abstract class Vehicle {
    public int speed(){
        return 0;
    }
}

class Car extends Vehicle{
    public int speed(){
        return 60;
    }
}

class RaceCar extends Car{
    public int speed(){
        return 150;
    }
}

public class Test{
    public static void main(String[] args) {
        RaceCar racer = new RaceCar();
        Car car = new RaceCar();
        Vehicle vehicle= new RaceCar();
        System.out.println(racer.speed() + "," + car.speed() + "," + vehicle.speed());
    }
}

------解决方案--------------------
探讨


引用:
选D，应该没错的。

这是哪个知识点呢？ 
不是说抽象类中一定要有抽象方法的吗？并且好像closing大括号也不够的。


------解决方案--------------------
图片看不到,代码有问题,真的能运行么?