java - 程序未正确加密

Question

我正在开发一个接受用户输入的程序(输入 txt 文件、要移动的空格数、移动方向以及他们要创建的 output.txt 文件的名称)。我的程序正在编译，当我运行它时，它会创建一个输出文件，但是结果与它们应该的结果相去甚远。例如，如果我将它设置为使用 3 的移位进行加密并且方向是正确的，则单词 The 应该更改为 WKH。目前，我还没有实现这个方向，因为我似乎无法弄清楚我将如何做到向左移动。任何人都可以看看我的代码并帮助指导我走向正确的方向吗？非常感谢您的宝贵时间!

import java.util.*;
import java.io.*;

public class CaeserCipher {

  public static void main(String[] args)throws IOException {

        String originalText="";
        String inputFile;
        String outputFile = "";
        String shiftDirection;
        int shiftValue;
        Scanner keyboard = new Scanner(System.in);

        //Prompt user for input file name
       Scanner in = new Scanner(System.in);
       System.out.print("What is the filename?: ");
       inputFile = in.nextLine();


       //make sure file does not exist
            File file = new File(inputFile);
               if (!file.exists())
               {
                  System.out.println("\nFile " + inputFile + " does not exist. File could not be opened.");

                  System.exit(0);
               }

         //send the filename to be read into String

         originalText = readFile(inputFile);


         //Prompt user for shift value
         System.out.print("\nWhat is the shift value? ");
         shiftValue = keyboard.nextInt();

         //Prompt user for shift direction
         Scanner sc = new Scanner(System.in);
         System.out.print("What direction would you like to shift? Press L for left or R for right: ");

         //validate the input
         while (!sc.hasNext("[LR]")) {
             System.out.println("That's not a valid form of input! Please enter only the letter 'L' or 'R': ");
             sc.next();
             shiftDirection = sc.next(); //stores the validated direction
         }//end while

         shiftDirection = sc.next(); //stores the validated direction

         //Return encrypted string
         String encryptedText = encrypt(originalText , shiftValue);

         //get the outputfile name
         System.out.print("What is the name of the output file you want to create?: ");
         outputFile = in.nextLine();

         //make sure file does not exist
         File file2 = new File(outputFile);
            if (file2.exists())
            {
               System.out.println("\nFile " + outputFile + " already exists. Output not written.");

               System.exit(0);
            }

        try {
            File file3 = new File(outputFile);
            BufferedWriter output = new BufferedWriter(new FileWriter(file3));
            output.write(encryptedText);
            output.close();
        } catch ( IOException e ) {
            e.printStackTrace();
        }
        System.out.println("\nOutput written to " + outputFile);        

    } //end main

    //rotate and change chars
    public static String rotate(String userString, int shiftValue) {

        String convertedText = "";
        for(int i = 0; i < userString.length(); i++){
        char lowerLetter = userString.charAt(i);

        //Convert to uppercase
        char upperLetter = Character.toUpperCase(lowerLetter);
        int charNumber = upperLetter;

        //Apply shift, remembering to wrap text
        int rotateShift = (charNumber + shiftValue) % 26;
        char shiftLetter = (char) rotateShift;

        //Create new string of shifted chars
        convertedText += shiftLetter;
        }
      return convertedText;
    }

    //encrypt
    public static String encrypt(String userString, int shiftValue) {
        String encryptedString = rotate(userString , shiftValue);
        return encryptedString;
    }

    private static String readFile(String inputFile) throws java.io.IOException {
      File file = new File(inputFile);
      StringBuilder fileContents = new StringBuilder((int) file.length());
      Scanner scanner = new Scanner(new BufferedReader(new FileReader(file)));
      String lineSeparator = System.getProperty("line.separator");

         try {
             if (scanner.hasNextLine()) {
                 fileContents.append(scanner.nextLine());
             }
             while (scanner.hasNextLine()) {
                 fileContents.append(lineSeparator + scanner.nextLine());
             }

         return fileContents.toString();
    }


     finally {
        scanner.close();
    }

 }
}

Answer 1

您的问题是 %26。你没有考虑如何ASCII角色工作。您需要这样做:

int rotateShift = ((charNumber - 'A' + shiftValue) % 26) + 'A';

您之前的操作是错误的，因为 char 是一个 ASCII 值。这意味着 'A' == 65，因此要将字符表示形式转换为数字，您应该首先从字符值中减去 'A'。这映射 A->0, B->1, C->2, ...。然后当您完成 Caesar Shift 时，您需要将 'A' 的值加回整数以将其转回 ASCII 字符。

您可能还会遇到 Java 的 % 运算符的另一个问题。 Java 的模块化运算符操作如下:

-4 % 5 == -4

因此我会写一个加密的 mod 函数:

public int crypto_mod(int num, int mod)
{
    num %= mod;
    if(num < 0) num += mod;
    return num;
}

这应该会产生您要查找的字符。