Java Regex does not match

Question

I know that this kind of questions are proposed very often, but I can't figure out why this RegEx does not match. I want to check if there is a "M" at the beginning of the line, or not. Finaly, i want the path at the end of the line. This is why startsWith() doesn't fit my Needs.

line = "M            72208    70779 koj          src\com\company\testproject\TestDomainf1.java";

if (line.matches("^(M?)(.*)$")) {}

I've also tried the other way out:

Pattern p = Pattern.compile("(M?)");
Matcher m = datePatt.matcher(line);
if (m.matches()) {
    System.out.println("yay!");
}

if (line.matches("(M?)(.*)")) {}

Thanks

Answer 1

The correct regex would be simply

line.matches("M.*")

since the matches method enforces that the whole input sequence must match. However, this is such a simple problem that I wonder if you really need a regex for it. A plain

line.startsWith("M")

or

line.length() > 0 && line.charAt(0) == 'M'

or even just

line.indexOf('M') == 0 

will work for your requirement.

Performance?

If you are also interested in performance, my second and third options win in that department, whereas the first one may easily be the slowest option: it must first compile the regex, then evaluate it. indexOf has the problem that its worst case is scanning the whole string.

UPDATE

In the meantime you have completely restated your question and made it clear that the regex is what you really need. In this case the following should work:

Matcher m = Pattern.compile("M.*?(\\S+)").matcher(input);
System.out.println(m.matches()? m.group(1) : "no match");

Note, this only works if the path doesn't contain spaces. If it does, then the problem is much harder.

Answer 2

You dont need a regex for that. Just use String#startsWith(String)

if (line.startsWith("M")) {
    // code here
}

OR else use String#toCharArray():

if (line.length() > 0 && line.toCharArray()[0] == 'M') {
    // code here
}

EDIT: After your edited requirement to get path from input string.

You still can avoid regex and have your code like this:

String path="";
if (line.startsWith("M"))
    path = line.substring(line.lastIndexOf(' ')+1);
System.out.println(path);

OUTPUT:

src\com\company\testproject\TestDomainf1.java