indexOf Case Sensitive

Question

Is the indexOf String  method case sensitive   If so  is there a case insensitive version of it

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static string Search string factMessage  string b                         int index   factMessage IndexOf b  StringComparison CurrentCultureIgnoreCase               string line   null              int i   index              if  i    -1                return  not matched                 else                               while  factMessage i                                                line   line   factMessage i                       i                                       return line

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Converting both strings to lower-case is usually not a big deal but it would be slow if some of the strings is long  And if you do this in a loop then it would be really bad  For this reason  I would recommend indexOfIgnoreCase

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But it s not hard to write one   public class CaseInsensitiveIndexOfTest extends TestCase       public void testOne   throws Exception           assertEquals 2  caseInsensitiveIndexOf  ABC    xxabcdef                public static int caseInsensitiveIndexOf String substring  String string            return string toLowerCase   indexOf substring toLowerCase

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The first question has already been answered many times  Yes  the String indexOf   methods are all case-sensitive   If you need a locale-sensitive indexOf   you could use the Collator  Depending on the strength value you set you can get case insensitive comparison  and also treat accented letters as the same as the non-accented ones  etc  Here is an example of how to do this   private int indexOf String original  String search        Collator collator   Collator getInstance        collator setStrength Collator PRIMARY       for  int i   0  i  lt   original length   - search length    i              if  collator equals search  original substring i  i   search length                    return i                      return -1

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There is an ignore case method in StringUtils class of Apache Commons Lang library  indexOfIgnoreCase CharSequence str  CharSequence searchStr

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Here s a version closely resembling Apache s StringUtils version   public int indexOfIgnoreCase String str  String searchStr        return indexOfIgnoreCase str  searchStr  0      public int indexOfIgnoreCase String str  String searchStr  int fromIndex           https   stackoverflow com questions 14018478 string-contains-ignore-case 14018511     if str    null    searchStr    null  return -1      if  searchStr length      0  return fromIndex      empty string found  use same behavior as Apache StringUtils     final int endLimit   str length   - searchStr length     1      for  int i   fromIndex  i  lt  endLimit  i              if  str regionMatches true  i  searchStr  0  searchStr length     return i            return -1

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indexOf is case sensitive  This is because it uses the equals method to compare the elements in the list  The same thing goes for contains and remove

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Yes  it is case-sensitive  You can do a case-insensitive indexOf by converting your String and the String parameter both to upper-case before searching   String str    Hello world   String search    hello   str toUpperCase   indexOf search toUpperCase       Note that toUpperCase may not work in some circumstances  For instance this   String str    Feldbergstra  e 23  Mainz   String find    mainz   int idxU   str toUpperCase   indexOf  find toUpperCase      int idxL   str toLowerCase   indexOf  find toLowerCase        idxU will be 20  which is wrong  idxL will be 19  which is correct  What s causing the problem is tha toUpperCase   converts the      character into TWO characters   SS  and this throws the index off   Consequently  always stick with toLowerCase

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Is the indexOf String  method case sensitive    Yes  it is case sensitive    Test public void indexOfIsCaseSensitive         assertTrue  Hello World   indexOf  Hello      -1       assertTrue  Hello World   indexOf  hello      -1          If so  is there a case insensitive version of it    No  there isn t  You can convert both strings to lower case before calling indexOf    Test public void caseInsensitiveIndexOf         assertTrue  Hello World   toLowerCase   indexOf  Hello  toLowerCase       -1       assertTrue  Hello World   toLowerCase   indexOf  hello  toLowerCase       -1

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Here is my solution which does not allocate any heap memory  therefore it should be significantly faster than most of the other implementations mentioned here   public static int indexOfIgnoreCase final String haystack                                      final String needle        if  needle isEmpty      haystack isEmpty                 Fallback to legacy behavior          return haystack indexOf needle              for  int i   0  i  lt  haystack length      i               Early out  if possible          if  i   needle length    gt  haystack length                  return -1                        Attempt to match substring starting at position i of haystack          int j   0          int ii   i          while  ii  lt  haystack length    amp  amp  j  lt  needle length                  char c   Character toLowerCase haystack charAt ii                char c2   Character toLowerCase needle charAt j                if  c    c2                    break                            j                ii                         Walked all the way to the end of the needle  return the start            position that this was found          if  j    needle length                  return i                       return -1      And here are the unit tests that verify correct behavior    Test public void testIndexOfIgnoreCase         assertThat StringUtils indexOfIgnoreCase  A    A    is 0        assertThat StringUtils indexOfIgnoreCase  a    A    is 0        assertThat StringUtils indexOfIgnoreCase  A    a    is 0        assertThat StringUtils indexOfIgnoreCase  a    a    is 0         assertThat StringUtils indexOfIgnoreCase  a    ba    is -1        assertThat StringUtils indexOfIgnoreCase  ba    a    is 1         assertThat StringUtils indexOfIgnoreCase  Royal Blue     Royal Blue    is -1        assertThat StringUtils indexOfIgnoreCase   Royal Blue    Royal Blue    is 1        assertThat StringUtils indexOfIgnoreCase  Royal Blue    royal    is 0        assertThat StringUtils indexOfIgnoreCase  Royal Blue    oyal    is 1        assertThat StringUtils indexOfIgnoreCase  Royal Blue    al    is 3        assertThat StringUtils indexOfIgnoreCase      royal    is -1        assertThat StringUtils indexOfIgnoreCase  Royal Blue        is 0        assertThat StringUtils indexOfIgnoreCase  Royal Blue    BLUE    is 6        assertThat StringUtils indexOfIgnoreCase  Royal Blue    BIGLONGSTRING    is -1        assertThat StringUtils indexOfIgnoreCase  Royal Blue    Royal Blue LONGSTRING    is -1

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Had the same problem  I tried regular expression and the apache StringUtils indexOfIgnoreCase-Method  but both were pretty slow    So I wrote an short method myself      public static int indexOfIgnoreCase final String chkstr  final String searchStr  int i        if  chkstr    null  amp  amp  searchStr    null  amp  amp  i  gt  -1              int serchStrLength   searchStr length              char   searchCharLc   new char serchStrLength             char   searchCharUc   new char serchStrLength             searchStr toUpperCase   getChars 0  serchStrLength  searchCharUc  0             searchStr toLowerCase   getChars 0  serchStrLength  searchCharLc  0             int j   0            for  int checkStrLength   chkstr length    i  lt  checkStrLength  i                      char charAt   chkstr charAt i                   if  charAt    searchCharLc j     charAt    searchCharUc j                          if    j    serchStrLength                               return i - j   1                                           else      faster than  else if  j    0                             i   i - j                           j   0                                                          return -1        According to my tests its much faster     at least if your searchString is rather short   if you have any suggestions for improvement or bugs it would be nice to let me know     since I use this code in an application  -

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Just to sum it up  3 solutions    using toLowerCase   or toUpperCase using StringUtils of apache using    regex   Now  what I was wondering was which one is the fastest  I m guessing on average the first one

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The indexOf   methods are all case-sensitive  You can make them  roughly  in a broken way  but working for plenty of cases  case-insensitive by converting your strings to upper lower case beforehand   s1   s1 toLowerCase Locale US   s2   s2 toLowerCase Locale US   s1 indexOf s2

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Yes  I am fairly sure it is  One method of working around that using the standard library would be   int index   str toUpperCase   indexOf  FOO

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I would like to lay claim to the ONE and only solution posted so far that actually works   -  Three classes of problems that have to be dealt with   Non-transitive matching rules for lower and uppercase  The Turkish I problem has been mentioned frequently in other replies  According to comments in Android source for String regionMatches  the Georgian comparison rules requires additional conversion to lower-case when comparing for case-insensitive equality   Cases where upper- and lower-case forms have a different number of letters  Pretty much all of the solutions posted so far fail  in these cases  Example  German STRASSE vs  Stra  e have case-insensitive equality  but have different lengths   Binding strengths of accented characters  Locale AND context effect whether accents match or not  In French  the uppercase form of      is  E   although there is a movement toward using uppercase accents   In Canadian French  the upper-case form of      is       without exception  Users in both countries would expect  quot e quot  to  match  quot    quot  when searching  Whether accented and unaccented characters match is locale-specific  Now consider  does  quot E quot  equal  quot    quot   Yes  It does  In French locales  anyway    I am currently using android icu text StringSearch to correctly implement previous implementations of case-insensitive indexOf operations  Non-Android users can access the same functionality through the ICU4J package  using the com ibm icu text StringSearch class  Be careful to reference classes in the correct icu package  android icu text or com ibm icu text  as Android and the JRE both have classes with the same name in other namespaces  e g  Collator       this collator    RuleBasedCollator Collator getInstance locale       this collator setStrength Collator PRIMARY                  StringSearch search   new StringSearch           pattern           new StringCharacterIterator targetText            collator       int index   search first        if  index    SearchString DONE                   remember that the match length may NOT equal the pattern length          length   search getMatchLength                         Test Cases  Locale  pattern  target text  expectedResult       testMatch Locale US  quot AbCde quot   quot aBcDe quot  true       testMatch Locale US  quot        quot   quot EEE quot  true        testMatch Locale GERMAN  quot STRASSE quot   quot Stra  e quot  true       testMatch Locale FRENCH  quot        quot   quot EEE quot  true       testMatch Locale FRENCH  quot EEE quot   quot        quot  true       testMatch Locale FRENCH  quot        quot   quot        quot  true        testMatch new Locale  quot tr-TR quot    quot TITLE quot   quot title quot  true       Turkish dotless I i     testMatch new Locale  quot tr-TR quot    quot TITLE quot   quot title quot  true       Turkish dotted I i     testMatch new Locale  quot tr-TR quot    quot TITLE quot   quot title quot  false       Dotless-I    dotted i   PS  As best as I can determine  the PRIMARY binding strength should do the right thing when locale-specific rules differentiate between accented and non-accented characters according to dictionary rules  but I don t which locale to use to test this premise  Donated test cases would be gratefully appreciated  -- Copyright notice  because StackOverflow s CC-BY SA copyrights as applied to code-fragments are unworkable for professional developers  these fragments are dual licensed under more appropriate licenses here   https   pastebin com 1YhFWmnU

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Yes  indexOf is case sensitive   The best way to do case insensivity I have found is   String original  int idx   original toLowerCase   indexOf someStr toLowerCase       That will do a case insensitive indexOf

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What are you doing with the index value once returned   If you are using it to manipulate your string  then could you not use a regular expression instead   import static org junit Assert assertEquals      import org junit Test   public class StringIndexOfRegexpTest         Test     public void testNastyIndexOfBasedReplace             final String source    Hello World           final int index   source toLowerCase   indexOf  hello  toLowerCase             final String target    Hi  concat source substring index                    hello  length    source length              assertEquals  Hi World   target               Test     public void testSimpleRegexpBasedReplace             final String source    Hello World           final String target   source replaceFirst    i hello    Hi            assertEquals  Hi World   target

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Test public void testIndexofCaseSensitive         TestCase assertEquals -1   abcDef  indexOf  d

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I ve just looked at the source  It compares chars so it is case sensitive

[java] indexOf Case Sensitive?

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