Question

我在OOP的第二周，我们的导师已经做了一个消息传递练习，我有一个我似乎无法解决的错误。错误是：

Obj_Orientated_CD_MOVIE_Library.Movie'未实现继承的抽象成员'Obj_Orientated_CD_MOVIE_Library.borrowCopy（）'

反过来导致了后续错误：

Obj_Orientated_CD_MOVIE_Library.Movie.borrowCopy（Obj_Orientated_CD_MOVIE_Library.Student）'：找不到合适的方法来覆盖

我不确定我是否已正确解释，这是代码。

abstract class Item
{
  protected int copies;
  protected int availCopies;
  protected string title;

  public Item(string newTitle, int newCopies, int newAvailCopies)
  {
      title = newTitle;
      copies = newCopies;
      availCopies = newAvailCopies;
  }

  public abstract void borrowCopy(Student objStudent);

  public abstract void returnCopy();

  public int Copies
  {
      get
      {
          return copies;
      }
      set
      {
          copies = value;
      }
  }

  public int AvailCopies
  {
      get
      {
          return availCopies;
      }
      set
      {
          availCopies = value;
      }
  }

  public string Title
  {
      get
      {
          return title;
      }
      set
      {
          title = value;
      }
  }
}


class Student
{
  public string date;
  public string returnDate;

  public Student(string newDate, string newReturnDate, string newTitle, int newCopies, int newAvailCopies)
      : base(newTitle, newCopies, newAvailCopies)
  {
      date = newDate;
      returnDate = newReturnDate;
  }
  public void borrowMovie(Movie objMovie)
  {
      objMovie.borrowCopy(this);
  }
  public void borrowCD(CD objCD)
  {
      objCD.borrowCopy(this);
  }
  public override void borrowCopy(Student objStudent)
  {
  }
  public override void returnCopy()
  {
  }
}

class Movie : Item
{
  public string runTime;

  public Movie(string newTitle, string newRunTime, int newCopies, int newAvailCopies)
      : base(newTitle, newCopies, newAvailCopies)
  {
      runTime = newRunTime;
  }
  public string Runtime
  {
      get
      {
          return runTime;
      }
      set
      {
          runTime = value;
      }
  }
  public override void returnCopy()
  {
      availCopies++;
      Console.Write("\nThank you for returning the Movie\n");
  }
  public override void borrowCopy(Student objStudent)
  {
      if (AvailCopies > 0)
      {
          AvailCopies--;
          Console.Write("Please refer to receipt for return date of the Movie\n");
      }
      else
      {
          Console.WriteLine("\nThis Movie is not available at this time, please try again later");
      }
  }
}

class CD : Item
{
  public string band;

  public CD(string newTitle, string newBand, int newCopies, int newAvailCopies)
      : base(newTitle, newCopies, newAvailCopies)
  {
      band = newBand;
  }
  public string Band
  {
      get
      {
          return band;
      }
      set
      {
          band = value;
      }
  }
  public override void returnCopy()
  {
      availCopies++;
      Console.Write("\nThank you for returning the CD\n");
  }
  public override void borrowCopy(Student objStudent)
  {
      if (AvailCopies > 0)
      {
          AvailCopies--;
          Console.Write("Please refer to receipt for return date of the CD\n");
      }
      else
      {
          Console.WriteLine("\nThis CD is not available at this time, please try again later");
      }
  }
}

建设性的批评和帮助请。

Answer 1

您似乎错误地覆盖了borrowCopy。我们需要查看Item的代码，但是您要提供的签名：

void borrowCopy(Student objStudent)

...与Item中抽象方法的签名不同。

从错误中看，Item中的方法没有任何参数。

所以你得到了两个错误，首先你没有提供带有所需签名的borrowCopy实现，其次你使用override关键字作为Item上不存在的签名。

试试这个：

    public override void borrowCopy()
    {
        if (AvailCopies > 0)
        {
            AvailCopies--;
            Console.Write("Please refer to receipt for return date of the Movie\n");
        }
        else
        {
            Console.WriteLine("\nThis Movie is not available at this time, please try again later");
        }
    }

Answer 2

你问了详细资料，你走了。这是你需要改变的东西。更新的Student类：

//is a Student an Item? I think not
class Student 
{
   public string date;
   public string returnDate;

   public Student(string newDate, string newReturnDate)
   {
       date = newDate;
       returnDate = newReturnDate;
   }
   public void borrowMovie(Movie objMovie)
   {
       objMovie.borrowCopy(this);
   }
   public void borrowCD(CD objCD)
   {
       objCD.borrowCopy(this);
   }
}

注意我在这里删除了Item抽象类的继承，Student不是Item（我挑战你提出你可以借用的情况“学生的副本，假设我们在谈论的是人类学生”。我可以看到你想要一些其他的类字段，比如一个名字值（我稍后会回到这里）。

然后Item更新了两个方法签名：

public abstract void borrowCopy(Student objStudent);

public abstract void returnCopy(Student objStudent);

然后，当您从movie.borrowCopy(this);内拨打Student时，您不会收到任何错误，并且可以使用该方法中Student中的任何方法或属性。如果您在Name中添加了Student属性，则可以修改Console.Writeline中的borrowCopy()以说“Joe Blow，请参阅电影的返回日期的收据”像这样更新它：Console.Write("{0}, please refer to receipt for return date of the Movie\n", student.Name);

消息传递问题

2 个答案: