Comments on: How to check if String is parseable to Integer or Double?

By: mithrandir

mithrandir — Wed, 03 Feb 2010 14:40:55 +0000

Also – if you already know that your data is a valid double but you want to store something like 1.00000 as an Integer you could simply use:

double do = Double.parseDouble(myData);
if(do % 1 == 0)
{
int i = (int) do;
}

By: sevencardz

sevencardz — Fri, 15 Jan 2010 22:32:11 +0000

If you are validating a String that might not be a number, write a for() loop and use Character.isDigit(char) before converting the String to a double. Then use the method above. Be sure to add a condition for numbers in scientific notation.

By: sevencardz

sevencardz — Fri, 15 Jan 2010 22:23:22 +0000

public static boolean isInt(double value) {
return Math.floor(value) == value;
}

By: Rastislav

Rastislav — Wed, 25 Nov 2009 10:51:24 +0000

You can use DecimalFormatSymbols to improve regexp to better match locale settings.

DecimalFormatSymbols dfs = DecimalFormatSymbols.getInstance(Locale.getDefault());
dfs.getDecimalSeparator();
dfs.getExponentSeparator();
dfs.getGroupingSeparator();

By: alberlau

alberlau — Fri, 13 Nov 2009 11:30:11 +0000

Why not use: org.apache.commons.lang.math.NumberUtils.isDigit(String number) or isNumber? I like apache.commons and I’m use them extensively.

Checks whether the String a valid Java number.
Valid numbers include hexadecimal marked with the 0x qualifier, scientific notation and numbers marked with a type qualifier (e.g. 123L).
Null and empty String will return false.

By: Trollhorn

Trollhorn — Fri, 13 Nov 2009 10:06:50 +0000

Well, data validation in general is quite hard and often done wrong… I think the best idea is to use some sort of validation framework…

By: Joe Darcy

Joe Darcy — Thu, 12 Nov 2009 22:15:42 +0000

The javadoc comment for Double.valueOf(String):
http://java.sun.com/javase/6/docs/api/java/lang/Double.html#valueOf(java.lang.String)
includes a regular expression that recognizes valid inputs.

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By: Dan Howard

Dan Howard — Thu, 12 Nov 2009 17:40:15 +0000

The real issue IMO is that NumberFormatException is useless. 99% of the time you really will just treat a non parsable int as 0.

A try/catch is really not that expensive though.

By: Björn

Björn — Thu, 12 Nov 2009 10:26:02 +0000

To achieve a total match with NumberFormat you have to evaluate your own ParsePosition object.

String input = “2,33abc”;
ParsePosition pp = new ParsePosition(0);
Number parsedNumber = NUMBERFORMAT.parse(input, pp);

if (input.length() == pp.getIndex()
&& parsedNumber != null {
// complete number was parsed
}