运算符重载
您可以重定义或重载 C# 中内置的运算符。因此，程序员也可以使用用户自定义类型的运算符。重载运算符是具有特殊名称的函数，是通过关键字 operator 后跟运算符的符号来定义的。与其他函数一样，重载运算符有返回类型和参数列表。
例如，请看下面的函数：
|
1 2 3 4 5 6 7 8 9 |
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> Box <span class="hljs-keyword">operator</span>+ (Box b, Box c) { Box box = <span class="hljs-keyword">new</span> Box(); box.length = b.length + c.length; box.breadth = b.breadth + c.breadth; box.height = b.height + c.height; <span class="hljs-keyword">return</span> box; } |
上面的函数为用户自定义的类 Box 实现了加法运算符（+）。它把两个 Box 对象的属性相加，并返回相加后的 Box 对象。
一、运算符重载的实现
下面的程序演示了完整的实现：
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 |
<span class="hljs-keyword">using</span> System; <span class="hljs-keyword">namespace</span> <span class="hljs-title">OperatorOvlApplication</span> { <span class="hljs-keyword">class</span> <span class="hljs-title">Box</span> { <span class="hljs-keyword">private</span> <span class="hljs-keyword">double</span> length; <span class="hljs-comment">// 长度</span> <span class="hljs-keyword">private</span> <span class="hljs-keyword">double</span> breadth; <span class="hljs-comment">// 宽度</span> <span class="hljs-keyword">private</span> <span class="hljs-keyword">double</span> height; <span class="hljs-comment">// 高度</span> <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">double</span> <span class="hljs-title">getVolume</span>() </span>{ <span class="hljs-keyword">return</span> length * breadth * height; } <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setLength</span>(<span class="hljs-params"> <span class="hljs-keyword">double</span> len </span>) </span>{ length = len; } <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setBreadth</span>(<span class="hljs-params"> <span class="hljs-keyword">double</span> bre </span>) </span>{ breadth = bre; } <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setHeight</span>(<span class="hljs-params"> <span class="hljs-keyword">double</span> hei </span>) </span>{ height = hei; } <span class="hljs-comment">// 重载 + 运算符来把两个 Box 对象相加</span> <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> Box <span class="hljs-keyword">operator</span>+ (Box b, Box c) { Box box = <span class="hljs-keyword">new</span> Box(); box.length = b.length + c.length; box.breadth = b.breadth + c.breadth; box.height = b.height + c.height; <span class="hljs-keyword">return</span> box; } } <span class="hljs-keyword">class</span> <span class="hljs-title">Tester</span> { <span class="hljs-function"><span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">Main</span>(<span class="hljs-params"><span class="hljs-keyword">string</span>[] args</span>) </span>{ Box Box1 = <span class="hljs-keyword">new</span> Box(); <span class="hljs-comment">// 声明 Box1，类型为 Box</span> Box Box2 = <span class="hljs-keyword">new</span> Box(); <span class="hljs-comment">// 声明 Box2，类型为 Box</span> Box Box3 = <span class="hljs-keyword">new</span> Box(); <span class="hljs-comment">// 声明 Box3，类型为 Box</span> <span class="hljs-keyword">double</span> volume = <span class="hljs-number">0.0</span>; <span class="hljs-comment">// 体积</span> <span class="hljs-comment">// Box1 详述</span> Box1.setLength(<span class="hljs-number">6.0</span>); Box1.setBreadth(<span class="hljs-number">7.0</span>); Box1.setHeight(<span class="hljs-number">5.0</span>); <span class="hljs-comment">// Box2 详述</span> Box2.setLength(<span class="hljs-number">12.0</span>); Box2.setBreadth(<span class="hljs-number">13.0</span>); Box2.setHeight(<span class="hljs-number">10.0</span>); <span class="hljs-comment">// Box1 的体积</span> volume = Box1.getVolume(); Console.WriteLine(<span class="hljs-string">"Box1 的体积： {0}"</span>, volume); <span class="hljs-comment">// Box2 的体积</span> volume = Box2.getVolume(); Console.WriteLine(<span class="hljs-string">"Box2 的体积： {0}"</span>, volume); <span class="hljs-comment">// 把两个对象相加</span> Box3 = Box1 + Box2; <span class="hljs-comment">// Box3 的体积</span> volume = Box3.getVolume(); Console.WriteLine(<span class="hljs-string">"Box3 的体积： {0}"</span>, volume); Console.ReadKey(); } } } |
当上面的代码被编译和执行时，它会产生下列结果：
|
1 2 3 4 |
Box1 的体积： <span class="hljs-number">210</span> Box2 的体积： <span class="hljs-number">1560</span> Box3 的体积： <span class="hljs-number">5400</span> |
二、可重载和不可重载运算符
下表描述了 C# 中运算符重载的能力：
| 运算符 | 描述 | ||
|---|---|---|---|
| +, -, !, ~, ++, — | 这些一元运算符只有一个操作数，且可以被重载。 | ||
| +, -, *, /, % | 这些二元运算符带有两个操作数，且可以被重载。 | ||
==, !=, <, >, <=, >= |
这些比较运算符可以被重载。 | ||
| &&, \ | \ | 这些条件逻辑运算符不能被直接重载。 | |
| +=, -=, *=, /=, %= | 这些赋值运算符不能被重载。 | ||
| =, ., ?:, ->, new, is, sizeof, typeof | 这些运算符不能被重载。 |
实例
针对上述讨论，让我们扩展上面的实例，重载更多的运算符：
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 |
<span class="hljs-keyword">using</span> System; <span class="hljs-keyword">namespace</span> <span class="hljs-title">OperatorOvlApplication</span> { <span class="hljs-keyword">class</span> <span class="hljs-title">Box</span> { <span class="hljs-keyword">private</span> <span class="hljs-keyword">double</span> length; <span class="hljs-comment">// 长度</span> <span class="hljs-keyword">private</span> <span class="hljs-keyword">double</span> breadth; <span class="hljs-comment">// 宽度</span> <span class="hljs-keyword">private</span> <span class="hljs-keyword">double</span> height; <span class="hljs-comment">// 高度</span> <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">double</span> <span class="hljs-title">getVolume</span>() </span>{ <span class="hljs-keyword">return</span> length * breadth * height; } <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setLength</span>(<span class="hljs-params"> <span class="hljs-keyword">double</span> len </span>) </span>{ length = len; } <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setBreadth</span>(<span class="hljs-params"> <span class="hljs-keyword">double</span> bre </span>) </span>{ breadth = bre; } <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setHeight</span>(<span class="hljs-params"> <span class="hljs-keyword">double</span> hei </span>) </span>{ height = hei; } <span class="hljs-comment">// 重载 + 运算符来把两个 Box 对象相加</span> <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> Box <span class="hljs-keyword">operator</span>+ (Box b, Box c) { Box box = <span class="hljs-keyword">new</span> Box(); box.length = b.length + c.length; box.breadth = b.breadth + c.breadth; box.height = b.height + c.height; <span class="hljs-keyword">return</span> box; } <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span> == (Box lhs, Box rhs) { <span class="hljs-keyword">bool</span> status = <span class="hljs-keyword">false</span>; <span class="hljs-keyword">if</span> (lhs.length == rhs.length && lhs.height == rhs.height && lhs.breadth == rhs.breadth) { status = <span class="hljs-keyword">true</span>; } <span class="hljs-keyword">return</span> status; } <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span> !=(Box lhs, Box rhs) { <span class="hljs-keyword">bool</span> status = <span class="hljs-keyword">false</span>; <span class="hljs-keyword">if</span> (lhs.length != rhs.length || lhs.height != rhs.height || lhs.breadth != rhs.breadth) { status = <span class="hljs-keyword">true</span>; } <span class="hljs-keyword">return</span> status; } <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span> <(Box lhs, Box rhs) { <span class="hljs-keyword">bool</span> status = <span class="hljs-keyword">false</span>; <span class="hljs-keyword">if</span> (lhs.length < rhs.length && lhs.height < rhs.height && lhs.breadth < rhs.breadth) { status = <span class="hljs-keyword">true</span>; } <span class="hljs-keyword">return</span> status; } <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span> >(Box lhs, Box rhs) { <span class="hljs-keyword">bool</span> status = <span class="hljs-keyword">false</span>; <span class="hljs-keyword">if</span> (lhs.length > rhs.length && lhs.height > rhs.height && lhs.breadth > rhs.breadth) { status = <span class="hljs-keyword">true</span>; } <span class="hljs-keyword">return</span> status; } <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span> <=(Box lhs, Box rhs) { <span class="hljs-keyword">bool</span> status = <span class="hljs-keyword">false</span>; <span class="hljs-keyword">if</span> (lhs.length <= rhs.length && lhs.height <= rhs.height && lhs.breadth <= rhs.breadth) { status = <span class="hljs-keyword">true</span>; } <span class="hljs-keyword">return</span> status; } <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span> >=(Box lhs, Box rhs) { <span class="hljs-keyword">bool</span> status = <span class="hljs-keyword">false</span>; <span class="hljs-keyword">if</span> (lhs.length >= rhs.length && lhs.height >= rhs.height && lhs.breadth >= rhs.breadth) { status = <span class="hljs-keyword">true</span>; } <span class="hljs-keyword">return</span> status; } <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">override</span> <span class="hljs-keyword">string</span> <span class="hljs-title">ToString</span>() </span>{ <span class="hljs-keyword">return</span> String.Format(<span class="hljs-string">"({0}, {1}, {2})"</span>, length, breadth, height); } } <span class="hljs-keyword">class</span> <span class="hljs-title">Tester</span> { <span class="hljs-function"><span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">Main</span>(<span class="hljs-params"><span class="hljs-keyword">string</span>[] args</span>) </span>{ Box Box1 = <span class="hljs-keyword">new</span> Box(); <span class="hljs-comment">// 声明 Box1，类型为 Box</span> Box Box2 = <span class="hljs-keyword">new</span> Box(); <span class="hljs-comment">// 声明 Box2，类型为 Box</span> Box Box3 = <span class="hljs-keyword">new</span> Box(); <span class="hljs-comment">// 声明 Box3，类型为 Box</span> Box Box4 = <span class="hljs-keyword">new</span> Box(); <span class="hljs-keyword">double</span> volume = <span class="hljs-number">0.0</span>; <span class="hljs-comment">// 体积</span> <span class="hljs-comment">// Box1 详述</span> Box1.setLength(<span class="hljs-number">6.0</span>); Box1.setBreadth(<span class="hljs-number">7.0</span>); Box1.setHeight(<span class="hljs-number">5.0</span>); <span class="hljs-comment">// Box2 详述</span> Box2.setLength(<span class="hljs-number">12.0</span>); Box2.setBreadth(<span class="hljs-number">13.0</span>); Box2.setHeight(<span class="hljs-number">10.0</span>); <span class="hljs-comment">// 使用重载的 ToString() 显示两个盒子</span> Console.WriteLine(<span class="hljs-string">"Box1： {0}"</span>, Box1.ToString()); Console.WriteLine(<span class="hljs-string">"Box2： {0}"</span>, Box2.ToString()); <span class="hljs-comment">// Box1 的体积</span> volume = Box1.getVolume(); Console.WriteLine(<span class="hljs-string">"Box1 的体积： {0}"</span>, volume); <span class="hljs-comment">// Box2 的体积</span> volume = Box2.getVolume(); Console.WriteLine(<span class="hljs-string">"Box2 的体积： {0}"</span>, volume); <span class="hljs-comment">// 把两个对象相加</span> Box3 = Box1 + Box2; Console.WriteLine(<span class="hljs-string">"Box3： {0}"</span>, Box3.ToString()); <span class="hljs-comment">// Box3 的体积</span> volume = Box3.getVolume(); Console.WriteLine(<span class="hljs-string">"Box3 的体积： {0}"</span>, volume); <span class="hljs-comment">//comparing the boxes</span> <span class="hljs-keyword">if</span> (Box1 > Box2) Console.WriteLine(<span class="hljs-string">"Box1 大于 Box2"</span>); <span class="hljs-keyword">else</span> Console.WriteLine(<span class="hljs-string">"Box1 不大于 Box2"</span>); <span class="hljs-keyword">if</span> (Box1 < Box2) Console.WriteLine(<span class="hljs-string">"Box1 小于 Box2"</span>); <span class="hljs-keyword">else</span> Console.WriteLine(<span class="hljs-string">"Box1 不小于 Box2"</span>); <span class="hljs-keyword">if</span> (Box1 >= Box2) Console.WriteLine(<span class="hljs-string">"Box1 大于等于 Box2"</span>); <span class="hljs-keyword">else</span> Console.WriteLine(<span class="hljs-string">"Box1 不大于等于 Box2"</span>); <span class="hljs-keyword">if</span> (Box1 <= Box2) Console.WriteLine(<span class="hljs-string">"Box1 小于等于 Box2"</span>); <span class="hljs-keyword">else</span> Console.WriteLine(<span class="hljs-string">"Box1 不小于等于 Box2"</span>); <span class="hljs-keyword">if</span> (Box1 != Box2) Console.WriteLine(<span class="hljs-string">"Box1 不等于 Box2"</span>); <span class="hljs-keyword">else</span> Console.WriteLine(<span class="hljs-string">"Box1 等于 Box2"</span>); Box4 = Box3; <span class="hljs-keyword">if</span> (Box3 == Box4) Console.WriteLine(<span class="hljs-string">"Box3 等于 Box4"</span>); <span class="hljs-keyword">else</span> Console.WriteLine(<span class="hljs-string">"Box3 不等于 Box4"</span>); Console.ReadKey(); } } } |
当上面的代码被编译和执行时，它会产生下列结果：
|
1 2 3 4 5 6 7 8 9 10 11 12 |
Box1： (<span class="hljs-number">6</span>, <span class="hljs-number">7</span>, <span class="hljs-number">5</span>) Box2： (<span class="hljs-number">12</span>, <span class="hljs-number">13</span>, <span class="hljs-number">10</span>) Box1 的体积： <span class="hljs-number">210</span> Box2 的体积： <span class="hljs-number">1560</span> Box3： (<span class="hljs-number">18</span>, <span class="hljs-number">20</span>, <span class="hljs-number">15</span>) Box3 的体积： <span class="hljs-number">5400</span> Box1 不大于 Box2 Box1 小于 Box2 Box1 不大于等于 Box2 Box1 小于等于 Box2 Box1 不等于 Box2 Box3 等于 Box4 |
