Question

我是一名工科学生，忙于使用DrJava作为IDE的项目（它是我们在课程中使用的标准IDE）和普林斯顿STDLIB。

我在理解，编写和使用对象方面遇到了问题。我想问一下我写下面代码的方式有什么问题。我将在编码后给出错误行：

public class GameObject 
{
 // Default implementation of a game object

 private  double  G = 6.67408e-11;
 private  double  radiusKoeff = 0.01;

 public class Planet
 {
   double mass;
   double size;
   double velocityX;
   double velocityY;
   double positionX;
   double positionY;

   public Planet(double m, double vx, double vy, double px, double py)
   {
     mass = m;
     size = m * radiusKoeff;
     velocityX = vx;
     velocityY = vy;
     positionX = px;
     positionY = py;
   }//constructor for the planet type

   public double GravForce(Planet a, Planet b)
   {
     double distanceX, distanceY, distance;
     distanceX = Math.abs(a.positionX - b.positionX);
     distanceY = Math.abs(a.positionY - b.positionY);
     distance = Math.sqrt((distanceX)*(distanceX) + (distanceY)*(distanceY));

     double force = (G * a.mass * b.mass) / (distance*distance);

     return force;
   }//calculates the gravitational force between two objects    
 }

 public static void main(String[] args)
 {
   String filename = args[0];

   Planet first = new Planet(1.25e24, 1, 0, 0, 0);
   Planet second = new Planet(1e24, 1, 0, 5, 0);

   **StdOut.println(GravForce( first, second ));**
 }
}

错误：对于GameObject类型，未定义GravForce（GameObject.Planet，GameObject.Planet）方法。

我尝试调用的GravForce函数抛出错误。

非常感谢任何帮助。

Answer 1

像这样修改你的方法

public double GravForce(Planet b)
   {
     double distanceX, distanceY, distance;
     distanceX = Math.abs(this.positionX - b.positionX);
     distanceY = Math.abs(this.positionY - b.positionY);
     distance = Math.sqrt((distanceX)*(distanceX) + (distanceY)*(distanceY));

     double force = (G * this.mass * b.mass) / (distance*distance);

     return force;
   }//calculates the gravitational force between two objects

然后在main

public static void main(String[] args)
 {
   String filename = args[0];

   Planet first = new Planet(1.25e24, 1, 0, 0, 0);
   Planet second = new Planet(1e24, 1, 0, 5, 0);

   StdOut.println(first.GravForce(second));
 }

无法对对象执行操作

1 个答案: