StringBuilder/string

Question

When s2 data type is StringBuilder no need for ToString() method but when s3 data type is string there is need for ToString() method. Is there any explanation for this? Problem is highlighted.

using System;
using System.Text;

class Program
{
static void Main(string[] args)
{
string s1 = "string1 ";

StringBuilder s2 = new StringBuilder("string1 ").Append(s1);

Console.WriteLine(s2);//string1 string1

string s3 = new StringBuilder("string1 ").Append(s1).ToString();

Console.WriteLine(s3);//string1 string1

Console.ReadKey();
}
}

Maha · Answer

Thank you for your explanation.

Vulpes · Answer

The Console.WriteLine method has 19 overloads which are listed here: http://msdn.microsoft.com/en-us/library/system.console.writeline(v=vs.100).aspx This line: Console.WriteLine(s2); is using the overload which takes a System.Object parameter. This overload automatically calls the ToString() method of whatever instance is passed to it. So in this case it calls StringBuilder's ToString() method which of course prints the string which it contains to the console. This line: Console.WriteLine(s3); is using the overload which takes a string parameter and this of course simply prints the string to the console. So in the first case ToString() is called implicitly by Console.WriteLine and in the second case it's called explicitly by the preceding line.