What is the simplest way to convert a Java string from all caps words separated by underscores to CamelCase no word separators

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The title pretty much says it all  What s the simplest most elegant way that I can convert  in Java  a string from the format  THIS IS AN EXAMPLE STRING  to the format  ThisIsAnExampleString   I figure there must be at least one way to do it using String replaceAll   and a regex   My initial thoughts are  prepend the string with an underscore      convert the whole string to lower case  and then use replaceAll to convert every character preceded by an underscore with its uppercase version

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Java 8 for multiple strings    import com google common base CaseFormat     String camelStrings    YOUR UPPER  YOUR TURN  ALT TAB    List lt String gt  camelList   Arrays asList camelStrings split        camelList stream   forEach i - gt  System out println CaseFormat UPPER UNDERSCORE to CaseFormat UPPER CAMEL  i

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public String withChars String inputa        String input   inputa toLowerCase        StringBuilder sb   new StringBuilder        final char delim            char value      boolean capitalize   false      for  int i 0  i lt input length      i            value   input charAt i           if  value    delim                capitalize   true                    else if  capitalize                sb append Character toUpperCase value                capitalize   false                    else               sb append value                        return sb toString       public String withRegex String inputa        String input   inputa toLowerCase        String   parts   input split           StringBuilder sb   new StringBuilder        sb append parts 0        for  int i 1  i lt parts length    i            sb append parts i  substring 0 1  toUpperCase             sb append parts i  substring 1               return sb toString        Times  in milli seconds   Iterations   1000 WithChars  start   1379685214671 end   1379685214683 diff   12 WithRegex  start   1379685214683 end   1379685214712 diff   29  Iterations   1000 WithChars  start   1379685217033 end   1379685217045 diff   12 WithRegex  start   1379685217045 end   1379685217077 diff   32  Iterations   1000 WithChars  start   1379685218643 end   1379685218654 diff   11 WithRegex  start   1379685218655 end   1379685218684 diff   29  Iterations   1000000 WithChars  start   1379685232767 end   1379685232968 diff   201 WithRegex  start   1379685232968 end   1379685233649 diff   681  Iterations   1000000 WithChars  start   1379685237220 end   1379685237419 diff   199 WithRegex  start   1379685237419 end   1379685238088 diff   669  Iterations   1000000 WithChars  start   1379685239690 end   1379685239889 diff   199 WithRegex  start   1379685239890 end   1379685240585 diff   695  Iterations   1000000000 WithChars  start   1379685267523 end   1379685397604 diff   130081 WithRegex  start   1379685397605 end   1379685850582 diff   452977

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It will convert Enum Constant into Camel Case  It would be helpful for anyone who is looking for such funtionality          public enum TRANSLATE LANGUAGES           ARABIC  ar    BULGARIAN  bg    CATALAN  ca    CHINESE SIMPLIFIED  zh-CN    CHINESE TRADITIONAL  zh-TW    CZECH  cs    DANISH  da    DUTCH  nl    ENGLISH  en    ESTONIAN  et    FINNISH  fi    FRENCH                   fr    GERMAN  de    GREEK  el    HAITIAN CREOLE  ht    HEBREW  he    HINDI  hi    HMONG DAW  mww    HUNGARIAN  hu    INDONESIAN  id    ITALIAN  it    JAPANESE  ja    KOREAN  ko    LATVIAN                   lv    LITHUANIAN  lt    MALAY  ms    NORWEGIAN  no    PERSIAN  fa    POLISH  pl    PORTUGUESE  pt    ROMANIAN  ro    RUSSIAN  ru    SLOVAK  sk    SLOVENIAN  sl    SPANISH  es    SWEDISH                   sv    THAI  th    TURKISH  tr    UKRAINIAN  uk    URDU  ur    VIETNAMESE  vi             private String code           TRANSLATE LANGUAGES String language                this code   language                     public String langCode                 return this code                     public String toCamelCase TRANSLATE LANGUAGES lang                String toString   lang toString                if  toString contains                         String st   toUpperLowerCase toString split                                   return                        private String toUpperLowerCase String   tempString                StringBuilder builder   new StringBuilder                 for  String temp   tempString                     String char1   temp substring 0  1                   String restString   temp substring 1  temp length    toLowerCase                    builder append char1  append restString  append                                   return builder toString

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protected String toCamelCase CaseFormat caseFormat  String    words           if  words length     0             throw new IllegalArgumentException  Word list is empty                        String firstWord   words 0           String    restOfWords   Arrays copyOfRange words  1  words length            StringBuffer buffer   new StringBuffer            buffer append firstWord           Arrays asList restOfWords  stream   forEach w- gt buffer append      w toUpperCase               return CaseFormat UPPER UNDERSCORE to caseFormat  buffer toString

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Another option is using Google Guava s com google common base CaseFormat  George Hawkins left a comment with this example of usage   CaseFormat UPPER UNDERSCORE to CaseFormat UPPER CAMEL   THIS IS AN EXAMPLE STRING

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Here is a code snippet which might help   String input    ABC DEF   StringBuilder sb   new StringBuilder    for  String oneString   input toLowerCase   split              sb append  oneString substring 0 1  toUpperCase          sb append  oneString substring 1           sb now holds your desired String

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static String toCamelCase String s      String   parts   s split          String camelCaseString          for  String part   parts         camelCaseString   camelCaseString   toProperCase part           return camelCaseString     static String toProperCase String s        return s substring 0  1  toUpperCase                    s substring 1  toLowerCase        Note  You need to add argument validation

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With Apache Commons Lang3 lib is it very easy   import org apache commons lang3 StringUtils  import org apache commons lang3 text WordUtils   public String getName String text      return StringUtils remove WordUtils capitalizeFully text                  Example   getName  SOME CONSTANT      Gives    SomeConstant

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You can use org modeshape common text Inflector   Specifically    String camelCase String lowerCaseAndUnderscoredWord      boolean uppercaseFirstLetter  char    delimiterChars         By default  this method converts strings to UpperCamelCase    Maven artifact is  org modeshape modeshape-common 2 3 0 Final  on JBoss repository  https   repository jboss org nexus content repositories releases  Here s the JAR file  https   repository jboss org nexus content repositories releases org modeshape modeshape-common 2 3 0 Final modeshape-common-2 3 0 Final jar

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Take a look at WordUtils in the Apache Commons lang library    Specifically  the capitalizeFully String str  char   delimiters  method should do the job   String blah    LORD OF THE RINGS   assertEquals  LordOfTheRings   WordUtils capitalizeFully blah  new char         replaceAll              Green bar

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public static final String  UPPER CAMEL    initUp   public static final String  LOWER CAMEL    initLow    public String toCamel String src  String separator  String format        StringBuilder builder   new StringBuilder src toLowerCase         int len   builder length         for  int idx   builder indexOf separator   idx  gt  0  amp  amp  idx  lt  len  idx   builder indexOf separator  idx             builder   builder replace idx  idx   2   String valueOf builder charAt idx   1   toUpperCase                 switch  format        case LOWER CAMEL          builder setCharAt 0  Character toLowerCase builder charAt 0             break      default          builder setCharAt 0  Character toUpperCase builder charAt 0             break             return builder toString         Invocation as   toCamel  THIS IS AN EXAMPLE STRING        UPPER CAMEL    Execution Time  14 ms

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You can Try this also     public static String convertToNameCase String s                if  s    null                        StringBuilder b   new StringBuilder                String   split   s split                   for  String srt   split                                if  srt length    gt  0                                        b append srt substring 0  1  toUpperCase    append srt substring 1  toLowerCase    append                                                   return b toString   trim                      return s

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Java 1 8 example using Streams  String text    THIS IS SOME TEXT    String bactrianCamel   Stream of text split    a-zA-Z0-9              map v - gt  v substring 0  1  toUpperCase     v substring 1  toLowerCase             collect Collectors joining     String dromedaryCamel   bactrianCamel toLowerCase   substring 0  1    bactrianCamel substring 1     System out printf   s is now  s n   text  dromedaryCamel      THIS IS SOME TEXT is now thisIsSomeText

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public String CamelCase String str        String CamelCase         String parts     str split           for String part parts                String as part toLowerCase            int a as length            CamelCase   CamelCase   as substring 0  1  toUpperCase    as substring 1 a                 return CamelCase      This is the Simplest Program to convert into CamelCase  hope it Will Help You

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protected String toCamelCase String input        if  input    null            return null             if  input length      0            return                   lowercase the first character     String camelCaseStr   input substring 0  1  toLowerCase         if  input length    gt  1            boolean isStartOfWord   false           for  int i   1  i  lt  input length    i                  char currChar   input charAt i               if  currChar                              new word  ignore underscore                 isStartOfWord   true                else if  Character isUpperCase currChar                        capital letter  if start of word  keep it                 if  isStartOfWord                        camelCaseStr    currChar                    else                       camelCaseStr    Character toLowerCase currChar                                     isStartOfWord   false                else                   camelCaseStr    currChar                  isStartOfWord   false                                     return camelCaseStr

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One more solution to this may be as follows   public static String toCamelCase String str  String    separators        String separatorsRegex        concat org apache commons lang3 StringUtils join separators               List splits   Arrays asList str toLowerCase   split separatorsRegex        String capitalizedString    String splits stream   map WordUtils  capitalize  reduce     String  concat       return capitalizedString substring 0  1  toLowerCase     capitalizedString substring 1

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public static void main String   args        String start    THIS IS A TEST       StringBuffer sb   new StringBuffer        for  String s   start split                 sb append Character toUpperCase s charAt 0             if  s length    gt  1                sb append s substring 1  s length    toLowerCase                         System out println sb

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The Apache Commons project does now have the CaseUtils class  which has a toCamelCase method that does exactly as OP asked   CaseUtils toCamelCase  quot THIS IS AN EXAMPLE STRING quot   true

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Not sure  but I think I can use less memory and get dependable performance by doing it char-by-char   I was doing something similar  but in loops in background threads  so I am trying this for now   I ve had some experience with String split being more expensive then expected   And I am working on Android and expect GC hiccups to be more of an issue then cpu use     public static String toCamelCase String value        StringBuilder sb   new StringBuilder         final char delimChar            boolean lower   false      for  int charInd   0  charInd  lt  value length      charInd          final char valueChar   value charAt charInd         if  valueChar    delimChar            lower   false          else if  lower            sb append Character toLowerCase valueChar            else           sb append Character toUpperCase valueChar            lower   true                     return sb toString          A hint that String split is expensive is that its input is a regex  not a char like String indexOf  and it returns an array  instead of say an iterator because the loop only uses one things at a time    Plus cases like  AB AB AB AB AB AB     break the efficiency of any bulk copy  and for long strings use an order of magnitude more memory then the input string   Whereas looping through chars has no canonical case   So to me the overhead of an unneeded regex and array seems generally less preferable  then giving up possible bulk copy efficiency    Interested to hear opinions   corrections  thanks

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A simple snnipet    public static String camelCase String in        if  in    null    in length    lt  1    return         validate in     String out           for  String part   in toLowerCase   split                 if  part length    lt  1      validate length             continue                    out    part substring 0  1  toUpperCase            if  part length    gt  1      validate length             out    part substring 1                       return out

[java] What is the simplest way to convert a Java string from all caps (words separated by underscores) to CamelCase (no word separators)?

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