Including comments in Java regular expressions

Question

I have some complex regular expressions which I need to comment for readability and maintenance. The Java spec is rather terse and I struggled for a long time getting this w

Answer 1

I found the following worked:

        String pattern2S = 
            "([A-Za-z]+)      # mandatory firstName\n" +
            "\\s+             # mandatory whitespace\n " +
            "([A-Z]\\.)?      # optional initial\n" +
            "\\s+             # whitespace\n " +
            "([A-Za-z]+)      # mandatory lastName\n"; 

The key thing was to include the newline character \n explicitly in the string

Answer 2

Why don't you just do this:

String pattern2S = 
    "([A-Za-z]+)" + //    mandatory firstName
    "\\s+" +        //    mandatory whitespace
    ...;

CONTINUATION:

If you want to keep the comments with the pattern and you need to read it in from a properties file, use this:

pattern=\
#comment1\\n\
(A-z)\
#comment2\\n\
(0-9)

Answer 3

See the post by Martin Fowler on ComposedRegex for some more ideas on improving regexp readability. In summary, he advocates breaking down a complex regexp into smaller parts which can be given meaningful variable names. e.g.

String mandatoryName = "([A-Za-z]+)";
String mandatoryWhiteSpace = "\\s+";
String optionalInitial = "([A-Z]\\.)?";
String pattern = mandatoryName + mandatoryWhiteSpace + optionalInitial +
    mandatoryWhiteSpace + mandatoryName;