4.24学习笔记

C#中
数组长度表示用.length;
arraylist集合中对象个数表示用.count;

c#数组的声明方式

int[] intArray;
int[] intArray = {99,34,56,12,1};
int[] intArray = new int[5];
int[] intArray = new int[varsize];
int[] intArray = new int[5]{99,34,56,12,1};

从旧数组复制到新数组，2表示新数组开始位置

oldArray.CopyTo(newArray, 2);

 循环迭代出Hashtable中对象
错误：

foreach(Person  p in peopleHashtable) // Will compile but not run!
{
    Response.Write(p.FullName + "<BR/>");
} 

 正确：

foreach (DictionaryEntry de in peopleHashtable)
{
    Response.Write(de.Key.ToString() + ":" + ((Person)de.Value).FullName + 
       "<BR/>");
}

SortedList

1创建空的SortedList
2手动迭代Hashtable的DictionaryEntry（Hashtable是无须存放的）
3把它们添加到SortedList（添加过程中自动排序）
实例：
SortedList peopleSortedList = new SortedList(peopleHashtable);
foreach (Person p in peopleSortedList.Values)
{
    Response.Write(p.FullName + "<BR/>");
}
Response.Write("Index of Srinivasa: " + peopleSortedList.IndexOfKey("ss"));

Queues适合于按照对象进入的顺序来存储它们（先进先出），

而Stack是一个先进后出结构。

但要取的话必须删一个取一个

BitArray
管理一个布尔值数组或者集合使用

强类型化的集合如PersonList类
注意：强制类型转换隐藏在了属性访问器中，属性的返回值是强类型化的。（这里this是C#属性访问器的关键字）

using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

using System.Collections;

/// <summary>
///PersonList 的摘要说明
/// </summary>
public class PersonList:System.Collections.IEnumerable
{
 public PersonList()
 {
  //
  //TODO: 在此处添加构造函数逻辑
  //
 }
    private ArrayList innerList = new ArrayList();

    public void Add(Person aPerson)
    {
        innerList.Add(aPerson);
    }

    public void Remove(Person aPerson)
    {
        innerList.Remove(aPerson);
    }

    public int Count
    {
        get
        {
            return innerList.Count;
        }
    }

    //Get/Set element at given index
    public Person this[int index]
    {
        get 
        {
            return (Person)innerList[index];
        }
        set
        {
            innerList[index] = value;
        }
    }

    public IEnumerator GetEnumerator()
    {
        return innerList.GetEnumerator();
    }
}

 泛型的Hashtable 和Hashtable区别，读取的时候不需要强制类型转化

LinkedList<T>是一个强类型化的双链接表，该链接表中的每个节点都指向前一个节点和后一个节点

 问题：谁能帮我讲解下BinarySearch方法？小女谢谢了。。

 ArrayList的binary search：

// Searches a section of the list for a given element using a binary search
        // algorithm. Elements of the list are compared to the search value using
        // the given IComparer interface. If comparer is null, elements of
        // the list are compared to the search value using the IComparable
        // interface, which in that case must be implemented by all elements of the
        // list and the given search value. This method assumes that the given
        // section of the list is already sorted; if this is not the case, the
        // result will be incorrect.
        //
        // The method returns the index of the given value in the list. If the
        // list does not contain the given value, the method returns a negative
        // integer. The bitwise complement operator (~) can be applied to a
        // negative result to produce the index of the first element (if any) that
        // is larger than the given search value. This is also the index at which
        // the search value should be inserted into the list in order for the list
        // to remain sorted.
        // 
        // The method uses the Array.BinarySearch method to perform the
        // search.
        // 
        public virtual int BinarySearch(int index, int count, Object value, IComparer comparer) {
            if (index < 0 || count < 0)
                throw new ArgumentOutOfRangeException((index<0 ? "index" : "count"), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (_size - index < count)
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
    
            return Array.BinarySearch((Array)_items, index, count, value, comparer);
        }

Array的：

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        public static int BinarySearch(Array array, int index, int length, Object value, IComparer comparer) {
            if (array==null) 
                throw new ArgumentNullException("array");
            int lb = array.GetLowerBound(0);
            if (index < lb || length < 0)
                throw new ArgumentOutOfRangeException((index<lb ? "index" : "length"), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (array.Length - (index - lb) < length)
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
            if (array.Rank != 1)
                throw new RankException(Environment.GetResourceString("Rank_MultiDimNotSupported"));
            
            if (comparer == null) comparer = Comparer.Default;
            if (comparer == Comparer.Default) {
                int retval;
                bool r = TrySZBinarySearch(array, index, length, value, out retval);
                if (r)
                    return retval;
            }

            int lo = index;
            int hi = index + length - 1;   
            Object[] objArray = array as Object[];
            if(objArray != null) {
                while (lo <= hi) {
                    // i might overflow if lo and hi are both large positive numbers. 
                    int i = GetMedian(lo, hi);

                    int c;
                    try {
                        c = comparer.Compare(objArray[i], value);
                    }
                    catch (Exception e) {
                        throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_IComparerFailed"), e);
                    }
                    catch {
                        throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_IComparerFailed"));
                    }
                    if (c == 0) return i;
                    if (c < 0) {
                        lo = i + 1;
                    }
                    else {
                        hi = i - 1;
                    }
                }
            }
            else {
                while (lo <= hi) {
                    int i = GetMedian(lo, hi);                    

                    int c;
                    try {
                        c = comparer.Compare(array.GetValue(i), value);
                    }
                    catch (Exception e) {
                        throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_IComparerFailed"), e);
                    }
                    catch {
                        throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_IComparerFailed"));
                    }
                    if (c == 0) return i;
                    if (c < 0) {
                        lo = i + 1;
                    }
                    else {
                        hi = i - 1;
                    }
                }
            }
            return ~lo;
        }

总的来说，就是二分法来查找元素，如果使用此方法前没有排序，或是查找的比较方式和排序的比较方式不一样的话，结果可能找不到。

 ArrayList的binary search：

// Searches a section of the list for a given element using a binary search
        // algorithm. Elements of the list are compared to the search value using
        // the given IComparer interface. If comparer is null, elements of
        // the list are compared to the search value using the IComparable
        // interface, which in that case must be implemented by all elements of the
        // list and the given search value. This method assumes that the given
        // section of the list is already sorted; if this is not the case, the
        // result will be incorrect.
        //
        // The method returns the index of the given value in the list. If the
        // list does not contain the given value, the method returns a negative
        // integer. The bitwise complement operator (~) can be applied to a
        // negative result to produce the index of the first element (if any) that
        // is larger than the given search value. This is also the index at which
        // the search value should be inserted into the list in order for the list
        // to remain sorted.
        // 
        // The method uses the Array.BinarySearch method to perform the
        // search.
        // 
        public virtual int BinarySearch(int index, int count, Object value, IComparer comparer) {
            if (index < 0 || count < 0)
                throw new ArgumentOutOfRangeException((index<0 ? "index" : "count"), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (_size - index < count)
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
    
            return Array.BinarySearch((Array)_items, index, count, value, comparer);
        }

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        public static int BinarySearch(Array array, int index, int length, Object value, IComparer comparer) {
            if (array==null) 
                throw new ArgumentNullException("array");
            int lb = array.GetLowerBound(0);
            if (index < lb || length < 0)
                throw new ArgumentOutOfRangeException((index<lb ? "index" : "length"), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (array.Length - (index - lb) < length)
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
            if (array.Rank != 1)
                throw new RankException(Environment.GetResourceString("Rank_MultiDimNotSupported"));
            
            if (comparer == null) comparer = Comparer.Default;
            if (comparer == Comparer.Default) {
                int retval;
                bool r = TrySZBinarySearch(array, index, length, value, out retval);
                if (r)
                    return retval;
            }

            int lo = index;
            int hi = index + length - 1;   
            Object[] objArray = array as Object[];
            if(objArray != null) {
                while (lo <= hi) {
                    // i might overflow if lo and hi are both large positive numbers. 
                    int i = GetMedian(lo, hi);

                    int c;
                    try {
                        c = comparer.Compare(objArray[i], value);
                    }
                    catch (Exception e) {
                        throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_IComparerFailed"), e);
                    }
                    catch {
                        throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_IComparerFailed"));
                    }
                    if (c == 0) return i;
                    if (c < 0) {
                        lo = i + 1;
                    }
                    else {
                        hi = i - 1;
                    }
                }
            }
            else {
                while (lo <= hi) {
                    int i = GetMedian(lo, hi);                    

                    int c;
                    try {
                        c = comparer.Compare(array.GetValue(i), value);
                    }
                    catch (Exception e) {
                        throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_IComparerFailed"), e);
                    }
                    catch {
                        throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_IComparerFailed"));
                    }
                    if (c == 0) return i;
                    if (c < 0) {
                        lo = i + 1;
                    }
                    else {
                        hi = i - 1;
                    }
                }
            }
            return ~lo;
        }

谢谢昂。····多用在什么时候呢？