package day803;
//汽車總類
public abstract class MotoVehicle {
     private int day;
     private String Brand;
     private String Color;
     private String No;
     private int dayMony;
     public void CalcRent(int day) {
        this.day = day;
    }
    public int getDay() {
        return
 
 day;
    }
    public void setDay(int day) {
        this.day = day;
    }
    public String getBrand() {
        return Brand;
    }
    public void setBrand(String brand) {
        Brand = brand;
    }
    public String getColor() {
        return Color;
    }
    public void setColor(String color) {
        Color = color;
    }
    public
 
 String getNo() {
        return No;
    }
    public void setNo(String no) {
        No = no;
    }
    public int getDayMony() {
        return dayMony;
    }
    public void setDayMony(int dayMony) {
        this.dayMony = dayMony;
    }
    public abstract int dayMoney();

    public int money() {
        int
 
 money = day*dayMony;
        return money;
    }
}

package day803;
//客車類
public class Bus extends MotoVehicle {
    private int SeatCount;

    public Bus(int day, int SeatCount) {
        this.SeatCount = SeatCount;
        setDay(day);
    }

    public int dayMoney() {
        int money = 0;
        if (SeatCount > 16) {
            setDayMony(1500);
        } else {
            setDayMony(800);
        }
        return getDayMony();
    }
}

package day803;
//轎車類
public class Car extends MotoVehicle{
    private String Type;
    public Car( int day ,String type) {
        setDay(day);
        this.Type = type;
    }
    public int dayMoney() {
        int money = 0;
        if (Type.equals("別克商務車")) {
            setDayMony(600);
        }else if (Type.equals("寶馬")) {
            setDayMony(500);
        }else if (Type.equals("別克林萌大道")) {
            setDayMony(300);
        }
        return getDayMony();
    }

}

package day803;
//測試類
import java.util.Scanner;

public class Rent {

    public static void main(String[] args) {
        System.out.println("請輸入您想租的車,car/bus");
        Scanner scanner = new Scanner(System.in);
        String cartype = scanner.next();
        int money = 0;
        if (cartype.equals("car")) {
            System.out.println("請輸入您想租的車型：1，別克商務車。2，寶馬。3，別克林萌大道");
            int key = scanner.nextInt();
            System.out.println("請輸入租用天數");
            int day = scanner.nextInt();
            Car car = null;
            switch (key) {
            case 1:
                car = new Car(day, "別克商務車");
                car.dayMoney();
                car.setDay(day);
                money = car.money();
                break;
            case 2:
                car = new Car(day, "寶馬");
                car.dayMoney();
                car.setDay(day);
                money = car.money();
                break;
            case 3:
                car = new Car(day, "別克林萌大道");
                car.dayMoney();
                car.setDay(day);
                money = car.money();
                break;
            default:
                System.out.println("輸入錯誤");
                break;
            }
        } else if (cartype.equals("bus")) {
            System.out.println("請輸入您想租的車型：1。16座以上。2。16座以下");
            int key = scanner.nextInt();
            System.out.println("請輸入租用天數");
            int day = scanner.nextInt();
            Bus bus = null;
            switch (key) {
            case 1:
                bus = new Bus(day, 17);
                bus.dayMoney();
                bus.setDay(day);
                money = bus.money();
                break;
            case 2:
                bus = new Bus(day, 15);
                bus.dayMoney();
                bus.setDay(day);
                money = bus.money();
                break;

            default:
                System.out.println("輸入錯誤");
                break;
            }
        }
        System.out.println("您的租金為" + money);
    }
}

總結：

第一次測試時發現租賃天數沒有傳過來。檢查了一遍後。加上.setDay(day)即可