Question

The following JUnit test will only run correctly for me when I set a breakpoint on the matcher line. When running it normally or debugging it without a breakpoint it will fail.

public class ParserTest {
@Test
public void test() {
    final String s = new Parser().parse("Hello(WORLD)");
}

public static class Parser {
    private static final Pattern pattern = Pattern
            .compile("([a-zA-Z\\s]*)\\(([A-Z]{5,5})\\)");

    public String parse(final String raw) {
        // put a breakpoint on the matcher in eclipse,
        // debug as junit test, then step over
        final Matcher matcher = pattern.matcher(raw);
        return matcher.group(2) + ":" + matcher.group(1);
    }
}
}

The following exception is thrown

java.lang.IllegalStateException: No match found
at java.util.regex.Matcher.group(Matcher.java:461)
at lab.ParserTest$Parser.parse(ParserTest.java:22)
at lab.ParserTest.test(ParserTest.java:11)

I create a RegEx Planet Cookbook here and it works fine.

Answer 1

You need to call matcher.matches() before matcher.group(). Sometimes examining code in a debugger cause the state of an object to change because it forces things to evaluate. I suspect that’s happening here.