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;elsereturn (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);}}}