String Join方法应用

案例1：

using System;



class Program

{

    static void Main()

    {

    string[] arr = { "one", "two", "three" };

    Console.WriteLine(string.Join(",", arr)); // "string" can be lowercase, or

    Console.WriteLine(String.Join(",", arr)); // "String" can be uppercase

    }

}

输出结果：

 

one,two,three 
one,two,three

案例2：

using System;

class Program
{
    static void Main()
    {
    // Problem: combine these words into lines in HTML
    string[] dinosaurs = new string[] { "Aeolosaurus",
        "Deinonychus", "Jaxartosaurus", "Segnosaurus" };

    // Solution: join with break tag.
    string html = string.Join("<br/>\r\n", dinosaurs);
    Console.WriteLine(html);
    }
}

输出结果：
Aeolosaurus<br/> 
Deinonychus<br/> 
Jaxartosaurus<br/> 
Segnosaurus

案例3：

using System;
using System.Text;

class Program
{
    static void Main()
    {
    string[] catSpecies = { "Aegean", "Birman", "Main Coon", "Nebulung" };
    Console.WriteLine(CombineA(catSpecies));
    Console.WriteLine(CombineB(catSpecies));
    }

    /// <summary>
    /// Combine strings with commas.
    /// </summary>
    static string CombineA(string[] arr)
    {
    return string.Join(",", arr);
    }

    /// <summary>
    /// Combine strings with commas.
    /// </summary>
    static string CombineB(string[] arr)
    {
    StringBuilder builder = new StringBuilder();
    foreach (string s in arr)
    {
        builder.Append(s).Append(",");
    }
    return builder.ToString().TrimEnd(new char[] { ',' });
    }
}

输出结果：
Aegean,Birman,Main Coon,Nebulung 
Aegean,Birman,Main Coon,Nebulung

案例4：

using System;

class Program
{
    static void Main()
    {
    try
    {
        string bug = string.Join(null, null); // Null arguments are bad
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex);
    }
    }
}
输出结果：
System.ArgumentNullException: Value cannot be null.
Parameter name: value

案例5：

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
    // List of cities
    List<string> cities = new List<string>();
    cities.Add("New York");
    cities.Add("Mumbai");
    cities.Add("Berlin");
    cities.Add("Istanbul");

    // Join strings into one CSV line
    string line = string.Join(",", cities.ToArray());
    Console.WriteLine(line);
    }
}
New York,Mumbai,Berlin,Istanbul
总结：Join与StringBuilder方法相比较，性能上要高出许多，有人测试过1000000条数据两方法分别耗时： 
string.Join:                 157 ms 
StringBuilder Append method: 270 ms