[ONOS-3892] implement YANG leaf data model

Change-Id: I996d4d3d60a0ad2142e173c6ba26c9cc355ccc80
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/datamodel/YangLeaf.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/datamodel/YangLeaf.java
new file mode 100644
index 0000000..d2837da
--- /dev/null
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/datamodel/YangLeaf.java
@@ -0,0 +1,281 @@
+/*
+ * Copyright 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.datamodel;
+
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.parser.Parsable;
+import org.onosproject.yangutils.parser.ParsableDataType;
+
+/*
+ * Reference:RFC 6020.
+ *  The "leaf" statement is used to define a leaf node in the schema
+ *  tree.  It takes one argument, which is an identifier, followed by a
+ *  block of sub-statements that holds detailed leaf information.
+ *
+ *  A leaf node has a value, but no child nodes in the data tree.
+ *  Conceptually, the value in the data tree is always in the canonical
+ *  form.
+ *
+ *  A leaf node exists in zero or one instances in the data tree.
+ *
+ *  The "leaf" statement is used to define a scalar variable of a
+ *  particular built-in or derived type.
+ *
+ * The leaf's sub-statements
+ *
+ *       +--------------+---------+-------------+------------------+
+ *       | substatement | section | cardinality |data model mapping|
+ *       +--------------+---------+-------------+------------------+
+ *       | config       | 7.19.1  | 0..1        | - boolean        |
+ *       | default      | 7.6.4   | 0..1        | - TODO           |
+ *       | description  | 7.19.3  | 0..1        | - string         |
+ *       | if-feature   | 7.18.2  | 0..n        | - TODO           |
+ *       | mandatory    | 7.6.5   | 0..1        | - boolean        |
+ *       | must         | 7.5.3   | 0..n        | - TODO           |
+ *       | reference    | 7.19.4  | 0..1        | - string         |
+ *       | status       | 7.19.2  | 0..1        | - YangStatus     |
+ *       | type         | 7.6.3   | 1           | - YangType       |
+ *       | units        | 7.3.3   | 0..1        | - String         |
+ *       | when         | 7.19.5  | 0..1        | - TODO           |
+ *       +--------------+---------+-------------+------------------+
+ */
+/**
+ * Leaf data represented in YANG.
+ *
+ * @param <T> YANG data type
+ */
+public class YangLeaf<T> implements YangCommonInfo, Parsable {
+
+    /**
+     * Name of leaf.
+     */
+    private String name;
+
+    /**
+     * If the leaf is a config parameter.
+     */
+    private boolean isConfig;
+
+    /**
+     * description of leaf.
+     */
+    private String description;
+
+    /**
+     * If mandatory leaf.
+     */
+    private boolean isMandatory;
+
+    /**
+     * The textual reference to this leaf.
+     */
+    private String reference;
+
+    /**
+     * Status of leaf in YANG definition.
+     */
+    private YangStatusType status;
+
+    /**
+     * Textual units info.
+     */
+    private String units;
+
+    /**
+     * Data type of the leaf.
+     */
+    private YangType<T> dataType;
+
+    /**
+     * Default constructor to create a YANG leaf.
+     */
+    public YangLeaf() {
+    }
+
+    /**
+     * Get the name of leaf.
+     *
+     * @return the leaf name.
+     */
+    public String getLeafName() {
+        return name;
+    }
+
+    /**
+     * Set the name of leaf.
+     *
+     * @param leafName the leaf name to set.
+     */
+    public void setLeafName(String leafName) {
+        this.name = leafName;
+    }
+
+    /**
+     * Get the config flag.
+     *
+     * @return if config flag.
+     */
+    public boolean isConfig() {
+        return isConfig;
+    }
+
+    /**
+     * Set the config flag.
+     *
+     * @param isCfg the flag value to set.
+     */
+    public void setConfig(boolean isCfg) {
+        isConfig = isCfg;
+    }
+
+    /**
+     * Get the description.
+     *
+     * @return the description.
+     */
+    public String getDescription() {
+        return description;
+    }
+
+    /**
+     * Set the description.
+     *
+     * @param description set the description.
+     */
+    public void setDescription(String description) {
+        this.description = description;
+    }
+
+    /**
+     * Get if the leaf is mandatory.
+     *
+     * @return if leaf is mandatory.
+     */
+    public boolean isMandatory() {
+        return isMandatory;
+    }
+
+    /**
+     * Set if the leaf is mandatory.
+     *
+     * @param isReq if the leaf is mandatory
+     */
+    public void setMandatory(boolean isReq) {
+        isMandatory = isReq;
+    }
+
+    /**
+     * Get the textual reference.
+     *
+     * @return the reference.
+     */
+    public String getReference() {
+        return reference;
+    }
+
+    /**
+     * Set the textual reference.
+     *
+     * @param reference the reference to set.
+     */
+    public void setReference(String reference) {
+        this.reference = reference;
+    }
+
+    /**
+     * Get the status.
+     *
+     * @return the status.
+     */
+    public YangStatusType getStatus() {
+        return status;
+    }
+
+    /**
+     * Set the status.
+     *
+     * @param status the status to set.
+     */
+    public void setStatus(YangStatusType status) {
+        this.status = status;
+    }
+
+    /**
+     * Get the units.
+     *
+     * @return the units.
+     */
+    public String getUnits() {
+        return units;
+    }
+
+    /**
+     * Set the units.
+     *
+     * @param units the units to set.
+     */
+    public void setUnits(String units) {
+        this.units = units;
+    }
+
+    /**
+     * Get the data type.
+     *
+     * @return the data type.
+     */
+    public YangType<T> getDataType() {
+        return dataType;
+    }
+
+    /**
+     * Set the data type.
+     *
+     * @param dataType the data type to set.
+     */
+    public void setDataType(YangType<T> dataType) {
+        this.dataType = dataType;
+    }
+
+    /**
+     * Returns the type of the parsed data.
+     *
+     * @return returns LEAF_DATA.
+     */
+    public ParsableDataType getParsableDataType() {
+        return ParsableDataType.LEAF_DATA;
+    }
+
+    /**
+     * Validate the data on entering the corresponding parse tree node.
+     *
+     * @throws DataModelException a violation of data model rules.
+     */
+    public void validateDataOnEntry() throws DataModelException {
+        // TODO auto-generated method stub, to be implemented by parser
+
+    }
+
+    /**
+     * Validate the data on exiting the corresponding parse tree node.
+     *
+     * @throws DataModelException a violation of data model rules.
+     */
+    public void validateDataOnExit() throws DataModelException {
+        // TODO auto-generated method stub, to be implemented by parser
+
+    }
+}