字典（散列表）：允许按照某个键来访问元素，能根据键快速查找元素，也可以*添加，删除元素。比较像List<T>类，但没有list向后移动元素的性能开销。
.net中最主要的字典类是Dictionary<Tkey,Tvalue>。
字典中的键：用作字典中键的类型必须重写Object类中的GetHashCode()方法。调用GetHashCode()方法主要是为了获得元素的位置。
键还必须实现IEquatable<T>.Equals方法或重写Object类的Equals()方法。因为不同的键代码可能返回相同的散列代码，所以使用equals方法比较键。字典比较两个键是否相等，调用A.Equals(B)方法，如果A.Equals(B)返回true，则A. GetHashCode()和B. GetHashCode()必须返回相同的散列代码！
public class EmployeeIdException : Exception
{
public EmployeeIdException(string message) : base(message) { }
} public class EmployeeId : IEquatable<EmployeeId>
{
private readonly char prefix;
private readonly int number; public EmployeeId(string id)
{
if (id == null || id == "")
{
throw new ArgumentNullException("id");
}
prefix = id.ToUpper()[];
int numberlength = id.Length - ;
try
{
number = int.Parse(id.Substring(, numberlength > ? : numberlength)); }
catch (FormatException)
{
throw new EmployeeIdException("无法格式化ID");
}
} public override string ToString()
{
return prefix.ToString() + string.Format("{0,6:000000}", number);
} public override int GetHashCode()
{
return (number ^ number << ) * 0x15051505;
} public bool Equals(EmployeeId other)
{
return (prefix == other.prefix && number == other.number);
} public override bool Equals(object obj)
{
return Equals((EmployeeId)obj);
} public static bool operator ==(EmployeeId left, EmployeeId right)
{
return left.Equals(right);
} public static bool operator !=(EmployeeId left, EmployeeId right)
{
return !(left == right);
}
} public class Employee
{
private string name;
private double salary;
private EmployeeId id;
public Employee(string name, double salary, EmployeeId id)
{
this.name = name;
this.salary = salary;
this.id = id;
} public override string ToString()
{
return string.Format("{0}:{1,-20}{2:C}", id, name, salary);
}
}
class Program
{
static void Main(string[] args)
{
var employees = new Dictionary<EmployeeId, Employee>(); var idrxm = new EmployeeId("A5");
var rxm = new Employee("rxm", 9.6, idrxm);
employees.Add(idrxm, rxm);
Console.WriteLine(rxm); var idcwr = new EmployeeId("B888888456");
var cwr = new Employee("cwr", 9.5, idcwr);
employees.Add(idcwr, cwr);
Console.WriteLine(cwr); while (true)
{
Console.WriteLine("请输入员工工号，X代表退出！");
var writeTxt = Console.ReadLine();
if (writeTxt.ToLower() == "x")
{
break;
}
EmployeeId id;
try
{
id = new EmployeeId(writeTxt);
Employee employ;
if (!employees.TryGetValue(id, out employ))
{
Console.WriteLine("{0},这个工号的人不存在", id);
}
else
{
Console.WriteLine(employ);
}
}
catch (EmployeeIdException ex)
{
Console.WriteLine(ex.Message);
}
}
}
}