Everyone use the type String in their daily programming more often. In addition, most of people do a common mistake to choose between String and StringBuilder.
In concatenation of Strings, if we are initially creating a string, say s = "Hello" and then we are appending to it as s = s + " World", we are actually creating two instances of string in memory. Both the original as well as the new string will be stored in the memory because String is immutable. Therefore, every time when we concatenate the new value, a new instance will be made and it will make a great performance loss if concatenation will be done many times. For that matter, all the activities we do to the string are stored in the memory as separate references and it must be avoided as much as possible.
We can use StringBuilder which is very useful in these kind of scenarios. For the example above, using a StringBuilder as, s.Append(" World"); which only stores the value in the original string and no additional reference is created that will definitely give us a performance boost.
For example-
(I) String Action:
- string str="";
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DateTime startTime = DateTime.Now;
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Response.Write(("<br>Start time:" + startTime.ToString()));
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int i;
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for(i=0;i<20000;i++)
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{
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str += i.ToString()+ "<br>";
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}
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DateTime EndTime= DateTime.Now;
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Response.Write(("<br>End time:" + EndTime.ToString()));
Output:
Start time:3/22/2006 10:23:44 AM
End time:3/22/2006 10:25:08 AM
The above code took 1 minute and 24 Seconds to complete its operation.
(II) String Builder Action:
- StringBuilder strbuilder = new StringBuilder();
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DateTime startTime1 = DateTime.Now;
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Response.Write(("<br>Start time:" + startTime1.ToString()));
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int i1;
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for (i1 = 0; i1 < 20000; i1++)
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{
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strbuilder.Append(i1 + "<br>");
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}
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DateTime EndTime1 = DateTime.Now;
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Response.Write(("<br>End time:" + EndTime1.ToString()));
Output:
Start time:3/22/2006 10:25:08 AM
End time:3/22/2006 10:25:09 AM
The above code took 1 Second to complete its operation.
So remember, when we do not want to concatenate then surely use the String and when we have to deal with multiple concatenations, then definitely use StringBuilder.
Thanks &Regs
Bharath Reddy VasiReddy
String and Stringbuilder Usage 
