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<p class="MsoNormal"><span style="FONT-FAMILY: 黑体">终结器</span><span style="FONT-FAMILY: 宋体">类似于构造函数，但是在</span><span lang="EN-US">CLR</span><span style="FONT-FAMILY: 宋体">检测到不再需要某个对象时调用。它们的名称与类相同，但前面有一个</span><span lang="EN-US">~</span><span style="FONT-FAMILY: 宋体">符号。</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">程序员应注意，终结器在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中比在</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">中用得较少一些，因为</span><span lang="EN-US">CLR</span><span style="FONT-FAMILY: 宋体">会自动进行垃圾收集，另外，不可能预测什么时候调用析构函数。第</span><span lang="EN-US">7</span><span style="FONT-FAMILY: 宋体">章将介绍终结器。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 黑体">运算符</span><span style="FONT-FAMILY: 宋体">执行的最简单的操作就是</span><span lang="EN-US">+</span><span style="FONT-FAMILY: 宋体">和–。在对两个整数进行相加操作时，严格地说，就是对整数使用</span><span lang="EN-US">+</span><span style="FONT-FAMILY: 宋体">运算符。</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">还允许指定把已有的运算符应用于自己的类</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">运算符重载</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。第</span><span lang="EN-US">5</span><span style="FONT-FAMILY: 宋体">章将详细论述运算符。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 黑体">索引器</span><span style="FONT-FAMILY: 宋体">允许对象以数组或集合的方式进行索引。第</span><span lang="EN-US">5</span><span style="FONT-FAMILY: 宋体">章介绍索引器。</span></p>
<h4 style="TEXT-INDENT: 21.45pt"><span lang="EN-US" style="FONT-FAMILY: 黑体">1. </span><span style="FONT-FAMILY: 黑体">方法</span></h4>
<p class="MsoNormal"><span><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">VB</span></span><span style="FONT-FAMILY: 宋体">、</span><span lang="EN-US">C</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">中，可以定义与某个特定类完全不相关的全局函数，但在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中不能这样做。在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中，每个函数都必须与一个类或结构相关。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">注意，正式的</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">术语实际上并没有区分函数和方法。在这个术语中，“函数”不仅包含方法，而且也包含类或结构的一些非数据成员。它包括索引器、运算符、构造函数和析构函数等，甚至还有属性。这些都不是数据成员，字段、常量和事件才是数据成员。本章将详细讨论方法。</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; TEXT-INDENT: 21.45pt"><span lang="EN-US">(1) </span><span style="FONT-FAMILY: 黑体">方法的声明</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中，定义方法的语法与</span><span lang="EN-US">C</span><span style="FONT-FAMILY: 宋体">风格的语言相同，与</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">Java</span><span style="FONT-FAMILY: 宋体">中的语法也相同。与</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">的主要语法区别是，在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中，每个方法都单独声明为</span><span lang="EN-US">public</span><span style="FONT-FAMILY: 宋体">或</span><span lang="EN-US">private</span><span style="FONT-FAMILY: 宋体">，不能使用</span><span lang="EN-US">public</span><span style="FONT-FAMILY: 宋体">：块把几个方法定义组合起来。另外，所有的</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">方法都在类定义中声明和定义。在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中，不能像在</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">中那样把方法的实现代码分隔开来。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中，方法的定义包括方法的修饰符</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">例如方法的可访问性</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">、返回值的类型，然后是方法名、输入参数的列表</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">用圆括号括起来</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">和方法体</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">用花括号括起来</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="a6" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">[modifiers] return_type MethodName([parameters])</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 15pt"><span lang="EN-US">{</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 15pt"><span lang="EN-US"> // Method body</span></p>
<p class="a6" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">每个参数都包括参数类型名及在方法体中的引用名称。但如果方法有返回值，</span><span lang="EN-US">return</span><span style="FONT-FAMILY: 宋体">语句就必须与返回值一起使用，指定出口点，例如：</span></p>
<p class="2" style="MARGIN: 9.8pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">public bool IsSquare(Rectangle rect)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 15pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 15pt"><span lang="EN-US"> return (rect.Height == rect.Width);</span></p>
<p class="2" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">这段代码使用一个表示矩形的</span><span lang="EN-US">.NET</span><span style="FONT-FAMILY: 宋体">基类</span><span lang="EN-US">System.Drawing.Rectangle</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">如果方法没有返回值，就把返回类型指定为</span><span lang="EN-US">void</span><span style="FONT-FAMILY: 宋体">，因为不能省略返回类型。如果方法不带参数，仍需要在方法名的后面写上一对空的圆括号</span><span lang="EN-US">()(</span><span style="FONT-FAMILY: 宋体">就像本章前面的</span><span lang="EN-US">Main()</span><span style="FONT-FAMILY: 宋体">方法</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。此时还包含一个可选的</span><span lang="EN-US">return</span><span style="FONT-FAMILY: 宋体">语句<span style="LETTER-SPACING: -1pt">——</span></span><span style="LETTER-SPACING: -1pt"> </span><span style="FONT-FAMILY: 宋体">当到达右花括号时，方法会自动返回。注意方法可以包含任意多个</span><span lang="EN-US">return</span><span style="FONT-FAMILY: 宋体">语句：</span></p>
<p class="2" style="MARGIN: 9.8pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">public bool IsPositive(int value)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 15pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 15pt"><span lang="EN-US"> if (value < 0)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 15pt"><span lang="EN-US"> return false;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 15pt"><span lang="EN-US"> return true;</span></p>
<p class="2" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; TEXT-INDENT: 21.45pt"><span lang="EN-US">(2) </span><span style="FONT-FAMILY: 黑体">调用方法</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中调用方法的语法与</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">Java</span><span style="FONT-FAMILY: 宋体">中的一样，</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">VB</span><span style="FONT-FAMILY: 宋体">的惟一区别是在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中调用方法时，必须使用圆括号，这要比</span><span lang="EN-US">VB 6</span><span style="FONT-FAMILY: 宋体">中有时需要括号，有时不需要括号的规则简单一些。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">下面的例子</span><span lang="EN-US">MathTest</span><span style="FONT-FAMILY: 宋体">说明了类的定义和实例化、方法的定义和调用的语法。除了包含</span><span lang="EN-US">Main()</span><span style="FONT-FAMILY: 宋体">方法的类之外，它还定义了类</span><span lang="EN-US">MathTest</span><span style="FONT-FAMILY: 宋体">，该类包含两个方法和一个字段。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">using System;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">namespace Wrox.ProCSharp. MathTestSample</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> class MainEntryPoint</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> static void Main()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> // Try calling some static functions</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("Pi is " + MathTest.GetPi());</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> int x = MathTest.GetSquareOf(5);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("Square of 5 is " + x);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> // Instantiate at MathTest object</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> MathTest math = new MathTest(); // this is C#'s way of</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> // instantiating a reference type</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> // Call non-static methods</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> math.value = 30;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine(</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> "Value field of math variable contains " + math.value);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("Square of 30 is " + math.GetSquare());</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> // Define a class named MathTest on which we will call a method</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> class MathTest</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> public int value;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> public int GetSquare()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> return value*value;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> public static int GetSquareOf(int x)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> {</span></p>
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