import java.util.HashMap;
import java.util.Map;

/**

• Created by mahuichao on 16/8/18.
  */
  public class Test {
  public static final int number = 2756;
  public static final String str = "bcea";

  public static void main(String[] args) {

  String enStr = encode(number);
  System.out.println("加密的结果为:" + enStr);
  int deNum = decode(str);
  System.out.println("解密后的结果为:" + deNum);
  

  }

  public static String encode(int number) {
  Map map = encode_rules();

  String strNum = String.valueOf(number);
  String result = "";
  char[] chNum = strNum.toCharArray();
  for (int i = 0; i < chNum.length; i++) {
      result += map.get(Integer.parseInt(chNum[i] + ""));
  }
  return result;
  

  }

  public static int decode(String number) {
  Map map = decode_rules();
  String result = "";
  char[] chNum = number.toCharArray();
  for (int i = 0; i < chNum.length; i++) {
  result += map.get(chNum[i] + "");
  }
  int finalResult = Integer.parseInt(result);
  return finalResult;
  }

  public static Map encode_rules() {
  Map map = new HashMap();
  map.put(0, "a");
  map.put(1, "b");
  map.put(2, "c");
  map.put(3, "d");
  map.put(4, "e");
  map.put(5, "f");
  map.put(6, "g");
  map.put(7, "h");
  map.put(8, "i");
  map.put(9, "j");

  return map;
  

  }

  public static Map decode_rules() {
  Map map = new HashMap();
  map.put("a", "0");
  map.put("b", "1");
  map.put("c", "2");
  map.put("d", "3");
  map.put("e", "4");
  map.put("f", "5");
  map.put("g", "6");
  map.put("h", "7");
  map.put("i", "8");
  map.put("j", "9");

  return map;
  

  }

}

你这就是数字和小写字母的ascii码差值了，附代码：

    private int span = 49;  // 差值

public String encode(long num) {
    char[] chars = String.valueOf(num).toCharArray();
    for(int i = 0; i< chars.length; i++) {
        chars[i] += 49;
    }
    return String.valueOf(chars);
}

public long decode(String cipher) {
    char[] chars = cipher.toCharArray();
    for(int i = 0; i< chars.length; i++) {
        chars[i] -= 49;
    }
    return Long.parseLong(String.valueOf(chars));
}

这个太简单，破解基本不费力；为何不选择现成的对称加密算法，比如DES啥的。