Regex compilation in intellij

Question

I am trying to do:

uri=uri.replaceFirst("{}",param.toString());

I'm supposed to use regex in place of {} but that should not be a compilation problem because method signature takes String and {} is a perfectly valid string. Below is replaceFirst() :

public String replaceFirst(String regex, String replacement) 

Help me understand how is this a compilation error.

IntellijIDEA 2018.1

Answer 1

The first parameter is expected to be a valid regex. Because there are metacharacters, you must escape:

uri=uri.replaceFirst("\\{\\}",param.toString());

IntelliJ does inspection that allows it to report such errors. This is an IDE feature. Compiling this code with javac wouldn't cause it to fail.

You can disable inspection (alt+enter, details on the page linked to above):

Answer 2

{} is a special regex character which represents the range operator so you have to escape it before using it

// normal use
    "".replaceFirst("a{1,2}","");

As shown, {} is recognised as range to match minimum and maximum occurrences of a

so while using regex you have to provide some character/word along with minimum and maximum value with range operator {} (otherwise it can cause regex engine to crash or behave unexpectedly so compiler is being proactive here)

solution : escape it using \\\\

uri = uri.replaceFirst("\\{\\}",param.toString());

Answer 3

This is NOT a compilation error that you receive. It's an inspection from IntelliJ, even though it's underlined in red.

You may disable the inspection by going into your settings