java - 为什么我的凯撒密码只能以小写形式工作

Question

我是 JAVA 编程新手，我正在尝试创建一个凯撒密码加密/解密程序。不幸的是，我的程序仅适用于小写字母。我看不出我哪里出了问题，我尝试检查我的代码好几次，但我似乎无法找出问题所在。这是到目前为止我的代码:

import java.util.Scanner;                                                                                                         

public class CaesarCipher {                                                                                                       

    public static String encrypt(String plainText, int shift) {                                                                   
        if (shift > 26) {                                                                                                         
            shift = shift % 26;                                                                                                   
        } else if (shift < 0) {                                                                                                   
            shift = (shift % 26) + 26;                                                                                            
        }                                                                                                                         

        String cipherText = "";                                                                                                   
        int length = plainText.length();                                                                                          

        for (int i = 0; i < length; i++) {                                                                                        
            char ch = plainText.charAt(i);                                                                                        

            if (Character.isLetter(ch)) {                                                                                         
                if (Character.isLowerCase(ch)) {                                                                                  
                    char c = (char) (ch + shift);                                                                                 
                    if (c > 'z') {                                                                                                
                        cipherText += (char) (ch - (26 - shift));                                                                 
                    } else {                                                                                                      
                        cipherText += c;                                                                                          
                    }                                                                                                             
                } else if (Character.isUpperCase(ch)) {                                                                           
                    char c = (char) (ch + shift);                                                                                 
                    if (c > 'Z') {                                                                                                
                        cipherText += (char) (ch - (26 - shift));                                                                 
                    } else {                                                                                                      
                        cipherText += c;                                                                                          
                    }                                                                                                             
                }                                                                                                                 
            } else {                                                                                                              
                cipherText += ch;                                                                                                 
            }                                                                                                                     
        }                                                                                                                         
        return cipherText;                                                                                                        

    }                                                                                                                             

    // Decrypt                                                                                                                    
    public static String decrypt(String plainText, int shift) {                                                                   
        if (shift > 26) {                                                                                                         
            shift = shift % 26;                                                                                                   
        } else if (shift < 0) {                                                                                                   
            shift = (shift % 26) + 26;                                                                                            
        }                                                                                                                         

        String cipherText = "";                                                                                                   
        int length = plainText.length();                                                                                          

        for (int i = 0; i < length; i++) {                                                                                        
            char ch = plainText.charAt(i);                                                                                        

            if (Character.isLetter(ch)) {                                                                                         
                if (Character.isLowerCase(ch)) {                                                                                  
                    char c = (char) (ch - shift);                                                                                 
                    if (c < 'a') {                                                                                                
                        cipherText += (char) (ch + (26 - shift));                                                                 
                    } else {                                                                                                      
                        cipherText += c;                                                                                          
                    }                                                                                                             
                } else if (Character.isUpperCase(ch)) {                                                                           
                    char c = (char) (ch + shift);                                                                                 
                    if (c < 'A') {                                                                                                
                        cipherText += (char) (ch + (26 - shift));                                                                 
                    } else {                                                                                                      
                        cipherText += c;                                                                                          
                    }                                                                                                             
                }                                                                                                                 
            } else {                                                                                                              
                cipherText += ch;                                                                                                 
            }                                                                                                                     
        }                                                                                                                         
        return cipherText;                                                                                                        

    }                                                                                                                             

    public static void main(String[] args) {                                                                                      
        Scanner input1 = new Scanner(System.in);                                                                                  
        Scanner input2 = new Scanner(System.in);                                                                                  
        System.out.print("Enter your phrase: ");                                                                                  
        String inputPlainText = input1.nextLine();                                                                                
        System.out.print("Enter your shift: ");                                                                                   
        int shiftForPlainText = input1.nextInt();                                                                                 
        String convertPlainText = encrypt(inputPlainText, shiftForPlainText);                                                     
        System.out.println(convertPlainText);                                                                                     

        System.out.print("Enter ciphertext: ");                                                                                   
        String inputCipherText = input2.nextLine();                                                                               
        System.out.print("Enter shift: ");                                                                                        
        int shiftForCipherText = input2.nextInt();                                                                                
        String convertCipherText = decrypt(inputCipherText, shiftForCipherText);                                                  
        System.out.println(convertCipherText);                                                                                    

    }                                                                                                                             
}                                                                                                                                 

Answer 1

在 decrypt 方法中，对于小写字母，您可以编写:

char c = (char)(ch-shift);

对于大写字母，你可以写:

char c = (char)(ch+shift);

我非常确定这两行在 ch 和 shift 之间应该具有相同的运算符。如果您不想犯这样的错误，请尝试重构您的代码，以免出现重复的行。