Is it bad practice to use break to exit a loop in Java

Question

I was wondering if it is a  bad practice  to use a break statement to exit a loop instead of fulfilling the loop condition   I do not have enough insight in Java and the JVM to know how a loop is handled  so I was wondering if I was overlooking something critical by doing so   The focus of this question  is there a specific performance overhead

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Good lord no  Sometimes there is a possibility that something can occur in the loop that satisfies the overall requirement  without satisfying the logical loop condition  In that case  break is used  to stop you cycling around a loop pointlessly    Example   String item   for int x   0  x  lt  10  x             Linear search      if array x  equals  Item I am looking for                   you ve found the item  Let s stop         item   array x          break             What makes more sense in this example  Continue looping to 10 every time  even after you ve found it  or loop until you find the item and stop  Or to put it into real world terms  when you find your keys  do you keep looking    Edit in response to comment   Why not set x to 11 to break the loop  It s pointless  We ve got break  Unless your code is making the assumption that x is definitely larger than 10 later on  and it probably shouldn t be  then you re fine just using break    Edit for the sake of completeness   There are definitely other ways to simulate break  For example  adding extra logic to your termination condition in your loop  Saying that it is either loop pointlessly or use break isn t fair  As pointed out  a while loop can often achieve similar functionality  For example  following the above example    while x  lt  10  amp  amp  item    null        if array x  equals  Item I am looking for                  item   array x              x        Using break simply means you can achieve this functionality with a for loop  It also means you don t have to keep adding in conditions into your termination logic  whenever you want the loop to behave differently  For example   for int x   0  x  lt  10  x         if array x  equals  Something that will make me want to cancel                break          else if array x  equals  Something else that will make me want to cancel                break          else if array x  equals  This is what I want                item   array x            Rather than a while loop with a termination condition that looks like this   while x  lt  10  amp  amp   array x  equals  Something that will make me want to cancel    amp  amp                    array x  equals  Something else that will make me want to cancel

User · Answer

break and continue breaks the readability for the reader  although it s often useful  Not as much as  goto  concept  but almost   Besides  if you take some new languages like Scala  inspired by Java and functional programming languages like Ocaml   you will notice that break and continue simply disappeared   Especially in functional programming  this style of code is avoided   Why scala doesn t support break and continue   To sum up  break and continueare widely used in Java for an imperative style  but for any coders that used to practice functional programming  it might be   weird

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Using break  just as practically any other language feature  can be a bad practice  within a specific context  where you are clearly misusing it  But some very important idioms cannot be coded without it  or at least would result in far less readable code  In those cases  break is the way to go   In other words  don t listen to any blanket  unqualified advice mdash about break or anything else  It is not once that I ve seen code totally emaciated just to literally enforce a  good practice    Regarding your concern about performance overhead  there is absolutely none  At the bytecode level there are no explicit loop constructs anyway  all flow control is implemented in terms of conditional jumps

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Using break in loops can be perfectly legitimate and it can even be the only way to solve some problems   However  it s bad reputation comes from the fact that new programmers usually abuse it  leading to confusing code  especially by using break to stop the loop in conditions that could have been written in the loop condition statement in the first place

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The JLS specifies a break is an abnormal termination of a loop  However  just because it is considered abnormal does not mean that it is not used in many different code examples  projects  products  space shuttles  etc  The JVM specification does not state either an existence or absence of a performance loss  though it is clear code execution will continue after the loop   However  code readability can suffer with odd breaks  If you re sticking a break in a complex if statement surrounded by side effects and odd cleanup code  with possibly a multilevel break with a label or worse  with a strange set of exit conditions one after the other   it s not going to be easy to read for anyone   If you want to break your loop by forcing the iteration variable to be outside the iteration range  or by otherwise introducing a not-necessarily-direct way of exiting  it s less readable than break    However  looping extra times in an empty manner is almost always bad practice as it takes extra iterations and may be unclear

User · Answer

No  it is not a bad practice to break out of a loop when if certain desired condition is reached like a match is found   Many times  you may want to stop iterations because you have already achieved what you want  and there is no point iterating further  But  be careful to make sure you are not accidentally missing something or breaking out when not required   This can also add to performance improvement if you break the loop  instead of iterating over thousands of records even if the purpose of the loop is complete i e  may be to match required record is already done    Example     for  int j   0  j  lt  type size    j              if  condition                   do stuff after which you want               break     stop further iteration

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While its not bad practice to use break and there are many excellent uses for it  it should not be all you rely upon  Almost any use of a break can be written into the loop condition  Code is far more readable when real conditions are used  but in the case of a long-running or infinite loop  breaks make perfect sense  They also make sense when searching for data  as shown above

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If you start to do something like this  then I would say it starts to get a bit strange and you re better off moving it to a seperate method that returns a result upon the matchedCondition   boolean matched   false  for int i   0  i  lt  10  i          for int j   0  j  lt  10  j              if matchedCondition                matched   true              break                      if matched            break            To elaborate on how to clean up the above code  you can refactor  moving the code to a function that returns instead of using breaks  This is in general  better dealing with complex messy breaks   public boolean  matches       for int i   0  i  lt  10  i              for int j   0  j  lt  10  j                  if matchedCondition                    return true                                    return false      However for something simple like my below example  By all means use break   for int i   0  i  lt  10  i          if wereDoneHere         we re done  break          break            And changing the conditions  in the above case i  and j s value  you would just make the code really hard to read  Also there could be a case where the upper limits  10 in the example  are variables so then it would be even harder to guess what value to set it to in order to exit the loop  You could of course just set i and j to Integer MAX VALUE  but I think you can see this starts to get messy very quickly

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If you know in advance where the loop will have to stop  it will probably improve code readability to state the condition in the for  while  or  do-while loop   Otherwise  that s the exact use case for break

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No  it is not a bad practice  It is the most easiest and efficient way

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In my opinion a For loop should be used when a fixed amount of iterations will be done and they won t be stopped before every iteration has been completed  In the other case where you want to quit earlier I prefer to use a While loop  Even if you read those two little words it seems more logical  Some examples   for  int i 0 i lt 10 i          System out println i       When I read this code quickly I will know for sure it will print out 10 lines and then go on   for  int i 0 i lt 10 i          if  someCondition  break      System out println i       This one is already less clear to me  Why would you first state you will take 10 iterations  but then inside the loop add some extra conditions to stop sooner   I prefer the previous example written in this way  even when it s a little more verbose  but that s only with 1 line more    int i 0  while  i lt 10  amp  amp   someCondition        System out println i       i        Everyone who will read this code will see immediatly that there is an extra condition that might terminate the loop earlier   Ofcourse in very small loops you can always discuss that every programmer will notice the break statement  But I can tell from my own experience that in larger loops those breaks can be overseen   And that brings us to another topic to start splitting up code in smaller chunks

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There are a number of common situations for which break is the most natural way to express the algorithm   They are called  loop-and-a-half  constructs  the paradigm example is  while  true        item   stream next        if  item    EOF          break      process item       If you can t use break for this you have to repeat yourself instead   item   stream next    while  item    EOF        process item       item   stream next        It is generally agreed that this is worse   Similarly  for continue  there is a common pattern that looks like this   for  item in list        if  ignore p item           continue      if  trivial p item             process trivial item           continue            process complicated item       This is often more readable than the alternative with chained else if  particularly when process complicated is more than just one function call   Further reading  Loop Exits and Structured Programming  Reopening the Debate

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It isn t bad practice  but it can make code less readable  One useful refactoring to work around this is to move the loop to a separate method  and then use a return statement instead of a break  for example this  example lifted from  Chris s answer    String item   for int x   0  x  lt  10  x             Linear search      if array x  equals  Item I am looking for                    you ve found the item  Let s stop          item   array x           break             can be refactored  using extract method  to this   public String searchForItem String itemIamLookingFor        for int x   0  x  lt  10  x                  if array x  equals itemIamLookingFor                         return array x                       Which when called from the surrounding code can prove to be more readable

[java] Is it bad practice to use break to exit a loop in Java?

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