String vs StringBuilder

Question

I understand the difference between String and StringBuilder  StringBuilder being mutable  but is there a large performance difference between the two    The program I   m working on has a lot of case driven string appends  500    Is using StringBuilder a better choice

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StringBuilder is probably preferable   The reason is that it allocates more space than currently needed  you set the number of characters  to leave room for future appends   Then those future appends that fit in the current buffer don t require any memory allocation or garbage collection  which can be expensive   In general  I use StringBuilder for complex string concatentation or multiple formatting  then convert to a normal String when the data is complete  and I want an immutable object again

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String and StringBuilder are actually both immutable  the StringBuilder has built in buffers which allow its size to be managed more efficiently  When the StringBuilder needs to resize is when it is re-allocated on the heap  By default it is sized to 16 characters  you can set this in the constructor   eg   StringBuilder sb   new StringBuilder 50

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If you re doing a lot of string concatenation  use a StringBuilder  When you concatenate with a String  you create a new String each time  using up more memory   Alex

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To clarify what Gillian said about 4 string  if you have something like this   string a b c d   a   b   c   d    then it would be faster using strings and the plus operator  This is because  like Java  as Eric points out   it internally uses StringBuilder automatically  Actually  it uses a primitive that StringBuilder also uses   However  if what you are doing is closer to   string a b c d   a   a   b   a   a   c   a   a   d    Then you need to explicitly use a StringBuilder    Net doesn t automatically create a StringBuilder here  because it would be pointless   At the end of each line   a  has to be an  immutable  string  so it would have to create and dispose a StringBuilder on each line   For speed  you d need to use the same StringBuilder until you re done building   string a b c d  StringBuilder e   new StringBuilder     e Append b    e Append c    e Append d    a   e ToString

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My approach has always been to use StringBuilder when concatenating 4 or more strings  OR When I don t know how may concatenations are to take place   Good performance related article on it here

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My approach has always been to use StringBuilder when concatenating 4 or more strings  OR When I don t know how may concatenations are to take place   Good performance related article on it here

User · Answer

This benchmark shows that regular concatenation is faster when combining 3 or fewer strings   http   www chinhdo com 20070224 stringbuilder-is-not-always-faster   StringBuilder can make a very significant improvement in memory usage  especially in your case of adding 500 strings together     Consider the following example   string buffer    The numbers are     for  int i   0  i  lt  5  i          buffer    i ToString      return buffer    What happens in memory   The following strings are created   1 -  The numbers are    2 -  0  3 -  The numbers are  0  4 -  1  5 -  The numbers are  01  6 -  2  7 -  The numbers are  012  8 -  3  9 -  The numbers are  0123  10 -  4  11 -  The numbers are  01234  12 -  5  13 -  The numbers are  012345    By adding those five numbers to the end of the string we created 13 string objects   And 12 of them were useless   Wow   StringBuilder fixes this problem   It is not a  mutable string  as we often hear  all strings in  NET are immutable    It works by keeping an internal buffer  an array of char   Calling Append   or AppendLine   adds the string to the empty space at the end of the char array  if the array is too small  it creates a new  larger array  and copies the buffer there   So in the example above  StringBuilder might only need a single array to contain all 5 additions to the string-- depending on the size of its buffer   You can tell StringBuilder how big its buffer should be in the constructor

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I believe StringBuilder is faster if you have more than 4 strings you need to append together  Plus it can do some cool things like AppendLine

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StringBuilder is preferable IF you are doing multiple loops  or forks in your code pass    however  for PURE performance  if you can get away with a SINGLE string declaration  then that is much more performant    For example    string myString    Some stuff    var1     more stuff                      var2     other stuff       etc    etc       is more performant than  StringBuilder sb   new StringBuilder    sb Append  Some Stuff    sb Append var1   sb Append   more stuff    sb Append var2   sb Append  other stuff       etc   etc   etc     In this case  StringBuild could be considered more maintainable  but is not more performant than the single string declaration    9 times out of 10 though    use the string builder    On a side note  string   var is also more performant that the string Format approach  generally  that uses a StringBuilder internally  when in doubt    check reflector

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String Vs String Builder   First thing you have to know that In which assembly these two classes lives   So   string is present in System namespace   and   StringBuilder is present in System Text namespace   For string declaration    You have to include the System namespace  something like this  Using System   and   For StringBuilder declaration    You have to include the System text namespace  something like this  Using System text   Now Come the the actual Question   What is the differene between string  amp  StringBuilder   The main difference between these two is that   string is immutable   and  StringBuilder is mutable   So Now lets discuss the difference between immutable and mutable  Mutable    means Changable   Immutable    means Not Changable   For example   using System   namespace StringVsStrigBuilder       class Program               static void Main string   args                           String Example              string name    Rehan               name   name    Shah               name   name    RS               name   name    ---               name   name    I love to write programs                    Now when I run this program this output will be look like this                 output    Rehan Shah RS --- I love to write programs                       So in this case we are going to changing same object 5-times   So the Obvious question is that   What is actually happen under the hood  when we change the same string 5-times   This is What Happen when we change the same string 5-times   let look at the figure      Explaination   When we first initialize this variable  name  to  Rehan  i-e string name    Rehan  this variable get created on stack  name  and pointing to that  Rehan  value  after this line is executed   name   name    Shah   the reference variable is no longer pointing to that object  Rehan  it now pointing to  Shah  and so on   So string is immutable meaning that once we create the object in the memory we can t change them   So when we concatinating the name variable the previous object remains there in the memory and another new string object is get created     So from the above figure we have five-objects the four-objects are thrown away they are not used at all  They stil remain in memory and they occuy the amount of memory   Garbage Collector  is responsible for that so clean that resources from the memory   So in case of string anytime when we manipulate the string over and over again we have some many objects Created ans stay there at in the memory   So this is the story of string Variable   Now Let s look at toward StringBuilder Object  For Example    using System  using System Text   namespace StringVsStrigBuilder       class Program               static void Main string   args                           StringBuilder Example              StringBuilder name   new StringBuilder                name Append  Rehan                name Append  Shah                name Append  RS                name Append  ---                name Append  I love to write programs                      Now when I run this program this output will be look like this                 output    Rehan Shah Rs --- I love to write programs                       So in this case we are going to changing same object 5-times   So the Obvious question is that   What is actually happen under the hood  when we change the same StringBuilder 5-times   This is What Happen when we change the same StringBuilder  5-times   let look at the figure    Explaination  In case of StringBuilder object  you wouldn t get the new object  The same object will be change in memory so even if you change the object et say 10 000 times we will still have only one stringBuilder object   You don t have alot of garbage objects or non referenced stringBuilder objects because why it can be change  It is mutable meaning it change over a time   Differences    String is present in System namespace where as Stringbuilder present in System Text namespace  string is immutable where as StringBuilder is mutabe

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Using strings for concatenation can lead to a runtime complexity on the order of O n 2    If you use a StringBuilder  there is a lot less copying of memory that has to be done   With the StringBuilder int capacity  you can increase performance if you can estimate how large the final String is going to be   Even if you re not precise  you ll probably only have to grow the capacity of StringBuilder a couple of times which can help performance also

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My approach has always been to use StringBuilder when concatenating 4 or more strings  OR When I don t know how may concatenations are to take place   Good performance related article on it here

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In  NET  StringBuilder is still faster than appending strings   I m pretty sure that in Java  they just create a StringBuffer under the hood when you append strings  so there s isn t really a difference   I m not sure why they haven t done this in  NET yet

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Consider  The Sad Tragedy of Micro-Optimization Theater

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StringBuilder reduces the number of allocations and assignments  at a cost of extra memory used   Used properly  it can completely remove the need for the compiler to allocate larger and larger strings over and over until the result is found   string result       for int i   0  i    N    i       result   result   i ToString         allocates a new string  then assigns it to result  which gets repeated N times     vs   String result  StringBuilder sb   new StringBuilder 10000        create a buffer of 10k for int i   0  i    N    i       sb Append i ToString                 fill the buffer  resizing if it overflows the buffer    result   sb ToString         assigns once

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I believe StringBuilder is faster if you have more than 4 strings you need to append together  Plus it can do some cool things like AppendLine

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Yes  the performance difference is significant   See the KB article  How to improve string concatenation performance in Visual C     I have always tried to code for clarity first  and then optimize for performance later   That s much easier than doing it the other way around  However  having seen the enormous performance difference in my applications between the two  I now think about it a little more carefully     Luckily  it s relatively straightforward to run performance analysis on your code to see where you re spending the time  and then to modify it to use StringBuilder where needed

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I have seen significant performance gains from using the EnsureCapacity int capacity  method call on an instance of StringBuilder before using it for any string storage  I usually call that on the line of code after instantiation  It has the same effect as if you instantiate the StringBuilder like this   var sb   new StringBuilder int capacity     This call allocates needed memory ahead of time  which causes fewer memory allocations during multiple Append   operations   You have to make an educated guess on how much memory you will need  but for most applications this should not be too difficult  I usually err on the side of a little too much memory  we are talking 1k or so

User · Answer

Using strings for concatenation can lead to a runtime complexity on the order of O n 2    If you use a StringBuilder  there is a lot less copying of memory that has to be done   With the StringBuilder int capacity  you can increase performance if you can estimate how large the final String is going to be   Even if you re not precise  you ll probably only have to grow the capacity of StringBuilder a couple of times which can help performance also

User · Answer

As a general rule of thumb  if I have to set the value of the string more than once  or if there are any appends to the string  then it needs to be a string builder  I have seen applications that I have written in the past before learning about string builders that have had a huge memory foot print that just seems to keep growing and growing  Changing these programs to use the string builder cut down the memory usage significantly  Now I swear by the string builder

User · Answer

As a general rule of thumb  if I have to set the value of the string more than once  or if there are any appends to the string  then it needs to be a string builder  I have seen applications that I have written in the past before learning about string builders that have had a huge memory foot print that just seems to keep growing and growing  Changing these programs to use the string builder cut down the memory usage significantly  Now I swear by the string builder

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StringBuilder will perform better  from a memory stand point  As for processing  the difference in time of execution may be negligible

User · Answer

As a general rule of thumb  if I have to set the value of the string more than once  or if there are any appends to the string  then it needs to be a string builder  I have seen applications that I have written in the past before learning about string builders that have had a huge memory foot print that just seems to keep growing and growing  Changing these programs to use the string builder cut down the memory usage significantly  Now I swear by the string builder

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StringBuilder is better for building up a string from many non-constant values   If you re building up a string from a lot of constant values  such as multiple lines of values in an HTML or XML document or other chunks of text  you can get away with just appending to the same string  because almost all compilers do  constant folding   a process of reducing the parse tree when you have a bunch of constant manipulation  it s also used when you write something like int minutesPerYear   24   365   60   And for simple cases with non-constant values appended to each other  the  NET compiler will reduce your code to something similar to what StringBuilder does   But when your append can t be reduced to something simpler by the compiler  you ll want a StringBuilder  As fizch points out  that s more likely to happen inside of a loop

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Further to the previous answers  the first thing I always do when thinking of issues like this is to create a small test application   Inside this app  perform some timing test for both scenarios and see for yourself which is quicker   IMHO  appending 500  string entries should definitely use StringBuilder

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StringBuilder is significantly more efficient but you will not see that performance unless you are doing a large amount of string modification  Below is a quick chunk of code to give an example of the performance  As you can see you really only start to see a major performance increase when you get into large iterations  As you can see the 200 000 iterations took 22 seconds while the 1 million iterations using the StringBuilder was almost instant  string s   string Empty  StringBuilder sb   new StringBuilder     Console WriteLine  quot Beginning String   at  quot    DateTime Now ToString      for  int i   0  i  lt   50000  i          s   s    A      Console WriteLine  quot Finished String   at  quot    DateTime Now ToString     Console WriteLine     Console WriteLine  quot Beginning String   at  quot    DateTime Now ToString      for  int i   0  i  lt   200000  i          s   s    A      Console WriteLine  quot Finished String   at  quot    DateTime Now ToString     Console WriteLine    Console WriteLine  quot Beginning Sb append at  quot    DateTime Now ToString      for  int i   0  i  lt   1000000  i          sb Append  quot A quot      Console WriteLine  quot Finished Sb append at  quot    DateTime Now ToString      Console ReadLine     Result of the above code   Beginning String   at 28 01 2013 16 55 40  Finished String   at 28 01 2013 16 55 40  Beginning String   at 28 01 2013 16 55 40  Finished String   at 28 01 2013 16 56 02  Beginning Sb append at 28 01 2013 16 56 02  Finished Sb append at 28 01 2013 16 56 02

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Using strings for concatenation can lead to a runtime complexity on the order of O n 2    If you use a StringBuilder  there is a lot less copying of memory that has to be done   With the StringBuilder int capacity  you can increase performance if you can estimate how large the final String is going to be   Even if you re not precise  you ll probably only have to grow the capacity of StringBuilder a couple of times which can help performance also

User · Answer

I believe StringBuilder is faster if you have more than 4 strings you need to append together  Plus it can do some cool things like AppendLine

User · Answer

Yes  the performance difference is significant   See the KB article  How to improve string concatenation performance in Visual C     I have always tried to code for clarity first  and then optimize for performance later   That s much easier than doing it the other way around  However  having seen the enormous performance difference in my applications between the two  I now think about it a little more carefully     Luckily  it s relatively straightforward to run performance analysis on your code to see where you re spending the time  and then to modify it to use StringBuilder where needed

User · Answer

String Vs String Builder   First thing you have to know that In which assembly these two classes lives   So   string is present in System namespace   and   StringBuilder is present in System Text namespace   For string declaration    You have to include the System namespace  something like this  Using System   and   For StringBuilder declaration    You have to include the System text namespace  something like this  Using System text   Now Come the the actual Question   What is the differene between string  amp  StringBuilder   The main difference between these two is that   string is immutable   and  StringBuilder is mutable   So Now lets discuss the difference between immutable and mutable  Mutable    means Changable   Immutable    means Not Changable   For example   using System   namespace StringVsStrigBuilder       class Program               static void Main string   args                           String Example              string name    Rehan               name   name    Shah               name   name    RS               name   name    ---               name   name    I love to write programs                    Now when I run this program this output will be look like this                 output    Rehan Shah RS --- I love to write programs                       So in this case we are going to changing same object 5-times   So the Obvious question is that   What is actually happen under the hood  when we change the same string 5-times   This is What Happen when we change the same string 5-times   let look at the figure      Explaination   When we first initialize this variable  name  to  Rehan  i-e string name    Rehan  this variable get created on stack  name  and pointing to that  Rehan  value  after this line is executed   name   name    Shah   the reference variable is no longer pointing to that object  Rehan  it now pointing to  Shah  and so on   So string is immutable meaning that once we create the object in the memory we can t change them   So when we concatinating the name variable the previous object remains there in the memory and another new string object is get created     So from the above figure we have five-objects the four-objects are thrown away they are not used at all  They stil remain in memory and they occuy the amount of memory   Garbage Collector  is responsible for that so clean that resources from the memory   So in case of string anytime when we manipulate the string over and over again we have some many objects Created ans stay there at in the memory   So this is the story of string Variable   Now Let s look at toward StringBuilder Object  For Example    using System  using System Text   namespace StringVsStrigBuilder       class Program               static void Main string   args                           StringBuilder Example              StringBuilder name   new StringBuilder                name Append  Rehan                name Append  Shah                name Append  RS                name Append  ---                name Append  I love to write programs                      Now when I run this program this output will be look like this                 output    Rehan Shah Rs --- I love to write programs                       So in this case we are going to changing same object 5-times   So the Obvious question is that   What is actually happen under the hood  when we change the same StringBuilder 5-times   This is What Happen when we change the same StringBuilder  5-times   let look at the figure    Explaination  In case of StringBuilder object  you wouldn t get the new object  The same object will be change in memory so even if you change the object et say 10 000 times we will still have only one stringBuilder object   You don t have alot of garbage objects or non referenced stringBuilder objects because why it can be change  It is mutable meaning it change over a time   Differences    String is present in System namespace where as Stringbuilder present in System Text namespace  string is immutable where as StringBuilder is mutabe

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StringBuilder reduces the number of allocations and assignments  at a cost of extra memory used   Used properly  it can completely remove the need for the compiler to allocate larger and larger strings over and over until the result is found   string result       for int i   0  i    N    i       result   result   i ToString         allocates a new string  then assigns it to result  which gets repeated N times     vs   String result  StringBuilder sb   new StringBuilder 10000        create a buffer of 10k for int i   0  i    N    i       sb Append i ToString                 fill the buffer  resizing if it overflows the buffer    result   sb ToString         assigns once

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String concatenation will cost you more  In Java  You can use either StringBuffer or StringBuilder based on your need  If you want a synchronized  and thread safe implementation  go for StringBuffer  This will be faster than the String concatenation   If you do not need synchronized or Thread safe implementation  go for StringBuilder  This will be faster than String concatenation and also faster than StringBuffer as their is no synchorization overhead

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A simple example to demonstrate the difference in speed when using String concatenation vs StringBuilder   System Diagnostics Stopwatch time   new Stopwatch    string test   string Empty  time Start    for  int i   0  i  lt  100000  i          test    i    time Stop    System Console WriteLine  Using String concatenation      time ElapsedMilliseconds     milliseconds      Result      Using String concatenation  15423 milliseconds   StringBuilder test1   new StringBuilder    time Reset    time Start    for  int i   0  i  lt  100000  i          test1 Append i     time Stop    System Console WriteLine  Using StringBuilder      time ElapsedMilliseconds     milliseconds      Result      Using StringBuilder  10 milliseconds   As a result  the first iteration took 15423 ms while the second iteration using StringBuilder took 10 ms   It looks to me that using StringBuilder is faster  a lot faster

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String and StringBuilder are actually both immutable  the StringBuilder has built in buffers which allow its size to be managed more efficiently  When the StringBuilder needs to resize is when it is re-allocated on the heap  By default it is sized to 16 characters  you can set this in the constructor   eg   StringBuilder sb   new StringBuilder 50

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Yes  StringBuilder gives better performance while performing repeated operation over a string  It is because all the changes are made to a single instance so it can save a lot of time instead of  creating a new instance like String   String Vs Stringbuilder   String   under System namespace immutable  read-only  instance performance degrades when continuous change of value occures thread safe  StringBuilder  mutable string    under System Text namespace mutable instance shows better performance since new changes are made to existing instance       Strongly recommend dotnet mob article   String Vs StringBuilder in C        Related Stack Overflow question  Mutability of string when string   doesn t change in C

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If you re doing a lot of string concatenation  use a StringBuilder  When you concatenate with a String  you create a new String each time  using up more memory   Alex

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I have seen significant performance gains from using the EnsureCapacity int capacity  method call on an instance of StringBuilder before using it for any string storage  I usually call that on the line of code after instantiation  It has the same effect as if you instantiate the StringBuilder like this   var sb   new StringBuilder int capacity     This call allocates needed memory ahead of time  which causes fewer memory allocations during multiple Append   operations   You have to make an educated guess on how much memory you will need  but for most applications this should not be too difficult  I usually err on the side of a little too much memory  we are talking 1k or so

User · Answer

StringBuilder is probably preferable   The reason is that it allocates more space than currently needed  you set the number of characters  to leave room for future appends   Then those future appends that fit in the current buffer don t require any memory allocation or garbage collection  which can be expensive   In general  I use StringBuilder for complex string concatentation or multiple formatting  then convert to a normal String when the data is complete  and I want an immutable object again

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To clarify what Gillian said about 4 string  if you have something like this   string a b c d   a   b   c   d    then it would be faster using strings and the plus operator  This is because  like Java  as Eric points out   it internally uses StringBuilder automatically  Actually  it uses a primitive that StringBuilder also uses   However  if what you are doing is closer to   string a b c d   a   a   b   a   a   c   a   a   d    Then you need to explicitly use a StringBuilder    Net doesn t automatically create a StringBuilder here  because it would be pointless   At the end of each line   a  has to be an  immutable  string  so it would have to create and dispose a StringBuilder on each line   For speed  you d need to use the same StringBuilder until you re done building   string a b c d  StringBuilder e   new StringBuilder     e Append b    e Append c    e Append d    a   e ToString

User · Answer

I have seen significant performance gains from using the EnsureCapacity int capacity  method call on an instance of StringBuilder before using it for any string storage  I usually call that on the line of code after instantiation  It has the same effect as if you instantiate the StringBuilder like this   var sb   new StringBuilder int capacity     This call allocates needed memory ahead of time  which causes fewer memory allocations during multiple Append   operations   You have to make an educated guess on how much memory you will need  but for most applications this should not be too difficult  I usually err on the side of a little too much memory  we are talking 1k or so

User · Answer

To clarify what Gillian said about 4 string  if you have something like this   string a b c d   a   b   c   d    then it would be faster using strings and the plus operator  This is because  like Java  as Eric points out   it internally uses StringBuilder automatically  Actually  it uses a primitive that StringBuilder also uses   However  if what you are doing is closer to   string a b c d   a   a   b   a   a   c   a   a   d    Then you need to explicitly use a StringBuilder    Net doesn t automatically create a StringBuilder here  because it would be pointless   At the end of each line   a  has to be an  immutable  string  so it would have to create and dispose a StringBuilder on each line   For speed  you d need to use the same StringBuilder until you re done building   string a b c d  StringBuilder e   new StringBuilder     e Append b    e Append c    e Append d    a   e ToString

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If you re doing a lot of string concatenation  use a StringBuilder  When you concatenate with a String  you create a new String each time  using up more memory   Alex

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Further to the previous answers  the first thing I always do when thinking of issues like this is to create a small test application   Inside this app  perform some timing test for both scenarios and see for yourself which is quicker   IMHO  appending 500  string entries should definitely use StringBuilder

User · Answer

This benchmark shows that regular concatenation is faster when combining 3 or fewer strings   http   www chinhdo com 20070224 stringbuilder-is-not-always-faster   StringBuilder can make a very significant improvement in memory usage  especially in your case of adding 500 strings together     Consider the following example   string buffer    The numbers are     for  int i   0  i  lt  5  i          buffer    i ToString      return buffer    What happens in memory   The following strings are created   1 -  The numbers are    2 -  0  3 -  The numbers are  0  4 -  1  5 -  The numbers are  01  6 -  2  7 -  The numbers are  012  8 -  3  9 -  The numbers are  0123  10 -  4  11 -  The numbers are  01234  12 -  5  13 -  The numbers are  012345    By adding those five numbers to the end of the string we created 13 string objects   And 12 of them were useless   Wow   StringBuilder fixes this problem   It is not a  mutable string  as we often hear  all strings in  NET are immutable    It works by keeping an internal buffer  an array of char   Calling Append   or AppendLine   adds the string to the empty space at the end of the char array  if the array is too small  it creates a new  larger array  and copies the buffer there   So in the example above  StringBuilder might only need a single array to contain all 5 additions to the string-- depending on the size of its buffer   You can tell StringBuilder how big its buffer should be in the constructor

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StringBuilder is probably preferable   The reason is that it allocates more space than currently needed  you set the number of characters  to leave room for future appends   Then those future appends that fit in the current buffer don t require any memory allocation or garbage collection  which can be expensive   In general  I use StringBuilder for complex string concatentation or multiple formatting  then convert to a normal String when the data is complete  and I want an immutable object again

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StringBuilder will perform better  from a memory stand point  As for processing  the difference in time of execution may be negligible

User · Answer

StringBuilder is better for building up a string from many non-constant values   If you re building up a string from a lot of constant values  such as multiple lines of values in an HTML or XML document or other chunks of text  you can get away with just appending to the same string  because almost all compilers do  constant folding   a process of reducing the parse tree when you have a bunch of constant manipulation  it s also used when you write something like int minutesPerYear   24   365   60   And for simple cases with non-constant values appended to each other  the  NET compiler will reduce your code to something similar to what StringBuilder does   But when your append can t be reduced to something simpler by the compiler  you ll want a StringBuilder  As fizch points out  that s more likely to happen inside of a loop

User · Answer

String concatenation will cost you more  In Java  You can use either StringBuffer or StringBuilder based on your need  If you want a synchronized  and thread safe implementation  go for StringBuffer  This will be faster than the String concatenation   If you do not need synchronized or Thread safe implementation  go for StringBuilder  This will be faster than String concatenation and also faster than StringBuffer as their is no synchorization overhead

User · Answer

StringBuilder is probably preferable   The reason is that it allocates more space than currently needed  you set the number of characters  to leave room for future appends   Then those future appends that fit in the current buffer don t require any memory allocation or garbage collection  which can be expensive   In general  I use StringBuilder for complex string concatentation or multiple formatting  then convert to a normal String when the data is complete  and I want an immutable object again

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StringBuilder reduces the number of allocations and assignments  at a cost of extra memory used   Used properly  it can completely remove the need for the compiler to allocate larger and larger strings over and over until the result is found   string result       for int i   0  i    N    i       result   result   i ToString         allocates a new string  then assigns it to result  which gets repeated N times     vs   String result  StringBuilder sb   new StringBuilder 10000        create a buffer of 10k for int i   0  i    N    i       sb Append i ToString                 fill the buffer  resizing if it overflows the buffer    result   sb ToString         assigns once

User · Answer

As a general rule of thumb  if I have to set the value of the string more than once  or if there are any appends to the string  then it needs to be a string builder  I have seen applications that I have written in the past before learning about string builders that have had a huge memory foot print that just seems to keep growing and growing  Changing these programs to use the string builder cut down the memory usage significantly  Now I swear by the string builder

User · Answer

String concatenation will cost you more  In Java  You can use either StringBuffer or StringBuilder based on your need  If you want a synchronized  and thread safe implementation  go for StringBuffer  This will be faster than the String concatenation   If you do not need synchronized or Thread safe implementation  go for StringBuilder  This will be faster than String concatenation and also faster than StringBuffer as their is no synchorization overhead

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In  NET  StringBuilder is still faster than appending strings   I m pretty sure that in Java  they just create a StringBuffer under the hood when you append strings  so there s isn t really a difference   I m not sure why they haven t done this in  NET yet

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String concatenation will cost you more  In Java  You can use either StringBuffer or StringBuilder based on your need  If you want a synchronized  and thread safe implementation  go for StringBuffer  This will be faster than the String concatenation   If you do not need synchronized or Thread safe implementation  go for StringBuilder  This will be faster than String concatenation and also faster than StringBuffer as their is no synchorization overhead

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The performance of a concatenation operation for a String or StringBuilder object depends on how often a memory allocation occurs  A String concatenation operation always allocates memory  whereas a StringBuilder concatenation operation only allocates memory if the StringBuilder object buffer is too small to accommodate the new data  Consequently  the String class is preferable for a concatenation operation if a fixed number of String objects are concatenated  In that case  the individual concatenation operations might even be combined into a single operation by the compiler  A StringBuilder object is preferable for a concatenation operation if an arbitrary number of strings are concatenated  for example  if a loop concatenates a random number of strings of user input    Source  MSDN

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String and StringBuilder are actually both immutable  the StringBuilder has built in buffers which allow its size to be managed more efficiently  When the StringBuilder needs to resize is when it is re-allocated on the heap  By default it is sized to 16 characters  you can set this in the constructor   eg   StringBuilder sb   new StringBuilder 50

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The performance of a concatenation operation for a String or StringBuilder object depends on how often a memory allocation occurs  A String concatenation operation always allocates memory  whereas a StringBuilder concatenation operation only allocates memory if the StringBuilder object buffer is too small to accommodate the new data  Consequently  the String class is preferable for a concatenation operation if a fixed number of String objects are concatenated  In that case  the individual concatenation operations might even be combined into a single operation by the compiler  A StringBuilder object is preferable for a concatenation operation if an arbitrary number of strings are concatenated  for example  if a loop concatenates a random number of strings of user input    Source  MSDN

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Using strings for concatenation can lead to a runtime complexity on the order of O n 2    If you use a StringBuilder  there is a lot less copying of memory that has to be done   With the StringBuilder int capacity  you can increase performance if you can estimate how large the final String is going to be   Even if you re not precise  you ll probably only have to grow the capacity of StringBuilder a couple of times which can help performance also

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StringBuilder is better for building up a string from many non-constant values   If you re building up a string from a lot of constant values  such as multiple lines of values in an HTML or XML document or other chunks of text  you can get away with just appending to the same string  because almost all compilers do  constant folding   a process of reducing the parse tree when you have a bunch of constant manipulation  it s also used when you write something like int minutesPerYear   24   365   60   And for simple cases with non-constant values appended to each other  the  NET compiler will reduce your code to something similar to what StringBuilder does   But when your append can t be reduced to something simpler by the compiler  you ll want a StringBuilder  As fizch points out  that s more likely to happen inside of a loop

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StringBuilder is preferable IF you are doing multiple loops  or forks in your code pass    however  for PURE performance  if you can get away with a SINGLE string declaration  then that is much more performant    For example    string myString    Some stuff    var1     more stuff                      var2     other stuff       etc    etc       is more performant than  StringBuilder sb   new StringBuilder    sb Append  Some Stuff    sb Append var1   sb Append   more stuff    sb Append var2   sb Append  other stuff       etc   etc   etc     In this case  StringBuild could be considered more maintainable  but is not more performant than the single string declaration    9 times out of 10 though    use the string builder    On a side note  string   var is also more performant that the string Format approach  generally  that uses a StringBuilder internally  when in doubt    check reflector

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StringBuilder is better for building up a string from many non-constant values   If you re building up a string from a lot of constant values  such as multiple lines of values in an HTML or XML document or other chunks of text  you can get away with just appending to the same string  because almost all compilers do  constant folding   a process of reducing the parse tree when you have a bunch of constant manipulation  it s also used when you write something like int minutesPerYear   24   365   60   And for simple cases with non-constant values appended to each other  the  NET compiler will reduce your code to something similar to what StringBuilder does   But when your append can t be reduced to something simpler by the compiler  you ll want a StringBuilder  As fizch points out  that s more likely to happen inside of a loop

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Consider  The Sad Tragedy of Micro-Optimization Theater

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In  NET  StringBuilder is still faster than appending strings   I m pretty sure that in Java  they just create a StringBuffer under the hood when you append strings  so there s isn t really a difference   I m not sure why they haven t done this in  NET yet

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I believe StringBuilder is faster if you have more than 4 strings you need to append together  Plus it can do some cool things like AppendLine

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StringBuilder is preferable IF you are doing multiple loops  or forks in your code pass    however  for PURE performance  if you can get away with a SINGLE string declaration  then that is much more performant    For example    string myString    Some stuff    var1     more stuff                      var2     other stuff       etc    etc       is more performant than  StringBuilder sb   new StringBuilder    sb Append  Some Stuff    sb Append var1   sb Append   more stuff    sb Append var2   sb Append  other stuff       etc   etc   etc     In this case  StringBuild could be considered more maintainable  but is not more performant than the single string declaration    9 times out of 10 though    use the string builder    On a side note  string   var is also more performant that the string Format approach  generally  that uses a StringBuilder internally  when in doubt    check reflector

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String and StringBuilder are actually both immutable  the StringBuilder has built in buffers which allow its size to be managed more efficiently  When the StringBuilder needs to resize is when it is re-allocated on the heap  By default it is sized to 16 characters  you can set this in the constructor   eg   StringBuilder sb   new StringBuilder 50

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Yes  the performance difference is significant   See the KB article  How to improve string concatenation performance in Visual C     I have always tried to code for clarity first  and then optimize for performance later   That s much easier than doing it the other way around  However  having seen the enormous performance difference in my applications between the two  I now think about it a little more carefully     Luckily  it s relatively straightforward to run performance analysis on your code to see where you re spending the time  and then to modify it to use StringBuilder where needed

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Further to the previous answers  the first thing I always do when thinking of issues like this is to create a small test application   Inside this app  perform some timing test for both scenarios and see for yourself which is quicker   IMHO  appending 500  string entries should definitely use StringBuilder

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StringBuilder is significantly more efficient but you will not see that performance unless you are doing a large amount of string modification  Below is a quick chunk of code to give an example of the performance  As you can see you really only start to see a major performance increase when you get into large iterations  As you can see the 200 000 iterations took 22 seconds while the 1 million iterations using the StringBuilder was almost instant  string s   string Empty  StringBuilder sb   new StringBuilder     Console WriteLine  quot Beginning String   at  quot    DateTime Now ToString      for  int i   0  i  lt   50000  i          s   s    A      Console WriteLine  quot Finished String   at  quot    DateTime Now ToString     Console WriteLine     Console WriteLine  quot Beginning String   at  quot    DateTime Now ToString      for  int i   0  i  lt   200000  i          s   s    A      Console WriteLine  quot Finished String   at  quot    DateTime Now ToString     Console WriteLine    Console WriteLine  quot Beginning Sb append at  quot    DateTime Now ToString      for  int i   0  i  lt   1000000  i          sb Append  quot A quot      Console WriteLine  quot Finished Sb append at  quot    DateTime Now ToString      Console ReadLine     Result of the above code   Beginning String   at 28 01 2013 16 55 40  Finished String   at 28 01 2013 16 55 40  Beginning String   at 28 01 2013 16 55 40  Finished String   at 28 01 2013 16 56 02  Beginning Sb append at 28 01 2013 16 56 02  Finished Sb append at 28 01 2013 16 56 02

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This benchmark shows that regular concatenation is faster when combining 3 or fewer strings   http   www chinhdo com 20070224 stringbuilder-is-not-always-faster   StringBuilder can make a very significant improvement in memory usage  especially in your case of adding 500 strings together     Consider the following example   string buffer    The numbers are     for  int i   0  i  lt  5  i          buffer    i ToString      return buffer    What happens in memory   The following strings are created   1 -  The numbers are    2 -  0  3 -  The numbers are  0  4 -  1  5 -  The numbers are  01  6 -  2  7 -  The numbers are  012  8 -  3  9 -  The numbers are  0123  10 -  4  11 -  The numbers are  01234  12 -  5  13 -  The numbers are  012345    By adding those five numbers to the end of the string we created 13 string objects   And 12 of them were useless   Wow   StringBuilder fixes this problem   It is not a  mutable string  as we often hear  all strings in  NET are immutable    It works by keeping an internal buffer  an array of char   Calling Append   or AppendLine   adds the string to the empty space at the end of the char array  if the array is too small  it creates a new  larger array  and copies the buffer there   So in the example above  StringBuilder might only need a single array to contain all 5 additions to the string-- depending on the size of its buffer   You can tell StringBuilder how big its buffer should be in the constructor

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Yes  StringBuilder gives better performance while performing repeated operation over a string  It is because all the changes are made to a single instance so it can save a lot of time instead of  creating a new instance like String   String Vs Stringbuilder   String   under System namespace immutable  read-only  instance performance degrades when continuous change of value occures thread safe  StringBuilder  mutable string    under System Text namespace mutable instance shows better performance since new changes are made to existing instance       Strongly recommend dotnet mob article   String Vs StringBuilder in C        Related Stack Overflow question  Mutability of string when string   doesn t change in C

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If you re doing a lot of string concatenation  use a StringBuilder  When you concatenate with a String  you create a new String each time  using up more memory   Alex

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My approach has always been to use StringBuilder when concatenating 4 or more strings  OR When I don t know how may concatenations are to take place   Good performance related article on it here

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To clarify what Gillian said about 4 string  if you have something like this   string a b c d   a   b   c   d    then it would be faster using strings and the plus operator  This is because  like Java  as Eric points out   it internally uses StringBuilder automatically  Actually  it uses a primitive that StringBuilder also uses   However  if what you are doing is closer to   string a b c d   a   a   b   a   a   c   a   a   d    Then you need to explicitly use a StringBuilder    Net doesn t automatically create a StringBuilder here  because it would be pointless   At the end of each line   a  has to be an  immutable  string  so it would have to create and dispose a StringBuilder on each line   For speed  you d need to use the same StringBuilder until you re done building   string a b c d  StringBuilder e   new StringBuilder     e Append b    e Append c    e Append d    a   e ToString

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This benchmark shows that regular concatenation is faster when combining 3 or fewer strings   http   www chinhdo com 20070224 stringbuilder-is-not-always-faster   StringBuilder can make a very significant improvement in memory usage  especially in your case of adding 500 strings together     Consider the following example   string buffer    The numbers are     for  int i   0  i  lt  5  i          buffer    i ToString      return buffer    What happens in memory   The following strings are created   1 -  The numbers are    2 -  0  3 -  The numbers are  0  4 -  1  5 -  The numbers are  01  6 -  2  7 -  The numbers are  012  8 -  3  9 -  The numbers are  0123  10 -  4  11 -  The numbers are  01234  12 -  5  13 -  The numbers are  012345    By adding those five numbers to the end of the string we created 13 string objects   And 12 of them were useless   Wow   StringBuilder fixes this problem   It is not a  mutable string  as we often hear  all strings in  NET are immutable    It works by keeping an internal buffer  an array of char   Calling Append   or AppendLine   adds the string to the empty space at the end of the char array  if the array is too small  it creates a new  larger array  and copies the buffer there   So in the example above  StringBuilder might only need a single array to contain all 5 additions to the string-- depending on the size of its buffer   You can tell StringBuilder how big its buffer should be in the constructor

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Yes  the performance difference is significant   See the KB article  How to improve string concatenation performance in Visual C     I have always tried to code for clarity first  and then optimize for performance later   That s much easier than doing it the other way around  However  having seen the enormous performance difference in my applications between the two  I now think about it a little more carefully     Luckily  it s relatively straightforward to run performance analysis on your code to see where you re spending the time  and then to modify it to use StringBuilder where needed

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StringBuilder will perform better  from a memory stand point  As for processing  the difference in time of execution may be negligible

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StringBuilder is preferable IF you are doing multiple loops  or forks in your code pass    however  for PURE performance  if you can get away with a SINGLE string declaration  then that is much more performant    For example    string myString    Some stuff    var1     more stuff                      var2     other stuff       etc    etc       is more performant than  StringBuilder sb   new StringBuilder    sb Append  Some Stuff    sb Append var1   sb Append   more stuff    sb Append var2   sb Append  other stuff       etc   etc   etc     In this case  StringBuild could be considered more maintainable  but is not more performant than the single string declaration    9 times out of 10 though    use the string builder    On a side note  string   var is also more performant that the string Format approach  generally  that uses a StringBuilder internally  when in doubt    check reflector

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StringBuilder will perform better  from a memory stand point  As for processing  the difference in time of execution may be negligible

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A simple example to demonstrate the difference in speed when using String concatenation vs StringBuilder   System Diagnostics Stopwatch time   new Stopwatch    string test   string Empty  time Start    for  int i   0  i  lt  100000  i          test    i    time Stop    System Console WriteLine  Using String concatenation      time ElapsedMilliseconds     milliseconds      Result      Using String concatenation  15423 milliseconds   StringBuilder test1   new StringBuilder    time Reset    time Start    for  int i   0  i  lt  100000  i          test1 Append i     time Stop    System Console WriteLine  Using StringBuilder      time ElapsedMilliseconds     milliseconds      Result      Using StringBuilder  10 milliseconds   As a result  the first iteration took 15423 ms while the second iteration using StringBuilder took 10 ms   It looks to me that using StringBuilder is faster  a lot faster

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StringBuilder reduces the number of allocations and assignments  at a cost of extra memory used   Used properly  it can completely remove the need for the compiler to allocate larger and larger strings over and over until the result is found   string result       for int i   0  i    N    i       result   result   i ToString         allocates a new string  then assigns it to result  which gets repeated N times     vs   String result  StringBuilder sb   new StringBuilder 10000        create a buffer of 10k for int i   0  i    N    i       sb Append i ToString                 fill the buffer  resizing if it overflows the buffer    result   sb ToString         assigns once

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I have seen significant performance gains from using the EnsureCapacity int capacity  method call on an instance of StringBuilder before using it for any string storage  I usually call that on the line of code after instantiation  It has the same effect as if you instantiate the StringBuilder like this   var sb   new StringBuilder int capacity     This call allocates needed memory ahead of time  which causes fewer memory allocations during multiple Append   operations   You have to make an educated guess on how much memory you will need  but for most applications this should not be too difficult  I usually err on the side of a little too much memory  we are talking 1k or so

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Further to the previous answers  the first thing I always do when thinking of issues like this is to create a small test application   Inside this app  perform some timing test for both scenarios and see for yourself which is quicker   IMHO  appending 500  string entries should definitely use StringBuilder

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In  NET  StringBuilder is still faster than appending strings   I m pretty sure that in Java  they just create a StringBuffer under the hood when you append strings  so there s isn t really a difference   I m not sure why they haven t done this in  NET yet

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