Input validation checking if the input is a double

Question

I want to check if the input I entered is the correct data type. For example if the user enters an int when I want them to enter a double then the program tells them there is an error. This is what I have so far:

System.out.println("Enter the temperature in double:");
String temp = input.nextLine();
try
{
    Double temperature = Double.parseDouble(temp);
}
catch(Exception e)
{
    isValid = false;
    System.out.println("Temperature  must be a double ");
}

All its doing is continuing on through the program and not printing out the error message when I enter an int. Been stuck on this for a while so any help would be appreciated.

Every int is a valid double, so why would you expect it to fail? — Jacob G.
– Jacob G., Commented Feb 15, 2019 at 16:37
An int is also a double! You have to explicitely test against intness, too. — Seelenvirtuose
– Seelenvirtuose, Commented Feb 15, 2019 at 16:38

Nicholas K · Accepted Answer · 2019-02-15 17:44:57Z

1

I think you are looking to validate only decimal numbers (not including integers). If that is the case then you can use a regex for the same :

System.out.println("Enter the temperature in double:");
String temp = input.nextLine();
while (temp != null && !temp.matches("^[0-9]*\\.([0-9]+)+$")) {       // use of regex here
    System.out.println("Enter the temperature in double:");
    temp = input.nextLine();                                          // read input again
}

This will loop until the user gives in only a valid decimal input. Explanation of this regex.

edited Feb 15, 2019 at 17:44

answered Feb 15, 2019 at 17:23

Nicholas K

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Comments

Manish Chandra Joshi · Accepted Answer · 2019-02-15 18:17:07Z

0

Since you don't want int to get accepted, you can just add an if to check whether the input String has a decimal point or not.

    System.out.println("Enter the temperature in double:");
    String temp = (new Scanner(System.in)).next();
    if (temp.contains(".")) {
        try {
            Double temperature = Double.parseDouble(temp);
        } catch(Exception e) {
            isValid = false;
            System.out.println("Temperature  must be a double ");
        }
    } else {
        isValid = false;
        System.out.println("Temperature  must be a double ");
    }

edited Feb 15, 2019 at 18:17

answered Feb 15, 2019 at 18:01

Manish Chandra Joshi

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1 Comment

Manish Chandra Joshi Over a year ago

Just retaining the original try catch should deal with that problem, edited!

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