Csharp 简明教程

C

你可以重新定义或重载 C# 中可用的内置运算符的大部分。因此，程序员可以使用自定义类型的运算符。重载的运算符是具有特殊名称的函数，关键词 operator 后跟要定义运算符的符号。与其他任何函数类似，重载的运算符具有一个返回类型和一个参数列表。

例如，仔细阅读以下函数 −

public static Box operator+ (Box b, Box c) {
   Box box = new Box();
   box.length = b.length + c.length;
   box.breadth = b.breadth + c.breadth;
   box.height = b.height + c.height;
   return box;
}

上述函数为用户自定义类 Box 实现了加法运算符 (+)。它添加了两个 Box 对象的属性并返回结果 Box 对象。

Implementing the Operator Overloading

以下程序显示了完整的实现 −

using System;

namespace OperatorOvlApplication {
   class Box {
      private double length;   // Length of a box
      private double breadth;  // Breadth of a box
      private double height;   // Height of a box

      public double getVolume() {
         return length * breadth * height;
      }
      public void setLength( double len ) {
         length = len;
      }
      public void setBreadth( double bre ) {
         breadth = bre;
      }
      public void setHeight( double hei ) {
         height = hei;
      }

      // Overload + operator to add two Box objects.
      public static Box operator+ (Box b, Box c) {
         Box box = new Box();
         box.length = b.length + c.length;
         box.breadth = b.breadth + c.breadth;
         box.height = b.height + c.height;
         return box;
      }
   }
   class Tester {
      static void Main(string[] args) {
         Box Box1 = new Box();   // Declare Box1 of type Box
         Box Box2 = new Box();   // Declare Box2 of type Box
         Box Box3 = new Box();   // Declare Box3 of type Box
         double volume = 0.0;    // Store the volume of a box here

         // box 1 specification
         Box1.setLength(6.0);
         Box1.setBreadth(7.0);
         Box1.setHeight(5.0);

         // box 2 specification
         Box2.setLength(12.0);
         Box2.setBreadth(13.0);
         Box2.setHeight(10.0);

         // volume of box 1
         volume = Box1.getVolume();
         Console.WriteLine("Volume of Box1 : {0}", volume);

         // volume of box 2
         volume = Box2.getVolume();
         Console.WriteLine("Volume of Box2 : {0}", volume);

         // Add two object as follows:
         Box3 = Box1 + Box2;

         // volume of box 3
         volume = Box3.getVolume();
         Console.WriteLine("Volume of Box3 : {0}", volume);
         Console.ReadKey();
      }
   }
}

编译并执行上述代码后，将产生以下结果 −

Volume of Box1 : 210
Volume of Box2 : 1560
Volume of Box3 : 5400

Overloadable and Non-Overloadable Operators

下表描述了 C# 中运算符的可重载性 −

Sr.No.	Operators & Description
1	, -, !, ~, +, -- 这些一元运算符带有一个操作数，并且可以重载。
2	*+, -, , /, %** 这些二元运算符带有一个操作数，并且可以重载。
3	==, !=, <, >, ⇐, >= 比较运算符可以重载。
4	*&&,
	*条件逻辑运算符不能直接重载。
5	*+=, -=, =, /=, %=** 赋值运算符不能重载。
6	=, ., ?:, →, new, is, sizeof, typeof 这些运算符不能重载。

Example

根据以上讨论，让我们扩展前一个示例，并重载更多运算符 −

using System;

namespace OperatorOvlApplication {
   class Box {
      private double length;    // Length of a box
      private double breadth;   // Breadth of a box
      private double height;    // Height of a box

      public double getVolume() {
         return length * breadth * height;
      }
      public void setLength( double len ) {
         length = len;
      }
      public void setBreadth( double bre ) {
         breadth = bre;
      }
      public void setHeight( double hei ) {
         height = hei;
      }

      // Overload + operator to add two Box objects.
      public static Box operator+ (Box b, Box c) {
         Box box = new Box();
         box.length = b.length + c.length;
         box.breadth = b.breadth + c.breadth;
         box.height = b.height + c.height;
         return box;
      }
      public static bool operator == (Box lhs, Box rhs) {
         bool status = false;
         if (lhs.length == rhs.length && lhs.height == rhs.height
            && lhs.breadth == rhs.breadth) {

            status = true;
         }
         return status;
      }
      public static bool operator !=(Box lhs, Box rhs) {
         bool status = false;

         if (lhs.length != rhs.length || lhs.height != rhs.height ||
            lhs.breadth != rhs.breadth) {

            status = true;
         }
         return status;
      }
      public static bool operator <(Box lhs, Box rhs) {
         bool status = false;

         if (lhs.length < rhs.length && lhs.height < rhs.height
            && lhs.breadth < rhs.breadth) {

            status = true;
         }
         return status;
      }
      public static bool operator >(Box lhs, Box rhs) {
         bool status = false;

         if (lhs.length > rhs.length && lhs.height >
            rhs.height && lhs.breadth > rhs.breadth) {

            status = true;
         }
         return status;
      }
      public static bool operator <=(Box lhs, Box rhs) {
         bool status = false;

         if (lhs.length <= rhs.length && lhs.height
            <= rhs.height && lhs.breadth <= rhs.breadth) {

            status = true;
         }
         return status;
      }
      public static bool operator >=(Box lhs, Box rhs) {
         bool status = false;

         if (lhs.length >= rhs.length && lhs.height
            >= rhs.height && lhs.breadth >= rhs.breadth) {

            status = true;
         }
         return status;
      }
      public override string ToString() {
         return String.Format("({0}, {1}, {2})", length, breadth, height);
      }
   }
   class Tester {
      static void Main(string[] args) {
         Box Box1 = new Box();   // Declare Box1 of type Box
         Box Box2 = new Box();   // Declare Box2 of type Box
         Box Box3 = new Box();   // Declare Box3 of type Box
         Box Box4 = new Box();
         double volume = 0.0;    // Store the volume of a box here

         // box 1 specification
         Box1.setLength(6.0);
         Box1.setBreadth(7.0);
         Box1.setHeight(5.0);

         // box 2 specification
         Box2.setLength(12.0);
         Box2.setBreadth(13.0);
         Box2.setHeight(10.0);

         //displaying the Boxes using the overloaded ToString():
         Console.WriteLine("Box 1: {0}", Box1.ToString());
         Console.WriteLine("Box 2: {0}", Box2.ToString());

         // volume of box 1
         volume = Box1.getVolume();
         Console.WriteLine("Volume of Box1 : {0}", volume);

         // volume of box 2
         volume = Box2.getVolume();
         Console.WriteLine("Volume of Box2 : {0}", volume);

         // Add two object as follows:
         Box3 = Box1 + Box2;
         Console.WriteLine("Box 3: {0}", Box3.ToString());

         // volume of box 3
         volume = Box3.getVolume();
         Console.WriteLine("Volume of Box3 : {0}", volume);

         //comparing the boxes
         if (Box1 > Box2)
            Console.WriteLine("Box1 is greater than Box2");
         else
            Console.WriteLine("Box1 is not greater than Box2");

         if (Box1 < Box2)
            Console.WriteLine("Box1 is less than Box2");
         else
            Console.WriteLine("Box1 is not less than Box2");

         if (Box1 >= Box2)
            Console.WriteLine("Box1 is greater or equal to Box2");
         else
            Console.WriteLine("Box1 is not greater or equal to Box2");

         if (Box1 <= Box2)
            Console.WriteLine("Box1 is less or equal to Box2");
         else
            Console.WriteLine("Box1 is not less or equal to Box2");

         if (Box1 != Box2)
            Console.WriteLine("Box1 is not equal to Box2");
         else
            Console.WriteLine("Box1 is not greater or equal to Box2");
         Box4 = Box3;

         if (Box3 == Box4)
            Console.WriteLine("Box3 is equal to Box4");
         else
            Console.WriteLine("Box3 is not equal to Box4");

         Console.ReadKey();
      }
   }
}

编译并执行上述代码后，将产生以下结果 −

Box 1: (6, 7, 5)
Box 2: (12, 13, 10)
Volume of Box1 : 210
Volume of Box2 : 1560
Box 3: (18, 20, 15)
Volume of Box3 : 5400
Box1 is not greater than Box2
Box1 is less than Box2
Box1 is not greater or equal to Box2
Box1 is less or equal to Box2
Box1 is not equal to Box2
Box3 is equal to Box4