Grouping has me stuck

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February 20th, 2009, 09:07 PM

fishtoprecords

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Grouping has me stuck

I'm using Java's regex libraries, and I can't get grouping to work. Or at least I can't get it to work they way I want.

What I want is to match from the begining of the string up to, but not including any number of trailing semicolon characters. I expected that grouping it would let the first group be the characters I want.
But no.

Here is a code snipet:

Code:

static final Pattern pat = Pattern.compile("^(.*?);*$");

private static final String[] list = {
"abc;",
"N:Berger;Gary;;;",
 "EMAIL;type=INTERNET;type=pref:halberman@alum.mit.edu"};

private void bar(String arg) {
    Matcher m = pat.matcher(arg);
    int count = 0;
    while(m.find()) {
        count++;
        System.out.println("Match number "+count);
        System.out.println("start(): "+m.start());
        System.out.println("end(): "+m.end());
        System.out.println(arg.substring(m.start(), m.end()));
        for (int i = 0; i < m.groupCount(); i++) {
            System.out.println(m.group(i));
        }
    }
}

Any pointers greatly appreciated.

February 21st, 2009, 10:06 AM

atlantisstorm

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hi, there are 2 little problems with what you're doing.

1. Your regular expression ("^(.*?);*$") is saying match smallest string which ends with zero or more semi-colons.

It should be "^(.*?);.*$" - match smallest string which end with semi-colon and zero or more of any character.

2. If/When you actually find a match your group count will be 1 as you only have 1 set of parenthesis, so your loop ...

Code:

    for (int i = 0; i < m.groupCount(); i++) 
    {
        System.out.println(m.group(i));
    }

...will never show m.group(1). You need to change it to ...

Code:

    for (int i = 0; i <= m.groupCount(); i++) 
    {
        System.out.println(m.group(i));
    }

Note : group(0) just means the whole string you're testing against.

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Last edited by atlantisstorm : February 21st, 2009 at 10:08 AM.

February 21st, 2009, 10:57 AM

fishtoprecords

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Join Date: Sep 2007

Location: outside Washington DC

Posts: 2,642

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Thanks, it was the missing <= that threw me.

Grouping has me stuck

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