Forward slash in Java Regex

Question

I can t figure out why the following code doesn t behave as expected   Hello You There  replaceAll                 Expected output  Hello  You  There Actual output  Hello You There   Do I need to escape forward slashes  I didn t think so but I also tried the following against my will     didn t work   Hello You There  replaceAll                  In the end I realized I don t need a regular expression and I can just use the following  which doesn t create a regular expression   Hello You There  replace                However  I d still like to understand why my first example doesn t work

User · Answer

Double escaping is required when presented as a string.

Whenever I'm making a new regular expression I do a bunch of tests with online tools, for example: http://www.regexplanet.com/advanced/java/index.html

That website allows you to enter the regular expression, which it'll escape into a string for you, and you can then test it against different inputs.

User · Answer

There is actually a reason behind why all these are messed up  A little more digging deeper is done in this thread and might be helpful to understand the reason why      behaves like this

User · Answer

The problem is actually that you need to double-escape backslashes in the replacement string  You see         as I m sure you know  means the replacement string is     and  as you probably don t know  the replacement string    actually just inserts    because Java is weird  and gives   a special meaning in the replacement string   It s supposedly so that    will be a literal dollar sign  but I think the real reason is that they wanted to mess with people  Other languages don t do it this way   So you have to write either    Hello You There  replaceAll                  or    Hello You There  replaceAll      Matcher quoteReplacement             Using java util regex Matcher quoteReplacement String

[java] Forward slash in Java Regex

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