
            System.out.println("hello");
        } else*/ if(a instanceof Cat) {
            Cat c = (Cat)a;
            c.catchMouse();
        } else if(a instanceof Dog) {
            Dog d = (Dog)a;
            d.KanJia();
        }
        
    }
    /*
    public static void function(Cat c) { //Cat c = new Cat();
        c.eat();
    }
    
    public static void function(Dog d) {
        d.eat();
    }
    
    public static void function(Pig p) {
        p.eat();
    }
    */
}

abstract class Student {
    public abstract void study();
    public void sleep() {
        System.out.println("躺着睡");
    }
}
//工具类
class DoStudent {
    public void doSomething(Student s) {
        s.study();
        s.sleep();
    }
}
//--------------------------------------------------------------
class BaseStudent extends Student {
    public void study() {
        System.out.println("base study");
    }
    public void sleep() {
        System.out.println("坐着睡");
    }
}
class AdvStudent extends Student {
    public void study() {
        System.out.println("adv study");
    }
}

public class DuoTaiDemo {

    public static void main(String[] args) {
        DoStudent ds = new DoStudent();
        ds.doSomething(new BaseStudent());
        ds.doSomething(new AdvStudent());
//        BaseStudent bs = new BaseStudent();
//        bs.study();
//        bs.sleep();
//        AdvStudent as = new AdvStudent();
//        as.study();
//        as.sleep();
    }
    
}