epiphany refactor

Crypto/src/ROT13.java

-import java.util.*;
-
 public class ROT13  {
-    private int shift;
-    private Map<Character, Character> cypher = new HashMap<>();
+    private String cryptKey;
+    private String alphabet = "abcdefghijklmnopqrstuvwxyz";
+
 
     ROT13(Character cs, Character cf) {
-        shift = Math.abs((int)cs - (int)cf);
-        setupHM();
+        int index = Math.abs((int)cs - (int)cf);
+        cryptKey = rotate(alphabet, alphabet.charAt(index));
     }
 
-    ROT13(){}
-
-    public void setupHM() {
-        String alphabet = "abcdefghijklmnopqrstuvwxyz";
-
-        for(Character c : alphabet.toCharArray()) {
-            int offset = (int)c + shift > 122 ? (int)c - shift : (int)c  + shift;
-            cypher.put(c, (char)offset);
-        }
-    }
+    ROT13(){ cryptKey = rotate(alphabet, 'n'); }
 
     public String crypt(String text) throws UnsupportedOperationException {
         StringBuilder result = new StringBuilder();
         for(Character c : text.toCharArray()) {
             if (Character.isLetter(c)) {
                 if (Character.isUpperCase(c)) {
-                    result.append(Character.toUpperCase(cypher.get(Character.toLowerCase(c))));
+                    result.append(Character.toUpperCase(cryptKey.charAt(alphabet.indexOf(Character.toLowerCase(c)))));
                 }
-                else result.append(cypher.get(c));
+                else result.append(cryptKey.charAt(alphabet.indexOf(c)));
             }
             else result.append(c);
         }
     public static String rotate(String s, Character c) {
         return s.substring(s.indexOf(c)) + s.substring(0, s.indexOf(c));
     }
-
 }