B4J Code Snippet String Contains a Valid Number

SubName: ValidNumber

Description: A multi purpose number validator

Private Sub ValidNumber(Str As String, Negative As Boolean, Decimal As Boolean) As Boolean
    If Str = "" Then Return False
    Dim RegexStr As StringBuilder
    RegexStr.Initialize
    If Negative Then RegexStr.Append("-?")
    If Decimal Then
        RegexStr.Append("[0-9]*\.[0-9]*|")
        If Negative Then RegexStr.Append("-?")
    End If
    RegexStr.Append("[0-9]*")
    Return Regex.IsMatch(RegexStr.ToString,Str)

    'Complete Regex String for all tests "-?[0-9]*\.[0-9]*|-?[0-9]*"
End Sub

Dependencies: None

Tags: Number Validator

The attached project for B4j shows the use I wrote it for with error reporting.
This requires CSSUtils.

 

[LucaMs]

Can this be useful (... and is it possible to optimize it?)?
It's your function (changed name) without Negative and Decimal parameters.

Private Sub IsValidNumber(Str As String) As Boolean
    If Str = "" Then Return False
 
    Dim Negative As Boolean, Decimal As Boolean
 
    Negative = Str.Trim.StartsWith("-")
 
    ' Decimal?
    Dim Matcher1 As Matcher
    Matcher1 = Regex.Matcher("\.", Str)
    Dim DecimalCount As Int = 0
    Do While Matcher1.Find
        DecimalCount = DecimalCount + 1
    Loop
    Decimal = (DecimalCount = 1)
 
    Dim RegexStr As StringBuilder
    RegexStr.Initialize
    If Negative Then RegexStr.Append("-?")
    If Decimal Then
        RegexStr.Append("[0-9]*\.[0-9]*|")
        If Negative Then RegexStr.Append("-?")
    End If
    RegexStr.Append("[0-9]*")
    Return Regex.IsMatch(RegexStr.ToString,Str)

    'Complete Regex String for all tests "-?[0-9]*\.[0-9]*|-?[0-9]*"
End Sub

 

[Harris]

Also - Valid Number: neg or dec...

If IsNumber("-12345.567") Then
        Log(" string as number was valid")
    Else
        Log(" string as number was NOT valid")
    End If

 

[Gianni M]

If IsNumber("8d") Then
        Log(" strange!")
    Else
        Log(" string as number was NOT valid")
    End If

 

[Harris]

IsNumber("8d")

Strange indeed!

Seems ( d, D, f, F, ) when found in string (1 time only - upper or lower case - following any valid digits)...

IsNumber("1d") , "2322d", "3333343F" all return as valid numbers -true

IsNumber("1d2") , "2d3d", "3F4" , "d1" ,"d15f" all return as NOT valid numbers -false

There must be a reason for this erroneous behaviour... (d and f as valid number - but only when above condition is met)

Program started.
 
 string as number 1a: false
 string as number 1b: false
 string as number 1c: false
 string as number 1d: true
 string as number 1e: false
 string as number 1f: true
 string as number 1g: false
 string as number 1h: false
 string as number 1i: false
 string as number 1j: false
 string as number 1k: false
 string as number 1l: false
 string as number 1m: false
 string as number 1n: false
 string as number 1o: false
 string as number 1p: false
 string as number 1q: false
 string as number 1r: false
 string as number 1s: false
 string as number 1t: false
 string as number 1u: false
 string as number 1v: false
 string as number 1w: false
 string as number 1x: false
 string as number 1y: false
 string as number 1z: false

 

[OliverA]

d or D = double
f or F = float
Helps with assignments to tell the compiler it is not an int.

 

[Harris]

d or D = double
f or F = float
Helps with assignments to tell the compiler it is not an int.

Ok, makes sense in that regard - but in the context of IsNumber ( string ) - where "d" should be evaluated as a string (char) - not a type (int, float, double)?

 

[OliverA]

The help for IsNumber says: "Tests whether the specified string can be safely parsed as a number." This parsing is for the underlying language, not a routine you would write. Since the underlying language understands the d and f, it's a valid part of a string representation of a number (for this case, seeing if the underlying language can safely parse the string as a number). I guess it's more of a CanMyLanguageTakeThisStringAndSeeItAsANumberICanAssignToMyLanguagesPrimitiveDataTypesForNumbers. IsNumber is just shorter.

 

[Harris]

The help for IsNumber says: "Tests whether the specified string can be safely parsed as a number." This parsing is for the underlying language, not a routine you would write. Since the underlying language understands the d and f, it's a valid part of a string representation of a number (for this case, seeing if the underlying language can safely parse the string as a number). I guess it's more of a CanMyLanguageTakeThisStringAndSeeItAsANumberICanAssignToMyLanguagesPrimitiveDataTypesForNumbers. IsNumber is just shorter.

Whew! That's a mouthful...
Great explanation!
I guess the key word is "safely" - and what you expect using the function.

Dim nn As String = "8d"
    Dim res As Double
    
    If IsNumber(nn) Then
        res = nn * 1.5
    End If
    Log(" Result: "&res)  ' safely returns  12

I guess it is "safe". Now I know (unless shown otherwise).

Thanks

 

[stevel05]

Can this be useful

Yes it could, I was approaching it from the perspective that you can allow or disallow negative or decimal numbers.