凯撒密码设计——Java

package java1;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;


public class java1_1{
	
	StringBuffer Str1 = new StringBuffer("");
	StringBuffer Str2 = new StringBuffer("");
	
	public static void main(String[] args) {
		while(true)
		{
		Scanner s = new Scanner(System.in);
		System.out.print("请输入密钥：");
		int key = s.nextInt()%26;//给密钥设置了偏移值
		java1_1 ks = new java1_1();
		System.out.print("选择加密按1，解密按2:");
		int a = s.nextInt();
		switch (a)
	      {  case 1:
	    	  ks.E(key);
	            break;
	         case 2:
	         ks.D(key);
	            break;
	      }
		}
	}
	 void E(int k) {
		try {
			System.out.println("请输入一段明文：");
			char b[];
			BufferedReader br2 = new BufferedReader(new InputStreamReader(System.in));
			String str2 = br2.readLine();
			b = str2.toCharArray();
			char ch = ' ';
			for (int i = 0; i < str2.length(); i++) {
				if (b[i] >= 'a' && b[i] <= 'z') {
					ch = (char) ((b[i] - 'a' + k) % 26 + 'a');
				}
				if(b[i] >= 'A' && b[i] <= 'Z'){
					ch = (char) ((b[i] - 'A' + k) % 26 + 'A');
				}
				Str1.append(ch);
			}
			System.out.println("密文为："+Str1+"密匙为：" + k);
		} catch (IOException e) {
			System.out.println(e.getMessage());
		}
	}
	void D(int k) {
		try {
			System.out.println("请输入一段密文：");
			char b[];
			BufferedReader br2 = new BufferedReader(new InputStreamReader(System.in));
			String str2 = br2.readLine();
			b = str2.toCharArray();
			char ch = ' ';
			for (int i = 0; i < str2.length(); i++) {
				if (b[i] >= 'a' && b[i] <= 'z') {
					ch = (char) ((b[i] - 'a' - k +26) % 26 + 'a');
				}
				if(b[i] >= 'A' && b[i] <= 'Z'){
					ch = (char) ((b[i] - 'A' - k +26) % 26 + 'A');
				}
				Str1.append(ch);
			}
			System.out.println("明文为："+Str1+"密匙为：" + k);
		} catch (IOException e) {
			System.out.println(e.getMessage());
		}
	}
}