How to replace case-insensitive literal substrings in Java

Question

Using the method replace CharSequence target  CharSequence replacement  in String  how can I make the target case-insensitive   For example  the way it works right now   String target    FooBar   target replace  Foo          would return  Bar   String target    fooBar   target replace  Foo          would return  fooBar    How can I make it so replace  or if there is a more suitable method  is case-insensitive so that both examples return  Bar

User · Answer

If you don t care about case  then you perhaps it doesn t matter if it returns all upcase   target toUpperCase   replace  FOO

User · Answer

org apache commons lang3 StringUtils   public static String replaceIgnoreCase String text                                         String searchString                                         String replacement   Case insensitively replaces all occurrences of a String within another String

User · Answer

I like smas s answer that uses replaceAll with a regular expression   If you are going to be doing the same replacement many times  it makes sense to pre-compile the regular expression once   import java util regex Pattern   public class Test         private static final Pattern fooPattern   Pattern compile    i foo         private static removeFoo s           if  s    null  s   fooPattern matcher s  replaceAll              return s             public static void main String   args            System out println removeFoo  FOOBar

User · Answer

For non-Unicode characters   String result   Pattern compile    i             Pattern UNICODE CASE  matcher source  replaceAll

User · Answer

Just make it simple without third party libraries       final String source    FooBar       final String target    Foo       final String replacement           final String result   Pattern compile target  Pattern LITERAL   Pattern CASE INSENSITIVE   Pattern UNICODE CASE  matcher source   replaceAll Matcher quoteReplacement replacement

User · Answer

String target    FOOBar   target   target replaceAll    i foo        System out println target     Output   Bar   It s worth mentioning that replaceAll treats the first argument as a regex pattern  which can cause unexpected results  To solve this  also use Pattern quote as suggested in the comments

User · Answer

Regular expressions are quite complex to manage due to the fact that some characters are reserved  for example   foo bar  replaceAll      produces an empty string  because the dot means  anything  If you want to replace only the point should be indicated as a parameter         A simpler solution is to use StringBuilder objects to search and replace text  It takes two  one that contains the text in lowercase version while the second contains the original version  The search is performed on the lowercase contents and the index detected will also replace the original text   public class LowerCaseReplace        public static String replace String source  String target  String replacement                StringBuilder sbSource   new StringBuilder source           StringBuilder sbSourceLower   new StringBuilder source toLowerCase             String searchString   target toLowerCase             int idx   0          while  idx   sbSourceLower indexOf searchString  idx      -1                sbSource replace idx  idx   searchString length    replacement               sbSourceLower replace idx  idx   searchString length    replacement               idx   replacement length                      sbSourceLower setLength 0           sbSourceLower trimToSize            sbSourceLower   null           return sbSource toString                public static void main String   args                System out println replace  xXXxyyyXxxuuuuoooo    xx                   System out println replace  FOoBaR    bar

User · Answer

String newstring     quot  quot   String target2    quot fooBar quot   newstring   target2 substring  quot foo quot  length    trim       logger debug  quot target2     quot  newstring       output  target2  Bar      String target3    quot FooBar quot   newstring   target3 substring  quot foo quot  length    trim    logger debug  quot target3     quot  newstring       output  target3  Bar

User · Answer

Not as elegant perhaps as other approaches but it s pretty solid and easy to follow  esp  for people newer to Java   One thing that gets me about the String class is this  It s been around for a very long time and while it supports a global replace with regexp and a global replace with Strings  via CharSequences   that last doesn t have a simple boolean parameter   isCaseInsensitive    Really  you d ve thought that just by adding that one little switch  all the trouble its absence causes for beginners especially could have been avoided   Now on JDK 7  String still doesn t support this one little addition     Well anyway  I ll stop griping   For everyone in particular newer to Java  here s your cut-and-paste deus ex machina   As I said  not as elegant and won t win you any slick coding prizes  but it works and is reliable   Any comments  feel free to contribute   Yes  I know  StringBuffer is probably a better choice of managing the two character string mutation lines  but it s easy enough to swap the techniques    public String replaceAll String findtxt  String replacetxt  String str           boolean isCaseInsensitive        if  str    null            return null            if  findtxt    null    findtxt length      0            return str            if  findtxt length    gt  str length              return str            int counter   0      String thesubstr           while   counter  lt  str length                  amp  amp   str substring counter  length    gt   findtxt length               thesubstr   str substring counter  counter   findtxt length             if  isCaseInsensitive                if  thesubstr equalsIgnoreCase findtxt                     str   str substring 0  counter    replacetxt                        str substring counter   findtxt length                        Failing to increment counter by replacetxt length   leaves you open                    to an infinite-replacement loop scenario  Go to replace  a  with  aa  but                    increment counter by only 1 and you ll be replacing  a s forever                  counter    replacetxt length                  else                   counter       No match so move on to the next character from                               which to check for a findtxt string match                          else               if  thesubstr equals findtxt                     str   str substring 0  counter    replacetxt                        str substring counter   findtxt length                     counter    replacetxt length                  else                   counter                                      return str

[java] How to replace case-insensitive literal substrings in Java

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