4、多态

根据传入的对象动态决定调用谁的方法

interface Animal1{
    eat():void
}
class Cat implements Animal1{
    eat():void{
        console.log("鱼");
    }
}
class Dog implements Animal1{
    eat():void{
        console.log("狗粮")
    }
}
class Farmer{
    feed(obj:Animal1){
        obj.eat();
    }
}
var f:Farmer = new Farmer()
f.feed(new Cat())
f.feed(new Dog())