Question

I’m new to Java. I want to be able to input operational characters in a Scanner.

My code should produce the following,

1. Enter two numbers: 13 6
2. What operation? *
3. What is 13 * 6? 78
4. Correct!

I’m using a Switch-statement to store the operations available for the user.
Those are: +, -, * and /.

I recieve a run time error everytime I write an operation after the output.

import java.util.Scanner;

public class Användardialog4 {
    public static void main(String[]args){
        Scanner sc = new Scanner(System.in);

    int svar;
    String op;
    char operator;

    System.out.println("Enter two numbers: ");
    int tal = sc.nextInt();
    int tal2 = sc.nextInt();

    System.out.println("Operation?");
    op = sc.nextLine();
    operator = op.charAt(0);

    switch(operator){
    case '+':
        System.out.println("What is "+tal+" + "+tal2);
        svar = sc.nextInt();
        if (svar == tal+tal2)
            System.out.println("Correct!");
        else
            System.out.println("Wrong - The right answer is: "+tal+tal2);
        break;
    case '*':
        System.out.println("What is "+tal+" * "+tal2);
        svar = sc.nextInt();
        if (svar ==tal*tal2)
            System.out.println("Correct!");
        else
            System.out.println("Wrong - The right answer is: "+tal*tal2);
        break;
    case '-':
        System.out.println("What is "+tal+" - "+tal2);
        svar = sc.nextInt();
        if (svar == tal-tal2)
            System.out.println("Correct!");
        else
            System.out.println("Wrong - The right answer is: "+(tal-tal2));
        break;
    case '/':
        System.out.println("What is "+tal+" / "+tal2);
        svar = sc.nextInt();
        if (svar == tal/tal2)
            System.out.println("Correct!");
        else
            System.out.println("Wrong - The right answer is: "+tal/tal2);
        break;
    }
}
}

The run time error I get is:

Exception in thread "main" java.util.InputMismatchException at
java.util.Scanner.throwFor(Unknown Source) at
java.util.Scanner.next(Unknown Source) at
java.util.Scanner.nextInt(Unknown Source) at
java.util.Scanner.nextInt(Unknown Source) at
Användardialog4.main(Dialog4.java:16)

So my question is, how do I use characters in a Scanner class?
Isn’t there a nextChar(); or something alike in Java?

Answer 1

Change op = sc.nextLine(); to op = sc.next();

public String next(); finds and returns the next complete token from this scanner. Since your operation is only one token/character, this is the way to go.

public String nextLine(); advances this scanner past the current line and returns the input that was skipped. Since you don’t have endline-character in your stream, this fails.