What are the distinctions between StringBuilder in Java and StringBuilder in C#?

[Onam]

I'm in the process of porting Java code to C#. The StringBuilder class in Java appears to have many more methods than the one in C#. I'm curious about (say) the Java functionality.

sb.indexOf(s);
sb.charAt(i);
sb.deleteCharAt(i);

This appears to be lacking in C#
The first two, I think, may be modeled by

sb.ToString().IndexOf(s);
sb.ToString().CharAt(i);

Would the third, however, work on a replica of the sb's contents rather than the real contents?

Is there a standardized way to add this capability to all missing methods?


Source: StringBuilder Class in Java