Is it better practice to use String format over string Concatenation in Java

Question

Is there a perceptible difference between using String format and String concatenation in Java   I tend to use String format but occasionally will slip and use a concatenation  I was wondering if one was better than the other   The way I see it  String format gives you more power in  formatting  the string  and concatenation means you don t have to worry about accidentally putting in an extra  s or missing one out   String format is also shorter   Which one is more readable depends on how your head works

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There could be a perceptible difference    String format is quite complex and uses a regular expression underneath  so don t make it a habit to use it everywhere  but only where you need it    StringBuilder would be an order of magnitude faster  as someone here already pointed out

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String format   is more than just concatenating strings  For example  you can display numbers in a specific locale using String format     However  if you don t care about localisation  there is no functional difference  Maybe the one is faster than the other  but in most cases it will be negligible

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I think we can go with MessageFormat format as it should be good at both readability and also performance aspects   I used the same program which one used by Icaro in his above answer and I enhanced it with appending code for using MessageFormat to explain the performance numbers     public static void main String   args        long start   System currentTimeMillis        for  int i   0  i  lt  1000000  i            String s    Hi     i      Hi to you     i   2            long end   System currentTimeMillis        System out println  Concatenation         end - start       millisecond         start   System currentTimeMillis        for  int i   0  i  lt  1000000  i            String s   String format  Hi  s  Hi to you  s   i   i   2             end   System currentTimeMillis        System out println  Format         end - start       millisecond         start   System currentTimeMillis        for  int i   0  i  lt  1000000  i            String s   MessageFormat format  Hi  s  Hi to you  s   i   i   2             end   System currentTimeMillis        System out println  MessageFormat         end - start       millisecond             Concatenation   69 millisecond      Format   1435 millisecond      MessageFormat   200 millisecond   UPDATES    As per SonarLint Report  Printf-style format strings should be used correctly  squid S3457   Because printf-style format strings are interpreted at runtime  rather than validated by the compiler  they can contain errors that result in the wrong strings being created  This rule statically validates the correlation of printf-style format strings to their arguments when calling the format      methods of java util Formatter  java lang String  java io PrintStream  MessageFormat  and java io PrintWriter classes and the printf      methods of java io PrintStream or java io PrintWriter classes    I replace the printf-style with the curly-brackets and I got something interesting results as below      Concatenation   69 millisecond Format   1107 millisecond   Format curly-brackets   416 millisecond MessageFormat   215   millisecond MessageFormat curly-brackets   2517 millisecond   My Conclusion  As I highlighted above  using String format with curly-brackets should be a good choice to get benefits of good readability and also performance

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Here s a test with multiple sample sizes in milliseconds     public class Time    public static String sysFile     sys class camera rear rear flash   public static String cmdString    echo  s  gt      sysFile   public static void main String   args       int i   1    for int run 1  run  lt   12  run           for int test  1  test  lt   2   test             System out println                  String format   nTEST   s  RUN   s  Iterations   s  run test i            test run  i                 System out println   n                                      i   i 3         public static void test int run  int iterations          long start   System nanoTime          for  int i 0 i lt iterations  i               String s    echo     i      gt     sysFile                long t   System nanoTime   - start           String r   String format     -13s   10d  s    Concatenation  t  nanosecond          System out println r           start   System nanoTime                for  int i 0 i lt iterations  i              String s    String format cmdString  i               t   System nanoTime   - start        r   String format     -13s   10d  s    Format  t  nanosecond         System out println r          start   System nanoTime                    for  int i 0 i lt iterations  i               StringBuilder b   new StringBuilder  echo               b append i  append    gt     append sysFile             String s   b toString                 t   System nanoTime   - start        r   String format     -13s   10d  s    StringBuilder  t  nanosecond         System out println r          TEST  1  RUN  1  Iterations  1   Concatenation       14911 nanosecond   Format              45026 nanosecond   StringBuilder        3509 nanosecond  TEST  1  RUN  2  Iterations  1   Concatenation        3509 nanosecond   Format              38594 nanosecond   StringBuilder        3509 nanosecond                                TEST  2  RUN  1  Iterations  3   Concatenation        8479 nanosecond   Format              94438 nanosecond   StringBuilder        5263 nanosecond  TEST  2  RUN  2  Iterations  3   Concatenation        4970 nanosecond   Format              92976 nanosecond   StringBuilder        5848 nanosecond                                TEST  3  RUN  1  Iterations  9   Concatenation       11403 nanosecond   Format             287115 nanosecond   StringBuilder       14326 nanosecond  TEST  3  RUN  2  Iterations  9   Concatenation       12280 nanosecond   Format             209051 nanosecond   StringBuilder       11818 nanosecond                                TEST  5  RUN  1  Iterations  81   Concatenation       54383 nanosecond   Format            1503113 nanosecond   StringBuilder       40056 nanosecond  TEST  5  RUN  2  Iterations  81   Concatenation       44149 nanosecond   Format            1264241 nanosecond   StringBuilder       34208 nanosecond                                TEST  6  RUN  1  Iterations  243   Concatenation       76018 nanosecond   Format            3210891 nanosecond   StringBuilder       76603 nanosecond  TEST  6  RUN  2  Iterations  243   Concatenation       91222 nanosecond   Format            2716773 nanosecond   StringBuilder       73972 nanosecond                                TEST  8  RUN  1  Iterations  2187   Concatenation      527450 nanosecond   Format           10291108 nanosecond   StringBuilder      885027 nanosecond  TEST  8  RUN  2  Iterations  2187   Concatenation      526865 nanosecond   Format            6294307 nanosecond   StringBuilder      591773 nanosecond                                TEST  10  RUN  1  Iterations  19683   Concatenation     4592961 nanosecond   Format           60114307 nanosecond   StringBuilder     2129387 nanosecond  TEST  10  RUN  2  Iterations  19683   Concatenation     1850166 nanosecond   Format           35940524 nanosecond   StringBuilder     1885544 nanosecond                                  TEST  12  RUN  1  Iterations  177147   Concatenation    26847286 nanosecond   Format          126332877 nanosecond   StringBuilder    17578914 nanosecond  TEST  12  RUN  2  Iterations  177147   Concatenation    24405056 nanosecond   Format          129707207 nanosecond   StringBuilder    12253840 nanosecond

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I d suggest that it is better practice to use String format    The main reason is that String format   can be more easily localised with text loaded from resource files whereas concatenation can t be localised without producing a new executable with different code for each language   If you plan on your app being localisable you should also get into the habit of specifying argument positions for your format tokens as well    Hello  1 s the time is  2 t    This can then be localised and have the name and time tokens swapped without requiring a recompile of the executable to account for the different ordering  With argument positions you can also re-use the same argument without passing it into the function twice   String format  Hello  1 s  your name is  1 s and the time is  2 t   name  time

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You cannot compare String Concatenation and String Format by the program above   You may try this also be interchanging the position of using your String Format and Concatenation in your code block like the below  public static void main String   args  throws Exception           long start   System currentTimeMillis       for  int i 0 i lt 1000000  i         String s   String format   Hi  s  Hi to you  s  i    i 2          long end   System currentTimeMillis      System out println  Format         end - start       millisecond      start   System currentTimeMillis       for  int i 0 i lt 1000000  i         String s    Hi     i      Hi to you     i 2         end   System currentTimeMillis      System out println  Concatenation         end - start       millisecond         You will be surprised to see that Format works faster here  This is since the intial objects created might not be released and there can be an issue with memory allocation and thereby the performance

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One problem with  format is that you lose static type safety  You can have too few arguments for your format  and you can have the wrong types for the format specifiers - both leading to an IllegalFormatException at runtime  so you might end up with logging code that breaks production   In contrast  the arguments to   can be tested by the compiler   The security history of printf  on which the format function is modeled  is long and frightening

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Which one is more readable depends on how your head works     You got your answer right there    It s a matter of personal taste   String concatenation is marginally faster  I suppose  but that should be negligible

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I haven t done any specific benchmarks  but I would think that concatenation may be faster  String format   creates a new Formatter which  in turn  creates a new StringBuilder  with a size of only 16 chars   That s a fair amount of overhead especially if you are formatting a longer string and StringBuilder keeps having to resize   However  concatenation is less useful and harder to read  As always  it s worth doing a benchmark on your code to see which is better  The differences may be negligible in server app after your resource bundles  locales  etc are loaded in memory and the code is JITted   Maybe as a best practice  it would be a good idea to create your own Formatter with a properly sized StringBuilder  Appendable  and Locale and use that if you have a lot of formatting to do

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Here s the same test as above with the modification of calling the toString   method on the StringBuilder   The results below show that the StringBuilder approach is just a bit slower than String concatenation using the   operator   file  StringTest java  class StringTest      public static void main String   args         String formatString    Hi  s  Hi to you  s        long start   System currentTimeMillis        for  int i   0  i  lt  1000000  i              String s   String format formatString  i   i   2              long end   System currentTimeMillis        System out println  Format         end - start       millisecond         start   System currentTimeMillis         for  int i   0  i  lt  1000000  i              String s    Hi     i      Hi to you     i   2             end   System currentTimeMillis         System out println  Concatenation         end - start       millisecond         start   System currentTimeMillis         for  int i   0  i  lt  1000000  i              StringBuilder bldString   new StringBuilder  Hi             bldString append i  append  Hi to you    append i   2  toString               end   System currentTimeMillis         System out println  String Builder         end - start       millisecond             Shell Commands    compile and run StringTest 5 times    gt  javac StringTest java  gt  sh -c  for i in    seq 1 5   do echo   Run    i     java StringTest  done    Results    Run 1 Format   1290 millisecond Concatenation   115 millisecond String Builder   130 millisecond  Run 2 Format   1265 millisecond Concatenation   114 millisecond String Builder   126 millisecond  Run 3 Format   1303 millisecond Concatenation   114 millisecond String Builder   127 millisecond  Run 4 Format   1297 millisecond Concatenation   114 millisecond String Builder   127 millisecond  Run 5 Format   1270 millisecond Concatenation   114 millisecond String Builder   126 millisecond

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About performance   public static void main String   args  throws Exception           long start   System currentTimeMillis      for int i   0  i  lt  1000000  i         String s    Hi     i      Hi to you     i 2        long end   System currentTimeMillis      System out println  Concatenation         end - start       millisecond        start   System currentTimeMillis      for int i   0  i  lt  1000000  i         String s   String format  Hi  s  Hi to you  s  i    i 2         end   System currentTimeMillis      System out println  Format         end - start       millisecond        The timing results are as follows    Concatenation   265 millisecond Format   4141 millisecond   Therefore  concatenation is much faster than String format

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Generally  string concatenation should be prefered over String format  The latter has two main disadvantages    It does not encode the string to be built in a local manner  The building process is encoded in a string    By point 1  I mean that it is not possible to understand what a String format   call is doing in a single sequential pass  One is forced to go back and forth between the format string and the arguments  while counting the position of the arguments  For short concatenations  this is not much of an issue  In these cases however  string concatenation is less verbose   By point 2  I mean that the important part of the building process is encoded in the format string  using a DSL   Using strings to represent code has many disadvantages  It is not inherently type-safe  and complicates syntax-highlighting  code analysis  optimization  etc   Of course  when using tools or frameworks external to the Java language  new factors can come into play

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It takes a little time to get used to String Format  but it s worth it in most cases  In the world of NRA  never repeat anything  it s extremely useful to keep your tokenized messages  logging or user  in a Constant library  I prefer what amounts to a static class  and call them as necessary with String Format regardless of whether you are localizing or not  Trying to use such a library with a concatenation method is harder to read  troubleshoot  proofread  and manage with any any approach that requires concatenation  Replacement is an option  but I doubt it s performant  After years of use  my biggest problem with String Format is the length of the call is inconveniently long when I m passing it into another function  like Msg   but that s easy to get around with a custom function to serve as an alias

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Since there is discussion about performance I figured I d add in a comparison that included StringBuilder  It is in fact faster than the concat and  naturally the String format option    To make this a sort of apples to apples comparison I instantiate a new StringBuilder in the loop rather than outside  this is actually faster than doing just one instantiation most likely due to the overhead of re-allocating space for the looping append at the end of one builder        String formatString    Hi  s  Hi to you  s        long start   System currentTimeMillis        for  int i   0  i  lt  1000000  i              String s   String format formatString  i   i   2              long end   System currentTimeMillis        log info  Format         end - start       millisecond         start   System currentTimeMillis         for  int i   0  i  lt  1000000  i              String s    Hi     i      Hi to you     i   2             end   System currentTimeMillis         log info  Concatenation         end - start       millisecond         start   System currentTimeMillis         for  int i   0  i  lt  1000000  i              StringBuilder bldString   new StringBuilder  Hi             bldString append i  append    Hi to you    append i   2              end   System currentTimeMillis         log info  String Builder         end - start       millisecond       2012-01-11 16 30 46 058 INFO  TestMain  - Format   1416 millisecond 2012-01-11 16 30 46 190 INFO  TestMain  - Concatenation   134 millisecond 2012-01-11 16 30 46 313 INFO  TestMain  - String Builder   117 millisecond

[java] Is it better practice to use String.format over string Concatenation in Java?

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