How do I check that a Java String is not all whitespaces

Question

I want to check that Java String or character array is not just made up of whitespaces  using Java   This is a very similar question except it s Javascript   How can I check if string contains characters  amp  whitespace  not just whitespace   EDIT  I removed the bit about alphanumeric characters  so it makes more sense

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public static boolean isStringBlank final CharSequence cs            int strLen          if  cs    null     strLen   cs length       0                return true                    for  int i   0  i  lt  strLen  i                  if   Character isWhitespace cs charAt i                      return false                                  return true

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Just an performance comparement on openjdk 13  Windows 10  For each of theese texts    abcd            r n t    ab      n n r t    n r t t t    r n r n r t  t t t r n n   lorem ipsum dolor sit amet  consectetur adipisici elit   1234657891234567891324569871234567891326987132654798    executed one of following tests      trim   empty input trim   isEmpty       simple match input matches    S       match with precompiled pattern final Pattern PATTERN   Pattern compile    S    PATTERN matcher input  matches       java 11 s isBlank input isBlank     each 10 000 000 times   The results   METHOD    min   max   note trim       18   313   much slower if text not trimmed match    1799  2010    pattern   571   662    isBlank    60   338   faster the earlier hits the first non-whitespace character   Quite surprisingly the trim empty is the fastest  Even if it needs to construct the trimmed text  Still faster then simple for-loop looking for one single non-whitespaced character     EDIT  The longer text  the more numbers differs  Trim of long text takes longer time than just simple loop  However  the regexs are still the slowest solution

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Shortest solution I can think of   if  string trim   length    gt  0        This only checks for  non  white space  If you want to check for particular character classes  you need to use the mighty match   with a regexp such as   if  string matches      w               which checks for at least one  ASCII  alphanumeric character

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With Java-11   you can make use of the String isBlank API to check if the given string is not all made up of whitespace -   String str1           System out println str1 isBlank        made up of all whitespaces  prints true  String str2        a   System out println str2 isBlank        prints false   The javadoc for the same is           Returns   code true  if the string is empty or contains only      link Character isWhitespace int  white space  codepoints     otherwise   code false          return   code true  if the string is empty or contains only              link Character isWhitespace int  white space  codepoints             otherwise   code false         since 11     public boolean isBlank

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Slightly shorter than what was mentioned by Carl Smotricz    string trim   isEmpty

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I would use the Apache Commons Lang library  It has a class called StringUtils that is useful for all sorts of String operations  For checking if a String is not all whitespaces  you can use the following   StringUtils isBlank  lt your string gt     Here is the reference  StringUtils isBlank

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Alternative    boolean isWhiteSpaces  String s         return s    null  amp  amp  s matches    s

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StringUtils isEmptyOrWhitespaceOnly  lt your string gt     will check    - is it null  - is it only space  - is it empty string     https   www programcreek com java-api-examples  class com mysql jdbc StringUtils amp method isEmptyOrWhitespaceOnly

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trim   and other mentioned regular expression do not work for all types of whitespaces  i e  Unicode Character  LINE SEPARATOR   http   www fileformat info info unicode char 2028 index htm  Java functions Character isWhitespace   covers all situations   That is why already mentioned solution StringUtils isWhitespace  String    or StringUtils isBlank String  should be used

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StringUtils isBlank CharSequence    https   commons apache org proper commons-lang javadocs api-release org apache commons lang3 StringUtils html isBlank-java lang CharSequence-

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If you are only checking for whitespace and don t care about null then you can use org apache commons lang StringUtils isWhitespace String str      StringUtils isWhitespace String str     Checks if the String contains only whitespace    If you also want to check for null including whitespace  then  StringUtils isBlank String str

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if target matches    S            then string contains at least one non-whitespace character   Note use of back-slash cap-S  meaning  non-whitespace char   I d wager this is the simplest  and perhaps the fastest   solution

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If you are using Java 11  the new isBlank string method will come in handy    s isBlank      If you are using Java 8  9 or 10  you could build a simple stream to check that a string is not whitespace only    s chars   allMatch Character  isWhitespace      In addition to not requiring any third-party libraries such as Apache Commons Lang  these solutions have the advantage of handling any white space character  and not just plain     spaces as would a trim-based solution suggested in many other answers  You can refer to the Javadocs for an exhaustive list of all supported white space types  Note that empty strings are also covered in both cases

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While personally I would be preferring  str isBlank    as others already suggested  or str - gt   str isBlank   as a Predicate   a more modern and efficient version of the str trim   approach mentioned above  would be using str strip   - considering nulls as  quot whitespace quot   if  str    null  amp  amp  str strip   length    gt  0         For example as Predicate  for use with streams  e  g  in a unit test   Test public void anyNonEmptyStrippedTest         String   strings   null      Predicate lt String gt  isNonEmptyStripped   str - gt  str    null  amp  amp  str strip   length    gt  0      assertTrue Optional ofNullable strings  map arr - gt  Stream of arr  noneMatch isNonEmptyStripped   orElse true        strings   new String     null   quot  quot    quot   quot    quot   n quot    quot   t quot    quot   r quot         assertTrue Optional ofNullable strings  map arr - gt  Stream of arr  anyMatch isNonEmptyStripped   orElse true        strings   new String     null   quot  quot    quot   quot    quot   n quot    quot   t quot    quot   r quot    quot test quot

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This answer focusses more on the sidenote  i e  has at least one alphanumeric character   Besides that  it doesn t add too much to the other  earlier  solution  except that it doesn t hurt you with NPE in case the String is null    We want false if  1  s is null or  2  s is empty or  3  s only contains whitechars   public static boolean containsNonWhitespaceChar String s      return    s    null        equals s trim

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The trim method should work great for you   http   download oracle com docs cd E17476 01 javase 1 4 2 docs api java lang String html trim       Returns a copy of the string  with   leading and trailing whitespace   omitted  If this String object   represents an empty character   sequence  or the first and last   characters of character sequence   represented by this String object both   have codes greater than   u0020   the   space character   then a reference to   this String object is returned       Otherwise  if there is no character   with a code greater than   u0020  in   the string  then a new String object   representing an empty string is   created and returned       Otherwise  let k be the index of the   first character in the string whose   code is greater than   u0020   and let   m be the index of the last character   in the string whose code is greater   than   u0020   A new String object is   created  representing the substring of   this string that begins with the   character at index k and ends with the   character at index m-that is  the   result of this substring k  m 1        This method may be used to trim   whitespace from the beginning and end   of a string  in fact  it trims all   ASCII control characters as well       Returns  A copy of this string with   leading and trailing white space   removed  or this string if it has no   leading or trailing white space leading or trailing white space    You could trim and then compare to an empty string or possibly check the length for 0

[java] How do I check that a Java String is not all whitespaces?

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