数组中字符串替换的几种方式

//方法1
protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            ReplaceStr();
        }
    }
    public void ReplaceStr()
    {
        ArrayList MyArray = new ArrayList();
        MyArray.Add("123");
        MyArray.Add("aaa");
        if (MyArray.Contains("aaa"))
        {
            MyArray.Remove("aaa");
            MyArray.Add("bbb");
        }
        for (int i = 0; i <= MyArray.Count - 1; i++)
        {
            Response.Write(MyArray[i].ToString()); 
        }
    }

//方法2
protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            ReplaceStr();
        }
    }
  public void ReplaceStr()
    {
        string [] tm = new string[] { "123", "aaa" };
        for (int i = 0; i < tm.Length; i++)
        {
            if (tm[i].ToString() == "aaa")
            {
                tm[i]=tm[i].Replace("aaa", "bbb");
                
            }
        }
        for (int i = 0; i <= tm.Length - 1; i++)
         {
             Response.Write(tm[i].ToString());
         }
    }
//方法3
 protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            string[] tm = new string[] { "123", "aaa" };
            string Array=ReplaceValue(tm, "aaa", "bbb", ",");
            Response.Write(Array);
        }
    }
 public static string ReplaceValue(string[] item, string oldSv, string newSv, string separator)
    {
        if (item == null) return string.Empty;
        StringBuilder sb = new StringBuilder();
        foreach (string s in item)
        {
            if (s == oldSv)
            {
                sb.Append(newSv);
                sb.Append(separator);
            }
            else
            {
                sb.Append(s);
                sb.Append(separator);
            }
        }
        string returnstr = sb.ToString();
        returnstr = (returnstr.EndsWith(separator)) ? returnstr.Substring(0, returnstr.Length - 1) : returnstr;
        return returnstr;
    }