Question

I’m trying to build a calculator without any operators that relate to the opration itself I try to solve (comparison operators and loops with operators are fine).
problem is, Eclipse is showing this in the console:

Exception in thread "main" java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at Calculator.addOne(Calculator.java:22)
at Calculator.add(Calculator.java:78)
at Program.main(Program.java:8)

And this is my code – Calculator class: http://pastebin.com/jLGe6atB

And my main() method:

public class Program {
public static void main(String[] args) {
    Calculator calculator1 = new Calculator(8135, 6);
    calculator1.add();
}
}

Can someone tell me what is the problem? (Please don’t ask why am I doing this, it’s just for fun)

Thanks and sorry for your time.

REQUEST: “post add() and addOne() here please:

        public int addOne(int DigitArray)
    {
            String stringNum1 = Integer.toString(DigitArray);
            String[] arrNum1 = stringNum1.split("");
            int[] newArrNum1 = new int[arrNum1.length];
               for (int i = 0; i < arrNum1.length; i++) {
                  newArrNum1[i] = Integer.parseInt(arrNum1[i]);
               }
            int lastDigit = newArrNum1[newArrNum1.length-1];
            switch(lastDigit)
            {
            case 0:
                    lastDigit = 1;
                    System.out.println(lastDigit);
                    return lastDigit;
            case 1:
                    lastDigit = 2;
                    System.out.println(lastDigit);
                    return lastDigit;
            case 2:
                    lastDigit = 3;
                    System.out.println(lastDigit);
                    return lastDigit;
            case 3:
                    lastDigit = 4;
                    System.out.println(lastDigit);
                    return lastDigit;
            case 4:
                    lastDigit = 5;
                    System.out.println(lastDigit);
                    return lastDigit;
            case 5:
                    lastDigit = 6;
                    System.out.println(lastDigit);
                    return lastDigit;
            case 6:
                    lastDigit = 7;
                    System.out.println(lastDigit);
                    return lastDigit;
            case 7:
                    lastDigit = 8;
                    System.out.println(lastDigit);
                    return lastDigit;
            case 8:
                    lastDigit = 9;
                    System.out.println(lastDigit);
                    return lastDigit;
            case 9:
                    lastDigit = 0;
                    updateNumberPlus(lastDigit, arrNum1, newArrNum1);
                    System.out.println(lastDigit);
                    return lastDigit;
            default:
                    return lastDigit;
            }
    }
    public int add()
    {
            int i = 0;
            while(i <= num2)
            {
                    i++;
                    this.addOne(num1);
                    if(i == num2)
                    {
                            result = 0;
                            System.out.print(result);
                            return result;
                    }
            }
            return result;
    }

Answer 1

When you do a String.split("") you will get an empty String element as the first and last elements of your Array.

You then iterate over the array, calling Integer.parseInt() on each element, which fails on the empty string elements.

A simple hack would be to change your for loop to look like;

for(int i = 1; i < arrNum1.length - 1; i++) {

It’s a little ugly though 😛