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https://issues.apache.org/jira/browse/LANG-992?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13949221#comment-13949221
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Sebb commented on LANG-992:
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Should octal numbers be validated or not?
Clearly a number such as 0xdefgh is invalid, because the 0x prefix unambiguosly
identifies a hex number.
However 0123 is potentially equally valid as an octal and a decimal number.
Which is correct depends on the context.
Now the Javadoc for isNumber says "Checks whether the String a valid Java
number."
If we take that to mean that the digit string must be valid as a numeric Java
literal, then clearly the leading 0 means octal.
However, numeric literals are not Strings.
JVM methods such as Integer.decode(String) that treat a leading 0 as meaning
octal will reject a parameter that contains non-octal digits - so again that
suggests octal should be validated.
As far as I know, there are no standard Java methods that accept number type
suffixes in Strings.
I think these are only accepted in numeric literals.
The fact that isNumber() accepts all these formats leads me to the conclusion
that the intention was probably to support the same syntax as Java literals,
and so the code should validate octal numbers accordingly.
> NumberUtils#isNumber() returns false for "0.0", "0.4790", et al
> ---------------------------------------------------------------
>
> Key: LANG-992
> URL: https://issues.apache.org/jira/browse/LANG-992
> Project: Commons Lang
> Issue Type: Bug
> Components: lang.math.*
> Affects Versions: 3.3.1
> Environment: Java 8, Windows 7
> Reporter: Adam Rauch
> Fix For: Review Patch
>
> Attachments: LANG-992-v2.patch
>
>
> After upgraded from 3.1 to 3.3.1 it seems that {{isNumber(String str)}}
> returns false for decimal numbers with leading zeros. In other words:
> {code:java}
> boolean ret = NumberUtils.isNumber("0.4790");
> {code}
> On 3.1, {{ret}} was true. In 3.3.1, {{ret}} is false.
> Guessing that LANG-972 is related... comment in the code states:
> {code:java}
> // leading 0, but not hex, must be octal
> {code}
> This is clearly a case where leading 0 does not mean hex.
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