C# Array类 【温故而知新】

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace Array类
{
    class Program
    {
        static void Main(string[] args)
        {

            //Array是一个抽象类，不能使用构造函数来创建数组

            //创建数组
            Array arr = Array.CreateInstance(typeof(int), 5);//创建类型为int，大小为5的数组。

            //设置对应元素的值SetValue()
            for (int i = 0; i < 5; i++)
            {
                arr.SetValue(33, i);
            }
            //读取对应元素的值
            for (int i = 0; i < 5; i++)
            {
                Console.WriteLine(arr.GetValue(i));
            }

            //强制转化
            int[] arrInt = (int[])arr;


            //创建多维数组和不基于0的数组，下面创建一个包含2*3个元素的二维数组。第一维基于1，第二维基于10
            int[] lengths = { 2, 3 };
            int[] lowerBounds = { 1, 10 };

            Array racers = Array.CreateInstance(typeof(Person), lengths, lowerBounds);

            racers.SetValue(new Person { FirstName = "aa", LastName = "bb" }, 1, 10);
            racers.SetValue(new Person { FirstName = "cc", LastName = "dd" }, 1, 11);
            racers.SetValue(new Person { FirstName = "ee", LastName = "ff" }, 1, 12);
            racers.SetValue(new Person { FirstName = "gg", LastName = "hh" }, 2, 10);
            racers.SetValue(new Person { FirstName = "ii", LastName = "jj" }, 2, 11);
            racers.SetValue(new Person { FirstName = "kk", LastName = "ll" }, 2, 12);


            //复制数组：
            //因为数组是引用类型，所以将一个数组变量赋予给另一个数组变量，就会得到两个引用同一数组的变量。
            //而复制数组，会使数组实现ICloneable接口，这个接口定义的Clone()方法会创建数组的浅表副本。

            //如果数组的元素是值类型，以下代码就会复制所有的值
            int[] arrClone = { 1, 2 };
            int[] arrClone2 = (int[])arrClone.Clone();

            //如果数组包含引用类型，则不复制元素，而复制引用。
            Person[] p1 =  {    
                               new Person { FirstName="aa", LastName="bb"},
                               new Person { FirstName="cc", LastName="dd"}
                           };

            Person[] p2 = (Person[])p1.Clone();

            p2[0] = new Person { FirstName = "ee", LastName = "ff" };

            //Clone()与Copy()区别
            //1.都是创建浅表副本
            //2.Clone()方法创建一个新的数组
            //3.Copy()方法必须传递阶数相同且有足够元素的已有数组

            //Copy()方法
            int[] arr1 = { 1, 2, 3, 4 };
            int[] arr2 = { 5, 6, 7, 8, 9, 10, 11 };
            arr1.CopyTo(arr2, 2);

            //浅表副本与深层副本:浅复制就是仅复制类中的值类型成员
            //深复制就是复制类中的值类型成员和引用类型的成员。



            //排序:注意IComparable<Person>接口与IComparer<Person>接口的不同
            //(1)
            string[] names = { "bb", "ff", "aa", "cc", "ee", "dd" };
            Array.Sort(names);
            foreach (string name in names)
            {
                Console.WriteLine(name);
            }

            //对自定义类数组进行排序，需要实现IComparable接口，
            Person[] p3 =  {    
                               new Person { FirstName="aa", LastName="bb"},
                               new Person { FirstName="cc", LastName="dd"},
                               new Person { FirstName="ee", LastName="ff"},
                               new Person { FirstName="dd", LastName="dd"}
                           };

            Array.Sort(p3);

            foreach (var p in p3)
            {
                Console.WriteLine(p.ToString());
            }

            //(2)
            Person[] p4 =  {    
                               new Person { FirstName="aa", LastName="bb"},
                               new Person { FirstName="cc", LastName="dd"},
                               new Person { FirstName="ee", LastName="ff"},
                               new Person { FirstName="dd", LastName="dd"}
                           };

            Array.Sort(p4, new PersonCompare(PersonCompareType.FirstName));

            foreach (var p in p3)
            {
                Console.WriteLine(p.ToString());
            }


            //数组作为参数

            //在方法中返回数组
            //static Person[] GetPersons()
            //{
            //    return new Person[]  {    
            //                           new Person { FirstName="aa", LastName="bb"},
            //                           new Person { FirstName="cc", LastName="dd"},
            //                           new Person { FirstName="ee", LastName="ff"},
            //                           new Person { FirstName="dd", LastName="dd"}
            //                        };
            //}

            //参数
            //static void DisplayPersons(Person[] person)
            //{

            //}


            //数组的协变
            //说明：数组支持协变。这表示数组可以声明为基类，其派生类型的元素可以赋予数组元素。
            //例如：可以声明一个object[]类型的参数，给它传递一个参数Person[]
            //static void DisplayPersons(object[] person)
            //{

            //}


            //ArraySegment<T>
            int[] ar1 = { 1, 3, 5, 7, 9 };
            int[] ar2 = { 2, 4, 6, 8, 10 };

            var segments = new ArraySegment<int>[2]
            {
                new ArraySegment<int>(ar1,2,3),
                 new ArraySegment<int>(ar2,1,4),
            };

            int sum = SumOfSegments(segments);

            Console.ReadKey();
        }

        static int SumOfSegments(ArraySegment<int>[] segments)
        {
            int sum = 0;

            foreach (var segment in segments)
            {
                int offset = segment.Offset;
                int count = segment.Count;
                for (int i = offset; i < offset + count; i++)
                {
                    sum = sum + segment.Array[i];
                }
            }
            return sum;
        }


    }
    public class Person : IComparable<Person>
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }

        public override string ToString()
        {
            return string.Format("{0},{1}", FirstName, LastName);
        }

        public int CompareTo(Person other)
        {
            if (other == null)
            {
                return 1;
            }
            int result = string.Compare(this.LastName, other.LastName);
            if (result == 0)
            {
                result = string.Compare(this.FirstName, other.FirstName);
            }
            return result;
        }
    }

    //排序（2）使用的类
    //解释说明：类PersonCompare实现了IComparable<Person>接口，可以按照FirstName或LastName对Person对象进行排序。
    //枚举PersonCompareType定义了可用于PersonCompare的排序选项：FirstName和LastName。
    //排序方式由PersonCompare类的构造函数定义，在该构造函数中设置了一个PersonCompareType值。
    //实现Compare()方法时用一个swith语句指定是按FirstName还是LastName排序。
    public enum PersonCompareType
    {
        FirstName,
        LastName
    }

    public class PersonCompare : IComparer<Person>
    {
        private PersonCompareType compareType;

        public PersonCompare(PersonCompareType compareType)
        {
            this.compareType = compareType;
        }

        public int Compare(Person x, Person y)
        {
            if (x == null && y == null) return 0;
            if (x == null) return 1;
            if (y == null) return -1;

            switch (compareType)
            {
                case PersonCompareType.FirstName:
                    return string.Compare(x.FirstName, y.FirstName);
                case PersonCompareType.LastName:
                    return string.Compare(x.LastName, y.LastName);
                default:
                    throw new ArgumentException("unexpected compare type");
            }
        }
    }
}