How to Properly Escape Backslashes in Java Strings using `replaceAll` and `replace`?

Escaping Backslashes in Strings using replaceAll

Attempting to convert the String "something" into "something" using String#replaceAll() is problematic due to the character's dual role as an escape character in both strings and regular expressions.

Applying the expression string.replaceAll("", "\") results in the error "java.util.regex.PatternSyntaxException: Unexpected internal error near index 1". This is because the regular expression interprets the first as an escape character for the second .

Solution 1: Double Escaping Using Regex

To escape the character in a regular expression, it must be double-escaped. The correct expression is:

string.replaceAll("\\", "\\\\");

Solution 2: Character-by-Character Replacement Using replace

If exact character-by-character replacement is desired, regular expressions are not necessary. The String#replace() method can be used instead:

string.replace("\", "\\");

Additional Note: Escaping for JavaScript

If the string is intended to be used in a JavaScript context, the StringEscapeUtils#escapeEcmaScript() method is recommended to cover a wider range of escape characters.

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