请问可以帮我看看这个接口的代码怎么完善吗

问题遇到的现象和发生背景

第二张图片是输出格式样例

用代码块功能插入代码，请勿粘贴截图

运行结果及报错内容

package Demo;
interface CarRent{
    int day=0;
    void carRent(int carfee, int day);
}
interface truckRent extends CarRent{
    int day=0;
     void truckRent(double ton,int day);
}
class Rent implements truckRent{
    public String number;
    public String brand;
    public int day;
    public int carfee;
    public int dailyfee;
    public double ton;
    public double truckfee;
    public double fee;
    public String client;
    Rent(String number,String brand){
        this.number=number;
        this.brand=brand;
    }
    @Override
    public void carRent(int carfee,int day) {
        // TODO Auto-generated method stub
        carfee=day*dailyfee;
    }
    @Override
    public void truckRent(double ton,int day) {
        // TODO Auto-generated method stub
        truckfee=day*dailyfee*ton;
        fee=carfee+truckfee;
    }
    public  String info() {
        String info=this.number+this.brand;
        return info;
    }
    public String clientinfo(String client) {
        String clientinfo = client;
        return clientinfo;
    }
    public int dayinfo(int day) {
        int dayinfo=day;
        return dayinfo;
    }
    public double getfee(int carfee,double truckfee) {
        fee=truckfee+carfee;
        return fee;
    }
}

public class App_4 {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        CarRent[] cr=new CarRent[6];
        cr[0]=new Rent("京A123","本田CRV");
        cr[1]=new Rent("京B123","福特");
        cr[2]=new Rent("京C123","本田HRV");
        cr[3]=new Rent("京D123","小客车");
        cr[4]=new Rent("京E123","大客车");
        cr[5]=new Rent("京F123","卡车");
        for(CarRent c:cr)
            System.out.println(((Rent) c).info());
        Rent c=null;
        System.out.print("客户名："+c.clientinfo("沈伟")+"天数："+c.dayinfo(1));
        
        
        

    }

}

我的解答思路和尝试过的方法

我想的是写一个汽车父接口，有轿车和客车；再加一个卡车的子接口；然后实现这两个接口。
输出的时候用数组输出车牌号和型号，但是我这样参数介绍车牌号和型号，
1.不知道应该在哪里给租金赋值了，
2.构造方法应该写几个参数呢
3.像客户，天数这两个参数应该在哪赋值呢

public class Test2 {


    public static void main(String[] args) {
        List<Car> list = new ArrayList<>();
        list.add(new BenTian("粤A123465", 5));
        list.add(new BenTian("粤A123477", 5));
        list.add(new FuTe("京A123465", 4));
        list.add(new KeChe("湘A155555", 5, false));
        list.add(new KeChe("湘A150000", 2, true));
        list.add(new KaChe("粤B123465", 5, 50));
        list.add(new KaChe("粤C123465", 5, 70));
        User user=new User("张三",list);
        user.costAll();

    }


}

class User {
    private String name;//姓名
    private List<Car> cars;//租赁汽车集合

    public User(String name, List<Car> cars) {
        this.name = name;
        this.cars = cars;
    }

    /**
     * 计算价格
     *
     * @param list 租赁汽车集合
     * @param day  租赁天数
     * @return
     */
    public int costAll() {
        int price = 0;
        for (Car car : cars) {
            price += car.cost();
        }
        System.out.println("客户名："+name+"，租赁费用："+price+"元");
        return price;
    }
}

//汽车抽象类
abstract class Car {

    //车牌号
    private String number;

    private String name;

    //租赁天数
    private int day;

    public Car(String number, int day) {
        this.number = number;
        this.day = day;
    }

    //获取日单价
    abstract int getPrice();

    protected void setName(String name) {
        this.name = name;
    }

    int cost() {
        int  total=getPrice() * day;
        String log = "车牌号："+number+",汽车类型："+name+"，日单价："+getPrice()+"元,租赁天数："+day+",总价:"+total+"元";
        System.out.println(log);
        return total;
    }


}

//本田
class BenTian extends Car {

    //日单价
    private static final int UNIT_PRICE = 500;

    public BenTian(String number, int day) {
        super(number, day);
        this.setName("本田");

    }


    @Override
    int getPrice() {
        return UNIT_PRICE;
    }
}

//福特
class FuTe extends Car {

    //日单价
    private static final int UNIT_PRICE = 600;

    public FuTe(String number, int day) {
        super(number, day);
        this.setName("福特");
    }


    @Override
    int getPrice() {
        return UNIT_PRICE;
    }
}


//客车
class KeChe extends Car {

    //是否小于16座
    private boolean isLt16;
    //小于16座日单价
    private static final int LT_16_UNIT_PRICE = 800;

    //大于16座日单价
    private static final int GT_16_UNIT_PRICE = 1000;

    public KeChe(String number, int day, boolean isLt16) {
        super(number, day);
        this.isLt16 = isLt16;
        if (isLt16) {
            this.setName("客车(小于16座)");
        } else {
            this.setName("客车(大于等于16座)");
        }
    }

    @Override
    int getPrice() {
        return isLt16 ? LT_16_UNIT_PRICE : GT_16_UNIT_PRICE;
    }
}


//卡车
class KaChe extends Car {

    //吨
    private int ton;

    //日单价
    private static final int UNIT_PRICE = 50;

    public KaChe(String number, int day, int ton) {
        super(number, day);
        this.ton = ton;
        this.setName("客车（" + ton + "吨）");
    }

    @Override
    int getPrice() {
        return ton * UNIT_PRICE;
    }
}

简单写了下，可优化，不一定要用这种方式