2. Java编写一个加密程序，要求从键盘输入一个字符串，然后输出加密后的字符串。加密规则是对每个字母转换为下一个字母表示，原来是a转换为b，原来是B转换为C，原来是z转换为a，原来是Z转换为A。比如：输入I like math.输出J mjlf nbui.再写出此程序的解密程序

加密程序代码：

import java.util.Scanner;

public class Encrypt {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入要加密的字符串：");
        String plaintext = scanner.nextLine();

        StringBuilder ciphertext = new StringBuilder();
        for (int i = 0; i < plaintext.length(); i++) {
            char c = plaintext.charAt(i);
            if (c >= 'a' && c < 'z' || c >= 'A' && c < 'Z') {
                c++;
            } else if (c == 'z') {
                c = 'a';
            } else if (c == 'Z') {
                c = 'A';
            }
            ciphertext.append(c);
        }

        System.out.println("加密后的字符串为：" + ciphertext);
    }
}

解密程序代码：

import java.util.Scanner;

public class Decrypt {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入要解密的字符串：");
        String ciphertext = scanner.nextLine();

        StringBuilder plaintext = new StringBuilder();
        for (int i = 0; i < ciphertext.length(); i++) {
            char c = ciphertext.charAt(i);
            if (c > 'a' && c <= 'z' || c > 'A' && c <= 'Z') {
                c--;
            } else if (c == 'a') {
                c = 'z';
            } else if (c == 'A') {
                c = 'Z';
            }
            plaintext.append(c);
        }

        System.out.println("解密后的字符串为：" + plaintext);
    }
}

运行程序时，先运行加密程序，再用加密后的字符串作为解密程序的输入，即可得到原始字符串。