gpt4 book ai didi

c# - 设置对象成员时出现 NullReferenceException

转载 作者:太空宇宙 更新时间:2023-11-03 17:14:08 24 4
gpt4 key购买 nike

当我运行以下程序时收到 NullReferenceException。我认为问题出在我正在创建一个包含 Point 类的 Line

using System;

class Driver
{
static void Main()
{
Point pOne = new Point();
Point pTwo = new Point(2, 1);

Console.Write("Point pOne: ");
PrintPoint(pOne);

Console.Write("Point pthree: ");
PrintPoint(pTwo);

Line lOne = new Line(pOne, pTwo);

Console.WriteLine("Line lOne: ");
PrintLine(lOne);

//Rectangle rOne = new Rectangle();
Rectangle rOne = new Rectangle(lOne);

Console.WriteLine("Rectangle rOne: ");
PrintRectangle(rOne);

Console.ReadLine();
}

// The PrintPoint method
// purpose: display the coordinates of a Point
// Parameters: a Point object
// returns: none
static void PrintPoint(Point p)
{
Console.Write("({0},{1})", p.GetXCoord(), p.GetYCoord());
}

// the PrintLine method
// purpose: display the endpoints of a line
// Parameters: a Line object
// returns: none
static void PrintLine(Line aline)
{
// notice how we get the point objects from the line
// and then print their coordinates
Point p1 = aline.GetStartPoint();
Point p2 = aline.GetEndPoint();
Console.Write(" \t");
PrintPoint(p1);
Console.Write(" - ");
PrintPoint(p2);
}

static void PrintRectangle(Rectangle aRec)
{
Line Left = aRec.getLeft();
Line Top = aRec.gettop();
Line Right = aRec.getRight();
Line Bottem = aRec.getBottem();

Console.Write("\t Left: ");
PrintLine(Left);
Console.Write("\n\t Top: ");
PrintLine(Top);
Console.Write("\n\t Right: ");
PrintLine(Right);
Console.Write("\n\t Bottem: ");
PrintLine(Bottem);

}
}

class Rectangle
{
private Line left;
private Line top;
private Line right;
private Line bottem;


public Rectangle()
{
Point zero = new Point();

left.setEndPoint(zero);
left.SetStartPoint(zero);

top.setEndPoint(zero);
top.SetStartPoint(zero);

right.setEndPoint(zero);
right.SetStartPoint(zero);

bottem.setEndPoint(zero);
bottem.SetStartPoint(zero);

}

public Rectangle(Line enter)
{
Point stDgl = new Point();
Point endDgl = new Point();

stDgl = enter.GetStartPoint();
endDgl = enter.GetEndPoint();

//stDgl
int a = stDgl.GetXCoord();
int b = stDgl.GetYCoord();

//endDgl
int c = endDgl.GetXCoord();
int d = endDgl.GetYCoord();

Point endright = new Point();

endright.SetXCoord(c);
endright.SetYCoord(b);

Point endleft = new Point();

endleft.SetXCoord(a);
endleft.SetYCoord(d);

//LEFT
left.SetStartPoint(stDgl); // **NullReferenceException**
left.setEndPoint(endleft);

//TOP
top.SetStartPoint(endleft);
top.setEndPoint(endDgl);

//RIGHT
right.SetStartPoint(endDgl);
right.setEndPoint(endright);

//BOTTEM
bottem.SetStartPoint(endright);
bottem.setEndPoint(stDgl);
}

public Line getLeft()
{
return left;
}

public Line gettop()
{
return top;
}

public Line getRight()
{
return right;
}

public Line getBottem()
{
return bottem;
}

}

// the Line class
class Line
{
// data members - notice that they are Point objects
private Point startPoint;
private Point endPoint;

// default constructor
// purpose: initialize data members to zero
// Parameters: none
// returns: none
public Line()
{
// notice how we call methods in the Point class
**startPoint.SetXCoord(0);** ***NullReferenceException***
startPoint.SetYCoord(0);
endPoint.SetXCoord(0);
endPoint.SetYCoord(0);
}

// parameterized constructor
// purpose: initialize data members to p1 and p2
// Parameters: Point objects p1 and p2
// returns: none
public Line(Point p1, Point p2)
{
startPoint = p1;
endPoint = p2;
}

/*
//LEFT
Point endleft = new Point();

endleft.SetXCoord(a);
endleft.SetYCoord(d);

left.SetStartPoint(stDgl);
left.setEndPoint(endleft);
* */


// the GetStartPoint method
// purpose: return the value of the starting point
// Parameters: none
// returns: the value of the starting point as a Point object
public Point GetStartPoint()
{
return startPoint;
}

// the GetEndPoint method
// purpose: return the value of the ending point
// Parameters: none
// returns: the value of the ending point as a Point object
public Point GetEndPoint()
{
return endPoint;
}

// the SetStartPoint method
// purpose: store the value of the starting point
// Parameters: the value of the starting point as a Point object
// returns: none
public void SetStartPoint(Point p1)
{
startPoint = p1;
}

// the SetEndPoint method
// purpose: store the value of the ending point
// Parameters: the value of the ending point as a Point object
// returns: none
public void setEndPoint(Point p2)
{
endPoint = p2;
}
}

// The Point class
class Point
{
// data members
private int xCoord;
private int yCoord;

// default constructor
// purpose: initialize data members to zero
// Parameters: none
// returns: none
public Point()
{
xCoord = 0;
yCoord = 0;
}

// parameterized constructor
// purpose: initialize data members to x an y
// Parameters: two integers x and y
// returns: none
public Point(int x, int y)
{
xCoord = x;
yCoord = y;
}

// the GetXCoord method
// purpose: return the value of the x-coordinate
// Parameters: none
// returns: the value of the x-coordinate as an int
public int GetXCoord()
{
return xCoord;
}

// the GetYCoord method
// purpose: return the value of the y-coordinate
// Parameters: none
// returns: the value of the y-coordinate as an int
public int GetYCoord()
{
return yCoord;
}

// the SetXCoord method
// purpose: stores the value of the x-coordinate
// Parameters: the value of the x-coordinate as an int
// returns: none
public void SetXCoord(int x)
{
xCoord = x;
}

// the SetYCoord method
// purpose: stores the value of the y-coordinate
// Parameters: the value of the y-coordinate as an int
// returns: none
public void SetYCoord(int y)
{
yCoord = y;
}
}

最佳答案

您试图在创建对象之前设置对象的成员。例如:

class Line
{
private Point startPoint;
private Point endPoint;

public Line()
{
startPoint.SetXCoord(0);
...

在构造函数的开头,startPoint 将是一个空引用。您需要创建一个新的 Point 对象并将引用分配给 startPoint ,如下所示:

startPoint = new Point();
startPoint.SetXCoord(0); // etc

我还建议您在感觉合适时尽快将 get/set 方法更改为属性 - 这样您的代码看起来更像地道的 C# 而不是 Java。

关于c# - 设置对象成员时出现 NullReferenceException,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/1702561/

24 4 0
Copyright 2021 - 2024 cfsdn All Rights Reserved 蜀ICP备2022000587号
广告合作:1813099741@qq.com 6ren.com