11.多态

根据传入的对象,动态决定调用谁的方法

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