[ONOS-3904] Derived data type and formatting fixes

Change-Id: I1d68899e0056fa0db6322e83f7e9d3ff9b3b1ee0
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/datamodel/YangStringRestriction.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/datamodel/YangStringRestriction.java
index 9cccaee..d2b6462 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/datamodel/YangStringRestriction.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/datamodel/YangStringRestriction.java
@@ -109,7 +109,19 @@
      *
      * @param patternRestriction pattern restriction for the type.
      */
-    public void setPatternRestriction(YangPatternRestriction patternRestriction) {
+    private void setPatternRestriction(YangPatternRestriction patternRestriction) {
         this.patternRestriction = patternRestriction;
     }
+
+    /**
+     * Add a new pattern restriction for the type.
+     *
+     * @param newPattern new pattern restriction for the type.
+     */
+    public void addPattern(String newPattern) {
+        if (getPatternRestriction() == null) {
+            setPatternRestriction(new YangPatternRestriction());
+        }
+        getPatternRestriction().addPattern(newPattern);
+    }
 }