Is there a performance difference between a for loop and a for-each loop

Question

What  if any  is the performance difference between the following two loops   for  Object o  objectArrayList        o DoSomething        and   for  int i 0  i lt objectArrayList size    i          objectArrayList get i  DoSomething

User · Accepted Answer

From Item 46 in Effective Java by Joshua Bloch :

The for-each loop, introduced in release 1.5, gets rid of the clutter and the opportunity for error by hiding the iterator or index variable completely. The resulting idiom applies equally to collections and arrays:
// The preferred idiom for iterating over collections and arrays
for (Element e : elements) {
    doSomething(e);
}
When you see the colon (:), read it as “in.” Thus, the loop above reads as “for each element e in elements.” Note that there is no performance penalty for using the for-each loop, even for arrays. In fact, it may offer a slight performance advantage over an ordinary for loop in some circumstances, as it computes the limit of the array index only once. While you can do this by hand (Item 45), programmers don’t always do so.

User · Answer

There appears to be a difference unfortunately   If you look at the generated bytes code for both kinds of loops  they are different   Here is an example from the Log4j source code   In  log4j-api src main java org apache logging log4j MarkerManager java we have a static inner class called Log4jMarker which defines                 Called from add while synchronized              private static boolean contains final Marker parent  final Marker    localParents              noinspection ForLoopReplaceableByForEach         for  final Marker marker   localParents                if  marker    parent                    return true                                  return false          With standard loop     private static boolean contains org apache logging log4j Marker  org apache logging log4j Marker          Code         0  iconst 0        1  istore 2        2  aload 1        3  arraylength        4  istore 3        5  iload 2        6  iload 3        7  if icmpge     29       10  aload 1       11  iload 2       12  aaload       13  astore        4       15  aload         4       17  aload 0       18  if acmpne     23       21  iconst 1       22  ireturn       23  iinc          2  1       26  goto          5       29  iconst 0       30  ireturn   With for-each     private static boolean contains org apache logging log4j Marker  org apache logging log4j Marker          Code         0  aload 1        1  astore 2        2  aload 2        3  arraylength        4  istore 3        5  iconst 0        6  istore        4        8  iload         4       10  iload 3       11  if icmpge     34       14  aload 2       15  iload         4       17  aaload       18  astore        5       20  aload         5       22  aload 0       23  if acmpne     28       26  iconst 1       27  ireturn       28  iinc          4  1       31  goto          8       34  iconst 0       35  ireturn   What is up with THAT Oracle   I ve tried this with Java 7 and 8 on Windows 7

User · Answer

The following code   import java lang reflect Array  import java util ArrayList  import java util List   interface Function lt T gt        long perform T parameter  long x      class MyArray lt T gt         T   array      long x       public MyArray int size  Class lt T gt  type  long x            array    T    Array newInstance type  size           this x   x             public void forEach Function lt T gt  function            for  T element   array                x   function perform element  x                      class Compute       int factor      final long constant       public Compute int factor  long constant            this factor   factor          this constant   constant             public long compute long parameter  long x            return x   factor   parameter   constant           public class Main        public static void main String   args            List lt Long gt  numbers   new ArrayList lt Long gt  50000000           for  int i   0  i  lt  50000000  i                  numbers add i   i   5L                      long x   234553523525L           long time   System currentTimeMillis            for  int i   0  i  lt  numbers size    i                  x    x   7   numbers get i    3                    System out println System currentTimeMillis   - time           System out println x           x   0          time   System currentTimeMillis            for  long i   numbers                x    x   7   i   3                    System out println System currentTimeMillis   - time           System out println x           x   0          numbers   null          MyArray lt Long gt  myArray   new MyArray lt Long gt  50000000  Long class  234553523525L           for  int i   0  i  lt  50000000  i                  myArray array i    i   i   3L                    time   System currentTimeMillis            myArray forEach new Function lt Long gt                   public long perform Long parameter  long x                    return x   8   parameter   5L                                    System out println System currentTimeMillis   - time           System out println myArray x           myArray   null          myArray   new MyArray lt Long gt  50000000  Long class  234553523525L           for  int i   0  i  lt  50000000  i                  myArray array i    i   i   3L                    time   System currentTimeMillis            myArray forEach new Function lt Long gt                   public long perform Long parameter  long x                    return new Compute 8  5  compute parameter  x                                     System out println System currentTimeMillis   - time           System out println myArray x             Gives following output on my system   224 -699150247503735895 221 -699150247503735895 220 -699150247503735895 219 -699150247503735895   I m running Ubuntu 12 10 alpha with OracleJDK 1 7 update 6   In general HotSpot optimizes a lot of indirections and simple reduntant operations  so in general you shouldn t worry about them unless there are a lot of them in seqence or they are heavily nested   On the other hand  indexed get on LinkedList is much slower than calling next on iterator for LinkedList so you can avoid that performance hit while retaining readability when you use iterators  explicitly or implicitly in for-each loop

User · Answer

The only way to know for sure is to benchmark it  and even that is not as simple as it may sound  The JIT compiler can do very unexpected things to your code

User · Answer

1  for Object o  objectArrayList       o DoSomthing      and  2  for int i 0  i lt objectArrayList size    i         objectArrayList get i  DoSomthing        Both does the same but for easy and safe programming use for-each  there are possibilities for error prone in 2nd way of using

User · Answer

Even with something like an ArrayList or Vector  where  get  is a simple array lookup  the second loop still has additional overhead that the first one doesn t   I would expect it to be a tiny bit slower than the first

User · Answer

The for-each loop should generally be preferred  The  get  approach may be slower if the List implementation you are using does not support random access  For example  if a LinkedList is used  you would incur a traversal cost  whereas the for-each approach uses an iterator that keeps track of its position in the list  More information on the nuances of the for-each loop   I think the article is now here   new location  The link shown here was dead

User · Answer

All these loops do the exact same  I just want to show these before throwing in my two cents   First  the classic way of looping through List   for  int i 0  i  lt  strings size    i         do something using strings get i         Second  the preferred way since it s less error prone  how many times have YOU done the  oops  mixed the variables i and j in these loops within loops  thing     for  String s   strings       do something using s        Third  the micro-optimized for loop   int size   strings size    for  int i   -1    i  lt  size        do something using strings get i         Now the actual two cents  At least when I was testing these  the third one was the fastest when counting milliseconds on how long it took for each type of loop with a simple operation in it repeated a few million times - this was using Java 5 with jre1 6u10 on Windows in case anyone is interested   While it at least seems to be so that the third one is the fastest  you really should ask yourself if you want to take the risk of implementing this peephole optimization everywhere in your looping code since from what I ve seen  actual looping isn t usually the most time consuming part of any real program  or maybe I m just working on the wrong field  who knows   And also like I mentioned in the pretext for the Java for-each loop  some refer to it as Iterator loop and others as for-in loop  you are less likely to hit that one particular stupid bug when using it  And before debating how this even can even be faster than the other ones  remember that javac doesn t optimize bytecode at all  well  nearly at all anyway   it just compiles it   If you re into micro-optimization though and or your software uses lots of recursive loops and such then you may be interested in the third loop type  Just remember to benchmark your software well both before and after changing the for loops you have to this odd  micro-optimized one

User · Answer

It s always better to use the iterator instead of indexing  This is because iterator is most likely optimzied for the List implementation while indexed  calling get  might not be  For example LinkedList is a List but indexing through its elements will be slower than iterating using the iterator

User · Answer

All these loops do the exact same  I just want to show these before throwing in my two cents   First  the classic way of looping through List   for  int i 0  i  lt  strings size    i         do something using strings get i         Second  the preferred way since it s less error prone  how many times have YOU done the  oops  mixed the variables i and j in these loops within loops  thing     for  String s   strings       do something using s        Third  the micro-optimized for loop   int size   strings size    for  int i   -1    i  lt  size        do something using strings get i         Now the actual two cents  At least when I was testing these  the third one was the fastest when counting milliseconds on how long it took for each type of loop with a simple operation in it repeated a few million times - this was using Java 5 with jre1 6u10 on Windows in case anyone is interested   While it at least seems to be so that the third one is the fastest  you really should ask yourself if you want to take the risk of implementing this peephole optimization everywhere in your looping code since from what I ve seen  actual looping isn t usually the most time consuming part of any real program  or maybe I m just working on the wrong field  who knows   And also like I mentioned in the pretext for the Java for-each loop  some refer to it as Iterator loop and others as for-in loop  you are less likely to hit that one particular stupid bug when using it  And before debating how this even can even be faster than the other ones  remember that javac doesn t optimize bytecode at all  well  nearly at all anyway   it just compiles it   If you re into micro-optimization though and or your software uses lots of recursive loops and such then you may be interested in the third loop type  Just remember to benchmark your software well both before and after changing the for loops you have to this odd  micro-optimized one

User · Answer

Accepted answer answers the question  apart from the exceptional case of ArrayList     Since most developers rely on ArrayList atleast I believe so   So I am obligated to add the correct answer here   Straight from the developer documentation -  The enhanced for loop  also sometimes known as  for-each  loop  can be used for collections that implement the Iterable interface and for arrays  With collections  an iterator is allocated to make interface calls to hasNext   and next    With an ArrayList  a hand-written counted loop is about 3x faster  with or without JIT   but for other collections the enhanced for loop syntax will be exactly equivalent to explicit iterator usage   There are several alternatives for iterating through an array   static class Foo       int mSplat     Foo   mArray        public void zero         int sum   0      for  int i   0  i  lt  mArray length    i            sum    mArray i  mSplat           public void one         int sum   0      Foo   localArray   mArray      int len   localArray length       for  int i   0  i  lt  len    i            sum    localArray i  mSplat           public void two         int sum   0      for  Foo a   mArray            sum    a mSplat            zero   is slowest  because the JIT can t yet optimize away the cost of getting the array length once for every iteration through the loop   one   is faster  It pulls everything out into local variables  avoiding the lookups  Only the array length offers a performance benefit   two   is fastest for devices without a JIT  and indistinguishable from one   for devices with a JIT  It uses the enhanced for loop syntax introduced in version 1 5 of the Java programming language   So  you should use the enhanced for loop by default  but consider a hand-written counted loop for performance-critical ArrayList iteration

User · Answer

The only way to know for sure is to benchmark it  and even that is not as simple as it may sound  The JIT compiler can do very unexpected things to your code

User · Answer

public class FirstJavaProgram        public static void main String   args                 int a    1 2 3 45 6 6       Method 1  this is simple way to print array           for int i 0 i lt a length i                            System out print a i                      Method 2  Enhanced For loop          for int i a                        System out print i

User · Answer

The only way to know for sure is to benchmark it  and even that is not as simple as it may sound  The JIT compiler can do very unexpected things to your code

User · Answer

The for-each loop should generally be preferred  The  get  approach may be slower if the List implementation you are using does not support random access  For example  if a LinkedList is used  you would incur a traversal cost  whereas the for-each approach uses an iterator that keeps track of its position in the list  More information on the nuances of the for-each loop   I think the article is now here   new location  The link shown here was dead

User · Answer

It s weird that no one has mentioned the obvious - foreach allocates memory  in the form of an iterator   whereas a normal for loop does not allocate any memory  For games on Android  this is a problem  because it means that the garbage collector will run periodically  In a game you don t want the garbage collector to run    EVER  So don t use foreach loops in your draw  or render  method

User · Answer

foreach makes the intention of your code clearer and that is normally preferred over a very minor speed improvement - if any   Whenever I see an indexed loop I have to parse it a little longer to make sure it does what I think it does E g  Does it start from zero  does it include or exclude the end point etc    Most of my time seems to be spent reading code   that I wrote or someone else wrote  and clarity is almost always more important than performance  Its easy to dismiss performance these days because Hotspot does such an amazing job

User · Answer

foreach makes the intention of your code clearer and that is normally preferred over a very minor speed improvement - if any   Whenever I see an indexed loop I have to parse it a little longer to make sure it does what I think it does E g  Does it start from zero  does it include or exclude the end point etc    Most of my time seems to be spent reading code   that I wrote or someone else wrote  and clarity is almost always more important than performance  Its easy to dismiss performance these days because Hotspot does such an amazing job

User · Answer

Even with something like an ArrayList or Vector  where  get  is a simple array lookup  the second loop still has additional overhead that the first one doesn t   I would expect it to be a tiny bit slower than the first

User · Answer

It s weird that no one has mentioned the obvious - foreach allocates memory  in the form of an iterator   whereas a normal for loop does not allocate any memory  For games on Android  this is a problem  because it means that the garbage collector will run periodically  In a game you don t want the garbage collector to run    EVER  So don t use foreach loops in your draw  or render  method

User · Answer

Well  performance impact is mostly insignificant  but isn t zero  If you look at JavaDoc of RandomAccess interface      As a rule of thumb  a List   implementation should implement this   interface if  for typical instances of   the class  this loop    for  int i 0  n list size    i  lt  n  i        list get i         runs faster than this loop    for  Iterator i list iterator    i hasNext           i next       And for-each loop is using version with iterator  so for ArrayList for example  for-each loop isn t fastest

User · Answer

It s always better to use the iterator instead of indexing  This is because iterator is most likely optimzied for the List implementation while indexed  calling get  might not be  For example LinkedList is a List but indexing through its elements will be slower than iterating using the iterator

User · Answer

foreach makes the intention of your code clearer and that is normally preferred over a very minor speed improvement - if any   Whenever I see an indexed loop I have to parse it a little longer to make sure it does what I think it does E g  Does it start from zero  does it include or exclude the end point etc    Most of my time seems to be spent reading code   that I wrote or someone else wrote  and clarity is almost always more important than performance  Its easy to dismiss performance these days because Hotspot does such an amazing job

User · Answer

public class FirstJavaProgram        public static void main String   args                 int a    1 2 3 45 6 6       Method 1  this is simple way to print array           for int i 0 i lt a length i                            System out print a i                      Method 2  Enhanced For loop          for int i a                        System out print i

User · Answer

Here is a brief analysis of the difference put out by the Android development team   https   www youtube com watch v MZOf3pOAM6A  The result is that there is a difference  and in very restrained environments with very large lists it could be a noticeable difference  In their testing  the for each loop took twice as long  However  their testing was over an arraylist of 400 000 integers  The actual difference per element in the array was 6 microseconds  I haven t tested and they didn t say  but I would expect the difference to be slightly larger using objects rather than primitives  but even still unless you are building library code where you have no idea the scale of what you will be asked to iterate over  I think the difference is not worth stressing about

User · Answer

By the variable name objectArrayList  I assume that is an instance of java util ArrayList  In that case  the performance difference would be unnoticeable   On the other hand  if it s an instance of java util LinkedList  the second approach will be much slower as the List get int  is an O n  operation   So the first approach is always preferred unless the index is needed by the logic in the loop

User · Answer

It s always better to use the iterator instead of indexing  This is because iterator is most likely optimzied for the List implementation while indexed  calling get  might not be  For example LinkedList is a List but indexing through its elements will be slower than iterating using the iterator

User · Answer

foreach makes the intention of your code clearer and that is normally preferred over a very minor speed improvement - if any   Whenever I see an indexed loop I have to parse it a little longer to make sure it does what I think it does E g  Does it start from zero  does it include or exclude the end point etc    Most of my time seems to be spent reading code   that I wrote or someone else wrote  and clarity is almost always more important than performance  Its easy to dismiss performance these days because Hotspot does such an amazing job

User · Answer

Accepted answer answers the question  apart from the exceptional case of ArrayList     Since most developers rely on ArrayList atleast I believe so   So I am obligated to add the correct answer here   Straight from the developer documentation -  The enhanced for loop  also sometimes known as  for-each  loop  can be used for collections that implement the Iterable interface and for arrays  With collections  an iterator is allocated to make interface calls to hasNext   and next    With an ArrayList  a hand-written counted loop is about 3x faster  with or without JIT   but for other collections the enhanced for loop syntax will be exactly equivalent to explicit iterator usage   There are several alternatives for iterating through an array   static class Foo       int mSplat     Foo   mArray        public void zero         int sum   0      for  int i   0  i  lt  mArray length    i            sum    mArray i  mSplat           public void one         int sum   0      Foo   localArray   mArray      int len   localArray length       for  int i   0  i  lt  len    i            sum    localArray i  mSplat           public void two         int sum   0      for  Foo a   mArray            sum    a mSplat            zero   is slowest  because the JIT can t yet optimize away the cost of getting the array length once for every iteration through the loop   one   is faster  It pulls everything out into local variables  avoiding the lookups  Only the array length offers a performance benefit   two   is fastest for devices without a JIT  and indistinguishable from one   for devices with a JIT  It uses the enhanced for loop syntax introduced in version 1 5 of the Java programming language   So  you should use the enhanced for loop by default  but consider a hand-written counted loop for performance-critical ArrayList iteration

User · Answer

The only way to know for sure is to benchmark it  and even that is not as simple as it may sound  The JIT compiler can do very unexpected things to your code

User · Answer

Even with something like an ArrayList or Vector  where  get  is a simple array lookup  the second loop still has additional overhead that the first one doesn t   I would expect it to be a tiny bit slower than the first

User · Answer

All these loops do the exact same  I just want to show these before throwing in my two cents   First  the classic way of looping through List   for  int i 0  i  lt  strings size    i         do something using strings get i         Second  the preferred way since it s less error prone  how many times have YOU done the  oops  mixed the variables i and j in these loops within loops  thing     for  String s   strings       do something using s        Third  the micro-optimized for loop   int size   strings size    for  int i   -1    i  lt  size        do something using strings get i         Now the actual two cents  At least when I was testing these  the third one was the fastest when counting milliseconds on how long it took for each type of loop with a simple operation in it repeated a few million times - this was using Java 5 with jre1 6u10 on Windows in case anyone is interested   While it at least seems to be so that the third one is the fastest  you really should ask yourself if you want to take the risk of implementing this peephole optimization everywhere in your looping code since from what I ve seen  actual looping isn t usually the most time consuming part of any real program  or maybe I m just working on the wrong field  who knows   And also like I mentioned in the pretext for the Java for-each loop  some refer to it as Iterator loop and others as for-in loop  you are less likely to hit that one particular stupid bug when using it  And before debating how this even can even be faster than the other ones  remember that javac doesn t optimize bytecode at all  well  nearly at all anyway   it just compiles it   If you re into micro-optimization though and or your software uses lots of recursive loops and such then you may be interested in the third loop type  Just remember to benchmark your software well both before and after changing the for loops you have to this odd  micro-optimized one

User · Answer

By the variable name objectArrayList  I assume that is an instance of java util ArrayList  In that case  the performance difference would be unnoticeable   On the other hand  if it s an instance of java util LinkedList  the second approach will be much slower as the List get int  is an O n  operation   So the first approach is always preferred unless the index is needed by the logic in the loop

User · Answer

It s always better to use the iterator instead of indexing  This is because iterator is most likely optimzied for the List implementation while indexed  calling get  might not be  For example LinkedList is a List but indexing through its elements will be slower than iterating using the iterator

User · Answer

Here is a brief analysis of the difference put out by the Android development team   https   www youtube com watch v MZOf3pOAM6A  The result is that there is a difference  and in very restrained environments with very large lists it could be a noticeable difference  In their testing  the for each loop took twice as long  However  their testing was over an arraylist of 400 000 integers  The actual difference per element in the array was 6 microseconds  I haven t tested and they didn t say  but I would expect the difference to be slightly larger using objects rather than primitives  but even still unless you are building library code where you have no idea the scale of what you will be asked to iterate over  I think the difference is not worth stressing about

User · Answer

The following code   import java lang reflect Array  import java util ArrayList  import java util List   interface Function lt T gt        long perform T parameter  long x      class MyArray lt T gt         T   array      long x       public MyArray int size  Class lt T gt  type  long x            array    T    Array newInstance type  size           this x   x             public void forEach Function lt T gt  function            for  T element   array                x   function perform element  x                      class Compute       int factor      final long constant       public Compute int factor  long constant            this factor   factor          this constant   constant             public long compute long parameter  long x            return x   factor   parameter   constant           public class Main        public static void main String   args            List lt Long gt  numbers   new ArrayList lt Long gt  50000000           for  int i   0  i  lt  50000000  i                  numbers add i   i   5L                      long x   234553523525L           long time   System currentTimeMillis            for  int i   0  i  lt  numbers size    i                  x    x   7   numbers get i    3                    System out println System currentTimeMillis   - time           System out println x           x   0          time   System currentTimeMillis            for  long i   numbers                x    x   7   i   3                    System out println System currentTimeMillis   - time           System out println x           x   0          numbers   null          MyArray lt Long gt  myArray   new MyArray lt Long gt  50000000  Long class  234553523525L           for  int i   0  i  lt  50000000  i                  myArray array i    i   i   3L                    time   System currentTimeMillis            myArray forEach new Function lt Long gt                   public long perform Long parameter  long x                    return x   8   parameter   5L                                    System out println System currentTimeMillis   - time           System out println myArray x           myArray   null          myArray   new MyArray lt Long gt  50000000  Long class  234553523525L           for  int i   0  i  lt  50000000  i                  myArray array i    i   i   3L                    time   System currentTimeMillis            myArray forEach new Function lt Long gt                   public long perform Long parameter  long x                    return new Compute 8  5  compute parameter  x                                     System out println System currentTimeMillis   - time           System out println myArray x             Gives following output on my system   224 -699150247503735895 221 -699150247503735895 220 -699150247503735895 219 -699150247503735895   I m running Ubuntu 12 10 alpha with OracleJDK 1 7 update 6   In general HotSpot optimizes a lot of indirections and simple reduntant operations  so in general you shouldn t worry about them unless there are a lot of them in seqence or they are heavily nested   On the other hand  indexed get on LinkedList is much slower than calling next on iterator for LinkedList so you can avoid that performance hit while retaining readability when you use iterators  explicitly or implicitly in for-each loop

User · Answer

The for-each loop should generally be preferred  The  get  approach may be slower if the List implementation you are using does not support random access  For example  if a LinkedList is used  you would incur a traversal cost  whereas the for-each approach uses an iterator that keeps track of its position in the list  More information on the nuances of the for-each loop   I think the article is now here   new location  The link shown here was dead

User · Answer

Well  performance impact is mostly insignificant  but isn t zero  If you look at JavaDoc of RandomAccess interface      As a rule of thumb  a List   implementation should implement this   interface if  for typical instances of   the class  this loop    for  int i 0  n list size    i  lt  n  i        list get i         runs faster than this loop    for  Iterator i list iterator    i hasNext           i next       And for-each loop is using version with iterator  so for ArrayList for example  for-each loop isn t fastest

User · Answer

Even with something like an ArrayList or Vector  where  get  is a simple array lookup  the second loop still has additional overhead that the first one doesn t   I would expect it to be a tiny bit slower than the first

User · Answer

There appears to be a difference unfortunately   If you look at the generated bytes code for both kinds of loops  they are different   Here is an example from the Log4j source code   In  log4j-api src main java org apache logging log4j MarkerManager java we have a static inner class called Log4jMarker which defines                 Called from add while synchronized              private static boolean contains final Marker parent  final Marker    localParents              noinspection ForLoopReplaceableByForEach         for  final Marker marker   localParents                if  marker    parent                    return true                                  return false          With standard loop     private static boolean contains org apache logging log4j Marker  org apache logging log4j Marker          Code         0  iconst 0        1  istore 2        2  aload 1        3  arraylength        4  istore 3        5  iload 2        6  iload 3        7  if icmpge     29       10  aload 1       11  iload 2       12  aaload       13  astore        4       15  aload         4       17  aload 0       18  if acmpne     23       21  iconst 1       22  ireturn       23  iinc          2  1       26  goto          5       29  iconst 0       30  ireturn   With for-each     private static boolean contains org apache logging log4j Marker  org apache logging log4j Marker          Code         0  aload 1        1  astore 2        2  aload 2        3  arraylength        4  istore 3        5  iconst 0        6  istore        4        8  iload         4       10  iload 3       11  if icmpge     34       14  aload 2       15  iload         4       17  aaload       18  astore        5       20  aload         5       22  aload 0       23  if acmpne     28       26  iconst 1       27  ireturn       28  iinc          4  1       31  goto          8       34  iconst 0       35  ireturn   What is up with THAT Oracle   I ve tried this with Java 7 and 8 on Windows 7

User · Answer

All these loops do the exact same  I just want to show these before throwing in my two cents   First  the classic way of looping through List   for  int i 0  i  lt  strings size    i         do something using strings get i         Second  the preferred way since it s less error prone  how many times have YOU done the  oops  mixed the variables i and j in these loops within loops  thing     for  String s   strings       do something using s        Third  the micro-optimized for loop   int size   strings size    for  int i   -1    i  lt  size        do something using strings get i         Now the actual two cents  At least when I was testing these  the third one was the fastest when counting milliseconds on how long it took for each type of loop with a simple operation in it repeated a few million times - this was using Java 5 with jre1 6u10 on Windows in case anyone is interested   While it at least seems to be so that the third one is the fastest  you really should ask yourself if you want to take the risk of implementing this peephole optimization everywhere in your looping code since from what I ve seen  actual looping isn t usually the most time consuming part of any real program  or maybe I m just working on the wrong field  who knows   And also like I mentioned in the pretext for the Java for-each loop  some refer to it as Iterator loop and others as for-in loop  you are less likely to hit that one particular stupid bug when using it  And before debating how this even can even be faster than the other ones  remember that javac doesn t optimize bytecode at all  well  nearly at all anyway   it just compiles it   If you re into micro-optimization though and or your software uses lots of recursive loops and such then you may be interested in the third loop type  Just remember to benchmark your software well both before and after changing the for loops you have to this odd  micro-optimized one

User · Answer

The for-each loop should generally be preferred  The  get  approach may be slower if the List implementation you are using does not support random access  For example  if a LinkedList is used  you would incur a traversal cost  whereas the for-each approach uses an iterator that keeps track of its position in the list  More information on the nuances of the for-each loop   I think the article is now here   new location  The link shown here was dead

User · Answer

1  for Object o  objectArrayList       o DoSomthing      and  2  for int i 0  i lt objectArrayList size    i         objectArrayList get i  DoSomthing        Both does the same but for easy and safe programming use for-each  there are possibilities for error prone in 2nd way of using

[java] Is there a performance difference between a for loop and a for-each loop?

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