Java凯撒密码

在这个凯撒密码中，我正在为大写字母获取不正确的输出。代码如下：Java凯撒密码

public class CaesarCipherCaseSensitive 
{ 
public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz"; 

public static String encrypt(String pt, int shiftKey) 
{ 
    String ct = ""; 
    for (int i = 0; i < pt.length(); i++) 
    { 
     int charPosition = ALPHABET.indexOf(pt.charAt(i)); 
     int keyVal = (shiftKey + charPosition) % 26; 
     char replaceVal = ALPHABET.charAt(keyVal); 
     ct += replaceVal; 
    } 
    return ct; 
} 

public static String decrypt(String ct, int shiftKey) 
{ 
    String pt = ""; 
    for (int i = 0; i < ct.length(); i++) 
    { 
     int charPosition = ALPHABET.indexOf(ct.charAt(i)); 
     int keyVal = (charPosition - shiftKey) % 26; 
     if (keyVal < 0) 
     { 
      keyVal = ALPHABET.length() + keyVal; 
     } 
     char replaceVal = ALPHABET.charAt(keyVal); 
     pt += replaceVal; 
    } 
    return pt; 
} 

public static void main(String[] args) 
{ 
    String message1 = "ABCDEFGHIJKLMOPQRSTUVWXYZ"; 
    System.out.println(encrypt(message1, 3)); 
    System.out.println(decrypt(encrypt(message1, 3), 3)); 
    System.out.println(encrypt(message1.toLowerCase(),5)); 
    System.out.println(decrypt(encrypt(message1.toLowerCase(),5),5)); 

} 
}

的输出如下所示： ccccccccccccccccccccccccc zzzzzzzzzzzzzzzzzzzzzzzzz fghijklmnopqrtuvwxyzabcde abcdefghijklmopqrstuvwxyz

所需的输出是： DEFGHIJKLMOPQRSTUVWXYZABC ABCDEFGHIJKLMOPQRSTUVWXYZ fghijklmnopqrtuvwxyzabcde abcdefghijklmopqrstuvwxyz

来源

2017-09-27 RaymondRay

只是一个小忠告：我会强烈建议您使用StringBuilder对象来连接地段的字符串，而不是使用“+ =”运算符。它会让你的代码更有效率。 – Discoverer98

问题是您正在将大写字母传递给方法indexOf()，该方法检查ALPHABET但未找到它，因此它返回-1。您需要将大写字母转换为小写字母，或者添加大写字母。

我的解决方案，改造大写字母为小写字母，然后加密/解密是：

public class CaesarCipherCaseSensitive{ 
public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz"; 

public static String encrypt(String pt, int shiftKey){ 
    String ct = ""; 
    for (int i = 0; i < pt.length(); i++){ 
     char letter = pt.charAt(i); 
     boolean upperCase = false; 
     if((int)letter < 91){ 
      letter = (char)((int)letter + 32); 
      upperCase = true; 
     } 
     int charPosition = ALPHABET.indexOf(letter); 
     int keyVal = (shiftKey + charPosition) % 26; 
     char replaceVal = ALPHABET.charAt(keyVal); 
     if(upperCase){ 
      replaceVal = (char)((int)replaceVal - 32); 
     } 
     ct += replaceVal; 
    } 
    return ct; 
} 

public static String decrypt(String ct, int shiftKey){ 
    String pt = ""; 
    for (int i = 0; i < ct.length(); i++){ 
     char letter = ct.charAt(i); 
     boolean upperCase = false; 
     if((int)letter < 91){ 
      letter = (char)((int)letter + 32); 
      upperCase = true; 
     } 
     int charPosition = ALPHABET.indexOf(letter); 
     int keyVal = (charPosition - shiftKey) % 26; 
     if (keyVal < 0){ 
      keyVal = ALPHABET.length() + keyVal; 
     } 
     char replaceVal = ALPHABET.charAt(keyVal); 
     if(upperCase){ 
      replaceVal = (char)((int)replaceVal - 32); 
     } 
     pt += replaceVal; 
    } 
    return pt; 
} 

public static void main(String[] args){ 
    String message1 = "ABCDEFGHIJKLMOPQRSTUVWXYZ"; 
    System.out.println(encrypt(message1, 3)); 
    System.out.println(decrypt(encrypt(message1, 3), 3)); 
    System.out.println(encrypt(message1.toLowerCase(),5)); 
    System.out.println(decrypt(encrypt(message1.toLowerCase(),5),5)); 
} 
}

来源

2017-09-27 02:39:12

Java凯撒密码

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