Collections of Objects 对象群集

定义：能在对象被创建时将他们收集在一起，作为一个群组来管理和进行整体操作，并且在需要的时候还能单独引用他们中的一个。

1：简单的群集——数组

　　遍历数组

　　for(int i=0;i<=99;i++){

　　　　if(studentBody[i] != null){//避开地雷

　　　　　　Console.WriteLine(studentBody[i].GetName());

　　　　}

　　}

2:有序列表

2.1有序列表和数组类似，但其中存储的项是以某种特定顺序放置的，在获取值的时候也按这种顺序取得，当新项被插入时，有序列表自动增加长度。(ArrayList)

using System;
using System.Collections;
public class SamplesArrayList  {

   public static void Main()  {

      // Creates and initializes a new ArrayList.
      ArrayList myAL = new ArrayList();
      myAL.Add("Hello");
      myAL.Add("World");
      myAL.Add("!");

      // Displays the properties and values of the ArrayList.
      Console.WriteLine( "myAL" );
      Console.WriteLine( "    Count:    {0}", myAL.Count );
      Console.WriteLine( "    Capacity: {0}", myAL.Capacity );
      Console.Write( "    Values:" );
      PrintValues( myAL );
   }

   public static void PrintValues( IEnumerable myList )  {
      foreach ( Object obj in myList )
         Console.Write( "   {0}", obj );
      Console.WriteLine();
   }

}

/*
This code produces output similar to the following:

myAL
    Count:    3
    Capacity: 4
    Values:   Hello   World   !

*/

2.2分类有序列表（是一种特殊的有序列表，普通的有序列表把新加入的对象自动添加到列表末尾，而分类有序列表把新加入的对象插入到列表的适当位置，以维持分类列表的分类排序，

　　　　　　　      对于分类有序列表我们必须定义对象的分类排序依据即定义一个分类键，典型的时SortedList.表示键/值对的集合，这些键值对按键排序并可按照键和索引访问。）

using System;
using System.Collections;
public class SamplesSortedList  {

   public static void Main()  {

      // Creates and initializes a new SortedList.
      SortedList mySL = new SortedList();
       mySL.Add("Third", "!");
       mySL.Add("Second", "World");
       mySL.Add("First", "Hello");

      // Displays the properties and values of the SortedList.
      Console.WriteLine( "mySL" );
      Console.WriteLine( "  Count:    {0}", mySL.Count );
      Console.WriteLine( "  Capacity: {0}", mySL.Capacity );
      Console.WriteLine( "  Keys and Values:" );
      PrintKeysAndValues( mySL );
   }

   public static void PrintKeysAndValues( SortedList myList )  {
      Console.WriteLine( "\t-KEY-\t-VALUE-" );
      for ( int i = 0; i < myList.Count; i++ )  {
         Console.WriteLine( "\t{0}:\t{1}", myList.GetKey(i), myList.GetByIndex(i) );
      }
      Console.WriteLine();
   }
}
/*
This code produces the following output.

mySL
  Count:    3
  Capacity: 16
  Keys and Values:
    -KEY-    -VALUE-
    First:    Hello
    Second:    World
    Third:    !
*/

3:集合（是一种未排序的群集，也就是说在将新项插入的集合中后，无法通过位置索引访问它）注意集合中不允许存在重复的对象引用但可以向有序列表中多次添加同一个对象。

4：字典（提供一种手段，让对象引用被存储时，同时存储一个唯一的查询键 典型的是Hashtable）

using System;
using System.Collections;

class Example
{
    public static void Main()
    {
        // Create a new hash table.
        //
        Hashtable openWith = new Hashtable();

        // Add some elements to the hash table. There are no
        // duplicate keys, but some of the values are duplicates.
        openWith.Add("txt", "notepad.exe");
        openWith.Add("bmp", "paint.exe");
        openWith.Add("dib", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");

        // The Add method throws an exception if the new key is
        // already in the hash table.
        try
        {
            openWith.Add("txt", "winword.exe");
        }
        catch
        {
            Console.WriteLine("An element with Key = \"txt\" already exists.");
        }

        // The Item property is the default property, so you
        // can omit its name when accessing elements.
        Console.WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]);

        // The default Item property can be used to change the value
        // associated with a key.
        openWith["rtf"] = "winword.exe";
        Console.WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]);

        // If a key does not exist, setting the default Item property
        // for that key adds a new key/value pair.
        openWith["doc"] = "winword.exe";

        // ContainsKey can be used to test keys before inserting
        // them.
        if (!openWith.ContainsKey("ht"))
        {
            openWith.Add("ht", "hypertrm.exe");
            Console.WriteLine("Value added for key = \"ht\": {0}", openWith["ht"]);
        }

        // When you use foreach to enumerate hash table elements,
        // the elements are retrieved as KeyValuePair objects.
        Console.WriteLine();
        foreach( DictionaryEntry de in openWith )
        {
            Console.WriteLine("Key = {0}, Value = {1}", de.Key, de.Value);
        }

        // To get the values alone, use the Values property.
        ICollection valueColl = openWith.Values;

        // The elements of the ValueCollection are strongly typed
        // with the type that was specified for hash table values.
        Console.WriteLine();
        foreach( string s in valueColl )
        {
            Console.WriteLine("Value = {0}", s);
        }

        // To get the keys alone, use the Keys property.
        ICollection keyColl = openWith.Keys;

        // The elements of the KeyCollection are strongly typed
        // with the type that was specified for hash table keys.
        Console.WriteLine();
        foreach( string s in keyColl )
        {
            Console.WriteLine("Key = {0}", s);
        }

        // Use the Remove method to remove a key/value pair.
        Console.WriteLine("\nRemove(\"doc\")");
        openWith.Remove("doc");

        if (!openWith.ContainsKey("doc"))
        {
            Console.WriteLine("Key \"doc\" is not found.");
        }
    }
}

/* This code example produces the following output:

An element with Key = "txt" already exists.
For key = "rtf", value = wordpad.exe.
For key = "rtf", value = winword.exe.
Value added for key = "ht": hypertrm.exe

Key = dib, Value = paint.exe
Key = txt, Value = notepad.exe
Key = ht, Value = hypertrm.exe
Key = bmp, Value = paint.exe
Key = rtf, Value = winword.exe
Key = doc, Value = winword.exe

Value = paint.exe
Value = notepad.exe
Value = hypertrm.exe
Value = paint.exe
Value = winword.exe
Value = winword.exe

Key = dib
Key = txt
Key = ht
Key = bmp
Key = rtf
Key = doc

Remove("doc")
Key "doc" is not found.
 */