一道关于面向对象面试题

//车辆类class Car {  constructor(num) {    this.num = num;  }}

//摄像头类class Camera {  constructor() {}  shot(car) {    return {      num: car.num,      inTime: Date.now()    };  }}

//显示屏类class Screen {  constructor() {}  show(car, inTime) {    console.log('车牌号：', car.num);    console.log('停车时间：', Date.now() - inTime);  }}
//停车场类class Park {  constructor(floors) {    this.floors = floors || [];    this.carList = {}; //存储摄像头拍摄返回的车辆信息    this.camera = new Camera(); //摄像头    this.screen = new Screen();  }  in(car) {    // 通过摄像头获取车辆进入信息    const info = this.camera.shot(car);    // 停到某个车位，这里取随机数    const i = parseInt((Math.random() * 100) % 100);    // 先假设位于一层的该车位    const place = this.floors[0].places[i];    place.in();    info.place = place;    //记录信息    this.carList[car.num] = info;  }  out(car) {    //获取信息    const info = this.carList[car.num];    //将车位清空    const place = info.place;    place.out();    //显示时间    this.screen.show(car, info.inTime);    //清空记录    delete this.carList[car.num];  }  emptyNum() {    return this.floors      .map(floor => {        return `${floor.index} 层还有 ${floor.emptyPlaceNum()}个空闲车位`;      })      .join('\n');  }}

// 层类class Floor {  constructor(index, places) {    this.index = index;    this.places = places || [];  }  emptyPlaceNum() {    let num = 0;    this.places.forEach(p => {      if (p.empty) num++;    });    return num;  }}

//车位类class Place {  constructor() {    this.empty = true;  }  in() {    this.empty = true;  }  out() {    this.empty = false;  }}