Question

我是Java新手，我尝试编写Caesar密码包括大写和小写字符。我不知道为什么编码错误。有人帮助我，我很感激它感谢一百万。这是我到目前为止的代码。

public class CaesarCipher{

    char[] encoder = new char[52]; 
    char[] decoder = new char[52]; 

     public CaesarCipher(int rotation) 
     {
       for(int k=0 ; k < 26 ; k++)
       {
           encoder[k] = (char) ('A' + (k + rotation) % 26);
           decoder[k] = (char) ('A' + (k - rotation + 26) % 26); 
       }
       for(int j = 26 ; j < 52 ; j++ )
       {
           encoder[j] = (char)('a' + (j + rotation) % 26); 
           decoder[j] = (char)('a' + (j - rotation) % 26); 
       }
     }

     public String encrypt(String message) { 
         char[] msg = message.toCharArray();
         for(int i = 0 ; i < msg.length ; i++){
            if(Character.isUpperCase(msg[i])){
                msg[i] = encoder[msg[i] - 'A'];
            }   
            else{
                int n = msg[i] - 'a' ;
                msg[i] = encoder[26 + n];
            }
         }
         return new String(msg); 
     }

     public String decrypt(String secret) { 
        char[] msg = secret.toCharArray();
         for(int i = 0 ; i < msg.length ; i++){
            if(Character.isUpperCase(msg[i])){
                msg[i] = decoder[msg[i] - 'A'];
            }   
            else{
                 int n = msg[i] - 'a';
                msg[i] = decoder[26 + n];
            }
         }
         return new String(msg); 
     }


  public static void main(String[] args) {
    CaesarCipher cipher = new CaesarCipher(3);
    String message = "There Is an APPle";
    String coded = cipher.encrypt(message);
    System.out.println("Secret:  " + coded);
    String answer = cipher.decrypt(coded);
    System.out.println("Message: " + answer);         
  }
}

Answer 1

运行我的代码

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Array index out of range: -39
  at t1.CaesarCipher.encrypt(CaesarCipher.java:30)
  at t1.CaesarCipher.main(CaesarCipher.java:54)

此时正在执行的代码是

            int n = msg[i] - 'a' ;
            msg[i] = encoder[26 + n];

我是5，但你的输入数据是＆＃34;有一个APPle＆＃34;

索引5处的字符是一个空格，但您正在尝试减去＆＃39; a＆＃39;从中获得负面指数。

凯撒密码包括大写和小写字符

1 个答案: