java凯撒密码加密解密算法

以下是Java中实现凯撒密码加密解密算法的示例代码：

public class CaesarCipher {
    // 加密函数
    public static String encrypt(String plaintext, int shift) {
        StringBuilder ciphertext = new StringBuilder();
        for (int i = 0; i < plaintext.length(); i++) {
            char ch = plaintext.charAt(i);
            if (Character.isLetter(ch)) {
                if (Character.isUpperCase(ch)) {
                    char encryptedChar = (char) ((ch - 'A' + shift) % 26 + 'A');
                    ciphertext.append(encryptedChar);
                } else {
                    char encryptedChar = (char) ((ch - 'a' + shift) % 26 + 'a');
                    ciphertext.append(encryptedChar);
                }
            } else {
                ciphertext.append(ch);
            }
        }
        return ciphertext.toString();
    }

    // 解密函数
    public static String decrypt(String ciphertext, int shift) {
        StringBuilder plaintext = new StringBuilder();
        for (int i = 0; i < ciphertext.length(); i++) {
            char ch = ciphertext.charAt(i);
            if (Character.isLetter(ch)) {
                if (Character.isUpperCase(ch)) {
                    char decryptedChar = (char) ((ch - 'A' - shift + 26) % 26 + 'A');
                    plaintext.append(decryptedChar);
                } else {
                    char decryptedChar = (char) ((ch - 'a' - shift + 26) % 26 + 'a');
                    plaintext.append(decryptedChar);
                }
            } else {
                plaintext.append(ch);
            }
        }
        return plaintext.toString();
    }

    public static void main(String[] args) {
        String plaintext = "Hello, World!";
        int shift = 3;

        String ciphertext = encrypt(plaintext, shift);
        System.out.println("Encrypted text: " + ciphertext);

        String decryptedText = decrypt(ciphertext, shift);
        System.out.println("Decrypted text: " + decryptedText);
    }
}