学用 ASP.Net 之 "字符串" (4): string 类的扩展方法

学到这里, 真是开眼界了...有太多陌生的概念.
string 类的扩展方法大都继承自 IEnumerable<T> 接口, 这些方法也大都可以在 foreach 语句中实现, 但这些方法太方便了.
尽管 string 类重载了其中很多方法, 但真正适合字符串操作的方法并不多; 此时我感觉, 前两天定下的学习计划出了问题, 因为仅用字符串很难理清这组方法; 不过要继续...

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string 类的扩展方法列表(基本相同于 IEnumerable<T> 接口的成员列表):

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Aggregate<>          //累加
All<>                //是否都满足条件
Any<>                //是否有一个满足条件
AsEnumerable<>       //
AsParallel<>         //
AsQueryable<>        //
Average<>            //平均值
Cast<>               //
Concat<>             //连接
Contains<>           //是否包含
Count<>              //总数
DefaultIfEmpty<>     //指定默认空值
Distinct<>           //去除重复
ElementAt<>          //获取指定位置的元素
ElementAtOrDefault<> //同 ElementAt, 但获取失败则返回默认的空值
Except<>             //差集
First<>              //获取第一个元素
FirstOrDefault<>     //同 First, 但获取失败返回默认的空值
GroupBy<>            //分组
GroupJoin<>          //关联分组
Intersect<>          //交集
Join<>               //串联
Last<>               //获取最后一个元素
LastOrDefault<>      //同 Last, 但获取失败返回默认的空值
LongCount<>          //同 Count, 但返回 Int64
Max<>                //最大值
Min<>                //最小值
OfType<>             //
OrderBy<>            //排序
OrderByDescending<>  //倒排序
Reverse<>            //翻转
Select<>             //映射
SelectMany<>         //深度映射
SequenceEqual<>      //
Single<>             //获取只是唯一的元素, 不唯一或获取不到则异常
SingleOrDefault<>    //获取只是唯一的元素, 不唯一则异常, 获取不到则取默认空值
Skip<>               //获取指定序号之后的
SkipWhile<>          //获取指定条件之后的
Sum<>                //求和
Take<>               //获取指定序号之前的
TakeWhile<>          //获取指定条件之前的
ToArray<>            //
ToCharArray<>        //
ToDictionary<>       //
ToList<>             //
ToLookup<>           //
Union<>              //并集
Where<>              //筛选
Zip<>                //合并

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获取首尾的字符(First、Last、FirstOrDefault、LastOrDefault):

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/* 函数及重载 */
First <Char>()                               // 函数名: First; <Char> 中的 Char 是返回值类型; () 表示这是一个无参数的重载
First <Char> (Func <Char, Boolean>)          // 这里的参数是个函数, 其(函参)返回值是 Boolean 类型, 参数是 Char 类型.
                                             // <> 中是函数参数与返回值的列表, 最后一个是返回值.
FirstOrDefault <Char>()                      // 同 First, 但如果找不到则返回默认值 null
FirstOrDefault <Char> (Func <Char, Boolean>) //
Last <Char>()                                // 顾名思义, 同上
Last <Char> (Func <Char, Boolean>)           //
LastOrDefault <Char>()                       //
LastOrDefault <Char> (Func <Char, Boolean>)  //


//下面例子很容易理解:
protected void Button1_Click(object sender, EventArgs e)
{
    string str = "ABCDEFG";
    char c1 = str.First(); // A
    char c2 = str.Last();  // G

    TextBox1.Text = string.Concat(c1, "\n", c2);
}

//下面例子使用了其第二种重载, 其参数是个函数, 使用了 Lambda 匿名函数表达式:
protected void Button2_Click(object sender, EventArgs e)
{
    string str = "ABCDEFG";
    char c1 = str.First(p => p != 'A'); // B : 这是获取不是 A 的第一个字符
    char c2 = str.Last(p => p < 70);    // E : 这是获取字符编码值大于 70(F) 的倒数第一个字符

    TextBox1.Text = string.Concat(c1, "\n", c2);
}

// Lambda 表达式中, 
// => 前面的是参数列表, 其类型可被自动识别所以可省略, 只有一个参数时可省略括号; 其中的 p 是自定义的变量名.
// => 后面的是函数内容, 通常只有一句话; 但其必须返回指定的类型(本例中是 Boolean).

//测试用于其它数组:
protected void Button3_Click(object sender, EventArgs e)
{
    int[] nArr = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    string[] sArr = { "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten" };

    int n1 = nArr.First();                     //1
    int n2 = nArr.First(x => x % 2 == 0);      //2
    string s1 = sArr.Last();                   //ten
    string s2 = sArr.Last(s => s.Length == 5); //eight
    TextBox1.Text = string.Concat(n1, "\n", n2, "\n", s1, "\n", s2);
}

---

获取指定位置的元素(ElementAt、ElementAtOrDefault):

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protected void Button1_Click(object sender, EventArgs e)
{
    string str = "Asp.Net 4.0";
    char c1 = str.ElementAt(1);            //s
    char c2 = str.ElementAtOrDefault(1);   //s
    char c3 = str.ElementAtOrDefault(999); //
    bool b1 = c3 == '\x00';                //True

    TextBox1.Text = string.Concat(c1, "\n", c2, "\n", c3, "\n", b1);
}

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统计操作(Aggregate、Count、LongCount、Max、Min、Sum、Average):

---

//用数字数组测试比较合适
protected void Button1_Click(object sender, EventArgs e)
{
    int[] nArr = { 2, 1, 4, 3, 6, 5 };

    int n1 = nArr.Count();                    //6 
    int n2 = nArr.Count(n => n % 2 == 0);     //3 : 偶数元素总数
    int n3 = nArr.Sum();                      //21
    int n4 = nArr.Max();                      //6
    int n5 = nArr.Min();                      //1
    double n6 = nArr.Average();               //3.5
    int n7 = nArr.Aggregate((x, y) => x * y); //720 : 累乘
    Int64 n8 = nArr.LongCount();              //6 : LongCount 和 Count 只是返回值的类型不同

    string r = "\n";
    TextBox1.Text = string.Concat(n1 + r + n2 + r + n3 + r + n4 + r + n5 + r + n6 + r + n7 + r + n8);
}

protected void Button2_Click(object sender, EventArgs e)
{
    string str = "one two three four five six seven eight nine ten";

    int n1 = str.Count();              //48 : 这相当于 str.Length
    int n2 = str.Count(s => s != ' '); //39 : 这是非空格字符的总数
    char c1 = str.Max();               //x  : 这是序号最大的字符
    char c2 = str.Min();               //序号最小的字符在这里是空格

    TextBox1.Text = string.Concat(n1, "\n", n2, "\n", c1, "\n", c2);
}

//通过 Aggregate 翻转字符串中的单词
protected void Button3_Click(object sender, EventArgs e)
{
    string str = "one two three four five six seven eight nine ten";
    string[] sArr = str.Split(' ');

    str = sArr.Aggregate((s1, s2) => s2 + " " + s1); //ten nine eight seven six five four three two one
    TextBox1.Text = str;
}

---

集合操作(Intersect、Except、Union):

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//测试整数数组的交集、差集、并集
protected void Button1_Click(object sender, EventArgs e)
{
    int[] nArr1 = { 1, 2, 3, 4, 5, 6 };
    int[] nArr2 = { 4, 5, 6, 7, 8, 9 };

    IEnumerable<int> R1 = nArr1.Intersect(nArr2); // 返回类型可以写作隐式类型 var
    var R2 = nArr1.Except(nArr2);
    var R3 = nArr1.Union(nArr2);

    string s1 = string.Join("", R1); //456
    string s2 = string.Join("", R2); //123
    string s3 = string.Join("", R3); //123456789

    TextBox1.Text = string.Concat(s1, "\n", s2, "\n", s3);
}

//测试字符串(字符数组)的交集、差集、并集
protected void Button2_Click(object sender, EventArgs e)
{
    string str1 = "Asp.Net 3.5";
    string str2 = "ASP.NET 4.0";

    var R1 = str1.Intersect(str2);
    var R2 = str1.Except(str2);
    IEnumerable<char> R3 = str1.Union(str2);

    string s1 = string.Join("", R1); //A.N 
    string s2 = string.Join("", R2); //spet35
    string s3 = string.Join("", R3); //Asp.Net 35SPET40

    TextBox1.Text = string.Concat(s1, "\n", s2, "\n", s3);
}


//定义一个 Person 类, 其有 Name 和 Age 两个属性
public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public Person(string name, int age) { Name = name; Age = age; } // 构造函数
}

//自定义的对比类, 以比较是否是同一个人
public class PersonComparer : IEqualityComparer<Person>
{
    public bool Equals(Person p1, Person p2)
    {
        return p1.Name == p2.Name && p1.Age == p2.Age;
    }

    public int GetHashCode(Person obj)
    {
        return 0;
    }
}

//获取两组人的交集、差集、并集
protected void Button3_Click(object sender, EventArgs e)
{
    string s1, s2, s3;
    s1 = s2 = s3 = "";

    Person[] PersonArr1 = { new Person("AA", 11), new Person("BB", 22), new Person("CC", 33) };
    Person[] PersonArr2 = { new Person("CC", 33), new Person("DD", 44), new Person("AA", 55) };

    var ps1 = PersonArr1.Intersect(PersonArr2, new PersonComparer());
    var ps2 = PersonArr1.Except(PersonArr2, new PersonComparer());
    IEnumerable<Person> ps3 = PersonArr1.Union(PersonArr2, new PersonComparer());

    foreach (Person p in ps1) { s1 += string.Format("{0}:{1} ", p.Name, p.Age); } //CC:33 
    foreach (Person p in ps2) { s2 += string.Format("{0}:{1} ", p.Name, p.Age); } //AA:11 BB:22 
    foreach (Person p in ps3) { s3 += string.Format("{0}:{1} ", p.Name, p.Age); } //AA:11 BB:22 CC:33 DD:44 AA:55

    TextBox1.Text = string.Concat(s1, "\n", s2, "\n", s3);
}

---

连接、合并与串联(Concat、Zip、Join):

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//Concat
protected void Button1_Click(object sender, EventArgs e)
{
    int[] nArr1 = { 1, 2, 3 };
    int[] nArr2 = { 4, 5, 6 };

    var R1 = nArr1.Concat(nArr2);
    var R2 = nArr2.Concat(nArr1);
    var R3 = nArr1.Concat(nArr1);

    string s1 = string.Join("", R1); //123456
    string s2 = string.Join("", R2); //456123
    string s3 = string.Join("", R3); //123123

    TextBox1.Text = string.Format("{0}\n{1}\n{2}", s1, s2, s3);
}

//Zip
protected void Button2_Click(object sender, EventArgs e)
{
    string[] sArr = { "one", "two", "there" };
    int[] nArr = { 1, 2, 3 };

    var R1 = sArr.Zip(nArr, (x1, x2) => x1 + ":" + x2 + " ");
    var R2 = sArr.Zip(nArr, (x1, x2) => x2 + ":" + x1 + " ");

    string s1 = string.Join("", R1); //one:1 two:2 there:3 
    string s2 = string.Join("", R2); //1:one 2:two 3:there 

    TextBox1.Text = string.Concat(s1, "\n", s2);
}

//Join
protected void Button3_Click(object sender, EventArgs e)
{
    int[] nArr = { 1, 2, 3, 4, 5, 6, 7 };
    string[] sArr = { "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten" };

    var R = nArr.Join(sArr, n => n, s => s.Length, (n, s) => new { n, s });

    string str = "";
    foreach (var obj in R)
    {
        str += obj.n + " : " + obj.s + "\n";
    }
    TextBox1.Text = str;

/* 输出结果:
    3 : one
    3 : two
    3 : six
    3 : ten
    4 : four
    4 : five
    4 : nine
    5 : three
    5 : seven
    5 : eight
*/
}

---

去除重复(Distinct):

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protected void Button1_Click(object sender, EventArgs e)
{
    string str = "aabbccc";
    var cs = str.Distinct();
    foreach (char c in cs) { TextBox1.Text += c; } //abc
}

protected void Button2_Click(object sender, EventArgs e)
{
    int[] nArr = { 1, 3, 2, 4, 3, 5, 4, 6, 5, 7, 6, 8, 7, 9, 8, 0 };
    var ns = nArr.Distinct().OrderBy(x => -x);
    foreach (int n in ns) { TextBox1.Text += n.ToString(); } //9876543210
}

---

排序(OrderBy、OrderByDescending):

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protected void Button1_Click(object sender, EventArgs e)
{
    int[] nArr = { 1, 3, 2, 4, 3, 5 };
    string[] sArr = { "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten" };
    string str = "Asp.Net";

    var R1 = nArr.OrderBy(x => x);
    var R2 = nArr.OrderByDescending(x => x);
    var R3 = sArr.OrderBy(x => x);
    var R4 = sArr.OrderByDescending(x => x);
    var R5 = str.OrderBy(x => x.ToString().ToLower());
    var R6 = str.OrderByDescending(x => x.ToString().ToLower());

    string s1 = string.Join("", R1);  //123345
    string s2 = string.Join("", R2);  //543321
    string s3 = string.Join(" ", R3); //eight five four nine one seven six ten three two 
    string s4 = string.Join(" ", R4); //two three ten six seven one nine four five eight 
    string s5 = string.Join("", R5);  //.AeNpst
    string s6 = string.Join("", R6);  //tspNeA. 

    TextBox1.Text = string.Concat(s1, "\n", s2, "\n", s3, "\n", s4, "\n", s5, "\n", s6);
}

---

翻转(Reverse):

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protected void Button1_Click(object sender, EventArgs e)
{
    string str = "Asp.Net";
    var cs = str.Reverse();
    foreach (char c in cs) { TextBox1.Text += c; } //teN.psA
}

---

筛选(Where):

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protected void Button1_Click(object sender, EventArgs e)
{
    int[] nArr = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    string[] sArr = { "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten" };

    var R1 = nArr.Where(n => n % 2 == 0);
    var R2 = sArr.Where(s => s.Length == 3);

    string s1 = string.Join(", ", R1); //2, 4, 6, 8
    string s2 = string.Join(", ", R2); //one, two, six, ten

    TextBox1.Text = string.Concat(s1, "\n", s2);
}

---

映射(Select、SelectMany):

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//Select
protected void Button1_Click(object sender, EventArgs e)
{
    int[] nArr = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    string[] sArr = { "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten" };

    var R1 = nArr.Select(n => n * n);
    var R2 = sArr.Select((str, index) => (index+1) + ":" + str.ToUpper());

    string s1 = string.Join(",", R1); //1,4,9,16,25,36,49,64,81
    string s2 = string.Join(" ", R2); //1:ONE 2:TWO 3:THREE 4:FOUR 5:FIVE 6:SIX 7:SEVEN 8:EIGHT 9:NINE 10:TEN

    TextBox1.Text = string.Concat(s1, "\n", s2);
}

//Select 与 SelectMany
protected void Button2_Click(object sender, EventArgs e)
{
    string[] sArr = { "AA:BB:CC", "DD:EE:FF", "GG:HH:II" };

    var R1 = sArr.Select(arr => arr.Split(':'));
    var R2 = sArr.SelectMany(arr => arr.Split(':'));

    var s1 = string.Join(" ", R1); //System.String[] System.String[] System.String[]
    var s2 = string.Join(" ", R2); //AA BB CC DD EE FF GG HH II

    var s3 = "";
    foreach (string[] ss in R1) { s3 += string.Join(" ", ss) + "; "; } //AA BB CC; DD EE FF; GG HH II; 

    TextBox1.Text = string.Concat(s1, "\n", s2 + "\n" + s3);
}

---

分组(GroupBy、GroupJoin):

---

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}
protected void Button1_Click(object sender, EventArgs e)
{
    Person[] pArr = 
    {
        new Person { Name="AA", Age=11 },
        new Person { Name="BB", Age=22 },
        new Person { Name="CC", Age=33 },
        new Person { Name="DD", Age=11 },
        new Person { Name="EE", Age=22 },
        new Person { Name="FF", Age=33 },
        new Person { Name="GG", Age=11 }
    };

    var R1 = pArr.GroupBy(p => p.Age, p => p.Name);
    var R2 = pArr.GroupBy(p => p.Age, p => p);

    string str1 = "";
    foreach (IGrouping<int, string> group in R1)
    {
        str1 += group.Key + "\n";
        foreach (string n in group) { 
            str1 += "\t" + n + "\n"; 
        }
    }

    string str2 = "";
    foreach (IGrouping<int, Person> group in R2)
    {
        str2 += group.Key + "\n";
        foreach (Person p in group)
        {
            str2 += string.Format("\t{0}:{1}\n", p.Name, p.Age);
        }
    }

    TextBox1.Text = string.Format("{0}----------\n{1}", str1, str2);

/* 输出结果:
11
	AA
	DD
	GG
22
	BB
	EE
33
	CC
	FF
----------
11
	AA:11
	DD:11
	GG:11
22
	BB:22
	EE:22
33
	CC:33
	FF:33
*/
}

//使用 GroupJoin, 测试效果同上
protected void Button1_Click(object sender, EventArgs e)
{
    int[] nArr = { 11, 22, 33 }; 
    Person[] pArr = 
    {
        new Person { Name="AA", Age=11 },
        new Person { Name="BB", Age=22 },
        new Person { Name="CC", Age=33 },
        new Person { Name="DD", Age=11 },
        new Person { Name="EE", Age=22 },
        new Person { Name="FF", Age=33 },
        new Person { Name="GG", Age=11 }
    };

    var R1 = nArr.GroupJoin(pArr, n => n, p => p.Age, (n, ps) => new { MyKey = n, MyNames = ps.Select(p => p.Name) });
    var R2 = nArr.GroupJoin(pArr, n => n, p => p.Age, (n, ps) => new { MyKey = n, MyNames = ps });

    string str1 = "";
    foreach (var obj in R1)
    {
        str1 += obj.MyKey + "\n";
        foreach (string s in obj.MyNames)
        {
            str1 += string.Format("\t{0}\n", s);
        }
    }

    string str2 = "";
    foreach (var obj in R2)
    {
        str2 += obj.MyKey + "\n";
        foreach (var p in obj.MyNames)
        {
            str2 += string.Format("\t{0}:{1}\n", p.Name, p.Age);
        }
    }

    TextBox1.Text = string.Format("{0}----------\n{1}", str1, str2);
}

---

获取指定条件之后的(Skip、SkipWhile)或之前的(Take、TakeWhile):

---

//Skip、SkipWhile
protected void Button1_Click(object sender, EventArgs e)
{
    int[] nArr = { 1, 3, 2, 4, 3, 5 };

    var R1 = nArr.Skip(3);                           //取第 3 个元素之后的
    var R2 = nArr.OrderBy(n => n).Skip(3);           //先排序, 再取第 3 个元素之后的
    var R3 = nArr.OrderByDescending(n => n).Skip(3); //先倒排序, 再取第 3 个元素之后的

    var R4 = nArr.OrderBy(n => n).SkipWhile(n => n <= 3);   //先排序(123345), 从不满足条件开始, 之后的
    var R5 = nArr.SkipWhile((num, index) => num != index); // 从第二个元素开始, 数字和序号就不一样了

    string s1 = string.Join("", R1); //435
    string s2 = string.Join("", R2); //345
    string s3 = string.Join("", R3); //321
    string s4 = string.Join("", R4); //45
    string s5 = string.Join("", R5); //2435

    TextBox1.Text = string.Format("{0}\n{1}\n{2}\n{3}\n{4}", s1, s2, s3, s4, s5);
}

//Take、TakeWhile 用法同上, 只是获取之前的
protected void Button2_Click(object sender, EventArgs e)
{
    int[] nArr = { 1, 3, 2, 4, 3, 5 };

    var R1 = nArr.Take(3);
    var R2 = nArr.OrderBy(n => n).Take(3);
    var R3 = nArr.OrderByDescending(n => n).Take(3);

    var R4 = nArr.OrderBy(n => n).TakeWhile(n => n <= 3);
    var R5 = nArr.TakeWhile((num, index) => num != index);

    string s1 = string.Join("", R1); //132
    string s2 = string.Join("", R2); //123
    string s3 = string.Join("", R3); //543
    string s4 = string.Join("", R4); //1233
    string s5 = string.Join("", R5); //13

    TextBox1.Text = string.Format("{0}\n{1}\n{2}\n{3}\n{4}", s1, s2, s3, s4, s5);
}

---

All 与 Any:

---

//都满足条件时 All 才返回 True
protected void Button1_Click(object sender, EventArgs e)
{
    int[] nArr = { 1, 3, 5, 7, 9 };
    bool b1 = nArr.All(n => n % 2 == 0); //False
    bool b2 = nArr.All(n => n % 2 == 1); //True

    TextBox1.Text = string.Concat(b1, "\n", b2);
}

//其中一个满足条件 Any 就返回 True
protected void Button2_Click(object sender, EventArgs e)
{
    string str1 = "Delphi";
    string str2 = "Asp.Net";
    string str3 = "";

    bool b1 = str1.Any();              //True
    bool b2 = str2.Any();              //True
    bool b3 = str3.Any();              //False

    bool b4 = str1.Any(c => c == 'D'); //True
    bool b5 = str2.Any(c => c == 'D'); //False
    bool b6 = str2.Any(c => c == 'D'); //False

    TextBox1.Text = string.Concat(b1, "\n", b2, "\n", b3, "\n", b4, "\n", b5, "\n", b6);
}

---

是否包含(Contains):

---

protected void Button1_Click(object sender, EventArgs e)
{
    string str = "Asp.Net 4.0";
    bool b1 = str.Contains('4');       //True
    bool b2 = str.Contains("Net 4.0"); //True
    bool b3 = str.Contains("Net4.0");  //False

    TextBox1.Text = string.Concat(b1, "\n", b2, "\n", b3, "\n");
}

---

获取只是唯一的元素(Single、SingleOrDefault):

---

protected void Button1_Click(object sender, EventArgs e)
{
    string str = "Microsoft";
    char c1, c2, c3, c4, c5, c6;
    c1 = c2 = c3 = c4 = c5 = c6 = '*';

    //Single
    c1 = str.Single(c => c == 'M'); //M

    try { c2 = str.Single(c => c == 'o'); }
    catch (Exception err) { Response.Write(err.Message + "<br/>"); } // 序列包含一个以上的匹配元素 

    try { c3 = str.Single(c => c == 'A'); }
    catch (Exception err) { Response.Write(err.Message + "<br/>"); } // 序列不包含任何匹配元素

    //SingleOrDefault
    c4 = str.SingleOrDefault(c => c == 'M'); //M

    try { c5 = str.SingleOrDefault(c => c == 'o'); }
    catch (Exception err) { Response.Write(err.Message + "<br/>"); } // 序列包含一个以上的匹配元素 

    c6 = str.SingleOrDefault(c => c == 'A'); // 这不会激发异常

    TextBox1.Text = string.Format("{0}{1}{2}{3}{4}{5}", c1, c2, c3, c4, c5, c6); //M**M*
}

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指定默认空值(DefaultIfEmpty):

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protected void Button1_Click(object sender, EventArgs e)
{
    string str1 = "Asp.Net 3.5";
    string str2 = "";

    string r1 = string.Join("|", str1.DefaultIfEmpty());    //A|s|p|.|N|e|t| |3|.|5
    string r2 = string.Join("|", str2.DefaultIfEmpty());    //
    string r3 = string.Join("|", str2.DefaultIfEmpty('*')); //*

    TextBox1.Text = string.Concat(r1, "\n", r2, "\n", r3);
}

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