为什么要使用受保护的变量（成员/属性）与继承？什么是使用它的优势是什么？ [英] Why should I use protected variables(members/property) with Inheritance? What are the advantages of using it?
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问题描述
我所经历的code的<一个样本href="http://www.wrox.com/WileyCDA/WroxTitle/Beginning-C-3-0-An-Introduction-to-Object-Oriented-Programming.productCd-0470261293.html"相对=nofollow>起始C＃3.0 并随后将样品code沿。
当我创建了一个公用/受保护的方法，然后我能够访问使用派生类对象的方法。例如：
类clsBuilding
{
保护字符串的地址{获得;组; }
保护十进制进价{获得;组; }
保护十进制monthlyPayment {获得;组; }
保护十进制税{获得;组; }
保护十进制保险{获得;组; }
受保护的DateTime购置日期{获得;组; }
保护INT buildingType {获得;组; }
公共无效PropertySummary（字符串[] DESC）
{
说明[0] =属性类型：+ whichType [buildingType] +
，+地址+
成本：+ purchasePrice.ToString（C）+
，每月付款方式：+ monthlyPayment.ToString（C）;
说明[1] =保险+ insurance.ToString（C）+
税：+ taxes.ToString（C）+
购买日期：+ datePurchased.ToShortDateString（）;
降序[2] =;
}
..............
}
类clsApartment：clsBuilding
{
........................
}
.......
myApt =新clsApartment（）;
myApt.PropertySummary（DESC）;
但是，什么是使用受保护的财产，我在父类的开头宣布。当我试图通过派生类或对象或者访问它们直接作为指导书中：
只是来驱动点回家，鉴于clsBuilding（父类）的行：
保护十进制货款;
你可以有行：
你可以有行进价= 150000M，在类的家，这将是完全可以接受的。 （第15章，第4段后447页），也不是一次成功的尝试。
我相信，肯定有我的概念错误，或错过了什么。如果没有的话，为什么任何人会保护声明变量或属性？
修改
公共类clsBuilding
{
// ---------------------符号常量-------------------
公共const int的公寓= 1;
公共const int的商业= 2;
公共const int的HOME = 3;
私人字符串[] whichType = {，公寓，商业，家};
// ---------------------实例变量-------------------
受保护的字符串地址;
保护十进制进价;
保护十进制monthlyPayment;
保护十进制税;
保护十进制保险;
受保护的DateTime购置日期;
保护INT buildingType;
// ---------------------构造--------------------------
公共clsBuilding（）
{
地址=没有关闭;
}
公共clsBuilding（字符串的地址，十进制价格，小数付款，
十进制税，小数INSUR，日期时间日期，int型的）：这个（）
{
如果（addr.Equals（）==假）
地址=地址;
进价=价格;
monthlyPayment =支付;
税费=税;
保险= INSUR;
购置日期=日期;
buildingType =类型;
}
// ---------------------属性方法---------------------
公共字符串地址
{
得到
{
退货地址;
}
组
{
如果（value.Length！= 0）
地址=价值;
}
}
公共小数进价
{
得到
{
返回进价;
}
组
{
如果（值GT; 0M）
进价=价值;
}
}
公共小数MonthlyPayment
{
得到
{
返回monthlyPayment;
}
组
{
如果（值GT; 0M）
monthlyPayment =价值;
}
}
公共小数税
{
得到
{
返回税;
}
组
{
如果（值GT; 0M）
税费=价值;
}
}
公共小数保险
{
得到
{
回归保险;
}
组
{
如果（值GT; 0M）
保险=价值;
}
}
公众的DateTime购置日期
{
得到
{
返回购置日期;
}
组
{
如果（value.Year＆GT; 2008）
购置日期=值;
}
}
公众诠释BuildingType
{
得到
{
返回buildingType;
}
组
{
如果（值GT =公寓式放大器;＆放大器;值小于= HOME）
buildingType =价值;
}
}
// ---------------------常规方法----------------------
/ *****
*目的：提供属性的基本描述
*
*参数列表：
*字符串[]递减一个字符串数组来保存说明
*
*返回值：
*无效
*
*注意：方法假定有数组3个元素
****** /
公共无效PropertySummary（字符串[] DESC）
{
说明[0] =房产类型：+ whichType [buildingType] +
，+地址+
成本：+ purchasePrice.ToString（C）+
，月付：+ monthlyPayment.ToString（C）;
说明[1] =保险+ insurance.ToString（C）+税：+ taxes.ToString（C）+
购买日期：+ datePurchased.ToShortDateString（）;
降序[2] =;
}
/ *****
*目的：找专业除雪，如果有的话
*
*参数列表：
* N / A
*
*返回值：
* 串
****** /
公共虚拟字符串RemoveSnow（）
{
返回whichType [buildingType] +：无除雪服务可用。
}
}
类clsCommercial：clsBuilding
{
// ---------------------实例变量-------------------
私人诠释squareFeet;
私人诠释parkingSpaces;
私人十进制rentPerSquareFoot;
// ---------------------构造--------------------------
公共clsCommercial（字符串的地址，十进制价格，小数付款，
十进制税，小数INSUR，日期时间日期，int型的）：
基地（地址，价格，付款，税收，INSUR，日期，类型）
{
buildingType =类型; //从基地商用型
}
// ---------------------属性方法---------------------
公众诠释SquareFeet
{
得到
{
返回squareFeet;
}
组
{
如果（值0）
squareFeet =价值;
}
}
公众诠释ParkingSpaces
{
得到
{
返回parkingSpaces;
}
组
{
parkingSpaces =价值;
}
}
公共小数RentPerSquareFoot
{
得到
{
返回rentPerSquareFoot;
}
组
{
如果（值GT; 0M）
rentPerSquareFoot =价值;
}
}
// ---------------------常规方法----------------------
公众覆盖字符串RemoveSnow（）
{
返回商业：呼叫尖端清雪：803.234.5566;
}
}
公共frmMain（）
{
的InitializeComponent（）;
数值指明MyTime = DateTime.Now;
myApt =新clsApartment（123安Dotson博士，列克星敦40502，550000 6000，
15000，3400，数值指明MyTime，1）;
myComm =新clsCommercial（4442帕克广场，纽约，SC 29745，120，9000，
22000，8000，数值指明MyTime，2）;
MYHOME =新clsHome（657达拉斯圣，灵戈尔德，GA 30736，260000，1100，
1750，900，数值指明MyTime，3）;
}
解决方案
建立在什么道格说。保护使一个属性，变量或提供给一个子类的功能，但不从类的外部。如果您是使用私有的，它仍然不能从类的外部访问，也不会从它的子类进行访问。
I was going through code samples of Begining C# 3.0 and followed the sample code along.
When I have created a public/protected method then I was able to access that method using the object of derived class. Ex:
class clsBuilding
{
protected string address { get; set; }
protected Decimal purchasePrice { get; set; }
protected decimal monthlyPayment { get; set; }
protected Decimal taxes { get; set; }
protected decimal insurance { get; set; }
protected DateTime datePurchased { get; set; }
protected int buildingType { get; set; }
public void PropertySummary(string[] desc)
{
desc[0] = "Property Type: "+whichType[buildingType] +
"," + address +
",Cost: " + purchasePrice.ToString("C")+
", Monthly Payment:" + monthlyPayment.ToString("C");
desc[1] = "Insurance: " + insurance.ToString("C") +
" Taxes: " + taxes.ToString("C")+
"Date Purchased: " + datePurchased.ToShortDateString();
desc[2] = "";
}
..............
}
class clsApartment : clsBuilding
{
........................
}
.......
myApt = new clsApartment();
myApt.PropertySummary(desc);
But what is the use of protected property that I have declared at the begining of the parent Class. When I was trying to access them either by using the object of the derived class or directly as instructed in the book:
Just to Drive the point home,given a line in clsBuilding(parent class):
protected decimal purchase price;
you could have the line :
you could have the line purchaseprice = 150000M ; in class home and it would be perfectly acceptable. (Chapter 15,page 447 after 4th paragraph) , neither was a successful on attempt.
I am sure , I must have got the concept wrong or missed something. If not then , why any one would be declaring protected variable or property?
EDIT:
public class clsBuilding
{
//--------------------- Symbolic constants -------------------
public const int APARTMENT = 1;
public const int COMMERCIAL = 2;
public const int HOME = 3;
private string[] whichType = { "", "Apartment", "Commercial", "Home" };
//--------------------- Instance variables -------------------
protected string address;
protected decimal purchasePrice;
protected decimal monthlyPayment;
protected decimal taxes;
protected decimal insurance;
protected DateTime datePurchased;
protected int buildingType;
//--------------------- Constructor --------------------------
public clsBuilding()
{
address = "Not closed yet";
}
public clsBuilding(string addr, decimal price, decimal payment,
decimal tax, decimal insur, DateTime date, int type):this()
{
if (addr.Equals("") == false)
address = addr;
purchasePrice = price;
monthlyPayment = payment;
taxes = tax;
insurance = insur;
datePurchased = date;
buildingType = type;
}
//--------------------- Property Methods ---------------------
public string Address
{
get
{
return address;
}
set
{
if (value.Length != 0)
address = value;
}
}
public decimal PurchasePrice
{
get
{
return purchasePrice;
}
set
{
if (value > 0M)
purchasePrice = value;
}
}
public decimal MonthlyPayment
{
get
{
return monthlyPayment;
}
set
{
if (value > 0M)
monthlyPayment = value;
}
}
public decimal Taxes
{
get
{
return taxes;
}
set
{
if (value > 0M)
taxes = value;
}
}
public decimal Insurance
{
get
{
return insurance;
}
set
{
if (value > 0M)
insurance = value;
}
}
public DateTime DatePurchased
{
get
{
return datePurchased;
}
set
{
if (value.Year > 2008)
datePurchased = value;
}
}
public int BuildingType
{
get
{
return buildingType;
}
set
{
if (value >= APARTMENT && value <= HOME)
buildingType = value;
}
}
//--------------------- General Methods ----------------------
/*****
* Purpose: Provide a basic description of the property
*
* Parameter list:
* string[] desc a string array to hold description
*
* Return value:
* void
*
* CAUTION: Method assumes that there are 3 elements in array
******/
public void PropertySummary(string[] desc)
{
desc[0] = "Property type: " + whichType[buildingType] +
", " + address +
", Cost: " + purchasePrice.ToString("C") +
", Monthly payment: " + monthlyPayment.ToString("C");
desc[1] = " Insurance: " + insurance.ToString("C") + " Taxes: " + taxes.ToString("C") +
" Date purchased: " + datePurchased.ToShortDateString();
desc[2] = " ";
}
/*****
* Purpose: To call someone for snow removal, if available
*
* Parameter list:
* n/a
*
* Return value:
* string
******/
public virtual string RemoveSnow()
{
return whichType[buildingType] + ": No snow removal service available.";
}
}
class clsCommercial : clsBuilding
{
//--------------------- Instance variables -------------------
private int squareFeet;
private int parkingSpaces;
private decimal rentPerSquareFoot;
//--------------------- Constructor --------------------------
public clsCommercial(string addr, decimal price, decimal payment,
decimal tax, decimal insur, DateTime date, int type) :
base(addr, price, payment, tax, insur, date, type)
{
buildingType = type; // Commercial type from base
}
//--------------------- Property Methods ---------------------
public int SquareFeet
{
get
{
return squareFeet;
}
set
{
if (value > 0)
squareFeet = value;
}
}
public int ParkingSpaces
{
get
{
return parkingSpaces;
}
set
{
parkingSpaces = value;
}
}
public decimal RentPerSquareFoot
{
get
{
return rentPerSquareFoot;
}
set
{
if (value > 0M)
rentPerSquareFoot = value;
}
}
//--------------------- General Methods ----------------------
public override string RemoveSnow()
{
return "Commercial: Call Acme Snow Plowing: 803.234.5566";
}
}
public frmMain()
{
InitializeComponent();
myTime = DateTime.Now;
myApt = new clsApartment("123 Ann Dotson Dr., Lexington, KY 40502", 550000, 6000,
15000, 3400, myTime, 1);
myComm = new clsCommercial("4442 Parker Place, York, SC 29745", 1200000, 9000,
22000, 8000, myTime, 2);
myHome = new clsHome("657 Dallas St, Ringgold, GA 30736", 260000, 1100,
1750, 900, myTime, 3);
}
解决方案
Building on what doug said. Protected makes a property, variable, or function available to a subclass, but not from outside the class. If you were to use private, it would still not be accessible from outside the class, nor would it be accessible from it's subclasses.
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