Исключение пустого стека!

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import java.util.*;

public class BiggerStackProject
{
   public static void main(String args[]){
      String tester = "5+8-6*8";
      Stack<string> test = stackTheString(tester);
      int size = test.size();
      System.out.println(mathTheStack(test));
   }

   public static Stack<string> stackTheString(String input){
      Stack<string> original = new Stack<string>();
      String superTemp = null;
      for(int x = 0; x < input.length(); x++){
         String temp = Character.toString(input.charAt(x));
         original.push(temp);
      }
      return original;
   }

   public static double mathTheStack(Stack<string> input){
      Stack<string> operators = new Stack<string>();
      Stack<string> numbers = new Stack<string>();
      for(int x = 0; x < input.size(); x++){
         if(!(input.peek() == "+" || input.peek() == "-" || input.peek() == "*" || input.peek() == "/" || input.peek() == "%")){
            numbers.push(input.pop());
         }
      }
      for(int x = 0; x < input.size(); x++){
         if(input.peek() == "*" || input.peek() == "/" || input.peek() == "%"){
            operators.push(input.pop());
         }
         else{
            if(operators.pop().equals("*")){
               numbers.push(String.valueOf(Double.parseDouble(numbers.pop()) * Double.parseDouble(numbers.pop())));
            }
            else if(operators.pop().equals("/")){
               numbers.push(String.valueOf(Double.parseDouble(numbers.pop()) / Double.parseDouble(numbers.pop())));
            }
            else if(operators.pop().equals("+")){
               numbers.push(String.valueOf(Double.parseDouble(numbers.pop()) + Double.parseDouble(numbers.pop())));
            }
            else if(operators.pop().equals("-")){
               numbers.push(String.valueOf(Double.parseDouble(numbers.pop()) - Double.parseDouble(numbers.pop())));
            }
            else if(operators.pop().equals("%")){
               numbers.push(String.valueOf(Double.parseDouble(numbers.pop()) % Double.parseDouble(numbers.pop())));
            }
         }
      }
      return Integer.parseInt(numbers.pop());
   }
}

Я продолжаю получать это:

Exception in thread "main" java.util.EmptyStackException
	at java.util.Stack.peek(Stack.java:85)
	at java.util.Stack.pop(Stack.java:67)
	at BiggerStackProject.mathTheStack(BiggerStackProject.java:32)
	at BiggerStackProject.main(BiggerStackProject.java:8)

Process completed.

Что я уже пробовал:

Я просто ничего не могу понять.

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