RPN计算器错误消息添加

Question

我一直在研究这个计算器进行课堂作业，而且无法找出找出错误的地方。声明如果没有足够数量的处理器数量。 我被允许有额外的数字（即3 3 3 +），但不能太少（即3 +）

如果您有任何想法，请告诉我......

 import java.util.*;
 class RPNCalculator{

 public static void main (String [] str){

Scanner scan = new Scanner(System.in);

System.out.println("Please enter numbers and operations in PRN format");
  String input = scan.nextLine();
  String [] split = input.split("\\s+");
  double [] numbers = new double [1000];
  int numAmount = 0;

    for (int i = 0; i < split.length; i++){
      if (split[i].equals("+")){
        numbers[numAmount-2] = numbers[numAmount-2] + numbers[numAmount-1];
        numAmount--;
      }
      else if (split[i].equals("-")){
        numbers[numAmount-2] = numbers[numAmount-2] - numbers[numAmount-1];
        numAmount--;
      }
      else if (split[i].equals("*")){
        numbers[numAmount-2] = numbers[numAmount-2] * numbers[numAmount-1];
        numAmount--;
      }
      else if (split[i].equals("/")){
        numbers[numAmount-2] = numbers[numAmount-2] / numbers[numAmount-1];
        numAmount--;
      } 
      else {
        numbers[numAmount] = Double.parseDouble(split[i]);
        numAmount++; 
      }
    }
  System.out.print (numbers[numAmount-1]);
  }
  }