What is the relative performance difference of if else versus switch statement in Java

Question

Worrying about my web application s performances  I am wondering which of  if else  or switch statement is better regarding performance

User · Answer

I totally agree with the opinion that premature optimization is something to avoid.

But it's true that the Java VM has special bytecodes which could be used for switch()'s.

See WM Spec (lookupswitch and tableswitch)

So there could be some performance gains, if the code is part of the performance CPU graph.

User · Answer

A good explanation at the link below  https   www geeksforgeeks org switch-vs-else  Test c  17  1 - If grouped 2 - If sequential 3 - Goto Array 4 - Switch Case - Jump Table https   onlinegdb com Su7HNEBeG

User · Answer

According to Cliff Click in his 2009 Java One talk A Crash Course in Modern Hardware      Today  performance is dominated by patterns of memory access   Cache misses dominate     memory is the new disk   Slide 65    You can get his full slides here     Cliff gives an example  finishing on Slide 30  showing that even with the CPU doing register-renaming  branch prediction  and speculative execution  it s only able to start 7 operations in 4 clock cycles before having to block due to two cache misses which take 300 clock cycles to return   So he says to speed up your program you shouldn t be looking at this sort of minor issue  but on larger ones such as whether you re making unnecessary data format conversions  such as converting  SOAP   XML   DOM   SQL        which  passes all the data through the cache

User · Answer

In my test the better performance is ENUM   MAP   SWITCH   IF ELSE IF in Windows7   import java util HashMap  import java util Map   public class StringsInSwitch   public static void main String   args        String doSomething   null          METHOD 1   SWITCH     long start   System currentTimeMillis        for  int i   0  i  lt  99999999  i              String input    Hello World     i  amp  0xF            switch  input            case  Hello World0               doSomething    Hello World0               break          case  Hello World1               doSomething    Hello World0               break          case  Hello World2               doSomething    Hello World0               break          case  Hello World3               doSomething    Hello World0               break          case  Hello World4               doSomething    Hello World0               break          case  Hello World5               doSomething    Hello World0               break          case  Hello World6               doSomething    Hello World0               break          case  Hello World7               doSomething    Hello World0               break          case  Hello World8               doSomething    Hello World0               break          case  Hello World9               doSomething    Hello World0               break          case  Hello World10               doSomething    Hello World0               break          case  Hello World11               doSomething    Hello World0               break          case  Hello World12               doSomething    Hello World0               break          case  Hello World13               doSomething    Hello World0               break          case  Hello World14               doSomething    Hello World0               break          case  Hello World15               doSomething    Hello World0               break                       System out println  Time taken for String in Switch      System currentTimeMillis   - start              METHOD 2   IF ELSE IF     start   System currentTimeMillis         for  int i   0  i  lt  99999999  i              String input    Hello World     i  amp  0xF            if input equals  Hello World0                 doSomething    Hello World0             else if input equals  Hello World1                 doSomething    Hello World0              else if input equals  Hello World2                 doSomething    Hello World0              else if input equals  Hello World3                 doSomething    Hello World0              else if input equals  Hello World4                 doSomething    Hello World0              else if input equals  Hello World5                 doSomething    Hello World0              else if input equals  Hello World6                 doSomething    Hello World0              else if input equals  Hello World7                 doSomething    Hello World0              else if input equals  Hello World8                 doSomething    Hello World0              else if input equals  Hello World9                 doSomething    Hello World0              else if input equals  Hello World10                 doSomething    Hello World0              else if input equals  Hello World11                 doSomething    Hello World0              else if input equals  Hello World12                 doSomething    Hello World0              else if input equals  Hello World13                 doSomething    Hello World0              else if input equals  Hello World14                 doSomething    Hello World0              else if input equals  Hello World15                 doSomething    Hello World0                        System out println  Time taken for String in if else if      System currentTimeMillis   - start                   METHOD 3   MAP       Create and build Map     Map lt String  ExecutableClass gt  map   new HashMap lt String  ExecutableClass gt         for  int i   0  i  lt   15  i              String input    Hello World     i  amp  0xF           map put input  new ExecutableClass                                public void execute String doSomething                                   doSomething    Hello World0                                                                           Start test map     start   System currentTimeMillis        for  int i   0  i  lt  99999999  i              String input    Hello World     i  amp  0xF           map get input  execute doSomething             System out println  Time taken for String in Map      System currentTimeMillis   - start                METHOD 4   ENUM  This doesn t use muliple string with space       start   System currentTimeMillis        for  int i   0  i  lt  99999999  i              String input    HW     i  amp  0xF           HelloWorld valueOf input  execute doSomething             System out println  Time taken for String in ENUM      System currentTimeMillis   - start                interface ExecutableClass       public void execute String doSomething           Enum version enum HelloWorld       HW0  Hello World0    HW1  Hello World1    HW2  Hello World2    HW3               Hello World3    HW4  Hello World4    HW5  Hello World5    HW6               Hello World6    HW7  Hello World7    HW8  Hello World8    HW9               Hello World9    HW10  Hello World10    HW11  Hello World11    HW12               Hello World12    HW13  Hello World13    HW14  Hello World4    HW15               Hello World15         private String name   null       private HelloWorld String name            this name   name             public String getName             return name             public void execute String doSomething           doSomething    Hello World0              public static HelloWorld fromString String input            for  HelloWorld hw   HelloWorld values                  if  input equals hw getName                       return hw                                  return null                  Enum version for betterment on coding format compare to interface ExecutableClass enum HelloWorld1       HW0  Hello World0                public void execute String doSomething               doSomething    Hello World0                         HW1  Hello World1                public void execute String doSomething               doSomething    Hello World0                        private String name   null       private HelloWorld1 String name            this name   name             public String getName             return name             public void execute String doSomething           super call  nothing here                 http   stackoverflow com questions 338206 why-cant-i-switch-on-a-string    https   docs oracle com javase specs jvms se7 html jvms-3 html jvms-3 10    http   forums xkcd com viewtopic php f 11 amp t 33524

User · Answer

Use switch   I hate to maintain if-else-blocks  Have a test   public class SpeedTestSwitch       private static void do1 int loop                int temp   0          for    loop  gt  0  --loop                        int r    int   Math random     10               switch  r                                case 0                      temp   9                      break                  case 1                      temp   8                      break                  case 2                      temp   7                      break                  case 3                      temp   6                      break                  case 4                      temp   5                      break                  case 5                      temp   4                      break                  case 6                      temp   3                      break                  case 7                      temp   2                      break                  case 8                      temp   1                      break                  case 9                      temp   0                      break                                  System out println  ignore      temp              private static void do2 int loop                int temp   0          for    loop  gt  0  --loop                        int r    int   Math random     10               if  r    0                  temp   9              else                 if  r    1                      temp   8                  else                     if  r    2                          temp   7                      else                         if  r    3                              temp   6                          else                             if  r    4                                  temp   5                              else                                 if  r    5                                      temp   4                                  else                                     if  r    6                                          temp   3                                      else                                         if  r    7                                              temp   2                                          else                                             if  r    8                                                  temp   1                                              else                                                 if  r    9                                                      temp   0                    System out println  ignore      temp              public static void main String   args                long time          int loop   1   100   1000   1000          System out println  warming up               do1 loop   100           do2 loop   100            System out println  start                run 1         System out println  switch             time   System currentTimeMillis            do1 loop           System out println   - gt  time needed       System currentTimeMillis   - time                run 2         System out println  if else             time   System currentTimeMillis            do2 loop           System out println   - gt  time needed       System currentTimeMillis   - time              My C  standard code for benchmarking

User · Answer

It s extremely unlikely that an if else or a switch is going to be the source of your performance woes  If you re having performance problems  you should do a performance profiling analysis first to determine where the slow spots are  Premature optimization is the root of all evil   Nevertheless  it s possible to talk about the relative performance of switch vs  if else with the Java compiler optimizations  First note that in Java  switch statements operate on a very limited domain -- integers  In general  you can view a switch statement as follows   switch   lt condition gt        case c 0         case c 1                case c n         default          where c 0  c 1       and c N are integral numbers that are targets of the switch statement  and  lt condition gt  must resolve to an integer expression    If this set is  dense  -- that is   max ci    1 - min ci     n    alpha   where 0  lt  k  lt   alpha   lt  1  where k is larger than some empirical value  a jump table can be generated  which is highly efficient  If this set is not very dense  but n     beta   a binary search tree can find the target in O 2   log n   which is still efficient too     For all other cases  a switch statement is exactly as efficient as the equivalent series of if else statements  The precise values of  alpha  and  beta  depend on a number of factors and are determined by the compiler s code-optimization module    Finally  of course  if the domain of  lt condition gt  is not the integers  a switch statement is completely useless

User · Answer

For most switch and most if-then-else blocks  I can t imagine that there are any appreciable or significant performance related concerns   But here s the thing   if you re using a switch block  its very use suggests that you re switching on a value taken from a set of constants known at compile time   In this case  you really shouldn t be using switch statements at all if you can use an enum with constant-specific methods   Compared to a switch statement  an enum provides better type safety and code that is easier to maintain   Enums can be designed so that if a constant is added to the set of constants  your code won t compile without providing a constant-specific method for the new value  On the other hand  forgetting to add a new case to a switch block can sometimes only be caught at run time if you re lucky enough to have set your block up to throw an exception   Performance between switch and an enum constant-specific method should not be significantly different  but the latter is more readable  safer  and easier to maintain

User · Answer

I remember reading that there are 2 kinds of Switch statements in Java bytecode   I think it was in  Java Performance Tuning  One is a very fast implementation which uses the switch statement s integer values to know the offset of the code to be executed  This would require all integers to be consecutive and in a well-defined range  I m guessing that using all the values of an Enum would fall in that category too   I agree with many other posters though    it may be premature to worry about this  unless this is very very hot code

User · Answer

That s micro optimization and premature optimization  which are evil  Rather worry about readabililty and maintainability of the code in question  If there are more than two if else blocks glued together or its size is unpredictable  then you may highly consider a switch statement   Alternatively  you can also grab Polymorphism  First create some interface   public interface Action        void execute String input       And get hold of all implementations in some Map  You can do this either statically or dynamically   Map lt String  Action gt  actions   new HashMap lt String  Action gt       Finally replace the if else or switch by something like this  leaving trivial checks like nullpointers aside    actions get name  execute input     It might be microslower than if else or switch  but the code is at least far better maintainable    As you re talking about webapplications  you can make use of HttpServletRequest getPathInfo   as action key  eventually write some more code to split the last part of pathinfo away in a loop until an action is found   You can find here similar answers     Using a custom Servlet oriented framework  too many servlets  is this an issue Java Front Controller   If you re worrying about Java EE webapplication performance in general  then you may find this article useful as well  There are other areas which gives a much more performance gain than only  micro optimizing the raw Java code

[java] What is the relative performance difference of if/else versus switch statement in Java?

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