1. interface Animal{
    2.     name:string
    3.     age:number
    4. }
    5. interface Dog extends Animal{
    6.     eat(str:string):void;
    7. }
    8. class WolfDog implements Dog{
    9.     name:string;
    10.     age: number;
    11.    eat(str:string):void{
    12.        console.log(str);
    13.    }
    14.    constructor(name:string,age:number){
    15.        this.name=name;
    16.        this.age=age
    17.    }
    19. }
    20. var w:WolfDog=new WolfDog('狗',8)