Checking the user input (scanner) before assigning to an int variable

Question

int i;
Scanner scan = new Scanner(System.in) {
i = scan.nextInt();
}

What I want to do is to catch the error in scanner when a user inputs a character instead of an integer. I tried the code below but ends up calling for another user input (bec. of calling another scan.nextInt() in assigning value to i after validating the first scan.nextInt() of numeric only):

int i;
Scanner scan = new Scanner(System.in) {

    while (scan.hasNextInt()){
    i = scan.nextInt();
    } else {
    System.out.println("Invalid input!");
    }
}

Elliott Frisch · Accepted Answer · 2014-11-07 01:46:20Z

1

Your logic seems a bit off, you have to consume an input if it isn't valid. Also, your anonymous block seems very odd. I think you wanted something like

int i = -1; // <-- give it a default value.
Scanner scan = new Scanner(System.in);
while (scan.hasNext()) { // <-- check for any input.
    if (scan.hasNextInt()) { // <-- check if it is an int.
        i = scan.nextInt(); // <-- get the int.
        break; // <-- end the loop.
    } else {
        // Read the non int.
        System.out.println("Invalid input! " + scan.next()); 
    }
}

answered Nov 7, 2014 at 1:46

Elliott Frisch

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1 Comment

Harambe Attack Helicopter Over a year ago

I had an error using "while (scan.hasNext())" so I changed it to "if (scan.hasNext())" and my problem was solved! Thanks!

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