我正在从一本名为Chegwidden Gladdis的书中学习C＃。我正在制作与书中所写相同的程序和相同的代码。但有一个问题。我无法覆盖父类的方法。我从章节的开头就已经完全重读了这本书，5次，每次都是相同但我无法弄清楚为什么我不能从父类中覆盖一个方法。这是基类PassFailActivity.cs
中的代码using System;
namespace ProtectedMembers
{
public class PassFailActivity : GradedActivity2
{
private double minPassingScore; // Minimum passing score
/// <summary>
/// The constructor sets the minimum passing score
/// </summary>
/// <param name="mps">The minimum passing score.</param>
public PassFailActivity(double mps)
{
minPassingScore = mps;
}
/// <summary>
/// The GetGrade method returns a letter grade determined
/// from the score field. This methos overrides the base class method.
/// </summary>
/// <returns>The letter grade</returns>
public override char GetGrade()
{
char letterGrade;
if (base.GetScore() >= minPassingScore)
letterGrade = 'P';
else
letterGrade = 'F';
return letterGrade;
}
}
}
和GradedActivity2.cs
using System;
namespace ProtectedMembers
{
public class GradedActivity2
{
protected double score; // Numberic score
/// <summary>
/// The SetScore method sets the score field.
/// </summary>
/// <param name="s">The value to store in score</param>
public void SetScore(double s)
{
score = s;
}
/// <summary>
/// The GetScore method returns the score.
/// </summary>
/// <returns>The value stored in the score field</returns>
public double GetScore()
{
return score;
}
/// <summary>
/// The GetGrade method returns a letter grade determined from the score field.
/// </summary>
/// <returns>Return the letter grade</returns>
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;
}
}
}
和PassFailExam
using System;
namespace ProtectedMembers
{
public class PassFailExam : PassFailActivity
{
private int numQuestions; // Number of questions
private double pointsEach; // Points for each question
private int numMissed; // Number of questions missed
/// <summary>
/// The constructor sets the number of questions, the number
/// of questions missed, and the minimum passing score.
/// </summary>
/// <param name="questions">The number of questions</param>
/// <param name="missed">The number of questions missed</param>
/// <param name="minPassing">The minimum passing score</param>
public PassFailExam(int questions, int missed, double minPassing) : base(minPassing)
{
// Declare a local variable for the score.
double numericScore;
// Set the numQuestions and numMissed fields.
numQuestions = questions;
numMissed = missed;
// Calculate the points for each questions and the numeric score for this exam.
pointsEach = 100.0 / questions;
numericScore = 100.0 - (missed * pointsEach);
// Call the base class's SetScore method to set the mumeric score.
SetScore(numericScore);
}
/// <summary>
/// The GetpointsEach method returns the number of points each questions is worth
/// </summary>
/// <returns>The value in the pointsEach field</returns>
public double GetPointsEach()
{
return pointsEach;
}
/// <summary>
/// The GetNumMissed method returns the number of questions missed
/// </summary>
/// <returns>The value in the numMissed field</returns>
public int GetNumMissed()
{
return numMissed;
}
}
}
这是我的主要
using System;
namespace ProtectedMembers
{
public class PassFailExamDemo
{
public static void Main111()
{
int questions, // Number of questions
missed; // Number of questions missed
double minPassing; // Minmum passing score
// Get the number of questions on the exam
Console.Write("How many questions are " + "on the exam? ");
questions = Convert.ToInt32(Console.ReadLine());
// Get the number of questions missed.
Console.Write("How many questions did " + "the student miss? ");
missed = Convert.ToInt32(Console.ReadLine());
// Get the minimum passing score
Console.Write("What is the minimum " + "passing score? ");
minPassing = Convert.ToInt32(Console.ReadLine());
// Create a PassFailExam project
PassFailExam exam = new PassFailExam(questions, missed, minPassing);
// Display the teset results.
Console.WriteLine("Each questions counts {0} points.",
exam.GetPointsEach());
Console.WriteLine("The exam score is {0} ",
exam.GetScore());
Console.WriteLine("The exam grade is {0} ",
exam.GetGrade());
Console.ReadLine();
}
}
}
输出应为
How many questions are on the exam? 100
How many questions did the student miss? 25
What is the minimum passing score? 60
Each question counts 1 points.
The exam score is 75
The exam grade is P
我试图将基本方法设为虚拟并在尝试覆盖它时调用覆盖，这只是让我得到这个错误“'ProtectedMembers.PassFailActivity.GetGrade（）'：无法覆盖继承的成员'ProtectedMembers.GradedActivity2.GetGrade（） '因为它没有标记为虚拟，抽象或覆盖“。我完全检查了