為了方便理解，畫了個UML圖，可以參考一下為了方便理解，畫了個UML圖，可以參考一下

定義Car類型：載人+載貨

public class Car {
	int id;
	String name;
	int seat;
	double load;
	double price;
	public Car(int id,String name,int seat,double load,double price){
		this.id = id;
		this.name = name;
		this.seat = seat;
		this.load = load;
		this.price = price;
	}
	public String toString(){
		return id+"\t"+name+"\t"+seat+"座\t"+load+"噸\t"+price+"元";
	}
}

定義LoadCar繼承Car，重寫構造方法（載貨，則座位=0）

public class LoadCar extends Car {
	public LoadCar(int id,String name,double load,double price){
		super(id,name,0,load,price);
	}
	public String toString(){
		return id+"\t"+name+"\t"+seat+"\t"+load+"\t"+price;
	}
}

`定義SeatCar繼承Car,重寫構造方法（載人，則載貨=0）

public class SeatCar extends Car {
	public SeatCar(int id,String name,int seat,double price){
		super(id,name,seat,0,price);
	}
	public String toString(){
		return id+"\t"+name+"\t"+seat+"\t"+load+"\t"+price;
	}
}

實現（主要就是業務流程）：

import java.util.Scanner;;

public class Initail {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		System.out.println("您是否要租車？1、是；2、否");
		Scanner in = new Scanner(System.in);
		if(in.nextInt()==1){
			Car[] cars = new Car[5];
			cars[0]=new SeatCar(1,"奧迪A8",4,400);
			cars[1]=new SeatCar(2,"特斯拉",4,500);
			cars[2]=new Car(3,"皮卡丘",4,2,200);
			cars[3]=new LoadCar(4,"松花江",10,200);
			cars[4]=new LoadCar(5,"黑龍江",20,300);
			System.out.println("現有5種車型可供您選擇:");
			System.out.println("序號"+"\t"+"車型"+"\t"+"座位(座)"+"\t"+"載重(噸)"+"\t"+"租金/天");
			for(Car c : cars){
				System.out.println(c);
			}
			int totalSeat = 0;
			double totalLoad = 0;
			double totalPrice = 0;
			String loadCarList = "";
			String seatCarList = "";
			System.out.println("請輸入您要租車的數量");
			int rentNum = in.nextInt();
			for(int i=0;i<rentNum;i++){
				System.out.println("你要選擇的第"+(i+1)+"輛車的序號");
				int rentId = in.nextInt();
				if(rentId<5){
					totalSeat = totalSeat + cars[rentId-1].seat;
					totalLoad = totalLoad + cars[rentId-1].load;
					totalPrice = totalPrice + cars[rentId-1].price;
					if(cars[rentId-1].seat!=0){
						seatCarList = seatCarList + cars[rentId-1] + "\n";						
					}else if(cars[rentId-1].load!=0){
						loadCarList = loadCarList + cars[rentId-1] + "\n";						
					}
				}else{
					System.out.println("不好意思，請選擇現有的車輛(序號1-5)");
				}
			}
			System.out.println("請輸入您要租車的天數");
			int rentDays = in.nextInt();
			System.out.println("/********************** 以下是您此次的租車賬單 **********************/");
			if(seatCarList==""){
				System.out.println("沒有可載人的車");
			}else{
				System.out.println("可載人的車輛有\n"+seatCarList);
				System.out.println("總座位數"+totalSeat);
			}
			if(loadCarList==""){
				System.out.println("沒有可載貨的車");
			}else{
				System.out.println("可載人的車輛有\n"+seatCarList);
				System.out.println("總載貨量"+totalLoad);
			}
			System.out.println("總價格："+totalPrice*rentDays+"元");
		}else{
			System.out.println("感謝您的使用");
		}
	}

}

慕課網Java入門第二季6.1 達達租車系統，使用到繼承、重寫、多態、toString函數