Need help with 'Exception in thread "main" java.util.NoSuchElementException'

[Wicked]

---SOLVED---

import java.util.Scanner;
class Calculator
{
  public static void main(String[] args)
  {
    double num1 = 0;
    double num2 = 0;
    double ans = 0;
    String op = new String();
    Scanner NumIn = new Scanner(System.in);
    Scanner OpIn = new Scanner(System.in);
    System.out.println("Would you like to 'add', 'subtract', 'multiply' or 'divide'?");
    op = OpIn.nextLine();
    OpIn.close();
    System.out.println("What is the first number?");
    num1=NumIn.nextDouble();
    System.out.println("Enter the second number");
    num2=NumIn.nextDouble();
    if(op.equals("add")){
    ans = num1 + num2;
    }
    if(op.equals("subtract")){
    ans = num1 - num2;
    }
    if(op.equals("multiply")){
    ans = num1 + num2;
    }
    if(op.equals("divide")){
    ans = num1 + num2;
    }
    System.out.println("= " + ans);
  }
}

I get that error instantly after entering a correct string (add).

.

[sunde887]

Your code seems overly complex, you might want to look into simplifying it. One error I noticed right away is you tried to use

correctoperator = false

in an if clause, which is incorrect.

Also, you are incorrectly comparing strings, try using .equals() instead of == when comparing strings.

Also, why are you nesting the tests for the operator?

if(operator.equals("add")){
  //set add to true
  //set all others to false
else if(operator.equals("mult")){
  //set mult to true
  //set all others to false
}
...

Might be smarted to prompt for the operator, and the two numbers initially, then use if else clauses like

prompt

if(operator.equals("add")){
  answer = x + y;
}

[Wicked]

Thanks for the help.

As for it being overcomplicated - It's the second thing I've ever written in Java so I have a bit of improving to do :)

I'll try and understand what you're saying.

[sunde887]

I can break it down better, of course the tutorials may explain it better.

When comparing strings you can't use ==, instead you want to use the method .equals() which compares two objects(in this case, strings)
String (Java 2 Platform SE 5.0)

It's a waste to first determine the value of the operator, then get the input, then apply the correct operation. You don't really need to be using .close on the scanner on something this small.

You have a weird condition "tree" I guess is the term. It states
if operator is add, test if operator is sub, if true, test div, and so on. It also sets the state of the items as it goes. With this conditional it only works if the user inputs add. If he says mult it fails the initial if clause.

if (operation == ("add"));
        {
          addition = true;
          correctoperator = true;

            if (operation == ("subtract"))
              {
                subtraction = true;
                correctoperator = true;

              if (operation == ("divide"))
                {
                  division = true;
                  correctoperator = true;

                if (operation == ("multiply"))
                  {
                    multiplication = true;
                    correctoperator = true;
              }
                }
                  }

is what you have, where you want it to be

if(something){
//do something
}
else if(something else){
//do something else
}

All the boolean variables are kind of a waste as well, the only variables you need are

String operator;
double number1;
double number2;
double answer;

I used doubles for more precision when working with division.

if you do

int x = 5;
int y = 2;
int answer = x / y;

you would expect 2.5, with integer arithmetic, the .5 is truncated and it will give you 2.

You don't need to initialize all the variables either, you can set them later. You just have to make sure you set them all.

instead of determining the input, then setting boolean variables, remove the boolean variables and do it all in one step. Ill give you one for free

System.out.println("Enter an operator");
Scanner operator = new Scanner();
String op = operator.nextLine();
System.out.println("Enter a number");
number1 = operator.nextInt();
System.out.println("Enter a number");
number2 = operator.nextInt();

if(op.equals("add")){
  answer = number1 + number2;
}

Ill leave the rest up to you. I gave you a LOT to work on, and way more than necessary to complete this.

to others: Im sorry if this is a bit of spoon feeding. I do however feel I simply corrected his major flaws and pushed him into a simpler solution.

[Wicked]

Thank you very much.

I took what you said into account and re-wrote the entire thing at about 1/4 of the length.

[sunde887]

Glad to have helped, did you get it working correct?

[Wicked]

Not exactly.
I still get that error when I try to run it but my code seems much better so I guess that's what matters.

#1547018 - Pastie

^ That's the new thing there.

[Junky]

I don't follow links. Copy and paste your code (only relevant part or a SSCCE) and the EXACT error message.

If you can't be bothered then I can't be bothered to help.

[sunde887]

You only need one scanner and really don't even need to close it. You also can leave all variables except ans uninitialized. If you paste your code you will get a lot more help. Can you post the exact error you are getting?

[Wicked]

You only need one scanner and really don't even need to close it. You also can leave all variables except ans uninitialized. If you paste your code you will get a lot more help. Can you post the exact error you are getting?

I removed one scanner and now it works perfectly.

Not sure why... But thanks :D

[Junky]

Reason - you attached 2 Scanner objects to the same input stream. Then one of your Scanner objects closed the stream. Therefore there was no longer any input for the other Scanner to read.

[sunde887]

Im glad you solved it, I hope I helped you understand some of the concepts.