一个对象处理具有相同代码的多个扩展对象

Question

我想让一个对象处理多个扩展对象。最终结果应该是，如果我通过一辆自行车或摩托车，它会显示信息。在下面的示例中，我希望类（Display）接受Bike或MotorBike（扩展了Bike）并适当地显示信息。故障点在显示中，最后一行打印摩托车特有的信息。我确信我错过了一些简单的事情，但我只是不明白我做错了什么。

谢谢你的帮助。

问题.java

public class Problem {
    public static void main(String[] args) {
        new Display(new Bike());
        new Display(new MotorBike());
    }
}

Bike.java

class Bike {
    private boolean frontTireOk;
    private boolean backTireOk;
    private int gears;
    public Bike() {}
    public boolean isFrontTireOk() {
        return frontTireOk;
    }
    public void setFrontTireOk(boolean frontTireOk) {
        this.frontTireOk = frontTireOk;
    }
    public boolean isBackTireOk() {
        return backTireOk;
    }
    public void setBackTireOk(boolean backTireOk) {
        this.backTireOk = backTireOk;
    }
    public int getGears() {
        return gears;
    }
    public void setGears(int gears) {
        this.gears = gears;
    }
}

摩托车，java

class MotorBike extends Bike {
    private int engineCC;
    public MotorBike() {}
    public int getEngineCC() {
        return engineCC;
    }
    public void setEngineCC(int engineCC) {
        this.engineCC = engineCC;
    }
}

Display.java

class Display {
    Bike bike;
    public Display(Bike bike) {
        this.bike = (Bike) bike;
        showBike();
    }
    Display(MotorBike motorBike) {
        this.bike = (MotorBike) motorBike;
        showBike();
    }
    private void showBike() {
        System.out.println("Front tire is OK ?" + bike.isFrontTireOk());
        System.out.println("Back tire is OK? " + bike.isBackTireOk());
        System.out.println("Gears? " + bike.getGears());
        if(bike instanceof MotorBike){
            System.out.println("Engine CC? " + bike.getEngineCC()); <--FAIL
        }
    }
}

Answer 1

在线上

System.out.println("Engine CC? " + bike.getEngineCC());

您正在从成员"bike"访问方法"getEngineCC"，但"bike"的类型是bike，而不是MotorBike，因此如果您仅单独使用"bike（自行车）"，则无法获取方法"getEngineCC"。尝试打字：

System.out.println("Engine CC? " + ((MotorBike)bike).getEngineCC());