diff --git a/src/main/java/me/hatter/tools/secureeditor/Main.java b/src/main/java/me/hatter/tools/secureeditor/Main.java
index 1fedb94..cc9b063 100644
--- a/src/main/java/me/hatter/tools/secureeditor/Main.java
+++ b/src/main/java/me/hatter/tools/secureeditor/Main.java
@@ -191,13 +191,13 @@ public class Main {
     }
 
     private static byte[] string2Bytes(String str) {
-        int len = str.length();
+        final int len = str.length();
         if ((len % 2) != 0) {
             throw new RuntimeException("String format error: " + str);
         }
-        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        final ByteArrayOutputStream baos = new ByteArrayOutputStream();
         for (int i = 0; i < len; i++) {
-            String substr = new String(new char[]{str.charAt(i++), str.charAt(i)});
+            final String substr = new String(new char[]{str.charAt(i++), str.charAt(i)});
             baos.write((byte) Integer.parseInt(substr, 16));
         }
         return baos.toByteArray();