java - 关于子类中重写的困惑

Question

这个问题已经有答案了:

Int division: Why is the result of 1/3 == 0? (19 个回答)

已关闭 3 年前。

所以我得到了以下 GradedActivity 类:

 public class GradedActivity
 {
    private double score;  // Numeric score

    public void setScore(double s)
    {
        if (s < 0)
        score = 0.0;
    else if (s > 100)
        score = 100.0;
        else
            score = s;
     }

    public double getScore()
    {
       return score;
    }


    public char getGrade()
   {
      char letterGrade;

      if (score >= 90)
         letterGrade = 'A';
      else if (score >= 80)
         letterGrade = 'B';
      else if (score >= 70)
         letterGrade = 'C';
      else if (score >= 60)
         letterGrade = 'D';
      else
         letterGrade = 'F';

      return letterGrade;
   }
}

我的任务是生成一个构造函数，该构造函数接受点 Obtaned 和 pointsTotal 的值作为参数，初始化它们，并设置相应的分数(获得的分数除以总分数)、获取的分数和总计的访问器和修改器。

这就是我的想法:

public class ProgrammingAssignment extends GradedActivity 
{
   public int pointsObtained;
   public int pointsTotal;

   public ProgrammingAssignment(int p, int t)
   {

      pointsObtained = p;
      pointsTotal = t;
   } 

   public int getPointsObtained()
   {
      return pointsObtained;
   }

   public int getPointsTotal()
   {
      return pointsTotal;
   }

   public double getScore()
   {
     return pointsObtained / pointsTotal;
   }

   public void setPointsObtained(int p)
   {
      pointsObtained = p;

   }

   public void setPointsTotal(int t)
   {
      pointsTotal = t;
   }     
  }

一切编译都没有错误，但在我的测试类中 getScore 没有计算获得的/总计(它返回 0):

 public class PADemo
 {
   public static void main(String[] args)
   {
        ProgrammingAssignment p1 = new ProgrammingAssignment(28,30);
            GradedActivity p2 = new ProgrammingAssignment(0,30);

      System.out.println (p1.getPointsObtained());
      System.out.println (p1.getPointsTotal());
      System.out.println (p1.getScore());  
      System.out.println (p1.getGrade());  

      System.out.println (p2.getScore());  
      System.out.println (p2.getGrade());  

      p1.setPointsObtained(25);
      p1.setPointsTotal(40);
      System.out.println (p1.getScore());  
      System.out.println (p1.getGrade() == 'F');  
 }
 }

如何使用 getScore() 获取分数(获得的分数/总分数)

测试类返回:

28
30
0.0
F
0.0
F
0.0
正确

Answer 1

从表面上看，解决问题最简单的方法是将 getScore() 更改为:

public double getScore()
   {
     return (pointsObtained * 100) / pointsTotal;
   }

你的代码所做的是给你 0.93 而不是 93，并且当放入整数时 0.93 会被截断为 0(如注释中所指出的)。