RPN计算器 java代码

RPN计算器 Program Input Each line of the input file (prob12.in) contains a series of numbers and operators. The program must evaluate these lines as RPN expressions. All tokens are separated by one or more spaces. Numbers may be negative. Valid operators are +(addition), -(subtraction), *(multiplication) and /(division). The last line of the file contains only the word END: 16 3 7 + * 4 32.125 13 – * 20 + 5 –3 * 4 2 / 6 3 1 – / + + END Program Output The program will print the computed result of each RPN expression on a separate line. 160 96.5 -10

import java.io.*;
import java.util.*;

public class RPNcalculator {
public static void main（String[] args） {

    String fileName=“RPNInput.txt“;
    String fileName2=“RPNOutput.txt“;
    Scanner inputStream = null;
    PrintWriter outputStream = null;

    //read
    try{
        inputStream = new Scanner（new File（fileName））; //try to open the file
    }
    catch（Exception e）{
        System.out.println（“Could not open the file named “+ fileName）; // if it doesn‘t find it tell them
        System.exit（0）;  // and then exit.
    }

    //write
    try{
        outputStream = new PrintWriter（new FileOutputStream（fileName2true））; //try to create the file
    }
    catch（Exception e）{
        System.out.println（“Could not open the file named “+ fileName2）; // if it doesn‘t find it tell them
        System.exit（0）;  // and then exit.
    }

    while（inputStream.hasNextLine（））{
        String equation = inputStream.nextLine（）;
        if （equation==null）  break;
        Stack tks = new Stack