Alternative to a goto statement in Java

Question

What is an alternative function for the goto keyword in Java   Since Java does not have a goto

User · Answer

While some commenters and downvoters argue that this isn't goto, the generated bytecode from the below Java statements really suggests that these statements really do express goto semantics.

Specifically, the do {...} while(true); loop in the second example is optimised by Java compilers in order not to evaluate the loop condition.

Jumping forward

label: {
  // do stuff
  if (check) break label;
  // do more stuff
}

In bytecode:

2  iload_1 [check]
3  ifeq 6          // Jumping forward
6  ..

Jumping backward

label: do {
  // do stuff
  if (check) continue label;
  // do more stuff
  break label;
} while(true);

In bytecode:

 2  iload_1 [check]
 3  ifeq 9
 6  goto 2          // Jumping backward
 9  ..

User · Answer

StephenC writes      There are two constructs that allow you to do some of the things you   can do with a classic goto    One more     Matt Wolfe writes      People always talk about never using a goto  but I think there is a   really good real world use case which is pretty well known and used     That is  making sure to execute some code before a return from a   function   Usually its releasing locks or what not  but in my case I d   love to be able to jump to a break right before the return so I can do   required mandatory cleanup    try          do stuff     return result      or break  etc    finally          clean up before actually returning  even though the order looks wrong      http   docs oracle com javase tutorial essential exceptions finally html     The finally block always executes when the try block exits  This   ensures that the finally block is executed even if an unexpected   exception occurs  But finally is useful for more than just exception   handling     it allows the programmer to avoid having cleanup code   accidentally bypassed by a return  continue  or break  Putting cleanup   code in a finally block is always a good practice  even when no   exceptions are anticipated    The silly interview question associated with finally is  If you return from a try   block  but have a return in your finally   too  which value is returned

User · Answer

Java doesn t have goto  because it makes the code unstructured and unclear to read  However  you can use break and continue as civilized form of goto without its problems     Jumping forward using break -   ahead        System out println  Before break        break ahead      System out println  After Break       This won t execute      After a line break ahead  the code flow starts from here  after the ahead block System out println  After ahead      Output   Before Break After ahead     Jumping backward using continue  before        System out println  Continue        continue before      This will result in an infinite loop as every time the line continue before is executed  the code flow will start again from before

User · Answer

The easiest is   int label   0  loop while true        switch state            case 0                 Some code             state   5              break           case 2                 Some code             state   4              break                      default              break loop

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public class TestLabel        enum Label LABEL1  LABEL2  LABEL3  LABEL4                   param args             public static void main String   args             Label label   Label LABEL1           while true                switch label                   case LABEL1                      print label                    case LABEL2                      print label                       label   Label LABEL4                      continue                   case LABEL3                      print label                       label   Label LABEL1                      break                   case LABEL4                      print label                       label   Label LABEL3                      continue                            break                       public final static void print Label label           System out println label

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You could use a labeled BREAK statement   search      for  i   0  i  lt  arrayOfInts length  i              for  j   0  j  lt  arrayOfInts i  length  j                  if  arrayOfInts i  j     searchfor                    foundIt   true                  break search                                  However  in properly designed code  you shouldn t need GOTO functionality

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Just for fun  here is a GOTO implementation in Java       Example      1 public class GotoDemo      2     public static void main String   args       3         int i   3     4         System out println i      5         i   i - 1     6         if  i  gt   0       7             GotoFactory getSharedInstance   getGoto   go 4      8              9            10         try     11             System out print  Hell      12             if  Math random    gt  0  throw new Exception                  13             System out println  World       14           catch  Exception e      15             System out print  o       16             GotoFactory getSharedInstance   getGoto   go 13     17             18         19         Running it     java -cp bin asm-3 1 jar GotoClassLoader GotoDemo               3    2    1    0    Hello World     Do I need to add  don t use it

User · Answer

Try the code below  It works for me   for  int iTaksa   1  iTaksa  lt  8  iTaksa          Count 8 Loop is  8 Taksa      strTaksaStringStar iCountTaksa    strTaksaStringCount iTaksa        LabelEndTaksa Exit             if  iCountTaksa    1      If count is 6 then next it s 2             iCountTaksa   2              break  LabelEndTaksa Exit                     if  iCountTaksa    2      If count is 2 then next it s 3             iCountTaksa   3              break  LabelEndTaksa Exit                     if  iCountTaksa    3      If count is 3 then next it s 4             iCountTaksa   4              break  LabelEndTaksa Exit                     if  iCountTaksa    4      If count is 4 then next it s 7             iCountTaksa   7              break  LabelEndTaksa Exit                     if  iCountTaksa    7      If count is 7 then next it s 5             iCountTaksa   5              break  LabelEndTaksa Exit                     if  iCountTaksa    5      If count is 5 then next it s 8             iCountTaksa   8              break  LabelEndTaksa Exit                     if  iCountTaksa    8      If count is 8 then next it s 6             iCountTaksa   6              break  LabelEndTaksa Exit                     if  iCountTaksa    6      If count is 6 then loop 1  as 1 2 3 4 7 5 8 6  -- gt  1             iCountTaksa   1              break  LabelEndTaksa Exit                      LabelEndTaksa Exit            for  int iTaksa   1  iTaksa  lt  8  iTaksa

User · Answer

If you really want something like goto statements  you could always try breaking to named blocks   You have to be within the scope of the block to break to the label   namedBlock      if  j  2           this will take you to the label above     break namedBlock          I won t lecture you on why you should avoid goto s - I m assuming you already know the answer to that

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There isn t any direct equivalent to the goto concept in Java  There are a few constructs that allow you to do some of the things you can do with a classic goto    The break and continue statements allow you to jump out of a block in a loop or switch statement  A labeled statement and break  lt label gt  allow you to jump out of an arbitrary compound statement to any level within a given method  or initializer block   If you label a loop statement  you can continue  lt label gt  to continue with the next iteration of an outer loop from an inner loop  Throwing and catching exceptions allows you to  effectively  jump out of many levels of a method call   However  exceptions are relatively expensive and are considered to be a bad way to do  ordinary  control flow1   And of course  there is return    None of these Java constructs allow you to branch backwards or to a point in the code at the same level of nesting as the current statement  They all jump out one or more nesting  scope  levels and they all  apart from continue  jump downwards  This restriction helps to avoid the goto  spaghetti code  syndrome inherent in old BASIC  FORTRAN and COBOL code2      1- The most expensive part of exceptions is the actual creation of the exception object and its stacktrace  If you really  really need to use exception handling for  normal  flow control  you can either preallocate   reuse the exception object  or create a custom exception class that overrides the fillInStackTrace   method  The downside is that the exception s printStackTrace   methods won t give you useful information     should you ever need to call them    2 - The spaghetti code syndrome spawned the structured programming approach  where you limited in your use of the available language constructs  This could be applied to BASIC  Fortran and COBOL  but it required care and discipline  Getting rid of goto entirely was a pragmatically better solution  If you keep it in a language  there is always some clown who will abuse it

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Use a labeled break as an alternative to goto

[java] Alternative to a goto statement in Java

Jumping forward

Jumping backward

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