[ONOS-4149],[ONOS-3909] YANG list translator impl and bug fixes.

Change-Id: Ia1a94142a3a114815766f661ed850bf9cacde66f
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/io/impl/YangFileScanner.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/io/impl/YangFileScanner.java
index 54adce9..9de5358 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/io/impl/YangFileScanner.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/io/impl/YangFileScanner.java
@@ -23,10 +23,13 @@
 import java.util.Stack;
 
 /**
- * Provides the IO services for Yangutils-maven-Plugin.
+ * Provides utility for searching the files in a directory.
  */
 public final class YangFileScanner {
 
+    private static final String JAVA_FILE_EXTENTION = ".java";
+    private static final String YANG_FILE_EXTENTION = ".yang";
+
     /**
      * Default constructor.
      */
@@ -44,7 +47,7 @@
      */
     public static List<String> getJavaFiles(String root) throws NullPointerException, IOException {
 
-        return getFiles(root, ".java");
+        return getFiles(root, JAVA_FILE_EXTENTION);
     }
 
     /**
@@ -58,7 +61,7 @@
      */
     public static List<String> getYangFiles(String root) throws NullPointerException, IOException {
 
-        return getFiles(root, ".yang");
+        return getFiles(root, YANG_FILE_EXTENTION);
     }
 
     /**
@@ -68,8 +71,7 @@
      * @param extension file extension
      * @return list of required files
      * @throws NullPointerException when no file is there
-     * @throws IOException when files get deleted while performing the
-     *             operations
+     * @throws IOException when files get deleted while performing the operations
      */
     public static List<String> getFiles(String root, String extension) throws NullPointerException, IOException {