Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at Calculator.main(Calculator.java:25)

Question

I wrote this code for a simple calculator and I get this error! Someone help me please!

public class Calculator { 

  public static void main (String[] args) {

    int num1 = Integer.parseInt(args[0]);
    int num2 = Integer.parseInt(args[1]);
    int sum = num1 + num2;
    int sub = num1 - num2;  
    int prod = num1 * num2;
    int quot = num1 / num2;
    int rem = num1 % num2;

    // print the other variables, sub, prod, quot, rem;     
    System.out.println(num1 + " + " + num2 + " = " + sum);      
    System.out.println(num1 + " - " + num2 + " = " + sub);      
    System.out.println(num1 + " * " + num2 + " = " + prod);     
    System.out.println(num1 + " / " + num2 + " = " + quot);     
    System.out.println(num1 + " % " + num2 + " = " + rem);
  }
}

I suggest adding `if (args.length != 2) throw new IllegalArgumentException("Expected 2 arguments, but got: " + Arrays.toString(args))` to the start of your main-method. This won't fix your problem, but will give you a better error message ;-). — yankee, Sep 23 '17 at 20:17

score 1 · Answer 1 · edited Sep 23 '17 at 20:20

1

You need to make sure that when the application is started, it is passed two strings that can be parsed as numbers because your code assumes that arguments will have an element at positions 0 and 1. If you don't pass two arguments, then you will get your error.

For example, if calling main from within the program:

Calculator.main(new String[] {"10","20"});

Or, if calling Calculator.class from the command line:

java Calculator 10 20

edited Sep 23 '17 at 20:20

OneCricketeer

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answered Sep 23 '17 at 20:12

Scott Marcus

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You don't typically call main directly. It's passed at the command line – OneCricketeer Sep 23 '17 at 20:17
@cricket_007 I know, I was just trying to reinforce the point and was adding the command line example at that moment. – Scott Marcus Sep 23 '17 at 20:17
But if I do that, then I get more errors? – K. Lujan Sep 23 '17 at 20:19
1

@K.Lujan Ok, then there are other issues with your code that need to be worked out. Take them one at a time. – Scott Marcus Sep 23 '17 at 20:19
@cricket_007 Thanks. I'm not a Java guy (I do C#), so I knew what the problem was, but a little rusty on the syntax. – Scott Marcus Sep 23 '17 at 20:21

VHS · Answer 2 · 2017-09-23T20:24:20.843

As the exception indicates, your program encountered an Array out of bounds exception when it tried to access an array within index of 0. The only place in your code above where in Array with an index of 0 is being accessed is at the following line

int num1 = Integer.parseInt(args[0]);

So in other words, your program couldn't find 0th index of the args array which means you haven't passed any arguments to your program. Looks like your program two arguments in fact. Run your program the following way if you are using command line

java Calculator 100 200

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at Calculator.main(Calculator.java:25)

2 Answers2