实现单字母密码的Java程序

单字母密码是一种密码，其中基于单个字母密钥将明文字母映射为密文字母。它是一对一的映射。

给定纯文本，任务是实现单字母密码。

例子：

Input:  Welcome to geeksforgeeks
Output: Plain text: Welcome to geeksforgeeks
        Encrypted message: VTSEGDT ZG UTTALYGKUTTAL
        Decrypted message: welcome to geeksforgeeks

Input:  Live the moment
Output: Plain text: Live the moment
        Encrypted message: SOCT ZIT DGDTFZ
        Decrypted message: live the moment

将字符映射到我们在代码中使用的密文字母：

a	b	c	d	e	f	g	h	i	j
Q	W	E	R	T	Y	U	I	O	P
k	l	m	n	o	p	q	r	s	t
A	S	D	F	G	H	J	K	L	Z
u	v	w	x	y	z
X	C	V	B	N	M

输出说明：

W – w – V	t – Z	g – U	g – U
e – T	o – G	e – T	e – T
l – S		e – T	e – T
c – E		k – A	k – A
o – G		s – L	s – L
m – D		f – Y
e – T		o – G
		r – K

欢迎来到 geeksforgeeks → VTSEGDT ZG UTTALYGKUTTAL

方法：

1.创建两个字符数组，一个用于普通字母表（比如 normalChar[]），另一个用于编码（比如 codedChar[]）。

2.我们将使用两个函数：

• stringEncryption：我们将字符串（所有字符均为小写的字符串）作为参数传递。初始化一个空字符串（比如 encryptedString ） 。我们使用 for 循环，将每个字符与普通的 char 数组进行比较，只要条件为真，就将具有 codedChar 对应索引的字符添加到加密字符串中。对于特殊字符，我们将它们直接添加到字符串中。
• stringDescryption：我们将加密的字符串作为参数传递。初始化一个空字符串（比如 descryptedString）。同理，我们运行for循环，将对应索引为normalChar的字符添加到解密后的字符串中。对于特殊字符，我们将它们直接添加到字符串中。

下面是上述方法的实现：

Java

// Java Program to Implement the Monoalphabetic Cypher
 
import java.io.*;
class GFG {
    public static char normalChar[]
        = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
            'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
            's', 't', 'u', 'v', 'w', 'x', 'y', 'z' };
 
    public static char codedChar[]
        = { 'Q', 'W', 'E', 'R', 'T', 'Y', 'U', 'I', 'O',
            'P', 'A', 'S', 'D', 'F', 'G', 'H', 'J', 'K',
            'L', 'Z', 'X', 'C', 'V', 'B', 'N', 'M' };
 
    // Function which returns encrypted string
    public static String stringEncryption(String s)
    {
        // initializing an empty String
        String encryptedString = "";
 
        // comparing each character of the string and
        // encoding each character using the indices
        for (int i = 0; i < s.length(); i++) {
            for (int j = 0; j < 26; j++) {
 
                // comparing the character and
                // adding the corresponding char
                // to the encryptedString
                if (s.charAt(i) == normalChar[j])
                {
                    encryptedString += codedChar[j];
                    break;
                }
 
                // if there are any special characters
                // add them directly to the string
                if (s.charAt(i) < 'a' || s.charAt(i) > 'z')
                {
                    encryptedString += s.charAt(i);
                    break;
                }
            }
        }
 
        // return encryptedString
        return encryptedString;
    }
 
    // Function which returns descryptedString
    public static String stringDecryption(String s)
    {
 
        // Initializing the string
        String decryptedString = "";
 
        // Run the for loop for total string
        for (int i = 0; i < s.length(); i++)
        {
            for (int j = 0; j < 26; j++) {
 
                // compare each characters and decode them
                // using indices
                if (s.charAt(i) == codedChar[j])
                {
                    decryptedString += normalChar[j];
                    break;
                }
 
                // Add the special characters directly to
                // the String
                if (s.charAt(i) < 'A' || s.charAt(i) > 'Z')
                {
                    decryptedString += s.charAt(i);
                    break;
                }
            }
        }
 
        // return the decryptedString
        return decryptedString;
    }
    public static void main(String args[])
    {
        String str = "Welcome to geeksforgeeks";
 
        // print plain text
        System.out.println("Plain text: " + str);
 
        // Changing whole string to lower case
        // function call to stringEncryption and storing in
        // encryptedString
        String encryptedString = stringEncryption(str.toLowerCase());
 
        // printing encryptedString
        System.out.println("Encrypted message: "
                           + encryptedString);
 
        // function call to stringDecryption and printing
        // the decryptedString
        System.out.println("Decrypted message: "
            + stringDecryption(encryptedString));
       
    }
}

输出

Plain text: Welcome to geeksforgeeks
Encrypted message: VTSEGDT ZG UTTALYGKUTTAL
Decrypted message: welcome to geeksforgeeks