C# 索引器练习总结

　　前言：主要是想通过写文章加深自己对C#理解，如果有写的错误的地方请指正，感激不尽。

　　C# 4.0 的 Visual Studio 2010 示例，中有一个索引器的的示例（http://code.msdn.microsoft.com/Indexers2-Sample-00f2f47a 源代码下载），示例主要是为了显示：C# 类如何声明索引器，以表示不同种类事物的类似数组的集合。功能实现为将一个字符串，通过分词程序，可以把字符串里面的单词识别出来，通过索引器进行相应的替换。

详见代码：

using System;
using Indexers_2;

public class Document
{
    // 以下类型允许以类似字数组的方式查看文档:
    public class WordCollection
    {
        readonly Document document;  // 包含文档

        internal WordCollection(Document d)
        {
           document = d;
        }

        // Helper 函数 -- 从字符“begin”开始在字符数组“text”中搜索
        // 字数“wordCount”。如果少于 
        // wordCount 字数，则返回 false。将“start”和
        // “length”设置为文本中字的位置和长度:
        private bool GetWord(char[] text, int begin, int wordCount, 
                                       out int start, out int length) 
        { 
            int end = text.Length;
            int count = 0;
            int inWord = -1;
            start = length = 0; 

            for (int i = begin; i <= end; ++i) 
            {
                bool isLetter = i < end && Char.IsLetterOrDigit(text[i]);

                if (inWord >= 0) 
                {
                    if (!isLetter) 
                    {
                        if (count++ == wordCount) 
                        {
                            start = inWord;
                            length = i - inWord;
                            return true;
                        }
                        inWord = -1;
                    }
                }
                else 
                {
                    if (isLetter)
                        inWord = i;
                }
            }
            return false;
        }

        // 获取和设置包含文档中的字的索引器:
        public string this[int index] 
        {
            get 
            { 
                int start, length;
                if (GetWord(document.TextArray, 0, index, out start, 
                                                          out length))
                    return new string(document.TextArray, start, length);
                else
                    throw new IndexOutOfRangeException();
            }
            set 
            {
                int start, length;
                if (GetWord(document.TextArray, 0, index, out start, 
                                                         out length)) 
                {
                    // 用字符串“value”替换位于 start/length 处的 
                    // 字:
                    if (length == value.Length) 
                    {
                        Array.Copy(value.ToCharArray(), 0, 
                                 document.TextArray, start, length);
                    }
                    else 
                    {
                        char[] newText = 
                            new char[document.TextArray.Length + 
                                           value.Length - length];
                        Array.Copy(document.TextArray, 0, newText, 
                                                        0, start);
                        Array.Copy(value.ToCharArray(), 0, newText, 
                                             start, value.Length);
                        Array.Copy(document.TextArray, start + length,
                                   newText, start + value.Length,
                                  document.TextArray.Length - start
                                                            - length);
                        document.TextArray = newText;
                    }
                }                    
                else
                    throw new IndexOutOfRangeException();
            }
        }

        // 获取包含文档中字的计数:
        public int Count 
        {
            get 
            { 
                int count = 0, start = 0, length = 0;
                while (GetWord(document.TextArray, start + length, 0, 
                                              out start, out length))
                    ++count;
                return count; 
            }
        }
    }

    // 以下类型允许以类似字符数组的方式查看文档
    // :
    public class CharacterCollection
    {
        readonly Document document;  // 包含文档

        internal CharacterCollection(Document d)
        {
          document = d; 
        }

        // 获取和设置包含文档中的字符的索引器:
        public char this[int index] 
        {
            get 
            { 
                return document.TextArray[index]; 
            }
            set 
            { 
                document.TextArray[index] = value; 
            }
        }

        // 获取包含文档中字符的计数:
        public int Count 
        {
            get 
            { 
                return document.TextArray.Length; 
            }
        }
    }

    // 由于字段的类型具有索引器， 
    // 因此这些字段显示为“索引属性”:
    public WordCollection Words;
    public CharacterCollection Characters;

    private char[] TextArray;  // 文档的文本。 

    public Document(string initialText)
    {
        TextArray = initialText.ToCharArray();
        Words = new WordCollection(this);
        Characters = new CharacterCollection(this);
    }

    public string Text 
    {
        get 
        { 
           return new string(TextArray); 
        }
    }
}

class Test
{
    static void Main()
    {
        Document d = new Document(
           "peter piper picked a peck of pickled peppers. How many pickled peppers did peter piper pick?"
        );

        // 将单词“peter”更改为“penelope”:
        for (int i = 0; i < d.Words.Count; ++i) 
        {
            if (d.Words[i] == "peter")
                d.Words[i] = "penelope";
        }

        // 将字符“p”更改为“P”
        for (int i = 0; i < d.Characters.Count; ++i) 
        {
            if (d.Characters[i] == 'p')
                d.Characters[i] = 'P';
        }
        
        Console.WriteLine(d.Text);
    }
}

　　代码中主要有三个类，Document 类，WordCollection类和CharacterCollection类，其中WordCollection类和CharacterCollection类是Document类的内部类，分别将Document类的字符串进行处理，可以单词化呈现和字母化呈现。

　　单词化呈现是由WordCollection类一个核心函数实现：bool GetWord(char[] text, int begin, int wordCount, out int start, out int length)

看一下函数代码：　　

  private bool GetWord(char[] text, int begin, int wordCount, 
                                       out int start, out int length) 
        { 
            int end = text.Length;
            int count = 0;
            int inWord = -1;
            start = length = 0; 

            for (int i = begin; i <= end; ++i) 

            {
                bool isLetter = i < end && Char.IsLetterOrDigit(text[i]);

                if (inWord >= 0) 
                {
                    if (!isLetter) 
                    {
                        if (count++ == wordCount) 
                        {
                            start = inWord;
                            length = i - inWord;
                            return true;
                        }
                        inWord = -1;
                    }
                }
                else 
                {
                    if (isLetter)
                        inWord = i;
                }
            }
            return false;
        }

　　函数的功能是从字符串的begin（最小合法值是0）开始，寻找第wordCount（最小合法值是0）个单词，如果存在则返回true和单词在字符串的位置start和长度length，不存在返回false。

　　每次从字符串查找第i个单词，WordCollection类则调用多次调用GetWord函数，效率比较低，于是我就想通过GetWord函数建立一个索引表，按照单词在字符串的起始位置和长度建立索引，这样可以方便访问字符串的单词，并对单词进行重新复制。

　　顺便感受一下C#的接口，内部类，父类子类有什么特性，加深自己对OO的理解。

　　设计接口：索引器用来返回字符串中对应的单词，Count用来返回字符串总共有多少个单词。

        public interface IIndexer
        {
            string this[int index] { get; set; }
            int Count { get; }
        }

　　WordCollection类继承IIndexer接口，主要实现GetWord函数，WordCollection类的子类WordCollectionA,WordCollectionB实现IIndexer接口。

        public class WordCollectionB : WordCollection
        {
            internal class WordIndexInfo 
            {
                private const int INCREMENT = 100;
                private int Count;
                private int[,] wordInfo;
                public int[] this[int index] 
                {
                    get 
                    {
                        return new int[2] { wordInfo[index, 0], wordInfo[index, 1] };
                    }
                }
                private int _pCurrent;
                public int PCurrent 
                {
                    get { return _pCurrent; }
                }
                public bool AddIndexInfo(int start, int length)
                {

                    if (_pCurrent + 1 >= Count)
                    {
                        if (!EnlargeWordInfo())
                            return false;
                    }
                    _pCurrent++;
                    wordInfo[_pCurrent, 0] = start;
                    wordInfo[_pCurrent, 1] = length;
                    return true;
                }
                private bool EnlargeWordInfo()
                {
                    bool OK = false;
                    try
                    {
                        int[,] temp = new int[Count + INCREMENT, 2];
                        for (int i = 0; i <= _pCurrent; i++)
                        {
                            temp[i, 0] = wordInfo[i, 0];
                            temp[i, 1] = wordInfo[i, 1];
                        }
                        Count = Count + INCREMENT;
                        wordInfo = temp;
                        OK = true;
                    }
                    catch (OutOfMemoryException e)
                    {
                        Console.WriteLine(e.ToString());
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine(ex.ToString());
                    }
                    finally
                    {
                        OK = false;
                    }
                    return OK;
                }
                public void mergeIndexInfo(int index,WordIndexInfo otherOne,int startOffset)
                {
                    if(otherOne._pCurrent<0||index<0)
                        return ;
                    //确保内存够用
                    while(Count<this._pCurrent+otherOne._pCurrent+1)
                    {
                        if(!EnlargeWordInfo())
                            throw new Exception();
                    }
                    //对this.wordInfo中要修改之后的单词位置信息进行修改和移动
                    int oldPos=_pCurrent;
                    int newPos=oldPos+otherOne._pCurrent;
                    while(oldPos>index)
                    {
                        wordInfo[newPos,0]=wordInfo[oldPos,0]+startOffset;
                        oldPos--;
                        newPos--;
                    }
                    int wstart=wordInfo[index,0];
                    for(int i=0;i<=otherOne._pCurrent;i++)
                    {
                        wordInfo[index+i,0]=wstart+otherOne.wordInfo[i,0];
                        wordInfo[index+i,1]=otherOne.wordInfo[i,1];
                    }
                    _pCurrent+=otherOne.PCurrent;
                }
                public WordIndexInfo() 
                {
                    wordInfo = new int[INCREMENT, 2];
                    Count = INCREMENT;
                    _pCurrent = -1;
                }
            }
            private WordIndexInfo wIndexInfo;        
            private void SetIndexInfo( char[] TextArray,WordIndexInfo info) 
            {
                int start=0,length=0;
                while (GetWord(TextArray, start, 0, out start, out length)) 
                {
                    info.AddIndexInfo(start, length);
                    start =start +length;
                }
            }
            public WordCollectionB(MyDocument d):base(d)
            {
                wIndexInfo = new WordIndexInfo();
                SetIndexInfo(d.TextArray, wIndexInfo);
            }
            public override string this[int index]
            {
                get
                {
                    if (!(index<0||index>wIndexInfo.PCurrent))
                    {
                        return new string(document.TextArray, wIndexInfo[index][0], wIndexInfo[index][1]);
                    }
                    else
                        throw new IndexOutOfRangeException();                    
                }
                set
                {
                    int start, length;
                    length=wIndexInfo[index][1];
                    start = wIndexInfo[index][0];
                    WordIndexInfo _tempwii=new WordIndexInfo();
                    if (length == value.Length)
                    {
                        Array.Copy(value.ToCharArray(), 0,
                               document.TextArray, start, length);

                        SetIndexInfo(value.ToCharArray(),_tempwii);
                        this.wIndexInfo.mergeIndexInfo(index,_tempwii,0);
                    }
                    else 
                    {
                        value.ToCharArray(0, value.Length);
                        char[] newText =
                        new char[document.TextArray.Length +
                                value.Length - length];
                        Array.Copy(document.TextArray, 0, newText,
                                                        0, start);
                        Array.Copy(value.ToCharArray(), 0, newText,
                                             start, value.Length);
                        Array.Copy(document.TextArray, start + length,
                                   newText, start + value.Length,
                                  document.TextArray.Length - start
                                                            - length);
                        document.TextArray = newText;
                        SetIndexInfo(value.ToCharArray(),_tempwii);
                        this.wIndexInfo.mergeIndexInfo(index,_tempwii,value.Length-length);
                    }
                   
                 }
            }
            public override int Count
            {
                get
                {
                   return wIndexInfo.PCurrent + 1;
                }
            }   
        }

　　WordCollectionB类中又嵌套WordIndexInfo类，用来封装字符串单词的索引表的。主要功能是：1可以动态的扩充，内存不足时可以抛出异常。2当使用索引器对单词进行替换时，可以自动的更新索引表，即，计算修改单词位置之后的单词索引的偏移量，计算相对应单词在字符串中新的start位置。3把替换的字符串分解为单词，计算它们在索引表的start位置，合并到索引表中。

　　无论是微软提供的算法还是我的算法都有一个bug，就是替换的字符串如果包含被替换的字符串时，就会陷入死循环中，"aa bb aa cc ac" 把单词中的"aa"替换成" aa bb aa aa "时，就会出现死循环，新的字符串如果只包含一个单词那么没有问题。　　

    public class MyDocument
    {
        public interface IIndexer
        {
            string this[int index] { get; set; }
            int Count { get; }
        }
        public class WordCollection:IIndexer 
        {
           protected readonly MyDocument document;  // 包含文档
            internal WordCollection() 
            {

            }
            public WordCollection(MyDocument d)
            {
                document = d;
            }
            protected bool GetWord(char[] text, int begin, int wordCount,
                               out int start, out int length) 
            {
                int end = text.Length;
                int count = 0;
                int inWord = -1;
                start = length = 0;
                for (int i = begin; i <= end; i++) 
                {
                    bool isLetter = i < end && Char.IsLetterOrDigit(text[i]);
                    if (inWord >= 0)
                    {
                        if (!isLetter)
                        {
                            if (count++ == wordCount)
                            {
                                start = inWord;
                                length = i - start;
                                return true;
                            }
                            inWord = -1;
                        }
                    }
                    else 
                    {
                        if (isLetter)
                            inWord = i;
                    }
                }
                return false;
            }
            public virtual string this[int index] 
            { 
                get
                {
                    int start, length;
                    if(GetWord(document.TextArray,0,index,out start,out length))
                        return new string(document.TextArray,start,length); 
                    else 
                        throw new IndexOutOfRangeException();
                }
                set
                {
                    int start,length;
                    if(GetWord(document.TextArray,0,index,out start,out length))
                    {
                        if(length==value.Length)
                        {
                             Array.Copy(value.ToCharArray(), 0, 
                                 document.TextArray, start, length);
                        }
                        else
                        {
                            char[] newText = 
                                new char[document.TextArray.Length + 
                                               value.Length - length];
                            Array.Copy(document.TextArray, 0, newText, 
                                                            0, start);
                            Array.Copy(value.ToCharArray(), 0, newText, 
                                                 start, value.Length);
                            Array.Copy(document.TextArray, start + length,
                                       newText, start + value.Length,
                                      document.TextArray.Length - start
                                                                - length);
                            document.TextArray = newText;
                        }
                    }
                }
            }
            public virtual int Count
            {
                set;
                get;
            }
        }
        public class WordCollectionA : WordCollection
        {
            public WordCollectionA(MyDocument d):base(d)
            {
            }
            public override string this[int index] 
            { 
                get
                {
                    int start, length;
                    if(GetWord(document.TextArray,0,index,out start,out length))
                        return new string(document.TextArray,start,length); 
                    else 
                        throw new IndexOutOfRangeException();
                }
                set
                {
                    int start,length;
                    if(GetWord(document.TextArray,0,index,out start,out length))
                    {
                        if(length==value.Length)
                        {
                             Array.Copy(value.ToCharArray(), 0, 
                                 document.TextArray, start, length);
                        }
                        else
                        {
                            char[] newText = 
                                new char[document.TextArray.Length + 
                                               value.Length - length];
                            Array.Copy(document.TextArray, 0, newText, 
                                                            0, start);
                            Array.Copy(value.ToCharArray(), 0, newText, 
                                                 start, value.Length);
                            Array.Copy(document.TextArray, start + length,
                                       newText, start + value.Length,
                                      document.TextArray.Length - start
                                                                - length);
                            document.TextArray = newText;
                        }
                    }
                }
            }
            public override int Count
            {
                get
                {
                    int count = 0, start = 0, length = 0;
                    while (GetWord(document.TextArray, start + length, 0,
                                                  out start, out length))
                        ++count;
                    return count; 
                }
            }
        }
        public class WordCollectionB : WordCollection
        {
            internal class WordIndexInfo 
            {
                private const int INCREMENT = 100;
                private int Count;
                private int[,] wordInfo;
                public int[] this[int index] 
                {
                    get 
                    {
                        return new int[2] { wordInfo[index, 0], wordInfo[index, 1] };
                    }
                }
                private int _pCurrent;
                public int PCurrent 
                {
                    get { return _pCurrent; }
                }
                public bool AddIndexInfo(int start, int length)
                {

                    if (_pCurrent + 1 >= Count)
                    {
                        if (!EnlargeWordInfo())
                            return false;
                    }
                    _pCurrent++;
                    wordInfo[_pCurrent, 0] = start;
                    wordInfo[_pCurrent, 1] = length;
                    return true;
                }
                private bool EnlargeWordInfo()
                {
                    bool OK = false;
                    try
                    {
                        int[,] temp = new int[Count + INCREMENT, 2];
                        for (int i = 0; i <= _pCurrent; i++)
                        {
                            temp[i, 0] = wordInfo[i, 0];
                            temp[i, 1] = wordInfo[i, 1];
                        }
                        Count = Count + INCREMENT;
                        wordInfo = temp;
                        OK = true;
                    }
                    catch (OutOfMemoryException e)
                    {
                        Console.WriteLine(e.ToString());
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine(ex.ToString());
                    }
                    finally
                    {
                        OK = false;
                    }
                    return OK;
                }
                public void mergeIndexInfo(int index,WordIndexInfo otherOne,int startOffset)
                {
                    if(otherOne._pCurrent<0||index<0)
                        return ;
                    //确保内存够用
                    while(Count<this._pCurrent+otherOne._pCurrent+1)
                    {
                        if(!EnlargeWordInfo())
                            throw new Exception();
                    }
                    //对this.wordInfo中要修改之后的单词位置信息进行修改和移动
                    int oldPos=_pCurrent;
                    int newPos=oldPos+otherOne._pCurrent;
                    while(oldPos>index)
                    {
                        wordInfo[newPos,0]=wordInfo[oldPos,0]+startOffset;
                        oldPos--;
                        newPos--;
                    }
                    int wstart=wordInfo[index,0];
                    for(int i=0;i<=otherOne._pCurrent;i++)
                    {
                        wordInfo[index+i,0]=wstart+otherOne.wordInfo[i,0];
                        wordInfo[index+i,1]=otherOne.wordInfo[i,1];
                    }
                    _pCurrent+=otherOne.PCurrent;
                }
                public WordIndexInfo() 
                {
                    wordInfo = new int[INCREMENT, 2];
                    Count = INCREMENT;
                    _pCurrent = -1;
                }
            }
            private WordIndexInfo wIndexInfo;        
            private void SetIndexInfo( char[] TextArray,WordIndexInfo info) 
            {
                int start=0,length=0;
                while (GetWord(TextArray, start, 0, out start, out length)) 
                {
                    info.AddIndexInfo(start, length);
                    start =start +length;
                }
            }
            public WordCollectionB(MyDocument d):base(d)
            {
                wIndexInfo = new WordIndexInfo();
                SetIndexInfo(d.TextArray, wIndexInfo);
            }
            public override string this[int index]
            {
                get
                {
                    if (!(index<0||index>wIndexInfo.PCurrent))
                    {
                        return new string(document.TextArray, wIndexInfo[index][0], wIndexInfo[index][1]);
                    }
                    else
                        throw new IndexOutOfRangeException();                    
                }
                set
                {
                    int start, length;
                    length=wIndexInfo[index][1];
                    start = wIndexInfo[index][0];
                    WordIndexInfo _tempwii=new WordIndexInfo();
                    if (length == value.Length)
                    {
                        Array.Copy(value.ToCharArray(), 0,
                               document.TextArray, start, length);

                        SetIndexInfo(value.ToCharArray(),_tempwii);
                        this.wIndexInfo.mergeIndexInfo(index,_tempwii,0);
                    }
                    else 
                    {
                        value.ToCharArray(0, value.Length);
                        char[] newText =
                        new char[document.TextArray.Length +
                                value.Length - length];
                        Array.Copy(document.TextArray, 0, newText,
                                                        0, start);
                        Array.Copy(value.ToCharArray(), 0, newText,
                                             start, value.Length);
                        Array.Copy(document.TextArray, start + length,
                                   newText, start + value.Length,
                                  document.TextArray.Length - start
                                                            - length);
                        document.TextArray = newText;
                        SetIndexInfo(value.ToCharArray(),_tempwii);
                        this.wIndexInfo.mergeIndexInfo(index,_tempwii,value.Length-length);
                    }
                   
                 }
            }
            public override int Count
            {
                get
                {
                   return wIndexInfo.PCurrent + 1;
                }
            }   
        }
        public class WordCollectionC : WordCollection 
        {
            internal class WordIndexInfo 
            {
                private const int INCREMENT = 100;
                private int Count;
                private int[,] wordInfo;
                public int[] this[int index] 
                {
                    get 
                    {
                        return new int[2] { wordInfo[index, 0], wordInfo[index, 1] };
                    }
                }
                private int _pCurrent;
                public int PCurrent 
                {
                    get { return _pCurrent; }
                    set { _pCurrent = value; }
                }
                public bool AddIndexInfo(int start, int length)
                {
                    if (_pCurrent + 1 >= Count)
                    {
                        if (!EnlargeWordInfo())
                            return false;
                    }
                    _pCurrent++;
                    wordInfo[_pCurrent, 0] = start;
                    wordInfo[_pCurrent, 1] = length;
                    return true;
                }
                private bool EnlargeWordInfo()
                {
                    bool OK = false;
                    try
                    {
                        int[,] temp = new int[Count + INCREMENT, 2];
                        for (int i = 0; i <= _pCurrent; i++)
                        {
                            temp[i, 0] = wordInfo[i, 0];
                            temp[i, 1] = wordInfo[i, 1];
                        }
                        Count = Count + INCREMENT;
                        wordInfo = temp;
                        OK = true;
                    }
                    catch (OutOfMemoryException e)
                    {
                        Console.WriteLine(e.ToString());
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine(ex.ToString());
                    }
                    finally
                    {
                        OK = false;
                    }
                    return OK;
                }
                public WordIndexInfo() 
                {
                    wordInfo = new int[INCREMENT, 2];
                    Count = INCREMENT;
                    _pCurrent = -1;
                }
            }
            private WordIndexInfo wIndexInfo;
            private void SetIndexInfo(char[] TextArray, WordIndexInfo info)
            {
                int start = 0, length = 0;
                while (GetWord(TextArray, start, 0, out start, out length))

                {
                    info.AddIndexInfo(start, length);
                    start = start + length;
                }
            }
            private int WordCount(char[] TextArray) 
            {
                int count = 0;
                int length=0, start = 0;
                while(GetWord(TextArray,start+length,0,out start,out length))
                {
                    count++;
                }
                return count;
            }
            public WordCollectionC(MyDocument d):base(d)
            {
                wIndexInfo = new WordIndexInfo();
                SetIndexInfo(d.TextArray, wIndexInfo);
                _count = wIndexInfo.PCurrent + 1;
            }
            public override string this[int index]
            {
                get
                {
                    if (index<_count)
                    {
                        if (index <= wIndexInfo.PCurrent)
                            return new string(document.TextArray, wIndexInfo[index][0], wIndexInfo[index][1]);
                        else 
                        {
                            int start, length;
                            start = 0;
                            length =0;
                            while (wIndexInfo.PCurrent < index)
                            {
                                if (GetWord(document.TextArray, start + length, 0, out start, out length))
                                {
                                    wIndexInfo.AddIndexInfo(start, length);
                                }
                                else
                                {
                                    throw new IndexOutOfRangeException();
                                }
                            }
                            return new string(document.TextArray, wIndexInfo[index][0], wIndexInfo[index][1]); 
                        }
                    }
                    else
                    {
                        throw new IndexOutOfRangeException();
                    }                  
                }
                set
                {
                    int start, length;
                    length=wIndexInfo[index][1];
                    start = wIndexInfo[index][0];
                    if (length == value.Length)
                    {
                        Array.Copy(value.ToCharArray(), 0,
                               document.TextArray, start, length);
                    }
                    else 
                    {
                        _count=wIndexInfo.PCurrent +WordCount( value.ToCharArray(0, value.Length));
                        char[] newText =
                        new char[document.TextArray.Length +
                                value.Length - length];
                        Array.Copy(document.TextArray, 0, newText,
                                                        0, start);
                        Array.Copy(value.ToCharArray(), 0, newText,
                                             start, value.Length);
                        Array.Copy(document.TextArray, start + length,
                                   newText, start + value.Length,
                                  document.TextArray.Length - start- length);
                        document.TextArray = newText;
                        wIndexInfo.PCurrent = index - 1;
                    }
                 }
            }
            public override int Count
            {
                get
                {
                    return _count;
                }
            }
            private int _count;
        }
    // 以下类型允许以类似字符数组的方式查看文档
    // :
    public class CharacterCollection
    {
        readonly MyDocument document;  // 包含文档

        internal CharacterCollection(MyDocument d)
        {
          document = d; 
        }

        // 获取和设置包含文档中的字符的索引器:
        public char this[int index] 
        {
            get 
            { 
                return document.TextArray[index]; 
            }
            set 
            { 
                document.TextArray[index] = value; 
            }
        }

        // 获取包含文档中字符的计数:
        public int Count 
        {
            get 
            { 
                return document.TextArray.Length; 
            }
        }
    }

    // 由于字段的类型具有索引器， 
    // 因此这些字段显示为“索引属性”:
    public IIndexer Words;
    public CharacterCollection Characters;

    private char[] TextArray;  // 文档的文本。 

    public MyDocument(string initialText)
    {
        TextArray = initialText.ToCharArray();
        Words = new WordCollectionC(this);
        Characters = new CharacterCollection(this);
    }

    public string Text 
    {
        get 
        { 
           return new string(TextArray); 
        }
    }
    }

　　总结代码书写中的经验

　　1 接口和抽象类的关系与不同

　　http://www.cnblogs.com/lovemyth/archive/2008/09/08/828909.html 这个是比较好的答案，至于我的理解1接口可以由抽象类（或者父类集成），然后由不同的子类实现。2接口的成员都是public，且public和private，protected不能修饰接口定义的东西。3接口是定义了可以什么，抽象类定义了你是什么

　　2 内部类的好处

　　http://www.cnblogs.com/qingyuan/archive/2010/08/25/1808177.html ，我的理解 1内部类可以访问外部类，即使是外部类的private的 2内部类更好的封装了外部类的一些东西。

　　3 abstract和 virtual 的不同

　　我的理解两者都要用Override去实现，但是virtual不强制，abstract必须实现。

　　4 父类子类实例化时对应的构造函数

　　base很重要，通过base调用父类的相关构造函数，默认是无参数的。

　　5 声明二维数组时int[,]与int[][]的不同点

　　一个是矩阵一个是交错数组。

 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　2013年4月8日23:33:08

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