parent - 为什么子类继承父类有错？

Question

如果继承 TrainCar 这是一个问题。如果继承 GCompoud 那很好。哪里错了？

家长：</p>

public class TrainCar extends GCompound{

    public TrainCar(double size){

        engine =  new Engine(size);
        add(engine);
        }
}

子类：</p>

public class Engine extends  TrainCar { 

    public Engine (double size){    //if inherit TrainCar that's a problem. 
                                    //if inherit GCompoud that's well.

        GPolygon engine = engine(size);     
        add(engine);
    }
}

Boxcar 继承了 TrainCar，这很好。

在讲义 #31 中：

public class Boxcar extends TrainCar {

 public Boxcar(Color color) {
}

http://www-cs-faculty.stanford.edu/~eroberts/courses/cs106a/handouts/30-graphical-structures.pdf

Answer 1

您必须TrainCar在 的构造函数中调用构造函数Engine。你可以这样做：

public Engine (double size) {
     super(size);

    GPolygon engine = engine(size);     
    add(engine);
}