C#自定义List类

代码如下：

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

namespace MyArrayList
{    
    public class MyArrayList
    {
        //容量
        private const int _defaultCapacity = 4;
        //存放数组元素
        private object[] _items;
        //数组大小
        private int _size;
        //元素个数为0的数组状态
        private static readonly object[] emptyArray = new object[0];

        /// <summary>
        /// 析构函数(为了不引发未将对象引用到实例，所以对_items赋值)
        /// </summary>
        public MyArrayList()
        {
            this._items = emptyArray;
        }

        public MyArrayList(int capacity) 
        {
            if(capacity<0)
                throw new ArgumentOutOfRangeException("capacity","ArrayList的容量不可为负数");
            this._items = new object[capacity];
        }

        /// <summary>
        /// 索引器
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        public virtual object this[int index] 
        {
            get 
            {
                if (index < 0 || index >= this._size)
                    throw new ArgumentOutOfRangeException("index", "索引超出范围");
                return this._items[index];
            }
            set 
            {
                if (index < 0 || index >= this._size)
                    throw new ArgumentOutOfRangeException("index","索引超出范围");
                this._items[index] = value;
            }
        }

        /// <summary>
        /// 获取当前数组元素个数
        /// </summary>
        public virtual int Count
        {
            get { return this._size; }
        }

        /// <summary>
        /// 数组的容量
        /// </summary>
        public virtual int Capacity 
        {
            get { return this._items.Length; }
            set 
            {
                if (value != this._items.Length)
                {
                    if (value < this._size)
                    {
                        throw new ArgumentOutOfRangeException("value", "容量太小");
                    }
                    if (value > 0)
                    {
                        //开辟新内存控件存储元素
                        object[] dest = new object[value];
                        if (this._size > 0)
                        {
                            //搬动元素
                            Array.Copy(this._items, 0, dest, 0, this._size);
                        }
                        this._items = dest;
                    }
                    else //数组最小的空间为4
                    {
                        this._items = new object[_defaultCapacity];
                    }
                }
            }
        }

        /// <summary>
        /// 添加元素
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public virtual int Add(object value)
        {
            //当空间已满
            if (this._size == this._items.Length)
                 this.EnsureCapacity(this._size + 1);
            this._items[this._size] = value;
            return this._size++;
        }

        /// <summary>
        /// 对数组进行扩容
        /// </summary>
        /// <param name="p"></param>
        public void EnsureCapacity(int p)
        {
            if (this._items.Length<p)
            {
                //空间加倍
                int num = (this._items.Length == 0) ? _defaultCapacity : (this._items.Length * 2);
                if (num <p)
                    num = p;
                this.Capacity = num;
            }
        }

        /// <summary>
        /// 向指定元素插入元素
        /// </summary>
        public virtual void Insert(int index,object value) 
        {
            if (index<0 || index>this._size)
                throw new ArgumentOutOfRangeException("index","索引超出范围");
            if (this._size == this._items.Length)
                this.EnsureCapacity(this._size + 1);
            if (index < this._size)
                Array.Copy(this._items, index, this._items, index + 1, this._size - index);

            this._items[index] = value;
            this._size++;
        }

        /// <summary>
        /// 移除指定索引的元素
        /// </summary>
        /// <param name="index">索引</param>
        public virtual void Remove(int index) 
        {
            if (index<0 || index>this._size)            
                throw new ArgumentOutOfRangeException("index","索引超出范围");
            this._size--;
            if (index < this._size)
                Array.Copy(this._items, index + 1, this._items, index, this._size - index);
            this._items[this._size] = null;
        }

        /// <summary>
        /// 裁剪空间
        /// </summary>
        public virtual void TrimToSize()
        {
            this.Capacity = this._size;
        }
    }
}