Finding a Digit using Pattern and Matcher

Question

I am trying to use Pattern and Matcher to determine if a given string has a space between 2 digits. For example "5 1" should come back as true, "51" should come back as false. At first I was using string.replaceAll with the regex and it worked great, but moveing to Pattern I can't seem to get it to work.

    String findDigit = "5      1/3";
    String regex = "(\\d) +(\\d)";
    findDigit = findDigit.replaceAll(regex, "$1 $2");

    Pattern p = Pattern.compile(regex);
    Matcher m = p.matcher(findDigit);
    System.out.println(m.matches());
    System.out.println(m.hitEnd());

I first started with this. The replaceAll works without a hitch and removes the extra spaces, but the m.matches and the m.hitEnd both return false. Then I thought I might be doing something wrong so I simplified the case to just

    String findDigit = "5";
    String regex = "\\d";
    Pattern p = Pattern.compile(regex);
    Matcher m = p.matcher(findDigit);
    System.out.println(m.matches());
    System.out.println(m.hitEnd());

and matches comes back true (obviously) but when I change it to this

    String findDigit = "5 3";
    String regex = "\\d";
    Pattern p = Pattern.compile(regex);
    Matcher m = p.matcher(findDigit);
    System.out.println(m.matches());
    System.out.println(m.hitEnd());

comes back both false. So I guess my main question is how to I determine that there is ANY digit in my string first and then more specifically, how do I deteremine if there is a digit space digit in my string. I thought that was the hitEnd, but I guess I am mistaken. Thanks in advance.

Well thank you to whoever voted me back up, and I realize now that I was being stupid... m.find(). smacks head on desk — jhnewkirk
– jhnewkirk, Commented May 15, 2014 at 16:06

Mena · Accepted Answer · 2014-05-15 16:08:27Z

2

If you're looking for a match with multiple spaces but would like to preserve the formatting of the output you could use groups and back-references.

For instance:

String input = "blah 5             6/7";
Pattern p = Pattern.compile("(\\d)\\s+(\\d)");
Matcher m = p.matcher(input);
while (m.find()) {
    System.out.printf("Whole match: %s\n\tFirst digit: %s\n\tSecond digit: %s\n", m.group(), m.group(1), m.group(2));
}

Output

Whole match: 5             6
    First digit: 5
    Second digit: 6

answered May 15, 2014 at 16:08

Mena

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1 Comment

jhnewkirk Over a year ago

This actually greatly helped me answer another question I was having so thank you!

jhnewkirk · Accepted Answer · 2014-05-15 16:07:42Z

0

The answer is of course m.find() sorry for being stupid this morning. Thanks to all who even looked at this :)

answered May 15, 2014 at 16:07

jhnewkirk

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