C#方法的重載

在前面的例子中，我們實際上已經看到了建構函式的重載。

程式清單11-7:

using System;class Vehicle //定義汽車類{  public int wheels; //公有成員：輪子個數  protected float weight; //保護成員：重量  public Vehicle(){;}  public Vehicle(int w,float g){      wheels=w;      weight=g;    }  public void Show(){     Console.WriteLine("the wheel of vehicle is:{0}",wheels);     Console.WriteLine("the weight of vehicle is:{0}",weight);    }  };

類的成員方法的重載也是類似的。類中兩個以上的方法（包括隱藏的繼承而來的方法），取的名字相同，只要使用的參數類型或者參數個數不同，編譯器便知道在何種情況下應該調用哪個方法，這就叫做方法的系列重載。

其實，我們非常熟悉的Console類之所以能夠實現對字串進行格式化的功能，就是因為它定義了多個重載的成員方法：

public static void WriteLine();
public static void WriteLine(int);
public static void WriteLine(float);
public static void WriteLine(long);
public static void WriteLine(uint);
public static void WriteLine(char);
public static void WriteLine(bool);
public static void WriteLine(double);
public static void WriteLine(char[]);
public static void WriteLine(string);
public static void WriteLine(Object);
public static void WriteLine(ulong);
public static void WriteLine(string,Object[]);
public static void WriteLine(string,Object);
public static void WriteLine(char[],int,int);
public static void WriteLine(string,Object,Object);
public static void WriteLine(string,Object,Object,Object);

我們舉例子來說明重載的使用。學生類中包含有學生姓名、性別、年齡、體重等資訊。我們需要比較學生之間的年齡和體重，我們可以採用下面的代碼。

程式清單11-8:

using System;class Student //定義學生類{     public string s_name;     public int s_age;     public float s_weight; public Student(string n,int a,float w){     s_name=n;     s_age=a;     s_weight=w;}     public int max_age(int x,int y){         if(x>y) return x;         else return y;     }     public float max_weight(float x,float y){        if(x>y) return x;        else return y;     } }   class Test   {    public static void Main(){       Student s1=new Student("Mike",21,70);       Student s2=new Student("John",21,70);       if(s1.max_age(s1.s_age,s2.s_age)==s1.s_age)          Console.WriteLine("{0}'s age is bigger than {1}'s",s1.s_name,s2.s_name);       else          Console.WriteLine("{0}'s age is smaller than {1}'s",s1.s_name,s2.s_name);       if(s1.max_weight(s1.s_weight,s2.s_weight)==s1.s_weight)          Console.WriteLie("{0}'s weight is bigger than {1}'s",s1.s_name,s2.s_name);       else          Console.WriteLine("{0}'s weight is smaller than {1}'s",s1.s_name,s2.s_name);     }}

由於C#支援重載，我們可以給兩個比較大小的方法取同一個名字max,程式員在調用方法時，只需要在其中帶入實參，編譯器就會根據實參類型來決定到底調用哪個重載方法。程式員只需要使用max這個方法名，剩下的就是系統的事了。那樣，代碼我們改寫為：

程式清單11-9:

using System;class Student //定義學生類{     public string s_name;     public int s_age;     public float s_weight; public Student(string n,int a,float w){     s_name=n;     s_age=a;     s_weight=w; }     public int max(int x,int y){          if(x>y) return x;          else return y;     }     public float max(float x,float y){         if(x>y) return x;         else return y;     }  }  class Test  {    public static void Main(){       Student s1=new Student("Mike",21,70);       Student s2=new Student("John",21,70);       if(s1.max(s1.s_age,s2.age)==s1.s_age)          Console.WriteLine("{0}'s age is bigger than {1}'s",s1.name,s2.s_name);       else         Console.WriteLine("{0}'s age is smaller than {1}'s",s1.s_name,s2.s_name);       if(s1.max(s1.s_weight,s2.s_weight)==s1.s_weight)          Console.WriteLine("{0}'s weight is bigger than {1}'s",s1.s_name,s2.s_name);       else          Console.WriteLine("{0}'s weight is smaller than {1}'s",s1.s_name,s2.s_name);    }}