创建一个抽象类Car,它有一个抽象方法display()和两个成员变量wheelNum、seatNum,分别表示轮子数和座位数。类bus和类motorcycle继承自类Car,实现输出成员变量的display()方法。在主方法中用向上转型对象调用display()方法

代码如下：

//定义抽象类Car
public abstract class Car {
    protected int wheelNum; //轮子数
    protected int seatNum;  //座位数
    
    public abstract void display();
}

//bus类继承自Car类
public class Bus extends Car {
    public Bus(int wheelNum, int seatNum) {
        this.wheelNum = wheelNum;
        this.seatNum = seatNum;
    }
    
    @Override
    public void display() {
        System.out.println("Bus: " + "wheelNum=" + wheelNum + ", seatNum=" + seatNum);
    }
}

//motorcycle类继承自Car类
public class Motorcycle extends Car {
    public Motorcycle(int wheelNum, int seatNum) {
        this.wheelNum = wheelNum;
        this.seatNum = seatNum;
    }
    
    @Override
    public void display() {
        System.out.println("Motorcycle: " + "wheelNum=" + wheelNum + ", seatNum=" + seatNum);
    }
}

//主方法中用向上转型对象调用display()方法
public class Main {
    public static void main(String[] args) {
        Car car1 = new Bus(4, 20); //向上转型为Car类型
        Car car2 = new Motorcycle(2, 2); //向上转型为Car类型
        
        car1.display(); //调用Bus类中的display()方法
        car2.display(); //调用Motorcycle类中的display()方法
    }
}

输出结果为：

Bus: wheelNum=4, seatNum=20
Motorcycle: wheelNum=2, seatNum=2