java - 类继承

Question

我有以下有效的代码:

public class Bicycle {

    int cadence = 0;
    int speed = 0;
    int gear = 1;

    void changeCadence(int newValue){
        cadence = newValue;
    }

    void changeGear(int newValue){
        gear = newValue;
    }

    void speedUp(int increment){
        speed = speed + increment;
    }

    void applyBrakes(int decrement){
        speed = speed - decrement;
    }

    void printStates(){
        System.out.println("cadence: " + cadence + "; speed: " + speed + "; gear: " + gear);
    }

    public static void main(String[] args) {

        // Create two different 'Bicycle' objects:
        Bicycle bike1 = new Bicycle();
        Bicycle bike2 = new Bicycle();

        // Invoke methods on the two new objects:
        bike1.changeCadence(50);
        bike1.speedUp(10);
        bike1.changeGear(2);
        bike1.printStates();

        bike2.changeCadence(45);
        bike2.speedUp(15);
        bike2.changeGear(2);
        bike2.changeCadence(40);
        bike2.speedUp(10);
        bike2.changeGear(3);
        bike2.printStates();
    }

}

然后我想要一个名为“MountainBike”的新类继承自“Bicycle”类，我编写了以下新代码:

package mountainbike;

public class MountainBike extends Bicycle {

    public static void main(String[] args) {
        // TODO code application logic here
    }

}

但在这里我在 public class MountainBike extends Bicycle { 行上得到一个错误指示，说 cannot find symbol class Bicycle。

我想我必须在某处放置一个“导入”，但我到底应该导入什么？

Answer 1

导入包含 Bicycle 类的包，将其添加到您的 MauntainBike 代码中:-

package mountainbike;

import packageName.Bicycle;

public class MountainBike extends Bicycle {

    public static void main(String[] args) {
        // TODO code application logic here
    }

}

或者如果没有 Bicycle 类的包(默认包)，将 Bicycle 添加到与 MountainBike 相同的包中

package mountainbike;

public class Bicycle {
.
.
.
}

现在 Bicycle 在同一个包中，因此对 MountainBike 类可见。