Difference between String replace and replaceAll

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What s the difference between java lang String  s replace   and replaceAll   methods   other than later uses regex  For simple substitutions like  replace   with       is there any difference

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Q  What s the difference between the java lang String methods replace   and replaceAll    other than that the latter uses regex  A  Just the regex   They both replace all    http   docs oracle com javase 8 docs api java lang String html PS  There s also a replaceFirst    which takes a regex

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replace works on char data type but replaceAll works on String datatype and both replace the all occurrences of first argument with second argument

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In java lang String  the replace method either takes a pair of char s or a pair of CharSequence s  of which String is a subclass  so it ll happily take a pair of String s   The replace method will replace all occurrences of a char or CharSequence  On the other hand  the first  String arguments of replaceFirst and replaceAll are regular expressions  regex   Using the wrong function can lead to subtle bugs

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From Java 9 there is some optimizations in replace method  In Java 8 it uses a regex  public String replace CharSequence target  CharSequence replacement        return Pattern compile target toString    Pattern LITERAL  matcher              this  replaceAll Matcher quoteReplacement replacement toString         From Java 9 and on   And Stringlatin implementation   Which perform way better  https   medium com madhash composite-pattern-in-a-nutshell-ad1bf78479cc source post internal links---------2------------------

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As alluded to in wickeD s answer  with replaceAll the replacement string is handled differently between replace and replaceAll   I expected a 3  and a 4  to have the same value  but they are different   public static void main String   args        String   a   new String 5       a 0              a 1     X       a 2    a 0    a 1       a 3    a 1  replaceAll  X   a 0     X        a 4    a 1  replace  X   a 0     X         for  String s   a            System out println s     t    s length               The output of this is       1 X   1  X  2 X   1  X  2   This is different from perl where the replacement does not require the extra level of escaping      bin perl  esc          s    X     s    s X   esc X   print   s     length  s      n     which prints  X 2  This can be quite a nuisance  as when trying to use the value returned by java sql DatabaseMetaData getSearchStringEscape   with replaceAll

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The replace   method is overloaded to accept both a primitive char and a CharSequence as arguments   Now as far as the performance is concerned  the replace   method is a bit faster than replaceAll   because the latter first compiles the regex pattern and then matches before finally replacing whereas the former simply matches for the provided argument and replaces   Since we know the regex pattern matching is a bit more complex and consequently slower  then preferring replace   over replaceAll   is suggested whenever possible   For example  for simple substitutions like you mentioned  it is better to use   replace               instead of   replaceAll                   Note  the above conversion method arguments are system-dependent

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Both replace   and replaceAll   accepts two arguments and replaces all occurrences of the first substring first argument  in a string with the second substring  second argument   replace   accepts a pair of char or charsequence and replaceAll   accepts a pair of regex  It is not true that replace   works faster than replaceAll   since both uses the same code in its implementation  Pattern compile regex  matcher this  replaceAll replacement     Now the question is when to use replace and when to use replaceAll    When you want to replace a substring with another substring regardless of its place of occurrence in the string use replace    But if you have some particular preference or condition like replace only those substrings at the beginning or end of a string use replaceAll    Here are some examples to prove my point   String str   new String    qwerty     replaceAll                str    qwerty    String str   new String    qwerty     replaceAll                str     qwerty   String str   new String     qwerty     replaceAll                 str    qwerty

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replace   method doesn t uses regex pattern whereas replaceAll   method uses regex pattern  So replace   performs faster than replaceAll

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String replace char oldChar  char newChar    Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar   String replaceAll String regex  String replacement   Replaces each substring of this string that matches the given regular expression with the given replacement

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To add to the already selected  Best Answer   and others that are just as good like Suragch s   String replace   is constrained by replacing characters that are sequential  thus taking CharSequence   However  String replaceAll   is not constrained by replacing sequential characters only  You could replace non-sequential characters as well as long as your regular expression is constructed in such a way   Also  most importantly and painfully obvious   replace   can only replace literal values  whereas replaceAll can replace  like  sequences  not necessarily identical

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Both replace   and replaceAll   replace all occurrences in the String   Examples  I always find examples helpful to understand the differences   replace    Use replace   if you just want to replace some char with another char or some String with another String  actually CharSequence    Example 1  Replace all occurrences of the character x with o    String myString      x   x   x x    xx     char oldChar    x   char newChar    o    String newString   myString replace oldChar  newChar        o   o   o o    oo    Example 2  Replace all occurrences of the string fish with sheep    String myString    one fish  two fish  three fish    String target    fish   String replacement    sheep    String newString   myString replace target  replacement      one sheep  two sheep  three sheep   replaceAll    Use replaceAll   if you want to use a regular expression pattern   Example 3  Replace any number with an x   String myString      1 6    3  6 345    0    String regex      d   String replacement    x    String newString   myString replaceAll regex  replacement         x x    x  x xxx    x   Example 4  Remove all whitespace   String myString       Horse         Cow n n    r Camel  t t Sheep  n Goat            String regex      s   String replacement        String newString   myString replaceAll regex  replacement       HorseCowCamelSheepGoat   See also  Documentation   replace char oldChar  char newChar  replace CharSequence target  CharSequence replacement  replaceAll String regex  String replacement  replaceFirst String regex  String replacement    Regular Expressions   Tutorial List of patterns

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Old thread I know but I am sort of new to Java and discover one of it s strange things  I have used String replaceAll   but get unpredictable results   Something like this mess up the string   sUrl   sUrl replaceAll              replaceAll                So I designed this function to get around the weird problem     String replaceAll does not work OK  that s why this function is here public String strReplace  String s1  String s2  String s          if    s    null       s length      0          s1    null       s1 length      0            return s        while   s    null   amp  amp   s indexOf  s1    gt   0          s   s replace  s1  s2        return s      Which make you able to do   sUrl this strReplace             sUrl    sUrl this strReplace             sUrl

[java] Difference between String replace() and replaceAll()

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