some cleanup

src/main/java/difflib/DiffUtils.java

@@ -29,7 +29,7 @@ import java.util.regex.Pattern;
  * @version 0.4.1
  * @param T The type of the compared elements in the 'lines'.
  */
-public class DiffUtils {
+public final class DiffUtils {
 
     private static Pattern unifiedDiffChunkRe = Pattern
             .compile("^@@\\s+-(?:(\\d+)(?:,(\\d+))?)\\s+\\+(?:(\\d+)(?:,(\\d+))?)\\s+@@$");
@@ -391,4 +391,6 @@ public class DiffUtils {
         return buffer;
     }
 
+    private DiffUtils() {
+    }
 }

src/main/java/difflib/StringUtills.java

@@ -19,7 +19,7 @@ import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
 
-public class StringUtills {
+public final class StringUtills {
 
     public static <T> String join(final Iterable<T> objs, final String delimiter) {
         Iterator<T> iter = objs.iterator();
@@ -93,4 +93,7 @@ public class StringUtills {
 
         return line;
     }
+    
+    private StringUtills() {
+    }
 }