凯撒加密

import java.io.*;  
import java.util.Scanner;   
public class KaiSa1{   
     public static void main(String[] args){   
         System.out.print("请输入密钥：");   
         Scanner s=new Scanner(System.in);   
         int a=s.nextInt();
         C(a);  
     }    
public static void C(int n){   
     try{      
        char b[];        
        BufferedReader br2=new BufferedReader(new InputStreamReader(System.in));          
        System.out.println("请输入一段明文：");         
        String str2=br2.readLine();         
        b=str2.toCharArray();            
        System.out.println("密文为：");         
        int k=n;         
        for(int i=0;i<str2.length();i++)
        {
            char ch=(char)((b[i]-‘a‘+k)%26+‘a‘);
            System.out.print(ch);
        }
            System.out.println("密匙K="+k);  
        }
        catch(IOException e){
            System.out.println(e.getMessage());   
        }
  }
}