求各位大佬帮忙写下java程序，初学多态真的搞不懂研究一天了

Question

Answer 1

public abstract class Automatic {
// 省略属性
public abstract int pay();
}

public class Car extends Automatic {
public int pay() {
return 5;
}
}

public class Truck {
private int weight;
public Truck(int weight) {
this.weight = weight;
}

    public int pay() {
        return weight < 20 ? 10 : weight >= 20 && weight <= 30 ? 15 : weight > 30 ? 20 : -1;
    }

}

public static void main(String[] args) {
Automatic a = new Truck(27);
shoufei(a);
}

public static void shoufei(Automatic a) {
System.out.println(a.pay());
}