How do I get the first n characters of a string without checking the size or going out of bounds

Question

How do I get up to the first n characters of a string in Java without doing a size check first  inline is acceptable  or risking an IndexOutOfBoundsException

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Apache Commons Lang has a StringUtils left method for this   String upToNCharacters   StringUtils left s  n

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Here s a neat solution   String upToNCharacters   s substring 0  Math min s length    n        Opinion  while this solution is  neat   I think it is actually less readable than a solution that uses if   else in the obvious way   If the reader hasn t seen this trick  he she has to think harder to understand the code   IMO  the code s meaning is more obvious in the if   else version   For a cleaner   more readable solution  see  paxdiablo s answer

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String upToNCharacters   String format       n   s   str     Awful if n is a variable  so you must construct the format string   but pretty clear if a constant   String upToNCharacters   String format    10s   str     docs

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Kotlin   If anyone needs   var mText   text substring 0  text length coerceAtMost 20

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Use the substring method  as follows   int n   8  String s    Hello  World    System out println s substring 0 n     If n is greater than the length of the string  this will throw an exception  as one commenter has pointed out   one simple solution is to wrap all this in the condition if s length   lt n  in your else clause  you can choose whether you just want to print return the whole String or handle it another way

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ApacheCommons surprised me   StringUtils abbreviate String str  int maxWidth  appends       there is no option to change postfix  WordUtils abbreviate String str  int lower  int upper  String appendToEnd  looks up to next empty space   I   m just going to leave this here   public static String abbreviate String s  int maxLength  String appendToEnd        String result   s      appendToEnd   appendToEnd    null        appendToEnd      if  maxLength  gt   appendToEnd length              if  s length   gt maxLength                result   s substring 0  Math min s length    maxLength - appendToEnd length       appendToEnd                  else           throw new StringIndexOutOfBoundsException  maxLength can not be smaller than appendToEnd parameter length               return result

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Don t reinvent the wheel      org apache commons lang StringUtils substring String s  int start  int len    Javadoc says    StringUtils substring null             null StringUtils substring                      StringUtils substring  abc   0  2       ab  StringUtils substring  abc   2  0         StringUtils substring  abc   2  4       c  StringUtils substring  abc   4  6         StringUtils substring  abc   2  2         StringUtils substring  abc   -2  -1     b  StringUtils substring  abc   -4  2      ab     Thus   StringUtils substring  abc   0  4     abc

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There s a class of question on SO that sometimes make less than perfect sense  this one is perilously close  -   Perhaps you could explain your aversion to using one of the two methods you ruled out   If it s just because you don t want to pepper your code with if statements or exception catching code  one solution is to use a helper function that will take care of it for you  something like   static String substring safe  String s  int start  int len            which will check lengths beforehand and act accordingly  either return smaller string or pad with spaces    Then you don t have to worry about it in your code at all  just call   String s2   substring safe  s  10  7     instead of   String s2   s substring  10 7     This would work in the case that you seem to be worried about  based on your comments to other answers   not breaking the flow of the code when doing lots of string building stuff

User · Answer

If you are lucky enough to develop with Kotlin  you can use take to achieve your goal   val someString    hello   someString take 10     result is  hello  someString take 4     result is  hell

[java] How do I get the first n characters of a string without checking the size or going out of bounds?

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