使用堆栈错误的后缀评估 (java)

Question

所以我正在编写一个程序来计算文件中的后缀表达式。但是我不断收到错误消息：

 0
Exception in thread "main" java.lang.NumberFormatException: For input string: "+"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:484)
    at java.lang.Integer.valueOf(Integer.java:582)
    at postfixEvaluater.postfixEvaluation(postfixEvaluater.java:89)
    at postfixEvaluater.readFromTheFile(postfixEvaluater.java:49)
    at postfixEvaluater.main(postfixEvaluater.java:21)

所以我根据这个猜测和我的运营商有关系。

输入的.txt文件内容如下：

 511+93/2-932/-149657%/*-+14+96*5/7%-149-+6*57%/

预期输出为：

这是我目前所有的代码：

import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;

public class postfixEvaluater {
   public static void main(String[] commandlineArguments) {
      //Error Checking
      if(commandlineArguments.length == 0){
         System.out.println("Please enter the file name.");
      }
      else{
         postfixEvaluater.readFromTheFile(commandlineArguments[0]);
      }

   }        


   public static void readFromTheFile(String fileName) {
         //connect to file 
      File file = new File(fileName);
      Scanner scanFile = null;
      try {
         scanFile = new Scanner(file);
      } 
      catch (FileNotFoundException exception) {

         System.out.print("File not found for " + fileName);

         System.exit(1);
      }        

      while (scanFile.hasNextLine()) {

         String line = scanFile.nextLine();

         Integer postfixLine = postfixEvaluater.postfixEvaluation(line);
         System.out.println(postfixLine);



      }
   }


   public static Integer postfixEvaluation(String input){




      StackInterface<Integer> stack = new LinkedStack<Integer>();

      Integer result = new Integer(0);



      for(int i=0;i<input.length();i++){

         String characterNum = input.substring(i, i+1);

         Integer integer1 = new Integer(0);
         Integer integer2 = new Integer(0);

        Integer character = (Integer.valueOf(characterNum));



         if (character.equals("0")) {
            stack.push(character);

         }
         else if (character.equals("1")) {
            stack.push(character);

         }
         else if (character.equals("2")) {
            stack.push(character);
         }
         else if (character.equals("3")) {
            stack.push(character);
         }
         else if (character.equals("4")) {
            stack.push(character);
         }
         else if (character.equals("5")) {
            stack.push(character);
         }
         else if (character.equals("6")) {
            stack.push(character);
         }
         else if (character.equals("7")) {
            stack.push(character);
         }
         else if (character.equals("8")) {
            stack.push(character);
         }
         else if (character.equals("9")) {
            stack.push(character);
         }
         else if (character.equals("*")) {
            integer2 = stack.pop();
            integer1 = stack.pop();


            result = integer1 * integer2;


            stack.push(result);



         }
        else if (character.equals("/")) {
            integer2 = stack.pop();
            integer1 = stack.pop();

             result = integer1 / integer2;


            stack.push(result);

         }
        else if (character.equals("%")) {
            integer2 = stack.pop();
            integer1 = stack.pop();


            result = integer1 % integer2;


            stack.push(result);
          }
         else if (character.equals("+")) {
            integer2 = stack.pop();
            integer1 = stack.pop();


            result = integer1 + integer2;


            stack.push(result);

         }
         else if (character.equals("-")) {
            integer2 = stack.pop();
            integer1 = stack.pop();

             result = integer1 - integer2;


            stack.push(result);

         }


      }
      return result;   
   }
}

这是我认为问题所在的代码部分（顺便说一句，我只推送和弹出整数）：

public static Integer postfixEvaluation(String input){




      StackInterface<Integer> stack = new LinkedStack<Integer>();

      Integer result = new Integer(0);



      for(int i=0;i<input.length();i++){

         String characterNum = input.substring(i, i+1);

         Integer integer1 = new Integer(0);
         Integer integer2 = new Integer(0);

        Integer character = (Integer.valueOf(characterNum));



         if (character.equals("0")) {
            stack.push(character);

         }
         else if (character.equals("1")) {
            stack.push(character);

         }
         else if (character.equals("2")) {
            stack.push(character);
         }
         else if (character.equals("3")) {
            stack.push(character);
         }
         else if (character.equals("4")) {
            stack.push(character);
         }
         else if (character.equals("5")) {
            stack.push(character);
         }
         else if (character.equals("6")) {
            stack.push(character);
         }
         else if (character.equals("7")) {
            stack.push(character);
         }
         else if (character.equals("8")) {
            stack.push(character);
         }
         else if (character.equals("9")) {
            stack.push(character);
         }
         else if (character.equals("*")) {
            integer2 = stack.pop();
            integer1 = stack.pop();


            result = integer1 * integer2;


            stack.push(result);



         }
        else if (character.equals("/")) {
            integer2 = stack.pop();
            integer1 = stack.pop();

             result = integer1 / integer2;


            stack.push(result);

         }
        else if (character.equals("%")) {
            integer2 = stack.pop();
            integer1 = stack.pop();


            result = integer1 % integer2;


            stack.push(result);
          }
         else if (character.equals("+")) {
            integer2 = stack.pop();
            integer1 = stack.pop();


            result = integer1 + integer2;


            stack.push(result);

         }
         else if (character.equals("-")) {
            integer2 = stack.pop();
            integer1 = stack.pop();

             result = integer1 - integer2;


            stack.push(result);

         }


      }
      return result;   
   }

Answer 1

您的问题是以下代码行：

Integer character = (Integer.valueOf(characterNum));

由于您正在尝试将任何字符转换为数字，并且您的字符串还包含运算符（无法转换为数字），因此出现异常。

你可能应该这样想：

我的字符是数字吗？

是 => 将其转换为数字并将其压入堆栈

否 => 它是一个操作数，因此从堆栈中弹出顶部的 2 个元素，执行操作并压入结果。

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