test if a string is an integer?

[dave]

I am reading input from a form. I want to validate the input by making sure
that the string is actually an integer. How would I do this? Do i need to
convert it to a character array and break down each character and test it?
or is there an easier way? Thanks.
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[Murray]

"dave" <go************ **********@nowh ere.com> wrote in message
news:FA******** **********@nwrd ny02.gnilink.ne t...

I am reading input from a form. I want to validate the input by making sure that the string is actually an integer. How would I do this? Do i need to
convert it to a character array and break down each character and test it?
or is there an easier way? Thanks.

Try to perform Integer.parseIn t(yourString) and if it throws a
NumberFormatExc eption you'll know the string isn't a valid integer

[Gary Labowitz]

"dave" <go************ **********@nowh ere.com> wrote in message
news:FA******** **********@nwrd ny02.gnilink.ne t...

I am reading input from a form. I want to validate the input by making sure that the string is actually an integer. How would I do this? Do i need to
convert it to a character array and break down each character and test it?
or is there an easier way? Thanks.

Hand the String to parseInt and catch NumberFormatExc eption.
see:
http://java.sun.com/j2se/1.4.2/docs/...va.lang.String)
--
Gary

[Liz]

"Murray" <pa***@SMAFFoff SPAMMER.optusne t.SPAMMAGE.com. au> wrote in message
news:6P******** ********@news-server.bigpond. net.au...

"dave" <go************ **********@nowh ere.com> wrote in message
news:FA******** **********@nwrd ny02.gnilink.ne t...

I am reading input from a form. I want to validate the input by making

sure

that the string is actually an integer. How would I do this? Do i need to convert it to a character array and break down each character and test it? or is there an easier way? Thanks.

Try to perform Integer.parseIn t(yourString) and if it throws a
NumberFormatExc eption you'll know the string isn't a valid integer

Do you really mean integer? Or is a "number" ok, then you can use
Double.parseDou ble(string); which will return a result for integers,
floats, and doubles.

[Chris Dutton]

As an alternative to the solution already provided...

import java.util.regex .*;

....

Pattern integerPattern = Pattern.compile ("^\d*$");
Matcher matchesInteger = integerPattern. matcher(myStrin g);
boolean isInteger = matchesInteger. matches();

or:

boolean isInteger = Pattern.matches ("^\d*$", myString);

[Tony Morris]

> I am reading input from a form. I want to validate the input by making
sure

that the string is actually an integer. How would I do this? Do i need to
convert it to a character array and break down each character and test it?
or is there an easier way? Thanks.

This question has been asked many times.
You'll receive answers ranging from checking that each char is between '0'
and '9' through to the use of regular expressions.
All of these suggestions are severely flawed, offering no benefit, and in
most cases creating a hindrance (i.e. not neutral side-effects).

The reason that these suggestions are attempted is because nobody (assuming
everybody knows what they are doing) likes catching a RuntimeExceptio n, and
especially not for the purpose of control flow. There is no suitable
alternative.

If it really bothers you (as it does me), encapsulate the "brokenness " in a
single method:

public boolean isParsableToInt (String i)
{
try
{
Integer.parseIn t(i);
return true;
}
catch(NumberFor matException nfe)
{
return false;
}
}

Note that there is a slight performance penalty for doing this - the only
suitable alternative is to simply catch the RuntimeExceptio n each time an
attempt to parse is made.

--
Tony Morris
http://xdweb.net/~dibblego/

[Raymond DeCampo]

Chris Dutton wrote:

As an alternative to the solution already provided...

import java.util.regex .*;

...

Pattern integerPattern = Pattern.compile ("^\d*$");
Matcher matchesInteger = integerPattern. matcher(myStrin g);
boolean isInteger = matchesInteger. matches();

or:

boolean isInteger = Pattern.matches ("^\d*$", myString);

Note that this method is *not* equivalent to the other methods which use
Integer.parseIn t(). This method will accept inputs that are outside the
range of a Java int, while Integer.parseIn t() will not. Use whichever
one is appropriate for your application.

Also, I believe you forgot about the negative sign. :)

HTH,
Ray

--
XML is the programmer's duct tape.

[lordy]

Raymond DeCampo <rd******@spam. twcny.spam.rr.s pam.com.spam> wrote in
news:sN******** ***********@twi ster.nyroc.rr.c om:

Chris Dutton wrote:

As an alternative to the solution already provided...

import java.util.regex .*;

...

Pattern integerPattern = Pattern.compile ("^\d*$");
Matcher matchesInteger = integerPattern. matcher(myStrin g);
boolean isInteger = matchesInteger. matches();

or:

boolean isInteger = Pattern.matches ("^\d*$", myString);
Note that this method is *not* equivalent to the other methods which

use Integer.parseIn t(). This method will accept inputs that are outside the range of a Java int, while Integer.parseIn t() will not. Use whichever
one is appropriate for your application.

Also, I believe you forgot about the negative sign. :)

It will also match the empty string so is a good example why one shouldnt
use tricks unless one is 37ETE HaX0r :)

--
Lordy

[Chris Dutton]

lordy wrote:

It will also match the empty string so is a good example why one shouldnt
use tricks unless one is 37ETE HaX0r :)

Yeah yeah... I never said it was perfect, but it is an alternative.
Maybe a pattern more like:

^-?\d+$

[Tony Morris]

"Chris Dutton" <ru******@hotma il.com> wrote in message
news:Y3_Jc.4439 9$od7.18972@pd7 tw3no...

lordy wrote:

It will also match the empty string so is a good example why one shouldnt use tricks unless one is 37ETE HaX0r :)

Yeah yeah... I never said it was perfect, but it is an alternative.
Maybe a pattern more like:

^-?\d+$

You will never achieve perfection with a regex, raising the question of "why
bother?".
After all, you will have to handle the cases that your regex misses (or the
ones that it doesn't depending on your proposed hack) negating the whole
purpose of attempting to check the validity of the data beforehand.

Declare to catch the NumberFormatExc eption.
The Number subclasses *should* have had a 'isParsable' method or declared
NumberFormatExc eption to be checked - the best workaround to this
unfortunate shortcoming of the core API is to explicitly catch the
NumberFormatExc eption. Sad, but true.

--
Tony Morris
http://xdweb.net/~dibblego/