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贴子主题： C#快餐－6

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发信人: walts (休息一会), 信区: DotNET
标  题: C#快餐－6
发信站: BBS 水木清华站 (Thu Jul 26 01:27:36 2001)

Lesson 6 Understanding static and instance  members.

   Static member of a class is shared by all instances
of the class. Here is a simple example:

using System;
class Demo{
    public static int k;
    public int i;
    public void show(){
        Console.WriteLine("k={0} i={1}", k, i);
    }
}

class Test{
public static void Main(){
    Demo a = new Demo();
    a.i = 1;
    Demo b = new Demo();
    b.i = 2;
    Demo.k = 4;
    a.show();
    b.show();
    }
}

Output:
k=4 j=1
k=4 j=2

Class Demo has a static member k and an instance member i.
Class Test has two objects of type Demo: a and b.
Since k is staticStatic variable is a property  of the class
Both a and b have the same value of k.
To  change value of k we cannot use a or b
but rather a special call Demo.k = 4 is required.
Instance variable i can have different values for
different objects.

Instance variable is a property of the object.
Non static member cannot reference  a static member.
The second property is especially important.
The compiler allocates static and non static objects
with different addressing schemes and one
has to be careful that no references are passed
between static and non static members. Here is a
simple example:

using System;
public class Test{
   public static void swap (ref int x, ref int y)
   {
      int temp=x;
      x = y;
      y = temp;
   }
   static void Main()
   {
      int a = 2;
      int b = 4;
      swap(ref a, ref b);
      Console.WriteLine("a={0}, b={1}",a,b);
   }
}

   Main and swap are two static methods of class Test and they can pass
references to each other. Alternatively you could pass a reference to an
object:

using System;
public class Swap{
   public void swap (ref int x, ref int y)
   {
      int temp=x;
      x=y;
      y=temp;
   }
}
public class Test
{
   static void Main()
   {
      int a=2;
      int b=4;
      Swap hi = new Swap();
      hi.swap(ref a, ref b);
      Console.WriteLine ("a={0}, b={1}", a, b);
   }
}

  I haven't discussed static members of methods. Could you come up with a
simple example?

--

A great poem is a fountain forever overflowing with the
　waters of wisdom and delight.
　　　　　　　　　　　
                                          —— Shelley

※ 来源:·BBS 水木清华站 smth.org·[FROM: 166.111.142.118]
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