What is wrong with my scanner code?

Question

Can anybody tell me what is wrong with my code as shown below? The first case works perfectly fine but the second and third case throws an exception :

Does this have something to do with the while loops at the start of case 2 and 3?

public static void main(String[] args) {

    Scanner scan = new Scanner(System.in);
    int option = scan.nextInt();

    switch (option) {
        case 1: int line = scan.nextInt();
                for (int i = 0; i < line; i++){

                    String operator = scan.next();

                    int n1 = scan.nextInt();
                    int n2 = scan.nextInt();

                    Boolean no1 = (n1 == 1) ? true:false;
                    Boolean no2 = (n2 == 1) ? true:false;

                    if (operator.equals("AND")) {
                        int result = (no1 && no2) ? 1:0;
                        System.out.println(result);
                    } else {
                        int result = (no1 || no2) ? 1:0;
                        System.out.println(result);
                    }

                }
                break;
        case 2: while (!scan.nextLine().equals("0")) {
                    String operator = scan.next();

                    int n1 = scan.nextInt();
                    int n2 = scan.nextInt();

                    Boolean no1 = (n1 == 1) ? true:false;
                    Boolean no2 = (n2 == 1) ? true:false;

                    if (operator.equals("AND")) {
                        int result = (no1 && no2) ? 1:0;
                        System.out.println(result);
                    } else {
                        int result = (no1 || no2) ? 1:0;
                        System.out.println(result);
                    }

                }
                break;
        case 3: while (scan.hasNextLine()) {
                    String operator = scan.next();

                    int n1 = scan.nextInt();
                    int n2 = scan.nextInt();

                    Boolean no1 = (n1 == 1) ? true:false;
                    Boolean no2 = (n2 == 1) ? true:false;

                    if (operator.equals("AND")) {
                        int result = (no1 && no2) ? 1:0;
                        System.out.println(result);
                    } else {
                        int result = (no1 || no2) ? 1:0;
                        System.out.println(result);
                    }
                }
                break;
        default: System.out.println("Error");
                 break;
    }
}

Exception in thread "main" java.util.NoSuchElementException

at java.util.Scanner.throwFor(Scanner.java:862)

at java.util.Scanner.next(Scanner.java:1371)

at HelloWorld.main(HelloWorld.java:64)

Please [edit] your question to include the full stack trace of any errors you get. — azurefrog, Aug 17 '16 at 18:04
Possible duplicate of [NoSuchElementException with Java.Util.Scanner](http://stackoverflow.com/questions/13729294/nosuchelementexception-with-java-util-scanner) — David, Aug 17 '16 at 18:05

Imesha Sudasingha · Answer 1 · 2016-08-18T09:54:41.687

0

In case 2:

while (scan.nextLine().equals("0"))

The above line reads the next line. Then the next time you call scan.next() you may not have anything to read. That's why you get java.util.NoSuchElementException exception.

In the while loop, check with scan.hasNext(). Then inside the while loop, read the input and check whether it equals to 0.

while (!scan.hasNext()) {
    String operator = scan.next();
    if (operator.equals("0")) break;
    int n1 = scan.nextInt();
    int n2 = scan.nextInt();

    boolean no1 = (n1 == 1) ? true:false;
    boolean no2 = (n2 == 1) ? true:false;

   if (operator.equals("AND")) {
           int result = (no1 && no2) ? 1:0;
           System.out.println(result);
   } else {
           int result = (no1 || no2) ? 1:0;
           System.out.println(result);
   }

}
break;

edited Aug 18 '16 at 09:54

answered Aug 17 '16 at 18:06

Imesha Sudasingha

2,885
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I tried doing as above and the program runs, but there is no output. To test my program I use the following code : `java HelloWorld < hello.in > output.out` In the file hello.in for case2 contains: 2\nOR 0 1\nAND 0 0\n0 – Pope Sua Aug 18 '16 at 09:05
I didnt call scan.nextLine() cause of this ^ @11thdimension – Pope Sua Aug 18 '16 at 09:11
There's an error in the code above, it should be while (scan.hasNext()) not !scan.hasNext(). Fixed that and case 2 runs fine :) – Pope Sua Aug 18 '16 at 09:25
Okay I got all 3 cases to work! Thanks everybody for the help. Much appreciated! @11thdimension – Pope Sua Aug 18 '16 at 09:27
ahh.. Yes, Fixed it – Imesha Sudasingha Aug 18 '16 at 09:54

11thdimension · Answer 2 · 2016-08-17T18:13:27.803

Scanner.nextInt() won't consume the new line followed by it.

That's why scan.nextLine() call in the second case would consume \n, a single new line character, making the while condition true.

Thus inputted "0" is still not consumed and would go in operator, input meant for the operator would be a string and would not be consumed by scan.nextInt(), this is the error.

To remedy this, call scan.nextLine() after the first scan.nextInt() call.

What is wrong with my scanner code?

2 Answers2