Question

What’s the difference between java.lang.String ‘s replace() and replaceAll() methods,
other than the latter uses regex? For simple substitutions like, replace . with /, is there any difference?

Answer 1

• In java.lang.String, the replace method either takes a pair of char’s or a pair of CharSequence‘s (which String is implementing, 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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Relevant sections from java.lang.String:

• String replace(char oldChar, char newChar)
  Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.

• String replace(CharSequence target, CharSequence replacement)
  Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.

• String replaceAll(String regex, String replacement)
  Replaces each substring of this string that matches the given regular expression with the given replacement.

• String replaceFirst(String regex, String replacement)
  Replaces the first substring of this string that matches the given regular expression with the given replacement.