自写的代码，请大神们多多指教

测试类：

package com.carcrental;

import java.util.Scanner;

public class Test {

private static final String NULL = null;

private static Scanner input;

public static void main(String[] args) {

// TODO Auto-generated method stub

for(;;){

System.out.println("欢迎使用答答租车系统！");

System.out.println("您是否需要租车：1是  0否");

input = new Scanner(System.in);

int i=input.nextInt();

if(i==1){

System.out.println("您可租车的类型及其价目表：");

Car[] carForRent={new PersonCar(1,"奥迪A4",500,4),new PersonCar(2,"马自达6",400,4),

                    new Pickup(3,"皮卡雪6",450,4,2),new PersonCar(4," 金龙 ",800,20),

                    new Truck(5,"松花江",400,4),new Truck(6,"依维柯",1000,20)};

System.out.println("序号"+"\t"+"汽车名称"+"\t"+"租金"+"\t"+"容量");

//遍历Car类

for(Car car : carForRent){

 if(car instanceof PersonCar){

                   //若它是客车类型的实例，则打印出客车应该有的属性值，这里注意强转，否则不会出现

                   //passengerCar类的CarCapacity属性

                   System.out.println(car.getCarNumber()+"\t"+car.getCarName()+"\t"+car.getCarPrice()

                                                 +"/天"+"\t"+"载人:"+((PersonCar)car).getCarCapacity()+"人");

               }

               if(car instanceof Pickup){

                   System.out.println(car.getCarNumber()+"\t"+car.getCarName()+"\t"+car.getCarPrice()

                                                 +"/天"+"\t"+"载人:"+((Pickup)car).getCarCapacity()+"人"+"\t"

                                                 +"载货:"+((Pickup)car).getCarrayingCapacity()+"吨");

               }

               if(car instanceof Truck){

                   System.out.println(car.getCarNumber()+"\t"+car.getCarName()+"\t"+car.getCarPrice()

                                                 +"/天"+"\t"+"载货:"+((Truck)car).getCarryingCapacity()+"吨");

               }

           }

System.out.print("请输入你租车的数量：");

int totalNum=input.nextInt(); //用于接收汽车的总数量

String[] name=new String[totalNum];

String[] name2=new String[totalNum];

int capacitySum=0;//总人数

int ccapacitySum=0;//总载货量

int sum=0;//用于接收租车的总价格

for(int i1=0;i1<totalNum;i1++){

System.out.print("请输入第"+(i1+1)+"辆车的序号：");

int num=input.nextInt();

System.out.print("请输入租这辆车的天数：");

int day=input.nextInt();

switch(num){

case 1:sum=sum+carForRent[num-1].getCarPrice()*day;

capacitySum=capacitySum+4;

break;

case 2:sum=sum+carForRent[num-1].getCarPrice()*day;

capacitySum=capacitySum+4;

break;

case 3:sum=sum+carForRent[num-1].getCarPrice()*day;

capacitySum=capacitySum+4;

ccapacitySum=ccapacitySum+2;

break;

case 4:sum=sum+carForRent[num-1].getCarPrice()*day;

capacitySum=capacitySum+20;

break;

case 5:sum=sum+carForRent[num-1].getCarPrice()*day;

ccapacitySum=ccapacitySum+4;

break;

case 6:sum=sum+carForRent[num-1].getCarPrice()*day;

ccapacitySum=ccapacitySum+20;

break;

}

if(carForRent[num-1] instanceof PersonCar){

name[i1]=carForRent[num-1].getCarName();

}else if(carForRent[num-1] instanceof Pickup){

name[i1]=carForRent[num-1].getCarName();

name2[i1]=carForRent[num-1].getCarName();

}else if(carForRent[num-1] instanceof Truck){

name2[i1]=carForRent[num-1].getCarName();

}

}

System.out.println("载人的车有：");

for(String n:name){

if(n==NULL){

continue;

}

System.out.print(n);

System.out.print("\t");

}

System.out.println("***可以乘坐人数："+capacitySum+"人");

for(String n2:name2){

if(n2==NULL){

continue;

}

System.out.print(n2);

System.out.print("\t");

}

System.out.println("***可载货："+ccapacitySum+"吨");

System.out.println("***你一共需要支付："+sum);

}else if(i==0){

System.out.println("欢迎下次使用！");break;

}

else{

System.out.println("你输入有误！请重新输入！");

}

System.out.println("\n");

System.out.println("\n");

}

}

/*if(i==1){

System.out.println("序号             汽车名称     租金            容量");

System.out.println(1+"\t"+p1.getCarName()+"\t"+p1.getCarPrice()+"元/天"+"\t"+"载人："+p1.getCarCapacity()+"人");

System.out.println(2+"\t"+p2.getCarName()+"\t"+p2.getCarPrice()+"元/天"+"\t"+"载人："+p2.getCarCapacity()+"人");

System.out.println(3+"\t"+p3.getCarName()+"\t"+p3.getCarPrice()+"元/天"+"\t"+"载人："+p3.getCarCapacity()+"人;"+"载货："+p3.getCarrayingCapacity()+"吨");

System.out.println(4+"\t"+p4.getCarName()+"\t"+p4.getCarPrice()+"元/天"+"\t"+"载人："+p4.getCarCapacity()+"人");

System.out.println(5+"\t"+p5.getCarName()+"\t"+p5.getCarPrice()+"元/天"+"\t"+"载货："+p5.getCarryingCapacity()+"吨");

System.out.println(6+"\t"+p6.getCarName()+"\t"+p6.getCarPrice()+"元/天 载货："+p6.getCarryingCapacity()+"吨");

}

System.out.print("请输入你租车的数量：");

int a=input.nextInt();

int sum=0;

for(int b=0;b<a;b++){

System.out.print("请输入你想租的车的序号：");

int c=input.nextInt();

System.out.print("请输入租这辆车的天数：");

int day=input.nextInt();

switch(c){

case 1:sum=sum+p1.getCarPrice()*day;break;

case 2:sum=sum+p2.getCarPrice()*day;break;

case 3:sum=sum+p3.getCarPrice()*day;break;

case 4:sum=sum+p4.getCarPrice()*day;break;

case 5:sum=sum+p5.getCarPrice()*day;break;

case 6:sum=sum+p6.getCarPrice()*day;break;

}

}

System.out.println("你一共需要支付："+sum);*/

}

Car类：

package com.carcrental;

//所有汽车的父类

public class Car {

private int carNumber;

private String carName;

private int carPrice;

public Car(int carNumber,String carName,int carPrice){

this.carNumber=carNumber;

this.carName=carName;

this.carPrice=carPrice;

}

public int getCarNumber() {

return carNumber;

}

public void setCarNumber(int carNumber) {

this.carNumber = carNumber;

}

public String getCarName() {

return carName;

}

public void setCarName(String carName) {

this.carName = carName;

}

public int getCarPrice() {

return carPrice;

}

public void setCarPrice(int carPrice) {

this.carPrice = carPrice;

}

}

载人车类：

package com.carcrental;

public class PersonCar extends Car{

private int carCapacity;

public PersonCar(int carNumber,String carName,int carPrice,int carCapacity){

super(carNumber,carName,carPrice);

/*this.setCarNumber(carNumber);

this.setCarName(carName);

this.setCarPrice(carPrice);*/

this.carCapacity=carCapacity;

}

public int getCarCapacity() {

return carCapacity;

}

public void setCarCapacity(int carCapacity) {

this.carCapacity = carCapacity;

}

}

皮卡车：

package com.carcrental;

//皮卡类，继承了父类Car

public class Pickup extends Car{

private int carCapacity;

private int carrayingCapacity;

//构造函数

public Pickup(int carNumber,String carName,int carPrice,int carCapacity,int carrayingCapacity){

super(carNumber,carName,carPrice);

/*this.setCarNumber(carNumber);

this.setCarName(carName);

this.setCarPrice(carPrice);*/

this.carCapacity=carCapacity;

this.carrayingCapacity=carrayingCapacity;

}

//封装过后必须有出口

public int getCarCapacity() {

return carCapacity;

}

public void setCarCapacity(int carCapacity) {

this.carCapacity = carCapacity;

}

public int getCarrayingCapacity() {

return carrayingCapacity;

}

public void setCarrayingCapacity(int carrayingCapacity) {

this.carrayingCapacity = carrayingCapacity;

}

}

货车：

package com.carcrental;

public class Truck extends Car{

private int carryingCapacity;

public Truck(int carNumber,String carName,int carPrice,int carryingCapacity){

super(carNumber,carName,carPrice);

/*this.setCarNumber(carNumber);

this.setCarName(carName);

this.setCarPrice(carPrice);*/

this.carryingCapacity=carryingCapacity;

}

public int getCarryingCapacity() {

return carryingCapacity;

}

public void setCarryingCapacity(int carryingCapacity) {

this.carryingCapacity = carryingCapacity;

}

}