How do I break out of nested loops in Java

Question

I ve got a nested loop construct like this   for  Type type   types        for  Type t   types2             if  some condition                    Do something and break                 break     Breaks out of the inner loop                      Now how can I break out of both loops  I ve looked at similar questions  but none concerns Java specifically  I couldn t apply these solutions because most used gotos   I don t want to put the inner loop in a different method   I don t want to rerun the loops  When breaking I m finished with the execution of the loop block

User · Answer

You can use a temporary variable   boolean outerBreak   false  for  Type type   types       if outerBreak  break      for  Type t   types2             if  some condition                    Do something and break                 outerBreak   true               break     Breaks out of the inner loop                      Depending on your function  you can also exit return from the inner loop   for  Type type   types        for  Type t   types2             if  some condition                    Do something and break                 return

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It s fairly easy to use label  You can break the outer loop from inner loop using the label  Consider the example below   public class Breaking      public static void main String   args            outerscope          for  int i 0  i  lt  5  i                  for  int j 0  j  lt  5  j                      if  condition                        break outerscope                                                      Another approach is to use the breaking variable flag to keep track of required break  consider the following example   public class Breaking       public static void main String   args            boolean isBreaking   false          for  int i 0  i  lt  5  i                  for  int j 0  j  lt  5  j                      if  condition                        isBreaking   true                      break                                              if isBreaking                   break                                    However  I prefer using the first approach

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Java does not have a goto feature like there is in C    But still  goto is a reserved keyword in Java  They might implement it in the future  For your question  the answer is that there is something called label in Java to which you can apply a continue and break statement  Find the code below   public static void main String    args        outerLoop  for int i 0 i lt 10 i          for int j 10 j gt 0 j--            System out println i     j           if i  j                System out println  Condition Fulfilled                break outerLoop                            System out println  Got out of the outer loop

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You can break from all loops without using any label  and flags   It s just tricky solution   Here condition1 is the condition which is used to break from loop K and J  And condition2 is the condition which is used to break from loop K   J and I   For example   public class BreakTesting       public static void main String   args            for  int i   0  i  lt  9  i                  for  int j   0  j  lt  9  j                      for  int k   0  k  lt  9  k                          if  condition1                            System out println  Breaking from Loop K and J                            k   9                          j   9                                            if  condition2                            System out println  Breaking from Loop K  J and I                            k   9                          j   9                          i   9                                                                          System out println  End of I   J   K

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Below is an example where  break  statement pushes the cursor out of the for loop whenever the condition is met   public class Practice3 FindDuplicateNumber        public static void main String   args            Integer   inp     2  3  4  3  3            Integer   aux arr   new Integer inp length           boolean isduplicate   false          for  int i   0  i  lt  aux arr length  i                   aux arr i    -1                     outer  for  int i   0  i  lt  inp length  i                  if  aux arr inp i      -200                    System out println  Duplicate Found at index      i     Carrying value      inp i                    isduplicate   true                  break outer                else                   aux arr inp i     -200                                   for  Integer integer   aux arr                System out println integer                      if  isduplicate    false                System out println  No Duplicates                   else               System out println  Duplicates

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You can do the following    set a local variable to false set that variable true in the first loop  when you want to break then you can check in the outer loop  that whether the condition is set then break from the outer loop as well   boolean isBreakNeeded   false  for  int i   0  i  lt  some length  i          for  int j   0  j  lt  some lengthasWell  j                want to set variable if             isBreakNeeded   true          break             if  isBreakNeeded            break    will make you break from the outer loop as well

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Rather unusual approach but in terms of code length  not performance  this is the easiest thing you could do   for int i   0  i    i  lt  j        if wanna exit            i   i   j     if more nested  also add the                        maximum value for the other loops

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Use a function   public void doSomething List lt Type gt  types  List lt Type gt  types2     for Type t1   types       for  Type t   types2          if  some condition                Do something and return             return

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Technically the correct answer is to label the outer loop  In practice if you want to exit at any point inside an inner loop then you would be better off externalizing the code into a method  a static method if needs be  and then call it   That would pay off for readability    The code would become something like that    private static String search             for  Type type   types            for  Type t   types2                if  some condition                       Do something and break                    return search                                    return null       Matching the example for the accepted answer    public class Test       public static void main String   args            loop            System out println  Done               public static void loop             for  int i   0  i  lt  5  i                  for  int j   0  j  lt  5  j                      if  i   j  gt  6                        System out println  Breaking                        return                                    System out println i         j

User · Answer

Like other answerers  I d definitely prefer to put the loops in a different method  at which point you can just return to stop iterating completely  This answer just shows how the requirements in the question can be met   You can use break with a label for the outer loop  For example   public class Test       public static void main String   args            outerloop          for  int i 0  i  lt  5  i                  for  int j 0  j  lt  5  j                      if  i   j  gt  6                        System out println  Breaking                        break outerloop                                    System out println i         j                                   System out println  Done              This prints   0 0 0 1 0 2 0 3 0 4 1 0 1 1 1 2 1 3 1 4 2 0 2 1 2 2 2 3 Breaking Done

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As most of the answers are suggesting to use the labels or return  The problem with labels is that it is not considered good practice in the industry because labels make your code difficult to read for other programmers  As for the return statement answers  The code example in the question is not inside some method  As the return statement will end the method and hence the loop will be broken with it  But that is not breaking off the loop that is ending the function  As  for the specific code example  this would be the good solution  boolean endNestedLoop false  for  Type type   types    for  Type t   types2    if  some condition    endNestedLoop true     Do something and break    break     Breaks out of the inner loop   if endNestLoop  break      This way code is easy to read

User · Answer

Using  break  keyword alone is not the appropriate way when you need to exit from more than one loops  You can exit from immediate loop No matter with how many loops your statement is surrounded with  You can use  break  with a label  Here I ve used the label  quot abc quot  You can write your code as following  within any function in Java This code shows how to exit from the most outer loop  abc       for  int i   0  i  lt  10  i               for  int j   0  j  lt  10  j                  for  int k   0  k  lt  10  k                     if  k    1                    break abc                                        Also you can use break statement to exit from any loop in a nested loop      for  int i   0  i  lt  10  i              abc for  int j   0  j  lt  10  j                  for  int k   0  k  lt  10  k                     if  k    1                    break abc                                        The following code shows an example of exiting from the innermost loop  In other works after executing the following code  you are at the outside of the loop of  k  variables and still inside the loop of  j  and  i  variables      for  int i   0  i  lt  10  i               for  int j   0  j  lt  10  j                  for  int k   0  k  lt  10  k                     if  k    1                    break

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Demo for break  continue  and label   Java keywords break and continue have a default value  It s the  nearest loop   and today  after a few years of using Java  I just got it   It s seem used rare  but useful   import org junit Test          Created by cui on 17-5-4       public class BranchLabel        Test     public void test             System out println  testBreak            testBreak             System out println  testBreakLabel            testBreakLabel             System out println  testContinue            testContinue            System out println  testContinueLabel            testContinueLabel                        testBreak      a 0 b 0      a 0 b 1      a 1 b 0      a 1 b 1      a 2 b 0      a 2 b 1      a 3 b 0      a 3 b 1      a 4 b 0      a 4 b 1             public void testBreak             for  int a   0  a  lt  5  a                  for  int b   0  b  lt  5  b                      if  b    2                        break                                    System out println  a     a     b     b                                               testContinue      a 0 b 0      a 0 b 1      a 0 b 3      a 0 b 4      a 1 b 0      a 1 b 1      a 1 b 3      a 1 b 4      a 2 b 0      a 2 b 1      a 2 b 3      a 2 b 4      a 3 b 0      a 3 b 1      a 3 b 3      a 3 b 4      a 4 b 0      a 4 b 1      a 4 b 3      a 4 b 4             public void testContinue             for  int a   0  a  lt  5  a                  for  int b   0  b  lt  5  b                      if  b    2                        continue                                    System out println  a     a     b     b                                               testBreakLabel      a 0 b 0 c 0      a 0 b 0 c 1               public void testBreakLabel             anyName          for  int a   0  a  lt  5  a                  for  int b   0  b  lt  5  b                      for  int c   0  c  lt  5  c                          if  c    2                            break anyName                                            System out println  a     a     b     b     c     c                                                                 testContinueLabel      a 0 b 0 c 0      a 0 b 0 c 1      a 1 b 0 c 0      a 1 b 0 c 1      a 2 b 0 c 0      a 2 b 0 c 1      a 3 b 0 c 0      a 3 b 0 c 1      a 4 b 0 c 0      a 4 b 0 c 1             public void testContinueLabel             anyName          for  int a   0  a  lt  5  a                  for  int b   0  b  lt  5  b                      for  int c   0  c  lt  5  c                          if  c    2                            continue anyName                                            System out println  a     a     b     b     c     c

User · Answer

Labeled break concept is used to break out nested loops in java  by using labeled break you can break nesting of loops at any position   Example 1   loop1   for int i  0  i lt 6  i         for int j 0  j lt 5  j               if i  3              break loop1                    suppose there are 3 loops and you want to terminate the loop3  Example 2   loop3   for int i  0  i lt 6  i     loop2    for int k  0  k lt 6  k     loop1      for int j 0  j lt 5  j               if i  3              break loop3

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I feel using labels makes the code seem very much like a goto statement  This is just a thought   Instead  throw an exception at the inner for loop and encapsulate the two for loops with a try catch block   Something like  try              for Object outerForLoop   objectsOuter                     for  Object innerForLoop   objectsInner                           if  isConditionTrue               throw new WrappedException  With some useful message  Probably some logging as well                  catch  WrappedException               Do something awesome or just don t do anything to swallow the exception        Just a thought  I prefer this code since it gives me better loggability  like that s a word  for me when this is being run in production or something

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for  int j   0  j  lt  5  j      inner loop should be replaced with      for  int j   0  j  lt  5  amp  amp   exitloops  j      Here  in this case complete nested loops should be exit if condition is True   But if we use  exitloops only to the upper loop    for  int i   0  i  lt  5  amp  amp   exitloops  i      upper loop   Then inner loop will continues  because there is no extra flag that notify this inner loop to exit       Example   if i   3 and j 2 then condition is false   But in next iteration of inner loop j 3  then condition  i j  become 9 which is true but inner loop will be continue till j become 5    So  it must use exitloops to the inner loops too   boolean exitloops   false  for  int i   0  i  lt  5  amp  amp   exitloops  i        here should exitloops as a Conditional Statement to get out from the loops if exitloops become true       for  int j   0  j  lt  5  amp  amp   exitloops  j        here should also use exitloops as a Conditional Statement           if  i   j  gt  6                exitloops   true              System out println  Inner loop still Continues For i   j is   gt    i j               break                    System out println i j

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I never use labels  It seems like a bad practice to get into  Here s what I would do   boolean finished   false  for  int i   0  i  lt  5  amp  amp   finished  i          for  int j   0  j  lt  5  j              if  i   j  gt  6                finished   true              break

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Java 8 Stream solution   List lt Type gt  types1       List lt Type gt  types2        types1 stream          flatMap type1 - gt  types2 stream   map type2 - gt  new Type   type1  type2           filter types - gt     some condition            findFirst          ifPresent types - gt     do something

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You just use label for breaking inner loops  public class Test   public static void main String   args        outerloop  for  int i 0  i  lt  5  i        for  int j 0  j  lt  5  j          if  i   j  gt  6          System out println  Breaking          break outerloop            System out println i         j         System out println  Done

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Even creating a flag for the outer loop and checking that after each execution of the inner loop can be the answer   Like this   for  Type type   types        boolean flag false      for  Type t   types2            if  some condition                   Do something and break                flag true              break     Breaks out of the inner loop                     if flag          break

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If it s a new implementation  you can try rewriting the logic as if-else if-else statements   while keep going         if keep going  amp  amp  condition one holds               Code           if keep going  amp  amp  condition two holds               Code           if keep going  amp  amp  condition three holds               Code           if keep going  amp  amp  something goes really bad            keep going false            if keep going  amp  amp  condition four holds               Code           if keep going  amp  amp  condition five holds               Code           Otherwise you can try setting a flag when that special condition has occured and check for that flag in each of your loop-conditions   something bad has happened   false  while something is true  amp  amp   something bad has happened          Code  things happen     while something else  amp  amp   something bad has happened              Lots of code  things happens         if something happened               - gt  Then control should be returned - gt              something bad has happened true              continue                      if something bad has happened       The things below will not be executed         continue                Other things may happen here as well  but they will not be executed         once control is returned from the inner cycle      HERE  So  while a simple break will not work  it can be made to work using continue   If you are simply porting the logic from one programming language to Java and just want to get the thing working you can try using labels

User · Answer

Best and Easy Method    outerloop  for int i 0  i lt 10  i            here we can break Outer loop by      break outerloop       innerloop      for int i 0  i lt 10  i                here we can break innerloop by          break innerloop

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You can use a named block around the loops   search        for  Type type   types            for  Type t   types2                if  some condition                       Do something and break                    break search

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For some cases  We can use while loop effectively here   Random rand   new Random       Just an example for  int k   0  k  lt  10    k        int count   0      while    rand nextInt 200     100            count               results k    count

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Another one solution  mentioned without example  it actually works in prod code    try       for  Type type   types            for  Type t   types2                if  some condition  1                       Do something and break the loop                  throw new BreakLoopException                                    catch  BreakLoopException e           Do something on look breaking      Of course BreakLoopException should be internal  private and accelerated with no-stack-trace   private static class BreakLoopException extends Exception        Override     public StackTraceElement   getStackTrace             return new StackTraceElement 0

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If you don t like breaks and gotos  you can use a  traditional  for loop instead the for-in  with an extra abort condition   int a  b  bool abort   false  for  a   0  a  lt  10  amp  amp   abort  a          for  b   0  b  lt  10  amp  amp   abort  b              if  condition                doSomeThing                abort   true

User · Answer

You can use labels   label1   for  int i   0          for  int g   0            break label1

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Like  1800 INFORMATION suggestion  use the condition that breaks the inner loop as a condition on the outer loop   boolean hasAccess   false  for  int i   0  i  lt  x  amp  amp  hasAccess    false  i         for  int j   0  j  lt  y  j             if  condition    true               hasAccess   true              break

User · Answer

If it is inside some function why don t you just return it    for  Type type   types        for  Type t   types2             if  some condition                return value

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I needed to do a similar thing  but I chose not to use the enhanced for loop to do it   int s   type size    for  int i   0  i  lt  s  i          for  int j   0  j  lt  t size    j              if  condition                   do stuff after which you want                 to completely break out of both loops             s   0     enables the  main  loop to terminate             break

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Usually in such cases  it is coming in scope of more meaningful logic  let s say some searching or manipulating over some of the iterated  for -objects in question  so I usually use the functional approach   public Object searching Object   types       Or manipulating     List lt Object gt  typesReferences   new ArrayList lt Object gt         List lt Object gt  typesReferences2   new ArrayList lt Object gt          for  Object type   typesReferences            Object o   getByCriterion typesReferences2  type           if o    null  return o            return null     private Object getByCriterion List lt Object gt  typesReferences2  Object criterion        for  Object typeReference   typesReferences2            if typeReference equals criterion                     here comes other complex or specific logic    typeReference equals new Object                 return typeReference                      return null      Major cons    roughly twice more lines more consumption of computing cycles  meaning it is slower from algorithmic point-of-view more typing work   The pros    the higher ratio to separation of concerns because of functional granularity the higher ratio of re-usability and control of searching manipulating logic without the methods are not long  thus they are more compact and easier to comprehend higher ratio of readability   So it is just handling the case via a different approach   Basically a question to the author of this question  what do you consider of this approach

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Use Labels   INNER for int j   0  j  lt  numbers length  j          System out println  Even number      i      break  from INNER label        break INNER      Refer to this article

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I prefer to add an explicit  exit  to the loop tests   It makes it clear to  any casual reader that the loop may terminate early   boolean earlyExit   false  for int i   0   i  lt  10  amp  amp   earlyExit  i           for int j   0   i  lt  10  amp  amp   earlyExit  j      earlyExit   true

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Demo  public static void main String   args        outer      while  true            while  true                break outer

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Check if the inner loop is exited with an if statement  by checking the inner loop s variable  You could also create another variable such as a boolean to check if the inner loop is exited    In this example it uses the inner loop s variable to check if it has been exited   int i  j  for i   0  i  lt  7  i      for j   0  j  lt  5  j            if  some condition                Do something and break             break     Breaks out of the inner loop               if j  lt  5         Checks if inner loop wasn t finished      break        Breaks out of the outer loop

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boolean broken   false     declared outside of the loop for efficiency for  Type type   types        for  Type t   types2            if  some condition                broken   true              break                       if  broken            break

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boolean condition   false  for  Type type   types        for  int i   0  i  lt  otherTypes size  amp  amp   condition  i               condition   true     If your condition is satisfied           Use condition as a flag for when you are done processing  Then the inner loop only continues on while the condition has not been met  Either way  the outer loop will keep on chuggin

[java] How do I break out of nested loops in Java?

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