为什么我在计算后缀最后一个运算符时出错了？

Question

2 3+

我错过了什么，导致了下面的错误？

线程“main”Java.lang.NumberFormatException：空字符串
位于sun.misc.FloatingDecimal.ReadJavaFormatString(FloatingDecimal.Java:1842)位于sun.misc.FloatingDecimal.ParseDouble（FloatingDecimal.Java:110)位于Java.lang.Double.ParseDouble（Double.Java:538)位于Java.lang.Double.(Double.Java:538)位于Java.lang.Double.(Double.Java:608)位于

package project;

import java.util.ArrayList;
import java.util.Stack;



public class Calculator {
    Stack<Double> calcStack = new Stack<>();
    ArrayList<String> operators = new ArrayList<>();

    public Calculator() {
        operators.add("+");
        operators.add("-");
        operators.add("/");
        operators.add("*");
    }

    public double processIn(String expression){
        String[] express = expression.split("");

        String temp = "";
        for(String j : express){
            if(operators.contains(j)){
                System.out.println("Operator Reached: " + j);
                double operand2 = calcStack.pop();
                double operand1 = calcStack.pop();

                double tmp = 0.0;
                if(j.compareTo("*") == 0){
                    tmp = operand1 * operand2;
                    System.out.println("Performing multiplication on " + operand1 + " and " + operand2);
                    calcStack.push(tmp);
                }
                else if(j.compareTo("/") == 0){
                    tmp = operand1 / operand2;
                    System.out.println("Performing division on " + operand1 + " and " + operand2);
                    calcStack.push(tmp);
                }
                else if(j.compareTo("-") == 0){
                    tmp = operand1 - operand2;
                    System.out.println("Performing subtraction on " + operand1 + " and " + operand2);
                    calcStack.push(tmp);
                }
                else if(j.compareTo("+") == 0){
                    tmp = operand1 + operand2;
                    System.out.println("Performing addition on " + operand1 + " and " + operand2);
                    calcStack.push(tmp);
                }
                System.out.println("Pushing result to stack: " + tmp);

            }
            else if(j.compareTo(" ") == 0){
                double newOperand = new Double(temp);
                temp = "";
                System.out.println("Pushing to stack: " + newOperand);
                calcStack.push(newOperand);
            }
            else{
                temp = temp + j;
                System.out.println("Current temp value: " + temp);
            }
        }
        return calcStack.pop();
    }
}

Answer 1

我想这会解决你的问题。用“”（空格）而不是“”拆分

String[] express = expression.split(" ");

然后把你的另一个改变成咆哮

else {
    double newOperand = new Double(j);
    System.out.println("Pushing to stack: " + newOperand);
    calcStack.push(newOperand);
}

如果大声喊话，则删除else

else if(j.compareTo(" ") == 0){
    double newOperand = new Double(temp);
    temp = "";
    System.out.println("Pushing to stack: " + newOperand);
    calcStack.push(newOperand);
}

else if(j.compareTo(" ") == 0){
    try{
    double newOperand = new Double(temp);
    temp = "";
    System.out.println("Pushing to stack: " + newOperand);
    calcStack.push(newOperand);
    }catch(NumberFormatException ex){
        //skip
    }
}