程序运行时，总是有两句出错（后有注释的），不明白问题在哪，希望哪位高手可以告知，多谢

package 同类;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
public class Car {
public  Set<Car> menu;
public String Number;
public String Name;
public String People;
public int Price;
public String Carrier;
public String Days;
public Car(){

}
public Car(String number,String name,String carrier,String people,int price){
this.Number=number;
this.Name=name;
this.Carrier=carrier;
this.People=people;
this.Price=price;
this.menu=new HashSet<Car>();
}
}
package 同类;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Xuanche {
public List<Car> xuan;
public Car xc;
Scanner console=new Scanner(System.in);
public int shuliang;
public Xuanche(){
this.xuan=new ArrayList<Car>();
}
public void adamenu(){
Car c1=new Car("1","奥迪A4","0","4",200);
xuan.add(c1);
Car c2=new Car("2","马自达6","0","4",300);
xuan.add(1, c2);
Car c3=new Car("3","皮卡","30","0",150);
xuan.add(2,c3);
Car c4=new Car("4","金龙","60","0",100);
xuan.add(3,c4);
Car c5=new Car("5","松花江","20","8",200);
xuan.add(4,c5);
Car c6=new Car("6","依维柯","10","8",300);
xuan.add(5,c6);
System.out.println("欢迎进入选车系统！下面是选车列表：");
for(Object obj:xuan){
Car che=(Car)obj;
System.out.println(che.Number+"、"+che.Name+"   "+che.Carrier+"   "+che.People+"   "+che.Price);
}
}
public void enter(){
int str=console.nextInt();
switch(str){
case 1:adamenu();break;
case 2:return;
default:System.out.println("输入错误，请重新输入！");return;
}
}
public void showinfo(){
xc=new Car();
System.out.println("请输入要选车的数量：");
shuliang=console.nextInt();
System.out.println("您选择了"+shuliang+"辆车");
for(int i=0;i<shuliang;i++){
System.out.println("请输入要选择的车辆的编号");
String num=console.next();
for(Car cc:xuan){
//Car qqq=(Car)cc;
if(cc.Number.equals(num)){
xc.menu.add(cc);//这句到底出了什么问题
}
}
}
foreach(xc);
for(Car zz:xc.menu){
Car car=(Car)zz;
System.out.println("您选择了："+car.Number+"       "+car.Name+"      "+car.Carrier+"     "+car.People+"     "+car.Price);
}
System.out.println("您一共选择了"+xc.menu.size()+"辆车");
System.out.println("请输入租借天数：");
int days=console.nextInt();
System.out.println("总计价钱为："+price()*days);
}
public int price(){
int price=0;
for(Car aa:xc.menu){
price+=aa.Price;
}
return price;
}
public void foreach(Car ca){
for(Car zz:ca.menu){
// Car car=(Car)zz;
System.out.println("您选择了："+zz.Number+"       "+zz.Name+"      "+zz.Carrier+"     "+zz.People+"     "+zz.Price);
}
}
public static void main(String[] args) {
// TODO Auto-generated method stub
Xuanche pp=new Xuanche();
System.out.println("欢迎进入选车系统！是否要进行选车？");
System.out.println("1、进入                                            2、退出");
pp.enter();
//pp.adamenu();
pp.showinfo();
}
}