Console. WriteLine(I)； When I is a value type, you can print out their values, and when I is a reference type, you can print out the data type of I instead of the value of I.

For example, when I is an int[] array element, a [0] =1; I = a[0]； At this time, it is not 0 but int that is printed. At this time, you need to rewrite the ToString () method, and only return the fields you want to print in the ToString method.