java - Invalid escape sequence (valid ones are  f " ' )

Question

I have a problem with a regex in java.

When I try to use this regex:

 ^(?:(?:([01]?d|2[0-3]):)?([0-5]?d):)?([0-5]?d)$  

I get the following error

"Invalid escape sequence (valid ones are   
 f 
 " '  )"  

I don't know how to handle that error. I already tried to double the backslashes, but it didn't work. I hope someone can help me with this.

Thanks

Answer 1

This should work ^(?:(?:([01]?\d|2[0-3]):)?([0-5]?\d):)?([0-5]?\d)$

The reason is that the listed symbols in the error message have special meaning, but d is not one of those defined special symbols for using , this means you have to escape it (by adding an extra in front of the symbol).