Question

我想让一个对象处理多个扩展对象。最终结果应该是我通过自行车或摩托车它会显示信息。在下面的例子中，我想要一个类（Display）接受Bike或MotorBike（它扩展Bike）并适当地显示信息。故障点在Display中，最后一行打印MotorBike独有的信息。我确定我错过了一些简单的事情，但我不知道我做错了什么。

感谢您的帮助。

Problem.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

行

runOnUiThread

您正在访问该方法＆＃39; getEngineCC＆＃39;来自会员＆＃39; bike＆＃39;，但＆＃39; bike＆＃39;是自行车，而不是摩托车，所以方法＆＃39; getEngineCC＆＃39;如果您只是使用＆＃39; bike＆＃39;在其自己的。尝试类型转换：

runOnBackgroundThread

一个对象处理具有相同代码的多个扩展对象

1 个答案: