C# ArrayList.BinarySearch 小问题 --- 必须是按顺序存储才可以这样查找

使用默认的比较器在整个已排序的 ArrayList 中搜索元素，并返回该元素从零开始的索引。

ArrayList.BinarySearch (Object, IComparer)	使用指定的比较器在整个已排序的 ArrayList 中搜索元素，并返回该元素从零开始的索引。
ArrayList.BinarySearch (Int32, Int32, Object, IComparer)	使用指定的比较器在已排序 ArrayList 的某个元素范围中搜索元素，并返回该元素从零开始的索引。由 .NET Compact Framework 支持。

---强调一点。因为是 2分查找。所以必须是按照顺序存放值，否则出错。

有2个方式实现 IComparer 和类自己实现一个接口 system 中的

D:\c_\arraylist>Test
person CompareTo(object obj) this person is 4 -- objthis person is 3
person CompareTo(object obj) this person is 2 -- objthis person is 3
person CompareTo(object obj) this person is 104 -- objthis person is 3
find   person p3 = new person(3); -3   比较后得不到结果严重问题
-----
person CompareTo(object obj) this person is 4 -- objthis person is 5
find   person p3 = new person(3); 6
-----
person CompareTo(object obj) this person is 4 -- objthis person is 1
person CompareTo(object obj) this person is 2 -- objthis person is 1
find person p1 = new person(1); 0
-----
person CompareTo(object obj) this person is 4 -- objthis person is 104
person CompareTo(object obj) this person is 5 -- objthis person is 104
person CompareTo(object obj) this person is 1 -- objthis person is 104
person CompareTo(object obj) this person is -88 -- objthis person is 104
find      person p6 = new person(104); -10 -- 比较后得不到结果严重问题
0 this person is 1
1 this person is 2
2 this person is 104
3 this person is 3
4 this person is 4
5 this person is 122
6 this person is 5
7 this person is 1
8 this person is -88

using System;

using System.Collections;

using System.Collections.Generic;

public class Test

{

public class person : IComparable

{

public int age = 0;

public person(int i)

{

this.age = i;

}

public override string ToString()

{

return "this person is " + age;

}

public int CompareTo(object obj)

{

Console.WriteLine(" person CompareTo(object obj) " + this.ToString() + " -- obj" + obj.ToString());

if (obj is person)

{

person temp = (person)obj;

return age.CompareTo(temp.age);

}

throw new ArgumentException("object is not a CompareTo ");

}

public static void Main(string[] args)

{

ArrayList list = new ArrayList(300);

person p1 = new person(1);

person p2 = new person(2);

person p3 = new person(3);

person p4 = new person(4);

person p5 = new person(5);

person p0 = new person(-88);

person p6 = new person(104);

person p7 = new person(122);

list.Add(p1);

list.Add(p2);

list.Add(p6);

list.Add(p3);

list.Add(p4);

list.Add(p7);

list.Add(p5);

list.Add(p1);

list.Add(p0);

Console.WriteLine(list[1]);

list.Remove(1); // 1 will be object for method input paramt

Console.WriteLine(list[1]);

list.RemoveAt(1);

Console.WriteLine(list[1]);

* ArrayList list0 = new ArrayList(2);

list0.Add(new person(12));

* list.AddRange(list0);

Console.WriteLine(" 合并集合 AddRange 新的集合都在最后 " + list[2]);

Console.WriteLine(" 老集合的包含的数量 --添加新的以用不修改老的集合 " + list0.Count);

Console.WriteLine("find person p3 = new person(3); " + list.BinarySearch(p3));

Console.WriteLine("-----");

Console.WriteLine("find person p3 = new person(3); " + list.BinarySearch(p5));

Console.WriteLine("-----");

Console.WriteLine(" find person p1 = new person(1); " + list.BinarySearch(p1));

Console.WriteLine("-----");

Console.WriteLine(" find person p6 = new person(104); " + list.BinarySearch(p6));

for (int i = 0; i < list.Count; i++ )

{

Console.WriteLine(i + " " + list[i].ToString() );

}

Summary:

Compares two objects and returns a value indicating whether one is less than, equal to, or greater than the other.

Parameters:

x: The first object to compare.

y: The second object to compare.

Return Values:

Value Condition Less than zero x is less than y. Zero x equals y. Greater than zero x is greater than y.

Exceptions:

System.ArgumentException: Neither x nor y implements the System.IComparable interface.-or- x and y are of different types and neither one can handle comparisons with the other.

class personIComparer : System.Collections.IComparer

{

public int Compare(object x, object y) {

Test.person p1 = x as Test.person;

Test.person p2 = y as Test.person;

if ( p1 == null ) {

//??

}

if (p1.age == p2.age ){

return 0;

}else{

if (p1.age > p2.age ) {

return 1;

}else{

return -1;

}

public class Temperature : IComparable {

/// <summary>

/// IComparable.CompareTo implementation.

/// </summary>

public int CompareTo(object obj) {

if(obj is Temperature) {

Temperature temp = (Temperature) obj;

return m_value.CompareTo(temp.m_value);

}

throw new ArgumentException("object is not a Temperature");

}

// The value holder

protected int m_value;

public int Value {

get {

return m_value;

}

set {

m_value = value;

}

public int Celsius {

get {

return (m_value-32)/2;

}

set {

m_value = value*2+32;

}

posted on 2008-02-25 21:08 小高阅读(1629) 评论(0) 编辑收藏

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