详解C#中的泛型以及编程中使用泛型的优点

// Declare the generic class.
public class GenericList<T>
{
  void Add(T input) { }
}
class TestGenericList
{
  private class ExampleClass { }
  static void Main()
  {
    // Declare a list of type int.
    GenericList<int> list1 = new GenericList<int>();

    // Declare a list of type string.
    GenericList<string> list2 = new GenericList<string>();

    // Declare a list of type ExampleClass.
    GenericList<ExampleClass> list3 = new GenericList<ExampleClass>();
  }
}

// type parameter T in angle brackets
public class GenericList<T> 
{
  // The nested class is also generic on T.
  private class Node
  {
    // T used in non-generic constructor.
    public Node(T t)
    {
      next = null;
      data = t;
    }

    private Node next;
    public Node Next
    {
      get { return next; }
      set { next = value; }
    }

    // T as private member data type.
    private T data;

    // T as return type of property.
    public T Data 
    {
      get { return data; }
      set { data = value; }
    }
  }

  private Node head;

  // constructor
  public GenericList() 
  {
    head = null;
  }

  // T as method parameter type:
  public void AddHead(T t) 
  {
    Node n = new Node(t);
    n.Next = head;
    head = n;
  }

  public IEnumerator<T> GetEnumerator()
  {
    Node current = head;

    while (current != null)
    {
      yield return current.Data;
      current = current.Next;
    }
  }
}

class TestGenericList
{
  static void Main()
  {
    // int is the type argument
    GenericList<int> list = new GenericList<int>();

    for (int x = 0; x < 10; x++)
    {
      list.AddHead(x);
    }

    foreach (int i in list)
    {
      System.Console.Write(i + " ");
    }
    System.Console.WriteLine("\nDone");
  }
}

// The .NET Framework 1.1 way to create a list:
System.Collections.ArrayList list1 = new System.Collections.ArrayList();
list1.Add(3);
list1.Add(105);

System.Collections.ArrayList list2 = new System.Collections.ArrayList();
list2.Add("It is raining in Redmond.");
list2.Add("It is snowing in the mountains.");

System.Collections.ArrayList list = new System.Collections.ArrayList();
// Add an integer to the list.
list.Add(3);
// Add a string to the list. This will compile, but may cause an error later.
list.Add("It is raining in Redmond.");

int t = 0;
// This causes an InvalidCastException to be returned.
foreach (int x in list)
{
  t += x;
}

// The .NET Framework 2.0 way to create a list
List<int> list1 = new List<int>();

// No boxing, no casting:
list1.Add(3);

// Compile-time error:
// list1.Add("It is raining in Redmond.");