C#学习日记 字典

字典能根据键快速查找值，也可以自由的添加元素和删除元素。键会转换成一个散列，利用散列创建一个数字，它将索引和值关联起来。索引包含一个到到值得链接。键必须重写GetHashCode（）方法。Equals（）方法必须重写GetHashCode（），不然编译会出错。字典常用字符串做键。

using System;
using System.Collections.Generic;

namespace Sample
{
	public class MainEntryPoint
	{
		static int Main(string[] args)
		{
			//容量一般设置为素数 如果设置的不是
			//类会使用传递给构造函数整数的最近一个素数
			var employees = new Dictionary<EmployeeId, Employee>(31);
			var julyId = new EmployeeId("C3755");
			var july = new Employee("July",379025.00m,julyId);
			employees.Add( julyId, july);
			Console.WriteLine(july);
			var joynId = new EmployeeId("F3547");
			var joyn = new Employee("Joyn",403466.00m,joynId);
			employees.Add(joynId, joyn);
			Console.WriteLine(joyn);
			var johnId = new EmployeeId("C3386");
			var john = new Employee("John",415216.00m,johnId);
			//通过索引把值传递进字典
			employees[johnId] = john;
			Console.WriteLine(john);
			Console.WriteLine();

			while(true)
			{
				Console.Write("Enter employee id(X to exit)>");
				var userInput = Console.ReadLine();
				userInput = userInput.ToUpper();
				if(userInput == "X")
					break;
				EmployeeId id;
				try
				{
					id = new EmployeeId(userInput);
					Employee employee;
					//先判断是否有对应这个键的值
					//返回布尔类型 还有一个out参数带回这个值
					if(!employees.TryGetValue(id, out employee))
					{
						Console.WriteLine("Employee with id {0} does not exist",id);
					}
					else
					{
						Console.WriteLine(employee);
					}
				}
				catch (EmployeeIdException ex)
				{
					Console.WriteLine(ex.Message);
				}
			}
			return 0;
		}
	}
	[Serializable]
	public class EmployeeIdException : Exception
	{
		public EmployeeIdException(string message) : base(message)
		{
		}
	}
	[Serializable]
	public struct EmployeeId :IEquatable<EmployeeId>
	{
		private readonly char prefix;
		private readonly int number;

		public EmployeeId(string id)
		{
			prefix = (id.ToUpper())[0];
			int numLength = id.Length - 1;
			try
			{
				number = int.Parse(id.Substring( 1, numLength > 6 ? 6 : numLength));
			}
			catch (FormatException)
			{
				throw new EmployeeIdException("Invalid EmployeeId format");
			}
		}
		public override string ToString()
		{
			return prefix.ToString()+string.Format("{0:6:000000}", number);
		}
		//把数值平均的分布在整型范围内
		public override int GetHashCode()
		{
			return (number ^ number << 16) * 0x15051505;
		}
		public bool Equals(EmployeeId other)
		{
			if(other == null)
				return false;
			else
				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);
		}
	}
	[Serializable]
	public class Employee
	{
		private string name;
		private decimal salary;
		private EmployeeId id;
		
		public Employee(string name, decimal 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.ToString(), name, salary);
		}
	}
}