Re: little off topic, need help understand a recursive call
Re: little off topic, need help understand a recursive call
- Subject: Re: little off topic, need help understand a recursive call
- From: Ramsey Gurley <email@hidden>
- Date: Wed, 12 Nov 2014 09:45:34 -0700
Learning new things from new languages is fascinating. Trying to apply this knowledge in the language you know doesn’t always go so well though. What happens if you give isNumber a really really long string? Stack overflow :-/ Recursion is not one of Java’s strengths.
If you want a really fast isNumber and you’re only looking for chars ‘0’ thru ‘9', have a look at ERXStringUtilities.luhnCheck. Treating your chars as ints is the fastest way I’ve found to determine isNumber. It is orders of magnitude faster than Character.isDigit.
On Nov 12, 2014, at 4:32 AM, Theodore Petrosky <email@hidden> wrote:
> I am trying like mad to learn more. So I have decided to put time into Recursive algorithms. I do not want to start a conversation whether or not one should or should not use recursion in this example. That is a conversation for another day. I don’t believe that using it here will impact the app at all.
>
> As an experiment I am trying to use one in my validation method. Would one of you great minds take a look at this. It works, but I feel I am jumping through too many hoops. This is my first attempt so have a little pity:
>
>
> public String validateHeight(String value) throws ValidationException {
> value = value.trim();
>
> if (!isNumber(value)) {
> throw new ValidationException("There can be only numbers in the Height field! (value was " + value +")");
> }
> return value;
> }
>
> private boolean isNumber(String stringToCheck) {
> if (stringToCheck.length() == 0) return true;
> if (!Character.isDigit(stringToCheck.charAt(0))) return false;
> return isNumber(stringToCheck.substring(1, stringToCheck.length()));
> }
>
>
> My desire is to get better at this and learning recursion is very important. Also, when I look at other people’s code, there are times that there are recursive calls and I struggle to understand them.
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