package Case.Encryption;import java.util.*;public abstract class Cipher {/**  * 所有的加密技术的基本操作都是用encrypt（）和decrypt（）方法对消息 * 进行分解和组合，其中消息是用空格分隔的字符串，除了encrypt（）和decrypt（） * 外每个加密类还需要encode（）和decode（）方法对每一个单词按照特定的算法 * 规则进行编码，。例如Caesar Cipher 和 Transpose Clipher *   按照设想由于加密都有相同的方法，因此首先定义一个通用的类Cipher类 *   封装公用的方法。 *  * */  public String encrypt(String s){            StringBuffer result=new StringBuffer();      StringTokenizer words=new StringTokenizer(s);      while(words.hasMoreTokens()){          result.append(encode(words.nextToken())+"");      }      return result.toString();  }  public String decrypt(String s)  {      StringBuffer result=new StringBuffer();      StringTokenizer words=new StringTokenizer(s);      while(words.hasMoreTokens())      {          result.append(decode(words.nextToken())+"");                }      return result.toString();              }  public abstract String encode(String word);  public abstract String decode(String woid);    }

package Case.Encryption;public class Caesar extends Cipher{    @Override    public String encode(String word) {        // TODO Auto-generated method stub        StringBuffer result =new StringBuffer();        for(int k=0;k<word.length();k++)        {            char ch=word.charAt(k);            ch=(char)(‘a‘+(ch-‘a‘+3)%26);//?正则表达式            result.append(ch);        }        return result.toString();    }    @Override    public String decode(String word) {        // TODO Auto-generated method stub        StringBuffer result =new StringBuffer();        for(int k=0;k<word.length();k++)        {            char ch=word.charAt(k);            ch=(char)(‘a‘+(ch-‘a‘+23)%26);//?正则表达式            result.append(ch);        }        return result.toString();    }}

package Case.Encryption;/**本例采用的是最简单的翻转易位方法，也可以采用其他的易位方法*/public class Transpose extends Cipher{    @Override    public String encode(String word) {        // TODO Auto-generated method stub        StringBuffer result =new StringBuffer();                return result.reverse().toString();    }    @Override    public String decode(String word) {        // TODO Auto-generated method stub        return encode(word);    }    }

 1 package Case.Encryption; 2  3 public class TestEncrypt { 4     public static void main(String[] args) { 5         Caesar caesar =new Caesar(); 6         String plain ="this is the secret message."; 7         String secret=caesar.encrypt(plain); 8         String decrypt=caesar.decrypt(secret); 9         System.out.println("*********Caesar Cipher Encryption**********");10         System.out.println("PlainText: "+plain);11         System.out.println("Encrypted: "+secret);12         System.out.println("Decrypted: "+decrypt);13         14         Transpose ts=new Transpose();15         String tsecret=ts.encrypt(plain);16         String tdecrypt=ts.decrypt(secret);17         System.out.println("**********Transpose Cipher Encryption**********");18         System.out.println("PlainText: "+plain);19         System.out.println("Encrypted: "+tsecret);20         System.out.println("Decrypted: "+tdecrypt);21     }22 23 }