diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseFileListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseFileListener.java
index 368f2af..527ce08 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseFileListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseFileListener.java
@@ -78,8 +78,8 @@
         checkStackIsNotEmpty(listener, MISSING_HOLDER, YANGBASE_DATA, "", EXIT);
 
         // Data Model tree root node is set.
-        if (listener.getParsedDataStack().peek() instanceof YangModule
-                || listener.getParsedDataStack().peek() instanceof YangSubModule) {
+        if ((listener.getParsedDataStack().peek() instanceof YangModule)
+                || (listener.getParsedDataStack().peek() instanceof YangSubModule)) {
             listener.setRootNode((YangNode) listener.getParsedDataStack().pop());
         } else {
             throw new ParserException(constructListenerErrorMessage(INVALID_CHILD, YANGBASE_DATA, "", EXIT));
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BelongsToListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BelongsToListener.java
index aec6562..fc9793f 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BelongsToListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BelongsToListener.java
@@ -77,11 +77,11 @@
                                              GeneratedYangParser.BelongstoStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, BELONGS_TO_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, BELONGS_TO_DATA, ctx.IDENTIFIER().getText(),
                              ENTRY);
 
         YangBelongsTo belongstoNode = new YangBelongsTo();
-        belongstoNode.setBelongsToModuleName(String.valueOf(ctx.IDENTIFIER().getText()));
+        belongstoNode.setBelongsToModuleName(ctx.IDENTIFIER().getText());
 
         // Push belongsto into the stack.
         listener.getParsedDataStack().push(belongstoNode);
@@ -98,7 +98,7 @@
                                             GeneratedYangParser.BelongstoStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, BELONGS_TO_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, BELONGS_TO_DATA, ctx.IDENTIFIER().getText(),
                              EXIT);
 
         Parsable tmpBelongstoNode = listener.getParsedDataStack().peek();
@@ -107,7 +107,7 @@
 
             // Check for stack to be empty.
             checkStackIsNotEmpty(listener, MISSING_HOLDER, BELONGS_TO_DATA,
-                                 String.valueOf(ctx.IDENTIFIER().getText()), EXIT);
+                                 ctx.IDENTIFIER().getText(), EXIT);
 
             Parsable tmpNode = listener.getParsedDataStack().peek();
             switch (tmpNode.getParsableDataType()) {
@@ -118,12 +118,12 @@
             }
             default:
                 throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, BELONGS_TO_DATA,
-                                                                        String.valueOf(ctx.IDENTIFIER().getText()),
+                                                                        ctx.IDENTIFIER().getText(),
                                                                         EXIT));
             }
         } else {
             throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, BELONGS_TO_DATA,
-                                                                    String.valueOf(ctx.IDENTIFIER().getText()), EXIT));
+                                                                    ctx.IDENTIFIER().getText(), EXIT));
         }
     }
 }
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContactListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContactListener.java
index aed2b5e..53c86cb 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContactListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContactListener.java
@@ -92,24 +92,24 @@
     public static void processContactEntry(TreeWalkListener listener, GeneratedYangParser.ContactStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, CONTACT_DATA, String.valueOf(ctx.string().getText()), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, CONTACT_DATA, ctx.string().getText(), ENTRY);
 
         // Obtain the node of the stack.
         Parsable tmpNode = listener.getParsedDataStack().peek();
         switch (tmpNode.getParsableDataType()) {
         case MODULE_DATA: {
             YangModule module = (YangModule) tmpNode;
-            module.setContact(String.valueOf(ctx.string().getText()));
+            module.setContact(ctx.string().getText());
             break;
         }
         case SUB_MODULE_DATA: {
             YangSubModule subModule = (YangSubModule) tmpNode;
-            subModule.setContact(String.valueOf(ctx.string().getText()));
+            subModule.setContact(ctx.string().getText());
             break;
         }
         default:
             throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, CONTACT_DATA,
-                                                                    String.valueOf(ctx.string().getText()), ENTRY));
+                                                                    ctx.string().getText(), ENTRY));
         }
     }
 }
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DefaultListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DefaultListener.java
new file mode 100644
index 0000000..f500cca
--- /dev/null
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DefaultListener.java
@@ -0,0 +1,88 @@
+/*
+ * Copyright 2014-2016 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * typedef-stmt        = typedef-keyword sep identifier-arg-str optsep
+ *                       "{" stmtsep
+ *                           ;; these stmts can appear in any order
+ *                           type-stmt stmtsep
+ *                          [units-stmt stmtsep]
+ *                           [default-stmt stmtsep]
+ *                           [status-stmt stmtsep]
+ *                           [description-stmt stmtsep]
+ *                           [reference-stmt stmtsep]
+ *                         "}"
+ * default-stmt        = default-keyword sep string stmtend
+
+ *
+ * ANTLR grammar rule
+ * typedefStatement : TYPEDEF_KEYWORD IDENTIFIER LEFT_CURLY_BRACE
+ *                (typeStatement | unitsStatement | defaultStatement | statusStatement
+ *                | descriptionStatement | referenceStatement)* RIGHT_CURLY_BRACE;
+ * defaultStatement : DEFAULT_KEYWORD string STMTEND;
+ */
+
+import org.onosproject.yangutils.datamodel.YangTypeDef;
+import org.onosproject.yangutils.parser.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.parser.ParsableDataType.DEFAULT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+public final class DefaultListener {
+
+    /**
+     * Creates a new default listener.
+     */
+    private DefaultListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (default), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object.
+     * @param ctx context object of the grammar rule.
+     */
+    public static void processDefaultEntry(TreeWalkListener listener,
+            GeneratedYangParser.DefaultStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, DEFAULT_DATA, ctx.string().getText(), ENTRY);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getParsableDataType()) {
+            case TYPEDEF_DATA: {
+                YangTypeDef typeDef = (YangTypeDef) tmpNode;
+                typeDef.setDefaultValueInString(ctx.string().getText());
+                break;
+            }
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                        DEFAULT_DATA, ctx.string().getText(), ENTRY));
+        }
+    }
+}
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java
index e47f466..1f5e113 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java
@@ -75,10 +75,10 @@
     public static void processImportEntry(TreeWalkListener listener, GeneratedYangParser.ImportStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, String.valueOf(ctx.IDENTIFIER().getText()), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, ctx.IDENTIFIER().getText(), ENTRY);
 
         YangImport importNode = new YangImport();
-        importNode.setModuleName(String.valueOf(ctx.IDENTIFIER().getText()));
+        importNode.setModuleName(ctx.IDENTIFIER().getText());
 
         // Push import node to the stack.
         listener.getParsedDataStack().push(importNode);
@@ -94,14 +94,14 @@
     public static void processImportExit(TreeWalkListener listener, GeneratedYangParser.ImportStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, String.valueOf(ctx.IDENTIFIER().getText()), EXIT);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, ctx.IDENTIFIER().getText(), EXIT);
 
         Parsable tmpImportNode = listener.getParsedDataStack().peek();
         if (tmpImportNode instanceof YangImport) {
             listener.getParsedDataStack().pop();
 
             // Check for stack to be non empty.
-            checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, ctx.IDENTIFIER().getText(),
                                  EXIT);
 
             Parsable tmpNode = listener.getParsedDataStack().peek();
@@ -118,12 +118,12 @@
             }
             default:
                 throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IMPORT_DATA,
-                                                                        String.valueOf(ctx.IDENTIFIER().getText()),
+                                                                        ctx.IDENTIFIER().getText(),
                                                                         EXIT));
             }
         } else {
             throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, IMPORT_DATA,
-                                                                    String.valueOf(ctx.IDENTIFIER().getText()), EXIT));
+                                                                    ctx.IDENTIFIER().getText(), EXIT));
         }
     }
 }
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IncludeListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IncludeListener.java
index 024d811..533db1f 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IncludeListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IncludeListener.java
@@ -74,11 +74,11 @@
     public static void processIncludeEntry(TreeWalkListener listener, GeneratedYangParser.IncludeStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, INCLUDE_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, INCLUDE_DATA, ctx.IDENTIFIER().getText(),
                              ENTRY);
 
         YangInclude includeNode = new YangInclude();
-        includeNode.setSubModuleName(String.valueOf(ctx.IDENTIFIER().getText()));
+        includeNode.setSubModuleName(ctx.IDENTIFIER().getText());
 
         listener.getParsedDataStack().push(includeNode);
     }
@@ -93,14 +93,14 @@
     public static void processIncludeExit(TreeWalkListener listener, GeneratedYangParser.IncludeStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, INCLUDE_DATA, String.valueOf(ctx.IDENTIFIER().getText()), EXIT);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, INCLUDE_DATA, ctx.IDENTIFIER().getText(), EXIT);
 
         Parsable tmpIncludeNode = listener.getParsedDataStack().peek();
         if (tmpIncludeNode instanceof YangInclude) {
             listener.getParsedDataStack().pop();
 
             // Check for stack to be non empty.
-            checkStackIsNotEmpty(listener, MISSING_HOLDER, INCLUDE_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, INCLUDE_DATA, ctx.IDENTIFIER().getText(),
                                  EXIT);
 
             Parsable tmpNode = listener.getParsedDataStack().peek();
@@ -117,12 +117,12 @@
             }
             default:
                 throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, INCLUDE_DATA,
-                                                                        String.valueOf(ctx.IDENTIFIER().getText()),
+                                                                        ctx.IDENTIFIER().getText(),
                                                                         EXIT));
             }
         } else {
             throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, INCLUDE_DATA,
-                                                                    String.valueOf(ctx.IDENTIFIER().getText()), EXIT));
+                                                                    ctx.IDENTIFIER().getText(), EXIT));
         }
     }
 }
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ModuleListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ModuleListener.java
index 2bc8d00..8e808a2 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ModuleListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ModuleListener.java
@@ -69,7 +69,7 @@
     public static void processModuleEntry(TreeWalkListener listener, GeneratedYangParser.ModuleStatementContext ctx) {
 
         // Check if stack is empty.
-        checkStackIsEmpty(listener, INVALID_HOLDER, MODULE_DATA, String.valueOf(ctx.IDENTIFIER().getText()), ENTRY);
+        checkStackIsEmpty(listener, INVALID_HOLDER, MODULE_DATA, ctx.IDENTIFIER().getText(), ENTRY);
 
         YangModule yangModule = new YangModule();
         yangModule.setName(ctx.IDENTIFIER().getText());
@@ -87,11 +87,11 @@
     public static void processModuleExit(TreeWalkListener listener, GeneratedYangParser.ModuleStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, MODULE_DATA, String.valueOf(ctx.IDENTIFIER().getText()), EXIT);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, MODULE_DATA, ctx.IDENTIFIER().getText(), EXIT);
 
         if (!(listener.getParsedDataStack().peek() instanceof YangModule)) {
             throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, MODULE_DATA,
-                                                                    String.valueOf(ctx.IDENTIFIER().getText()), EXIT));
+                                                                    ctx.IDENTIFIER().getText(), EXIT));
         }
     }
 }
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NamespaceListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NamespaceListener.java
index db53363..4030ada 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NamespaceListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NamespaceListener.java
@@ -77,9 +77,9 @@
                                              GeneratedYangParser.NamespaceStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, NAMESPACE_DATA, String.valueOf(ctx.string().getText()), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, NAMESPACE_DATA, ctx.string().getText(), ENTRY);
 
-        if (!validateUriValue(String.valueOf(ctx.string().getText()))) {
+        if (!validateUriValue(ctx.string().getText())) {
             ParserException parserException = new ParserException("Invalid namespace URI");
             parserException.setLine(ctx.string().STRING(0).getSymbol().getLine());
             parserException.setCharPosition(ctx.string().STRING(0).getSymbol().getCharPositionInLine());
@@ -92,13 +92,13 @@
         case MODULE_DATA: {
             YangModule module = (YangModule) tmpNode;
             YangNameSpace uri = new YangNameSpace();
-            uri.setUri(String.valueOf(ctx.string().getText()));
+            uri.setUri(ctx.string().getText());
             module.setNameSpace(uri);
             break;
         }
         default:
             throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, NAMESPACE_DATA,
-                                                                    String.valueOf(ctx.string().getText()), ENTRY));
+                                                                    ctx.string().getText(), ENTRY));
         }
     }
 
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OrganizationListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OrganizationListener.java
index 7260c1c..ab8681c 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OrganizationListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OrganizationListener.java
@@ -95,7 +95,7 @@
                                                 GeneratedYangParser.OrganizationStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, ORGANIZATION_DATA, String.valueOf(ctx.string().getText()),
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, ORGANIZATION_DATA, ctx.string().getText(),
                              ENTRY);
 
         // Obtain the node of the stack.
@@ -103,17 +103,17 @@
         switch (tmpNode.getParsableDataType()) {
         case MODULE_DATA: {
             YangModule module = (YangModule) tmpNode;
-            module.setOrganization(String.valueOf(ctx.string().getText()));
+            module.setOrganization(ctx.string().getText());
             break;
         }
         case SUB_MODULE_DATA: {
             YangSubModule subModule = (YangSubModule) tmpNode;
-            subModule.setOrganization(String.valueOf(ctx.string().getText()));
+            subModule.setOrganization(ctx.string().getText());
             break;
         }
         default:
             throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, ORGANIZATION_DATA,
-                                                                    String.valueOf(ctx.string().getText()), ENTRY));
+                                                                    ctx.string().getText(), ENTRY));
         }
     }
 }
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PrefixListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PrefixListener.java
index 774af7c..6b6db62 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PrefixListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PrefixListener.java
@@ -76,7 +76,7 @@
     public static void processPrefixEntry(TreeWalkListener listener, GeneratedYangParser.PrefixStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, PREFIX_DATA, String.valueOf(ctx.IDENTIFIER().getText()), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, PREFIX_DATA, ctx.IDENTIFIER().getText(), ENTRY);
 
         // Obtain the node of the stack.
         Parsable tmpNode = listener.getParsedDataStack().peek();
@@ -98,7 +98,7 @@
         }
         default:
             throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, PREFIX_DATA,
-                                                                    String.valueOf(ctx.IDENTIFIER().getText()), ENTRY));
+                                                                    ctx.IDENTIFIER().getText(), ENTRY));
         }
     }
 }
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionDateListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionDateListener.java
index 8cd6d67..bef6f8e3 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionDateListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionDateListener.java
@@ -23,6 +23,10 @@
 import org.onosproject.yangutils.parser.exceptions.ParserException;
 import org.onosproject.yangutils.parser.impl.TreeWalkListener;
 
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+
 import static org.onosproject.yangutils.parser.ParsableDataType.REVISION_DATE_DATA;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
@@ -82,26 +86,57 @@
                                                 GeneratedYangParser.RevisionDateStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATE_DATA, String.valueOf(ctx.DATE_ARG().getText()),
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATE_DATA, ctx.DATE_ARG().getText(),
                              ENTRY);
 
+        if (!isDateValid(ctx.DATE_ARG().getText())) {
+            ParserException parserException = new ParserException("Input date is not correct");
+            parserException.setLine(ctx.DATE_ARG().getSymbol().getLine());
+            parserException.setCharPosition(ctx.DATE_ARG().getSymbol().getCharPositionInLine());
+            throw parserException;
+        }
+
         // Obtain the node of the stack.
         Parsable tmpNode = listener.getParsedDataStack().peek();
         switch (tmpNode.getParsableDataType()) {
         case IMPORT_DATA: {
             YangImport importNode = (YangImport) tmpNode;
-            importNode.setRevision(String.valueOf(ctx.DATE_ARG().getText()));
+            importNode.setRevision(ctx.DATE_ARG().getText());
             break;
         }
         case INCLUDE_DATA: {
             YangInclude includeNode = (YangInclude) tmpNode;
-            includeNode.setRevision(String.valueOf(ctx.DATE_ARG().getText()));
+            includeNode.setRevision(ctx.DATE_ARG().getText());
             break;
         }
         default:
             throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, REVISION_DATE_DATA,
-                                                                    String.valueOf(ctx.DATE_ARG().getText()), ENTRY));
+                                                                    ctx.DATE_ARG().getText(), ENTRY));
         }
     }
-    // TODO Implement the DATE_ARG validation as per RFC 6020.
-}
+
+    /**
+     * Validates the revision date.
+     *
+     * @param dateToValidate input revision date.
+     * @return validation result, true for success, false for failure.
+     */
+    private static boolean isDateValid(String dateToValidate) {
+
+        if (dateToValidate == null) {
+            return false;
+        }
+
+        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
+        sdf.setLenient(false);
+
+        try {
+            //if not valid, it will throw ParseException
+            Date date = sdf.parse(dateToValidate);
+            System.out.println(date);
+        } catch (ParseException e) {
+            return false;
+        }
+        return true;
+    }
+}
\ No newline at end of file
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionListener.java
index 7904656..a135891 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionListener.java
@@ -82,7 +82,7 @@
                                             GeneratedYangParser.RevisionStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATA, String.valueOf(ctx.DATE_ARG().getText()), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATA, ctx.DATE_ARG().getText(), ENTRY);
 
         // Validate for reverse chronological order of revision & for revision
         // value.
@@ -92,7 +92,7 @@
         }
 
         YangRevision revisionNode = new YangRevision();
-        revisionNode.setRevDate(String.valueOf(ctx.DATE_ARG().getText()));
+        revisionNode.setRevDate(ctx.DATE_ARG().getText());
 
         listener.getParsedDataStack().push(revisionNode);
     }
@@ -108,14 +108,14 @@
             ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATA, String.valueOf(ctx.DATE_ARG().getText()), EXIT);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATA, ctx.DATE_ARG().getText(), EXIT);
 
         Parsable tmpRevisionNode = listener.getParsedDataStack().peek();
         if (tmpRevisionNode instanceof YangRevision) {
             listener.getParsedDataStack().pop();
 
             // Check for stack to be non empty.
-            checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATA, String.valueOf(ctx.DATE_ARG().getText()),
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATA, ctx.DATE_ARG().getText(),
                                  EXIT);
 
             Parsable tmpNode = listener.getParsedDataStack().peek();
@@ -132,12 +132,12 @@
             }
             default:
                 throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, REVISION_DATA,
-                                                                        String.valueOf(ctx.DATE_ARG().getText()),
+                                                                        ctx.DATE_ARG().getText(),
                                                                         EXIT));
             }
         } else {
             throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, REVISION_DATA,
-                                                                    String.valueOf(ctx.DATE_ARG().getText()), EXIT));
+                                                                    ctx.DATE_ARG().getText(), EXIT));
         }
     }
 
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java
index 42c753c..b577bcf 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java
@@ -71,7 +71,7 @@
                                              GeneratedYangParser.SubModuleStatementContext ctx) {
 
         // Check if stack is empty.
-        checkStackIsEmpty(listener, INVALID_HOLDER, SUB_MODULE_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+        checkStackIsEmpty(listener, INVALID_HOLDER, SUB_MODULE_DATA, ctx.IDENTIFIER().getText(),
                           ENTRY);
 
         YangSubModule yangSubModule = new YangSubModule();
@@ -91,12 +91,12 @@
                                             GeneratedYangParser.SubModuleStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, SUB_MODULE_DATA, String.valueOf(ctx.IDENTIFIER().getText()),
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, SUB_MODULE_DATA, ctx.IDENTIFIER().getText(),
                              EXIT);
 
         if (!(listener.getParsedDataStack().peek() instanceof YangSubModule)) {
             throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, SUB_MODULE_DATA,
-                                                                    String.valueOf(ctx.IDENTIFIER().getText()), EXIT));
+                                                                    ctx.IDENTIFIER().getText(), EXIT));
         }
     }
 }
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java
new file mode 100644
index 0000000..9d41253
--- /dev/null
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java
@@ -0,0 +1,203 @@
+/*
+ * Copyright 2014-2016 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * body-stmts          = *((extension-stmt /
+ *                          feature-stmt /
+ *                          identity-stmt /
+ *                          typedef-stmt /
+ *                          grouping-stmt /
+ *                          data-def-stmt /
+ *                          augment-stmt /
+ *                          rpc-stmt /
+ *                          notification-stmt /
+ *                          deviation-stmt) stmtsep)
+ *
+ * typedef-stmt        = typedef-keyword sep identifier-arg-str optsep
+ *                       "{" stmtsep
+ *                           ;; these stmts can appear in any order
+ *                           type-stmt stmtsep
+ *                          [units-stmt stmtsep]
+ *                           [default-stmt stmtsep]
+ *                           [status-stmt stmtsep]
+ *                           [description-stmt stmtsep]
+ *                           [reference-stmt stmtsep]
+ *                         "}"
+ *
+ * ANTLR grammar rule
+ * typedefStatement : TYPEDEF_KEYWORD IDENTIFIER LEFT_CURLY_BRACE
+ *                (typeStatement | unitsStatement | defaultStatement | statusStatement
+ *                | descriptionStatement | referenceStatement)* RIGHT_CURLY_BRACE;
+ */
+
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.YangTypeDef;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.parser.Parsable;
+import org.onosproject.yangutils.parser.ParsableDataType;
+import static org.onosproject.yangutils.parser.ParsableDataType.TYPEDEF_DATA;
+import static org.onosproject.yangutils.parser.ParsableDataType.UNITS_DATA;
+import static org.onosproject.yangutils.parser.ParsableDataType.DEFAULT_DATA;
+import static org.onosproject.yangutils.parser.ParsableDataType.TYPE_DATA;
+import static org.onosproject.yangutils.parser.ParsableDataType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.parser.ParsableDataType.REFERENCE_DATA;
+import static org.onosproject.yangutils.parser.ParsableDataType.STATUS_DATA;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+import org.onosproject.yangutils.parser.impl.YangUtilsParserManager;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CARDINALITY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Implements listener based call back function corresponding to the "typedef"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class TypeDefListener {
+
+    private static ParsableDataType yangConstruct;
+
+    /**
+     * Creates a new typedef listener.
+     */
+    private TypeDefListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (typedef), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object.
+     * @param ctx context object of the grammar rule.
+     */
+    public static void processTypeDefEntry(TreeWalkListener listener,
+            GeneratedYangParser.TypedefStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, TYPEDEF_DATA, ctx.IDENTIFIER().getText(), ENTRY);
+
+        boolean result = validateSubStatementsCardinality(ctx);
+        if (!result) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_CARDINALITY, yangConstruct, "", ENTRY));
+        }
+
+        YangTypeDef typeDefNode = new YangTypeDef();
+        typeDefNode.setDerivedName(ctx.IDENTIFIER().getText());
+
+        Parsable curData = listener.getParsedDataStack().peek();
+
+        if (curData instanceof YangModule | curData instanceof YangSubModule | curData instanceof YangContainer
+                | curData instanceof YangList) {
+            /*
+             * TODO YangGrouping, YangRpc, YangInput, YangOutput, Notification.
+             */
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(typeDefNode);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        TYPEDEF_DATA, ctx.IDENTIFIER().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(typeDefNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                    TYPEDEF_DATA, ctx.IDENTIFIER().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (typedef), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object.
+     * @param ctx context object of the grammar rule.
+     */
+    public static void processTypeDefExit(TreeWalkListener listener,
+            GeneratedYangParser.TypedefStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, TYPEDEF_DATA, ctx.IDENTIFIER().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangTypeDef) {
+            listener.getParsedDataStack().pop();
+        } else {
+            listener.getErrorInformation().setErrorFlag(true);
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, TYPEDEF_DATA,
+                    ctx.IDENTIFIER().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of typedef sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule.
+     * @return true/false validation success or failure.
+     */
+    private static boolean validateSubStatementsCardinality(GeneratedYangParser.TypedefStatementContext ctx) {
+
+        if ((!ctx.unitsStatement().isEmpty())
+                && (ctx.unitsStatement().size() != YangUtilsParserManager.SUB_STATEMENT_CARDINALITY)) {
+            yangConstruct = UNITS_DATA;
+            return false;
+        }
+
+        if ((!ctx.defaultStatement().isEmpty())
+                && (ctx.defaultStatement().size() != YangUtilsParserManager.SUB_STATEMENT_CARDINALITY)) {
+            yangConstruct = DEFAULT_DATA;
+            return false;
+        }
+
+        if (ctx.typeStatement().size() != YangUtilsParserManager.SUB_STATEMENT_CARDINALITY) {
+            yangConstruct = TYPE_DATA;
+            return false;
+        }
+
+        if ((!ctx.descriptionStatement().isEmpty())
+                && (ctx.descriptionStatement().size() != YangUtilsParserManager.SUB_STATEMENT_CARDINALITY)) {
+            yangConstruct = DESCRIPTION_DATA;
+            return false;
+        }
+
+        if ((!ctx.referenceStatement().isEmpty())
+                && (ctx.referenceStatement().size() != YangUtilsParserManager.SUB_STATEMENT_CARDINALITY)) {
+            yangConstruct = REFERENCE_DATA;
+            return false;
+        }
+
+        if ((!ctx.statusStatement().isEmpty())
+                && (ctx.statusStatement().size() != YangUtilsParserManager.SUB_STATEMENT_CARDINALITY)) {
+            yangConstruct = STATUS_DATA;
+            return false;
+        }
+        return true;
+    }
+}
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java
index f9d904d..021ae0d 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java
@@ -85,7 +85,7 @@
                                            GeneratedYangParser.YangVersionStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, VERSION_DATA, String.valueOf(ctx.INTEGER().getText()), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, VERSION_DATA, ctx.INTEGER().getText(), ENTRY);
 
         Integer version = Integer.valueOf(ctx.INTEGER().getText());
         if (!isVersionValid(version)) {
@@ -110,7 +110,7 @@
         }
         default:
             throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, VERSION_DATA,
-                                                                    String.valueOf(ctx.INTEGER().getText()), ENTRY));
+                                                                    ctx.INTEGER().getText(), ENTRY));
         }
     }