CODEWITHSUNDEEP
javavalidation
jjkk0990
jjkk0990

Reputation: 93

How to check if user input is not an int value

I need to check if a user input value is not an int value. I've tried different combinations of what I know but I either get nothing or random errors

For example:

If the user inputs "adfadf 1324" it'll raise a warning message.

What I have:

       // Initialize a Scanner to read input from the command line
       Scanner sc = new Scanner(System.in);
       int integer, smallest = 0, input;
       boolean error = false;

       System.out.print("Enter an integer between 1-100: ");
       range = sc.nextInt();

       if(!sc.hasNextInt()) {

          error = true;
          System.out.println("Invalid input!");
          System.out.print("How many integers shall we compare? (Enter an integer between 1-100: ");
          sc.next();
    }

       while(error) {
          for(int ii = 1; ii <= integer; ii++) {

              ...

          } // end for loop
      }
      System.out.println("The smallest number entered was: " + smallest);

      }
  }

Upvotes: 9

Views: 145594

Answers (7)

Pandiyan Cool
Pandiyan Cool

Reputation: 6585

Simply throw Exception if input is invalid

Scanner sc=new Scanner(System.in);
try
{
  System.out.println("Please input an integer");
  //nextInt will throw InputMismatchException
  //if the next token does not match the Integer
  //regular expression, or is out of range
  int usrInput=sc.nextInt();
}
catch(InputMismatchException exception)
{
  //Print "This is not an integer"
  //when user put other than integer
  System.out.println("This is not an integer");
}

Upvotes: 18

Salah Assaf
Salah Assaf

Reputation: 1

This is to keep requesting inputs while this input is integer and find whether it is odd or even else it will end.

int counter = 1;
    System.out.println("Enter a number:");
    Scanner OddInput = new Scanner(System.in);
        while(OddInput.hasNextInt()){
            int Num = OddInput.nextInt();
            if (Num %2==0){
                System.out.println("Number " + Num + " is Even");
                System.out.println("Enter a number:");
            }
            else {
                System.out.println("Number " + Num + " is Odd");
                System.out.println("Enter a number:");
                }
            }
        System.out.println("Program Ended");
    }

Upvotes: 0

shady
shady

Reputation: 455

Maybe you can try this:

int function(){
Scanner input = new Scanner(System.in);   
System.out.print("Enter an integer between 1-100: ");   
int range;
while(true){   
    if(input.hasNextInt()){   
    range = input.nextInt();
    if(0<=range && range <= 100)
        break;
    else
        continue;
    }
    input.nextLine();  //Comsume the garbage value
    System.out.println("Enter an integer between 1-100:");
}
return range;
}

Upvotes: 0

Rajendra_Prasad
Rajendra_Prasad

Reputation: 1304

try this code [updated]:

Scanner scan = null;
       int range, smallest = 0, input;

     for(;;){
         boolean error=false;
        scan = new Scanner(System.in);
        System.out.print("Enter an integer between 1-100:  ");


            if(!scan.hasNextInt()) {
                System.out.println("Invalid input!");                      
                continue;
            }
         range = scan.nextInt();
            if(range < 1) {
                System.out.println("Invalid input!");
                error=true;
            }
        if(error)
        {
        //do nothing
        }
        else
        {
       break;
        }

        }
             for(int ii = 1; ii <= range; ii++) {
            scan = new Scanner(System.in);
            System.out.print("Enter value " + ii + ": ");

            if(!scan.hasNextInt()) {
                System.out.println("Invalid input!"); 
               ii--;
                continue;
            } 
        }

Upvotes: 2

Rajendra_Prasad
Rajendra_Prasad

Reputation: 1304

Try this one:

    for (;;) {
        if (!sc.hasNextInt()) {
            System.out.println(" enter only integers!: ");
            sc.next(); // discard
            continue;
        }
        choose = sc.nextInt();
        if (choose >= 0) {
            System.out.print("no problem with input");

        } else {
            System.out.print("invalid inputs");

        }
    break;
  }

Upvotes: 7

Rajendra_Prasad
Rajendra_Prasad

Reputation: 1304

you have following errors which in turn is causing you that exception, let me explain it

this is your existing code:

if(!scan.hasNextInt()) {
        System.out.println("Invalid input!");
        System.out.print("Enter an integer: ");
        usrInput= sc.nextInt();
    }

in the above code if(!scan.hasNextInt()) will become true only when user input contains both characters as well as integers like your input adfd 123.

but you are trying to read only integers inside the if condition using usrInput= sc.nextInt();. Which is incorrect,that's what is throwing Exception in thread "main" java.util.InputMismatchException.

so correct code should be 

 if(!scan.hasNextInt()) {
            System.out.println("Invalid input!");
            System.out.print("Enter an integer: ");
            sc.next(); 
            continue;
        }

in the above code sc.next() will help to read new input from user and continue will help in executing same if condition(i.e if(!scan.hasNextInt())) again.

Please use code in my first answer to build your complete logic.let me know if you need any explanation on it.

Upvotes: 2

ElliotSchmelliot
ElliotSchmelliot

Reputation: 8402

Taken from a related post:

public static boolean isInteger(String s) {
    try { 
        Integer.parseInt(s); 
    } catch(NumberFormatException e) { 
        return false; 
    }
    // only got here if we didn't return false
    return true;
}

Upvotes: 0

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