Regex Expression Mixed Fraction

Question

public class MixedNumberRegex {

    public static void main(String[] args) {

        Pattern FRACTION_PATTERN = Pattern.compile("(?:(\\d+)\\s+)?(\\d+)/(\\d+)");

        Matcher m = FRACTION_PATTERN.matcher("1/2 + 1 1/2");

        System.out.print(m.group(1));
    }
}

Hi, I am trying to extract out the mixed number from the string. Is my pattern expression correct? From the example, I want the output to be "1 1/2".

I keep getting the exception

Exception in thread "main" java.lang.IllegalStateException: No match found at java.util.regex.Matcher.group(Unknown Source) at MixedNumberRegex.main(MixedNumberRegex.java:15) `

Answer 1

You can simplify your regex a bit and do it this way:

    Pattern FRACTION_PATTERN = Pattern.compile("(?:\\d+\\s+)?\\d/\\d");

    Matcher m = FRACTION_PATTERN.matcher("1/2 + 1 1/2");

    while (m.find()) {
        String found = m.group();
    }

It will find 1/2 and 1 1/2.

---

If you want to capture only 1 1/2, use pattern:

Pattern FRACTION_PATTERN = Pattern.compile("\\d+\\s+\\d/\\d");