将数组作为参数传递

在以下示例中，初始化字符串数组，并将其作为参数传递给字符串的PrintArray方法。该方法显示数组的元素。接下来，调用方法ChangeArray和ChangeArrayElement来证明按值发送数组参数不会阻止对数组元素的更改。我的问题是数组在方法changeArray中是如何不发生变化的。。但是方法ChangeArrayElements发生了变化？这是一个例子：

class ArrayClass
{
    static void PrintArray(string[] arr)
    {
        for (int i = 0; i < arr.Length; i++)
        {
            System.Console.Write(arr[i] + "{0}", i < arr.Length - 1 ? " " : "");
        }
        System.Console.WriteLine();
    }
    static void ChangeArray(string[] arr)
    {
        // The following attempt to reverse the array does not persist when 
        // the method returns, because arr is a value parameter.
        arr = (arr.Reverse()).ToArray();
        // The following statement displays Sat as the first element in the array.
        System.Console.WriteLine("arr[0] is {0} in ChangeArray.", arr[0]);
    }
     static void ChangeArrayElements(string[] arr)
    {
        // The following assignments change the value of individual array  
        // elements. 
        arr[0] = "Sat";
        arr[1] = "Fri";
        arr[2] = "Thu";
        // The following statement again displays Sat as the first element 
        // in the array arr, inside the called method.
        System.Console.WriteLine("arr[0] is {0} in ChangeArrayElements.", arr[0]);
    }
    static void Main()
    {
        // Declare and initialize an array. 
        string[] weekDays = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
        // Pass the array as an argument to PrintArray.
        PrintArray(weekDays);
        // ChangeArray tries to change the array by assigning something new 
        // to the array in the method. 
        ChangeArray(weekDays);
        // Print the array again, to verify that it has not been changed.
        System.Console.WriteLine("Array weekDays after the call to ChangeArray:");
        PrintArray(weekDays);
        System.Console.WriteLine();
        // ChangeArrayElements assigns new values to individual array 
        // elements.
        ChangeArrayElements(weekDays);
        // The changes to individual elements persist after the method returns. 
        // Print the array, to verify that it has been changed.
        System.Console.WriteLine("Array weekDays after the call to      ChangeArrayElements:");
        PrintArray(weekDays);
    } 
}
// Output:  
// Sun Mon Tue Wed Thu Fri Sat 
// arr[0] is Sat in ChangeArray. 
// Array weekDays after the call to ChangeArray: 
// Sun Mon Tue Wed Thu Fri Sat 
//  
// arr[0] is Sat in ChangeArrayElements. 
// Array weekDays after the call to ChangeArrayElements: 
// Sat Fri Thu Wed Thu Fri Sat

static void ChangeArray(string[] arr)
{
    // The following attempt to reverse the array does not persist when 
    // the method returns, because arr is a value parameter.
    arr = (arr.Reverse()).ToArray();
    // The following statement displays Sat as the first element in the array.
    System.Console.WriteLine("arr[0] is {0} in ChangeArray.", arr[0]);
}

static void ChangeArray(ref string[] arr)
{
    // Since 'arr' is passed by reference, changing the value of 'arr'
    // changes the reference that the caller has.
    arr = (arr.Reverse()).ToArray();
    // The following statement displays Sat as the first element in the array.
    System.Console.WriteLine("arr[0] is {0} in ChangeArray.", arr[0]);
}