爲什麼子類繼承父類有錯？

Question

如果繼承TrainCar這是一個問題。如果繼承GCompoud那很好。錯在哪裏？

父：

public class TrainCar extends GCompound{ 

    public TrainCar(double size){ 

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

子類：

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); 
    } 
} 

的棚車繼承TrainCar這是很好。

在單張＃31：

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

您必須調用TrainCar構造函數中的Engine構造。你可以這樣做：

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

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