Regex expression grouping

[Bill Clar]

I have a regular expression that looks for any number divisible by 4 surrounded by brackets.

I have the working regex, but I'm unsure why it works and mine doesn't.

        String test = "[2014]";         // Not divisible by 4.  Should not match.

        Pattern modWorking = Pattern.compile(
                    "\\[(\\d*(([02468][048])|([13579][26]))|[048])\\]");

        Pattern modMine = Pattern.compile(
                    "\\[(\\d*(([02468][048])|([13579][26])|([048])))\\]");

        Matcher matcher = modWorking.matcher(test);

        if( matcher.find() )
            System.out.println("Working - True");
        else
            System.out.println("Working - False");

        matcher = modMine.matcher(test);

        if( matcher.find() )
            System.out.println("Mine    - True");
        else
            System.out.println("Mine    - False");

Output:
Working - False
Mine    - True

My pattern doesn't work. It accepts [2014] as a valid match.

I use an even grouping of conditions: (condition1|condition2|condition3), but it fails. The working solution utilizes ((condition1|condition2)|condition3). I don't understand the difference in the logic considering it's an OR condition.

[Henry Wong]

Bill Clar wrote:
I use an even grouping of conditions: (condition1|condition2|condition3), but it fails. The working solution utilizes ((condition1|condition2)|condition3). I don't understand the difference in the logic considering it's an OR condition.

You forgot to include the "\\d*" part in the condition in your description. After all, it is inside the parens, so shouldn't it have some effect?

Henry

[K. Tsang]

Well looking at the 2 regex, the bolded parts are different.

Working = "\\[(\\d*(([02468][048])|([13579][26]))|[048])\\]"
Yours = "\\[(\\d*(([02468][048])|([13579][26])|([048])))\\]"

[fred rosenberger]

Bill Clar wrote:...look for any number divisible by 4 surrounded by brackets.

ughh...Why in the world would you use a regex to do this?

[Bill Clar]

fred rosenberger wrote:

Bill Clar wrote:...look for any number divisible by 4 surrounded by brackets.

ughh...Why in the world would you use a regex to do this?

It's a challenge from a coding site. It had to be done by regex.

[Winston Gutkowski]

Bill Clar wrote:It's a challenge from a coding site. It had to be done by regex.

OK, but why surrounded by brackets? Maybe it's the same answer, but it seems kind of pointless...

Winston