Why does replaceAll fail with “illegal group reference”?

Question

I am in need to replace

\\\\\\s+\\\\$\\\\$ to $$

I used

String s = \"  $$\";
s = s.replaceAll(\"\\\\s+\\\\$\\\\$\",\"$$\"         


        

Answer 1

Use "\\$\\$" in the second parameter:

String s="  $$";
s=s.replaceAll("\\s+\\$\\$","\\$\\$");
//or
//s=s.replaceAll("\\s+\\Q$$\\E","\\$\\$");

The $ is group symbol in regex's replacement parameter

So you need to escape it