Java 入門指南 V2.00 - 單元 17 範例




Encrypt.java


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public class Encrypt {
   // 密碼表字元陣列
   private char[] code = new char[26];
 
   // 建構子    
   public Encrypt() {
      setCode();
   }
 
   // setter
   public void setCode() {
      int a = 0;
      int b = 0;
 
      while (a % 2 == 0) {
         a = (int) (Math.random() * 10);
         b = (int) (Math.random() * 10);
      }
 
      int x, y, m, i;
      char c = 'a';
      for (i = 0; i < 26; i++) {
         x = c;
         y = x * a + b;
         m = y % 26;
         code[i] = (char) (m + 97);
         c++;
      }
   }
 
   // getter
   public char[] getCode() {
      return code;
   }
 
   // 編碼的方法
   public String toEncode(String s) {
      char[] cs = s.toCharArray();
      int i, ci, d, m;
      char r;
      String rs = "";
      Character cc;
          
      for (i = 0; i < cs.length; i++) {
         if (cs[i] >= 97 && cs[i] <= 122) {
            ci = cs[i];
            m = ci - 97;
            cs[i] = code[m];
         }
      }
          
      for (i = 0; i < cs.length; i++) {
         cc = new Character(cs[i]);
         rs = rs.concat(cc.toString());
      }
          
      return rs;
   }
 
   // 解碼的方法
   public String toDecode(String s) {
      char[] cs = s.toCharArray();
      int i, j;
      char r;
      String rs = "";
      Character cc;
          
      for (i = 0; i < cs.length; i++) {
         if (cs[i] >= 97 && cs[i] <= 122) {
            for (j = 0; j <= code.length; j++) {
               if (cs[i] == code[j]) {
                  cs[i] = (char) (j + 97);
                   break;
               }
            }
         }
      }
  
      for (i = 0; i < cs.length; i++) {
         cc = new Character(cs[i]);
         rs = rs.concat(cc.toString());
      }
          
      return rs;      
   }
 
   // 測試的 main()
   public static void main(String[] args) {
      Encrypt e = new Encrypt();
      System.out.println(e.getCode());
      String s = "There is no spoon";
      System.out.println(s);
      String s1 = e.toEncode(s);
      System.out.println(s1);
      String s2 = e.toDecode(s1);
      System.out.println(s2);
   }
}
  
/* 檔名： Encrypt.java
   作者： Kaiching Chang
   時間： September, 2014  */

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