String type is immutable. Immutable basically means "cannot be changed". Consider the following code:
1: string name = "Mark";
2: name += " Moeykens";
3: name = string.Format("Mr. {0}", name);
On line 1 a string was assigned "Mark". On line 2 "Mark" was thrown away and a new string was created, "Mark Moeykens". On line 3 "Mark Moeykens" was thrown away and a new string, "Mr. Mark Moeykens" was created. Since strings are immutable, a new place in memory has to be created everytime the value changes.
StringBuilder manipulates strings much more efficiently. In cases where you have a lot of string manipulation, StringBuilder would be a better candidate.
StringBuilder sb = new StringBuilder();
sb.Append("Mark");
sb.Append(" Moeykens");
sb.Insert(0, "Mr. ");
Notes
- StringBuilder still outperforms string when concatenating just two strings.
- There is not much of a difference in time (milliseconds) until you go over about 10,000 concatenations
- StringBuilder is a good choice for applications that need to scale, like web applications.
More Info:
MSDN: Using the StringBuilder Class
