while-else-loop

Question

Of course this is an impossible statement in java  to-date   however ideally I would like to implement it as it is at the heart of many iterations  For example the first multiple times it is called I m doing it 650 000  times when it is creating the ArrayList  Unfortunately the reality is that my actual code does not have the set inside the else loop  thus it will pass over both the add and then the set commands and wasting time   After that I have it also in another loop where it is only performing the set as the data is already created and this is multi-nested with in many others so it is a lengthy process   ArrayList lt Integer gt   dataColLinker   new java util ArrayList lt Integer gt             public void setLinkerAt  int value  int rowIndex                while rowIndex  gt   dataColLinker size              dataColLinker add value         else           dataColLinker set rowIndex  value           Any ideas or theories  I m unsure about speeds in java when it comes to if statements and ArrayList commands and so on

User · Answer

I don t see why there is a encapsulation of a while     Use    Use the appropriate start and end    for int rowIndex   0  e   65536  i  lt  e    i               if rowIndex  gt   dataColLinker size               dataColLinker add value          else           dataColLinker set rowIndex  value

User · Answer

Java does not have this control structure  It should be noted though  that other languages do  Python for example  has the while-else construct     In Java s case  you can mimic this behaviour as you have already shown     if  rowIndex  gt   dataColLinker size          do           dataColLinker add value         while rowIndex  gt   dataColLinker size       else       dataColLinker set rowIndex  value

User · Answer

Am I missing something   Doesn t this hypothetical code  while rowIndex  gt   dataColLinker size          dataColLinker add value     else       dataColLinker set rowIndex  value       mean the same thing as this   while rowIndex  gt   dataColLinker size          dataColLinker add value     dataColLinker set rowIndex  value     or this   if  rowIndex  gt   dataColLinker size          do           dataColLinker add value         while rowIndex  gt   dataColLinker size       else       dataColLinker set rowIndex  value        The latter makes more sense     I guess    Either way  it is obvious that you can rewrite the loop so that the  else test  is not repeated inside the loop     as I have just done     FWIW  this is most likely a case of premature optimization   That is  you are probably wasting your time optimizing code that doesn t need to be optimized    For all you know  the JIT compiler s optimizer may have already moved the code around so that the  else  part is no longer in the loop  Even if it hasn t  the chances are that the particular thing you are trying to optimize is not a significant bottleneck     even if it might be executed 600 000 times    My advice is to forget this problem for now   Get the program working   When it is working  decide if it runs fast enough   If it doesn t then profile it  and use the profiler output to decide where it is worth spending your time optimizing

User · Answer

This while else statement should only execute the else code when the condition is false  this means it will always execute it  But  there is a catch  when you use the break keyword within the while loop  the else statement should not execute   The code that satisfies does condition is only   boolean entered   false  while  condition       entered   true     Set it to true stright away       While loop code         If you want to break out of this loop    if  condition          entered   false        break         if   entered          else code

User · Answer

Wrap the  set  statement to mean  set if not set  and put it naked above the while loop   You are correct  the language does not provide what you re looking for in exactly that syntax  but that s because there are programming paradigms like the one I just suggested so you don t need the syntax you are proposing

User · Answer

boolean entered   false  last  while    entered    last     condition                   Do while   if    entered                Else     You r welcome

User · Answer

Assuming you are coming from Python and accept this as the same thing   def setLinkerAt value  rowIndex       isEnough   lambda i  return i  lt  dataColLinker count       while  not isEnough rowIndex            dataColLinker append value      else          dataColLinker rowIndex    value    The most similar I could come up with was   public void setLinkerAt  int value  int rowIndex        isEnough    i  - gt    return i  lt  dataColLine size        if isEnough             dataColLinker set rowIndex  value             else while  isEnough rowInex             dataColLinker add value           Note the need for the logic  and the reverse logic  I m not sure this is a great solution  duplication of the logic   but the braceless else is the closest syntax I could think of  while maintaining the same act of not executing the logic more than required

[java] while-else-loop

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