How to check whether the input is a number or string by using isNan() in groovy

Question

Hello i am a beginner to groovy i am cofused how to check whether the given input is a number or not i tried the following

def a= ' 12.571245ERROR'
if(a.isNan()==0)
{
println("not a number")
}
else
{
println("number")
}

Kindly help me how to use isNan in groovy.I googled it lot but didnt find any result . Thanks in advance

Chiro

Answer 1

You can try to cast it to number and catch an exception if its not a number

def a= ' 12.571245ERROR'

try {
    a as Double
    println "a is number"
}catch (e) {
    println "a is not a number"
}

Or

if(a instanceof Number)
    println "Number"
else
    println "NaN"

Although keep in mind, in the second way of checking it, it would fail even if a is a valid number but in a String like "123". 123 is Number but "123" is not.

Sticky

I'm not thrilled that this is the top answer, if the behaviour of the program is to handle the data whether it is a number type or otherwise, then an exception should not be used. exceptions, as their name suggests, catch unexpected/undesired behaviour. – Rag

Answer 2

Groovy's String::isNumber() to the rescue:

def a = "a"

assert !a.isNumber()

def b = "10.90"

assert b.isNumber()
assert b.toDouble() == 10.90

Tenant

Answer 3

To answer your question, I would not consider isNan(). It is mentioned on the web, but it does not appear in the String doc for the GDK.

Consider this:

def input = "12.37"
def isNumber = input.isDouble() 

println "isNumber : ${isNumber}"

Or use something that is more Java-esque:

def input = "12.37error"

def isNumber = false

try {
    double value = Double.parseDouble(input)
    isNumber = true
} catch (Exception ex) {
}

println "isNumber : ${isNumber}"

Valero

Answer 4

This will fail for the number format with commas (eg: 10,00,000)

def aNumber = "10,00,000" aNumber.isNumber() and aNumber.isDouble() give answer as false.

Cytogenetics