EmptyStackException error with Stack in Java

java, stack

Solution

There's a few issues I can see:

`eval.substring(i,i);` will return an empty string every time. You want `eval.substring(i,i + 1);`, or even better, `eval.charAt(i);`.

You'll want to put the returned substring/charAt character in it's own variable within your `for` loop. Currently it is overriding the `eval` string after the first iteration.

`if (eval.equals(alphabet.substring(0, 52)))` doesn't do what you seem to think it does judging by your comment. If you want to check if a string contains another string (or even just a single character), use the methods: `String#contains` or `String#indexOf`.

Here's a simple corrected snippet:

    String alphabet = "abcdefghjiklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    String eval = "blah";
    Stack<Character> chars = new Stack<Character>();

    for(char c : eval.toCharArray()) {
        if(alphabet.indexOf(c) != -1) {
            chars.push(c);
            System.out.println(chars.pop());
        }
    }

Problem

What I'm trying to do is to get the eval variable to have each of its letters put into a stack and then printed out. I'm getting an EmptyStackException error(assuming that means that there isn't anything in the stack). What I don't understand is that I thought that the eval string was put into the variable stack. Why is it empty? ``` public static void main(String[] args) { Stack<String> variable = new Stack<String>(); String eval = StdIn.readString(); String alphabet = "abcdefghjiklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; for (int i = 0; i < eval.length(); i++) { eval = eval.substring(i,i); if (eval.equals(alphabet.substring(0, 52)))// checks if eval is equal to any letter of alphabet { variable.push(eval); System.out.println(variable.pop()); } } } } ``` Im using eclipse Sample Runs: ``` input: hello Exception in thread "main" java.util.EmptyStackException at java.util.Stack.peek(Unknown Source) at java.util.Stack.pop(Unknown Source) at eval.main(eval.java:31) ```

Original source