我想问问这几个方法是什么意思啊

我想问问这几个方法怎么写啊，没有思路了，应该用到哪方面的知识，谢谢啦

这里主要考察Java继承，子类和父类是is-a, Car和Bus都是交通工具

public class VehicleTest {
    public static void main(String[] args) {
        Car bmw = new Car();
        bmw.setBrand("宝马");
        bmw.setType("750");
        System.out.println(bmw.info() + " : " + bmw.calRent(1));

        Bus bus=new Bus();
        bus.setBrand("大众");
        bus.setSeatNum(8);

        System.out.println(bus.info()+" : "+bus.calRent(3));
    }

    public static class Vehicle {

        private String no;

        private String brand;

        public String getNo() {
            return no;
        }

        public void setNo(String no) {
            this.no = no;
        }

        public String getBrand() {
            return brand;
        }

        public void setBrand(String brand) {
            this.brand = brand;
        }
    }

    public static class Car extends Vehicle {
        private static Map<String, Integer> rentMap = new HashMap<>();

        static {
            rentMap.put("宝马750", 700);
            rentMap.put("大众polo", 400);
            rentMap.put("大众golf", 00);
        }

        private String type;

        public String info() {
            String str = getBrand() + getType();
            return str;
        }

        public int calRent(int days) {
            return rentMap.getOrDefault(info(), 0) * days;
        }

        public String getType() {
            return type;
        }

        public void setType(String type) {
            this.type = type;
        }
    }

    public static class Bus extends Vehicle {
        private static Map<String, Integer> rentMap = new HashMap<>();

        static {
            rentMap.put("<=20座", 800);
            rentMap.put(">20", 1200);
        }

        private int seatNum;

        private String info() {
            String info = seatNum <= 20 ? "<=20座" : ">20";
            return info;
        }

        public int calRent(int days) {
            return rentMap.getOrDefault(info(), 0) * days;
        }

        public int getSeatNum() {
            return seatNum;
        }

        public void setSeatNum(int seatNum) {
            this.seatNum = seatNum;
        }
    }
}

父类，应该是继承吧，Car和Bus都继承Vehicle，然后重写基类成员，成员方法的功能不是也给出了吗

用到了继承重写方法知识，还有小小的计算，可用if语句，字符串等等，参数类型