Question

我已经制作了以下类和子类。

import java.io.*; 
import java.util.*; 

   public class ShapeTester{ 
     //--------------------------------------------------------------------------- 
     // Read the dimensions of various 3-D shapes from an input file, then 
     // displays pertinent information about each shape. 
     //--------------------------------------------------------------------------- 
     public static void main (String[] args){ 
       try{ 
          Scanner scan = new Scanner (new File("shapes.txt")); 
          double width, length, height, side, radius; 

          // Read the data from the input file 
          while (scan.hasNext()){ 
             String shapeType = scan.next(); 

             if (shapeType.equalsIgnoreCase("cylinder")){ 
                radius = scan.nextDouble(); 
                height = scan.nextDouble(); 
                System.out.println (new Cylinder (radius, height)); 
             } 
             if (shapeType.equalsIgnoreCase("cone")){ 
                radius = scan.nextDouble(); 
                height = scan.nextDouble(); 
                System.out.println (new Cone (radius, height)); 
             }
             if (shapeType.equalsIgnoreCase("cuboid")){ 
                length = scan.nextDouble(); 
                width = scan.nextDouble();
                height = scan.nextDouble(); 
                System.out.println (new Cuboid (length, width)); 
             }
          } 
       } 
       catch (Exception except){ 
          System.err.println(except); 
       } 
     } 
    }//end class ShapeTester



public abstract class Shape{ 
   abstract public double computeArea(); 
   abstract public double computePerimeter(); 
}//end class Shape




import java.text.*; 
public class Circle extends Shape{ 
 protected double radius; 
 protected static DecimalFormat form = new DecimalFormat("0.##"); 

 public Circle (double rad){ 
   radius = rad; 
 } 

 public double computeArea(){ 
   return Math.pow(radius,2) * 3.14; 
 } 

 public double computePerimeter(){ 
   return radius * 6.28; 
 } 

 public String toString(){ 
   return "Circle: radius is " + form.format(radius) + 
   "\nperimeter is " + form.format(computePerimeter()) + 
   ", area is " + form.format(computeArea()); 
 } 
} //end class Circle






public class Cylinder extends Circle{ 
   private double height; 

   public Cylinder (double rad, double hei){ 
      super(rad); 
      height = hei; 
   } 

   // Returns the calculated value of face height  
   public double faceHeight(){ 
      return height; 
   }

   // Returns the calculated value of face area  
   public double faceArea(){ 
      return faceHeight() * radius * 6.28; 
   } 

   // Returns the calculated value of the surface area  
   public double computeArea(){ 
      return faceArea() + super.computeArea() + super.computeArea(); 
   } 

   // Returns the calculated value of the volume  
   public double computeVolume(){ 
      return super.computeArea() * height; 
   } 

   public String toString(){ 
      return "Cylinder: Height is " + form.format(height) + 
      "\nperimeter of base is " + form.format(computePerimeter()) + 
      ", area is " + form.format(computeArea()) + 
      "\nvolume is " + form.format(computeVolume()) + "\n"; 
   } 
}//end class Cylinder

到目前为止，该程序运行良好。我可以编译ShapeTester 我收到了每个值的预期结果。（那是在我之前插入了长方体的if命令）（还有一个if命令对于那里的锥形，它也有效，我只是没有包括锥形类因为这已经足够长了。）

import java.text.*; 
public class Rectangle extends Shape{ 
 protected double length; 
 protected double width;
 protected static DecimalFormat form = new DecimalFormat("0.##"); 

 public Rectangle (double len, double wid){ 
   length = len;
   width = wid; 
 } 

 public double computeArea(){ 
   return length * width; 
 }  

 public double computePerimeter(){ 
   return (2*length) + (2*width); 
 } 

 public String toString(){ 
   return "Rectangle: length is " + form.format(length) + 
   "\nwidth is " + form.format(width) +
   "\nperimeter is " + form.format(computePerimeter()) + 
   ", area is " + form.format(computeArea()); 
 } 
}//end class Rectangle

这节课也很好。以下类是给我一个问题的类。

public class Cuboid extends Rectangle{ 
   private double height;

   public Cuboid (double len, double wid, double hei){ 
      super(len);
      super(wid);
      height = hei;
   } 

   // Returns the calculated value of the surface area 
   public double computeArea(){ 
      return (2 * height * width) + (2 * super.computeArea()) + (2 * length * height) ; 
   } 

   // Returns the calculated value of the volume  
   public double computeVolume(){ 
      return super.computeArea() * height; 
   } 

   public String toString(){ 
      return "Rectangle Cuboid: Height is " + form.format(height) + 
      "\nlength is " + form.format(length) + 
      "\nwidth is " + form.format(width) +
      "\nperimeter of base is " + form.format(computePerimeter()) + 
      ", area is " + form.format(computeArea()) + 
      "\nvolume is " + form.format(computeVolume()) + "\n"; 
   } 
}//end class Cuboid

当我尝试编译这个最后一个类时，我得到了这些错误，但我遵循了与其他类（Cylinder）相同的格式。有人可以告诉我为什么吗？

Cuboid.java:5: error: constructor Rectangle in class Rectangle cannot be applied to given types;
      super(len);
      ^
  required: double,double
  found: double
  reason: actual and formal argument lists differ in length
Cuboid.java:6: error: call to super must be first statement in constructor
      super(wid);
           ^
2 errors

Answer 1

You must call super exactly as the super constructor is defined.您不希望通过编写

将宽度和高度传递给Rectangle构造函数

new Rectangle(lenth);
new Rectangle(height);

...对吧？你打电话给new Rectangle(length, height)。所以，改变

public Cuboid (double len, double wid, double hei){ 
  super(len);
  super(wid);
  height = hei;
}

到

public Cuboid (double len, double wid, double hei){ 
  super(len, wid);
  height = hei;
}

Answer 2

Cuboid的{{1}}超类会收到两个参数，但是当您使用Rectangle在子类Rectangle中调用它时，您只提供一个参数。而不是：

super

执行此操作：super(len); super(wid); - super(len,wid)使用匹配的参数列表调用超类构造函数。你不能两次调用构造函数。即使在JVM字节码级别，也可以在任何给定对象上最多调用一次方法链。第二个错误准确地说明了这一点：super(parameter list)

为什么我会收到以下错误？（帖子末尾的错误）

2 个答案: