[读书笔记]数据字典
这是一个关于数据字典使用的例子
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace DictionaryExample
{
public struct EmployeeId : IEquatable<EmployeeId>
{
private readonly char prefix;
private readonly int number;
public EmployeeId(string id)
{
if (id == null)
throw new ArgumentNullException("id");
prefix = (id.ToUpper())[0];
int numLength = id.Length - 1;
number = int.Parse(id.Substring(1, numLength > 6 ? 6 : numLength));
}
public override string ToString()
{
return prefix.ToString() + string.Format("{0,6:000000}", number);
}
public override int GetHashCode()
{
return (number ^ number << 16) * 0x15051505;
}
public bool Equals(EmployeeId other)
{
return (prefix == other.prefix && number == other.number);
}
}
public class Employee
{
private string name;
private decimal salary;
private readonly EmployeeId id;
public Employee(EmployeeId id, string name, decimal salary)
{
this.id = id;
this.name = name;
this.salary = salary;
}
public override string ToString()
{
return String.Format("{0}: {1, -20} {2:C}", id.ToString(), name, salary);
}
}
class Program
{
static void Main(string[] args)
{
Dictionary<EmployeeId, Employee> employees = new Dictionary<EmployeeId, Employee>(31);
EmployeeId idJeff = new EmployeeId("C7102");
Employee jeff = new Employee(idJeff, "Jeff Gordon", 5164580.00m);
employees.Add(idJeff, jeff);
Console.WriteLine(jeff);
EmployeeId idTony = new EmployeeId("C7105");
Employee Tony = new Employee(idTony, "Tony Stewart", 4814200.00m);
employees.Add(idTony, Tony);
Console.WriteLine(Tony);
EmployeeId idDenny = new EmployeeId("C8011");
Employee Denny = new Employee(idDenny, "Denny Hamlin", 3718710.00m);
employees.Add(idDenny, Denny);
Console.WriteLine(Denny);
EmployeeId idCarl = new EmployeeId("F7908");
Employee Carl = new Employee(idCarl, "Carl Edwards", 3285710.00m);
employees[idCarl] = Carl;
Console.WriteLine(Carl);
EmployeeId idMatt = new EmployeeId("F7203");
Employee Matt = new Employee(idMatt, "Matt Kensenth", 4520330.00m);
employees.Add(idMatt, Matt);
Console.WriteLine(Matt);
while (true)
{
Console.Write("Enter employee id (X to exit)>");
string userInput = Console.ReadLine();
userInput = userInput.ToUpper();
if (userInput == "X") break;
EmployeeId id = new EmployeeId(userInput);
Employee employee;
if (!employees.TryGetValue(id, out employee))
{
Console.WriteLine("Employee with id " + "{0} does not exist", id);
}
else
{
Console.WriteLine(employee);
}
}
}
}
}
主要关注这里面的对于GetHashCode的重载的算法。这里GetHashCode使用的算法将数字向左移动16位，再与原来的数字进行异或操作，最后将结果乘以十六进制数15051505。散列码在整数取值区域上的分布相当均匀。