In this program to convert prefix to postfix why is the runtime error "ArrayIndexOutOfBound" displayed on executing the following code?

Question

import java.util.Scanner;
import java.util.Stack;

class Postfix2 {
public static void postfix2(String str)
{
    String s[] = str.split("");
    Stack <String>st = new Stack<String>();
    String result = "";
    String num1 = "", num2 = "";

    for (int i=s.length; i>0; i--) 
    {

        if (!"+".equals(s[i]) && !"-".equals(s[i]) && !"*".equals(s[i]) && !"/".equals(s[i]))
            st.push(s[i]);
        else
        {
            num1 = st.pop();
            num2 = st.pop();
            result = num1 + num2 + s[i];
            st.push(result);
        }
    }

    System.out.println("Result: "+st.pop());
}

public static void main(String[] args) 
{
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter input string.");
    String str = sc.next();
    postfix2(str);
}
}

Indexes in array are from `0` to `length - 1` – Ivan Aug 23 '18 at 21:01 — Ivan, Aug 23 '18 at 21:01
Check the values you attempt to split – akortex Aug 23 '18 at 21:01 — akortex, Aug 23 '18 at 21:01

John Ciociola · Answer 1 · 2018-08-23T21:03:40.393

1

i needs to be equal to (s.length - 1) to account for the fact that the indexes start at zero in the first for loop.

Also, you may want to change the condition to i >= 0 since there will be an index of 0 as well unless you skipped that on purpose.

for (int i=(s.length -1); i>0; i--) 
{

edited Aug 23 '18 at 21:03

answered Aug 23 '18 at 21:01

John Ciociola

97
7

@Ivan yeah I just caught that while fixing a typo, thanks! – John Ciociola Aug 23 '18 at 21:04

score 1 · Answer 2 · edited Aug 23 '18 at 21:14

1

In the for loop you are starting to index outside of the length of the array. For example, if the array s = [x,y,z], s.length returns 3, but the last element z has index of 2 since elements are indexed starting from 0.

Try changing this for (int i=s.length; i>0; i--)

to this: for (int i=s.length-1; i>=0; i--)

edited Aug 23 '18 at 21:14

GBlodgett

12,704
4
31
45

answered Aug 23 '18 at 21:02

Rosa Mohammadi

46
1

In this program to convert prefix to postfix why is the runtime error "ArrayIndexOutOfBound" displayed on executing the following code?

2 Answers2