Put the Mouse Down and Step Away from the Keyboard

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Revision as of 03:15, 6 March 2009 by BurkHufnagel (Talk | contribs)
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While cleaning up some legacy code, I found a method designed to verify that a formatted string (cleverly named “time”) contained a valid time.

The expected format was “hh:mm:ss xx”, where ‘hh’ represents the hour, ‘mm’ represents minutes, ‘ss’ represents seconds, and ‘xx’ is either ‘AM’ or ‘PM’. When called, the method would report “05:23:42 AM” as valid, but “5:23:42 AM” would fail.

The method used the following code to convert two characters representing the hour into a number, and verify that it was in the proper range:

try {
    Integer.parseInt( time.substring(0, 2) );
} catch ( Exception x ) {
    return false;
}
if ( Integer.parseInt(time.substring(0, 2) ) > 12) {
    return false;
}

The same basic code appeared twice more, with appropriate changes to the character offset and upper limit, to test the minutes and seconds. The method ended with these lines to test for ‘AM’ or ‘PM’:

if ( !time.substring(9, 11).equals("AM") & !time.substring(9, 11).equals("PM") ) {
    return false;
}

If none of the previous code found a problem and returned “false” then the method returned “true”.

If the preceding code seems wordy and difficult to follow, don’t worry. Even an experienced Java developer might think the same; which meant I’d found something worth cleaning up. I refactored it and wrote a few unit tests - just to make sure it still worked.

When I was done, the new version was easier to read, half the size, and more accurate. The original code only tested upper bounds for the hour, minutes, and seconds. Not bad for half an hour’s work.

While getting ready for work the next day an idea popped in my head. Use a regular expression to validate the string. After a short round at the keyboard, I had a method that only needed one line of code, but it felt too complicated so I split it up to make it more readable. Here it is:

public static boolean validateTime( String time ) {
    String REGEX_PATTERN = "(0[1-9]|1[0-2]):[0-5][0-9]:[0-5][0-9] ([AP]M)";
    return time.matches( REGEX_PATTERN );
}

The point of this story is not that I eventually wrote one line of code that did what the original didn’t quite accomplish with over thirty. The point is that until I got away from the computer, I thought my first attempt was the best solution to the problem.

If you’ve been programming for a while, you’ve probably had similar experiences. You’re focused for hours on some gnarly problem with no solution in sight so you get up for a bio-break or to hit the vending machines, and on the way back the answer suddenly becomes obvious.

The trick is that while you’re coding, the logical part of your brain is active and the creative side is shut out. It can’t present anything to you until the logical side takes a break. So put the mouse down and step away from the keyboard. The insights you get may surprise you.

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