While Not Condition

Question

How can I say the following:

while(input is not an int){
do this
}

I tried this code but I know it's wrong:

 int identificationnumber;
 Scanner sc3 = new Scanner(System.in);
identificationnumber = sc3.nextInt();

while( identificationnumber != int){ // this line is wrong 

Scanner sc4 = new Scanner(System.in);
identificationnumber = sc4.nextInt();

}

Any suggestions please.Thanks.

So you get an int and want to check if it is not one? What else should it be then? — guitarflow, Feb 09 '12 at 00:49
http://stackoverflow.com/questions/2674554/how-know-a-variable-type-in-java — AJP, Feb 09 '12 at 00:50

score 6 · Accepted Answer · answered Feb 09 '12 at 00:50

Javadocs are your friend: http://docs.oracle.com/javase/6/docs/api/java/util/Scanner.html

nextInt() throws an exception if the next token isn't an int. You're probably looking for hasNextInt()

Also, why are you creating a new Scanner every time you loop? (Or at all - you already have one before the loop)

score 6 · Answer 2 · answered Feb 09 '12 at 00:50

6

try :

while (! scanner.hasNextInt()) { // while the next token is not an int...
    scanner.next();              // just skip it
}
int i = scanner.nextInt();       // then read the int

answered Feb 09 '12 at 00:50

Olivier Croisier

5,881
23
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score 1 · Answer 3 · answered Feb 09 '12 at 00:55

1

Scanner throws an exception before getting to that line http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Scanner.html#nextInt()

The following code will work:

    int i = 0;
    while(true){
        Scanner scan = new Scanner(System.in);
        try{
            i = scan.nextInt();
        }catch (Exception e) {
            break;
        }
    }

answered Feb 09 '12 at 00:55

Alin Stoian

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Thanks for the link - very helpful. – Adegoke A Feb 09 '12 at 10:57

score 1 · Answer 4 · answered Feb 09 '12 at 02:23

1

You want this?

String identificationnumber;
Scanner scanner = new Scanner(System.in);//Only one Scanner is needed

while (scanner.hasNext()) { // Is there has next input?
    identificationnumber = scanner.next();//Get next input
    try {
        Integer.parseInt(identificationnumber);//Try to parse to integer
        System.out.println(identificationnumber + " is a number!");
    } catch (NumberFormatException e) {
        System.out.println(identificationnumber + " is not a number!");
    }
}

answered Feb 09 '12 at 02:23

plucury

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Thanks for this - but it just leaves me in an infinite loop. Is there a way I can do this with a for loop? – Adegoke A Feb 09 '12 at 10:56
@ayokunleadeosun If you want break the loop you can define a end flag string or just use "control + c" – plucury Feb 09 '12 at 13:41

score 0 · Answer 5 · answered Feb 09 '12 at 00:50

0

By writing sc3.nextInt() I assume you always get an int back, so checking for a non int seems a bit strange.

Maybe its better to return a string with the number inside. If the string is empty stop (you can just check against "") and otherwise convert it to an integer.

answered Feb 09 '12 at 00:50

Michel Keijzers

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I used sc3.nextInt to get the input into an int variable. – Adegoke A Feb 09 '12 at 10:58
a hasNextInt method is indeed the better solution. – Michel Keijzers Feb 09 '12 at 11:29

score 0 · Answer 6 · answered Feb 09 '12 at 00:51

0

Use nextInt() method of scanner class.

It throws,

InputMismatchException - if the next token does not match the Integer regular expression, or is out of range

answered Feb 09 '12 at 00:51

RanRag

43,987
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score 0 · Answer 7 · edited May 23 '17 at 11:58

0

You should be doing this:

if (sc3.hasNextInt())

Check this out: How to use Scanner to accept only valid int as input

With regards to class/type comparison, read this: What is the difference between instanceof and Class.isAssignableFrom(...)?

edited May 23 '17 at 11:58

Community

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answered Feb 09 '12 at 00:53

caleb

1,449
12
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While Not Condition

7 Answers7