java NaN和-infinity

Question

I am failing to figure out a way to catch, or give order to my program if the result equals with NaN or -infinity. Whenever I enter 0 into my program it gives me a result of NaN and -Infinity. The problem I am facing is that the x1 and x2 are double types, that obviously can't be compared with String type. Any help would be much appreciated.

public class Exercise {

public static void main(String[] args){
    double x1 = 0;
    double x2 = 0;

    Scanner scanner = new Scanner(System.in);

    System.out.println("Feed me with a, b and c");

    try{
            double a = scanner.nextDouble();
            double b = scanner.nextDouble();
            double c = scanner.nextDouble();
            scanner.close();
            double discriminant = (b * b) - 4 * (a * c);

        if (discriminant > 0){

            x1 = (-b + Math.sqrt(discriminant)) / (2 * a);
            x2 = (-b - Math.sqrt(discriminant)) / (2 * a);

            System.out.println("The dish of yours has two components " + x1 
        + " and " + x2);
        }

        if (discriminant == 0){

            x1 = -b / (2 * a);
            System.out.println("The dish of yours has two identical 
        components " + x1 +" and " + x1);

        }

        if (discriminant < 0){

            System.out.println("The dish of yours doesn't have any 
         component");

        }

        }
        catch (InputMismatchException e) {
            System.out.println("I can't digest letters");
        }
        catch (Exception e) {
            System.out.println("This is inedible");
    }
    }
    }

Answer 1

You can check for NaN by doing

if (Double.isNaN(yourResult)) { ... }

And infinities by doing:

if (Double.isInfinite(yourResult)) { ... }

You should never use == to check for NaN because NaN is considered not equal to NaN !

Or, you can just check whether a is 0. Because that is probably the only case where Infinity and NaN will come out. If it is, say something like "Where's my a dish?" :)

Also, I just tried giving Nan NaN NaN and it output nothing. Consider checking whether a, b and c are NaN or Infinities as well. :)

Answer 2

Simply your error can be avoided by validating your inputs a,b and c before using.

Ex : check whether a!=0.