Work on #404, updated class diagram and javadoc. Passed checkstyle checks

dao/etc/dao.ucls

@@ -1,45 +1,71 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <class-diagram version="1.1.8" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
   associations="true" dependencies="false" nesting-relationships="true">  
-  <class id="1" language="java" name="com.iluwatar.Customer" project="dao" 
+  <class id="1" language="java" name="com.iluwatar.dao.App" project="dao" 
-    file="/dao/src/main/java/com/iluwatar/Customer.java" binary="false" corner="BOTTOM_RIGHT">    
+    file="/dao/src/main/java/com/iluwatar/dao/App.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="176" y="337"/>    
+    <position height="-1" width="-1" x="910" y="191"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
       sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <attributes public="true" package="true" protected="true" private="false" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+      <operations public="true" package="true" protected="true" private="false" static="true"/>    
     </display>  
   </class>  
-  <class id="2" language="java" name="com.iluwatar.CustomerDaoImpl" project="dao" 
+  <interface id="2" language="java" name="com.iluwatar.dao.CustomerDao" project="dao" 
-    file="/dao/src/main/java/com/iluwatar/CustomerDaoImpl.java" binary="false" corner="BOTTOM_RIGHT">    
+    file="/dao/src/main/java/com/iluwatar/dao/CustomerDao.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="540" y="334"/>    
+    <position height="-1" width="-1" x="536" y="187"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <interface id="3" language="java" name="com.iluwatar.CustomerDao" project="dao" 
-    file="/dao/src/main/java/com/iluwatar/CustomerDao.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="536" y="131"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
       sort-features="false" accessors="true" visibility="true">      
       <attributes public="true" package="true" protected="true" private="true" static="true"/>      
       <operations public="true" package="true" protected="true" private="true" static="true"/>    
     </display>  
   </interface>  
-  <realization id="4">    
+  <class id="3" language="java" name="com.iluwatar.dao.InMemoryCustomerDao" project="dao" 
-    <end type="SOURCE" refId="2"/>    
+    file="/dao/src/main/java/com/iluwatar/dao/InMemoryCustomerDao.java" binary="false" corner="BOTTOM_RIGHT">    
-    <end type="TARGET" refId="3"/>  
+    <position height="-1" width="-1" x="289" y="455"/>    
-  </realization>  
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-  <association id="5">    
+      sort-features="false" accessors="true" visibility="true">      
-    <end type="SOURCE" refId="2" navigable="false">      
+      <attributes public="true" package="true" protected="true" private="false" static="true"/>      
-      <attribute id="6" name="customers"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-      <multiplicity id="7" minimum="0" maximum="2147483647"/>    
+    </display>  
+  </class>  
+  <class id="4" language="java" name="com.iluwatar.dao.DBCustomerDao" project="dao" 
+    file="/dao/src/main/java/com/iluwatar/dao/DBCustomerDao.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="751" y="456"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="false" static="true"/>      
+      <operations public="true" package="true" protected="true" private="false" static="true"/>    
+    </display>  
+  </class>  
+  <interface id="5" language="java" name="javax.sql.DataSource" project="dao" 
+    file="/opt/Softwares/Eclipses/MARS/eclipse/jre/lib/rt.jar" binary="true" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="1083" y="459"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </interface>  
+  <association id="6">    
+    <end type="SOURCE" refId="4" navigable="false">      
+      <attribute id="7" name="dataSource"/>      
+      <multiplicity id="8" minimum="0" maximum="1"/>    
     </end>    
-    <end type="TARGET" refId="1" navigable="true"/>    
+    <end type="TARGET" refId="5" navigable="true"/>    
     <display labels="true" multiplicity="true"/>  
   </association>  
+  <realization id="9">    
+    <end type="SOURCE" refId="3"/>    
+    <end type="TARGET" refId="2"/>  
+  </realization>  
+  <dependency id="10">    
+    <end type="SOURCE" refId="1"/>    
+    <end type="TARGET" refId="2"/>  
+  </dependency>  
+  <realization id="11">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="2"/>  
+  </realization>  
   <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
     sort-features="false" accessors="true" visibility="true">    
     <attributes public="true" package="true" protected="true" private="true" static="true"/>    

dao/pom.xml

@@ -47,6 +47,7 @@
     <dependency>
         <groupId>com.h2database</groupId>
         <artifactId>h2</artifactId>
+        <scope>compile</scope>
       </dependency>
     <dependency>
       <groupId>de.bechte.junit</groupId>

dao/src/main/java/com/iluwatar/dao/App.java

@@ -20,31 +20,39 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+
 package com.iluwatar.dao;
 
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.sql.Statement;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.stream.Stream;
+
+import javax.sql.DataSource;
 
 import org.apache.log4j.Logger;
+import org.h2.jdbcx.JdbcDataSource;
 
 /**
- * 
  * Data Access Object (DAO) is an object that provides an abstract interface to some type of
  * database or other persistence mechanism. By mapping application calls to the persistence layer,
  * DAO provide some specific data operations without exposing details of the database. This
  * isolation supports the Single responsibility principle. It separates what data accesses the
  * application needs, in terms of domain-specific objects and data types (the public interface of
  * the DAO), from how these needs can be satisfied with a specific DBMS.
- * <p>
+ *
- * With the DAO pattern, we can use various method calls to retrieve/add/delete/update data without
+ * <p>With the DAO pattern, we can use various method calls to retrieve/add/delete/update data 
- * directly interacting with the data. The below example demonstrates basic CRUD operations: select,
+ * without directly interacting with the data source. The below example demonstrates basic CRUD 
- * add, update, and delete.
+ * operations: select, add, update, and delete.
+ * 
  * 
  */
 public class App {
-
+  private static final String DB_URL = "jdbc:h2:~/dao:customerdb";
   private static Logger log = Logger.getLogger(App.class);
-
+  
   /**
    * Program entry point.
    * 
@@ -52,17 +60,54 @@ public class App {
    * @throws Exception if any error occurs. 
    */
   public static void main(final String[] args) throws Exception {
-    final CustomerDao customerDao = new InMemoryCustomerDao();
+    final CustomerDao inMemoryDao = new InMemoryCustomerDao();
+    performOperationsUsing(inMemoryDao);
+    
+    final DataSource dataSource = createDataSource();
+    createSchema(dataSource);
+    final CustomerDao dbDao = new DbCustomerDao(dataSource);
+    performOperationsUsing(dbDao);
+    deleteSchema(dataSource);
+  }
+
+  private static void deleteSchema(DataSource dataSource) throws SQLException {
+    try (Connection connection = dataSource.getConnection();
+        Statement statement = connection.createStatement()) {
+      statement.execute("DROP TABLE CUSTOMERS");
+    }
+  }
+
+  private static void createSchema(DataSource dataSource) throws SQLException {
+    try (Connection connection = dataSource.getConnection();
+        Statement statement = connection.createStatement()) {
+      statement.execute("CREATE TABLE CUSTOMERS (ID NUMBER, FNAME VARCHAR(100), "
+          + "LNAME VARCHAR(100))");
+    }
+  }
+
+  private static DataSource createDataSource() {
+    JdbcDataSource dataSource = new JdbcDataSource();
+    dataSource.setURL(DB_URL);
+    return dataSource;
+  }
+
+  private static void performOperationsUsing(final CustomerDao customerDao) throws Exception {
     addCustomers(customerDao);
-    log.info("customerDao.getAllCustomers(): " + customerDao.getAll());
+    log.info("customerDao.getAllCustomers(): ");
-    log.info("customerDao.getCusterById(2): " + customerDao.getById(2));
+    try (Stream<Customer> customerStream = customerDao.getAll()) {
+      customerStream.forEach((customer) -> log.info(customer));
+    }
+    log.info("customerDao.getCustomerById(2): " + customerDao.getById(2));
     final Customer customer = new Customer(4, "Dan", "Danson");
     customerDao.add(customer);
     log.info("customerDao.getAllCustomers(): " + customerDao.getAll());
     customer.setFirstName("Daniel");
     customer.setLastName("Danielson");
     customerDao.update(customer);
-    log.info("customerDao.getAllCustomers(): " + customerDao.getAll());
+    log.info("customerDao.getAllCustomers(): ");
+    try (Stream<Customer> customerStream = customerDao.getAll()) {
+      customerStream.forEach((cust) -> log.info(cust));
+    }
     customerDao.delete(customer);
     log.info("customerDao.getAllCustomers(): " + customerDao.getAll());
   }

dao/src/main/java/com/iluwatar/dao/Customer.java

@@ -20,11 +20,11 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+
 package com.iluwatar.dao;
 
 /**
- * 
+ * A customer POJO that represents the data that will be read from the data source.
- * Customer
  *
  */
 public class Customer {
@@ -34,7 +34,7 @@ public class Customer {
   private String lastName;
 
   /**
-   * Constructor
+   * Creates an instance of customer.
    */
   public Customer(final int id, final String firstName, final String lastName) {
     this.id = id;
@@ -73,12 +73,12 @@ public class Customer {
   }
 
   @Override
-  public boolean equals(final Object o) {
+  public boolean equals(final Object that) {
     boolean isEqual = false;
-    if (this == o) {
+    if (this == that) {
       isEqual = true;
-    } else if (o != null && getClass() == o.getClass()) {
+    } else if (that != null && getClass() == that.getClass()) {
-      final Customer customer = (Customer) o;
+      final Customer customer = (Customer) that;
       if (getId() == customer.getId()) {
         isEqual = true;
       }

dao/src/main/java/com/iluwatar/dao/CustomerDao.java

@@ -20,12 +20,12 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+
 package com.iluwatar.dao;
 
 import java.util.stream.Stream;
 
 /**
- * 
  * In an application the Data Access Object (DAO) is a part of Data access layer. It is an object
  * that provides an interface to some type of persistence mechanism. By mapping application calls
  * to the persistence layer, DAO provides some specific data operations without exposing details 
@@ -33,25 +33,25 @@ import java.util.stream.Stream;
  * data accesses the application needs, in terms of domain-specific objects and data types 
  * (the public interface of the DAO), from how these needs can be satisfied with a specific DBMS,
  * database schema, etc.
- * <br/><br/>
+ * 
- * Any change in the way data is stored and retrieved will not change the client code as the client
+ * <p>Any change in the way data is stored and retrieved will not change the client code as the 
- * will be using interface and need not worry about exact source.
+ * client will be using interface and need not worry about exact source.
  * 
  * @see InMemoryCustomerDao
- * @see DBCustomerDao
+ * @see DbCustomerDao
  */
 public interface CustomerDao {
 
   /**
-   * @return all the customers as a stream. The stream may be lazily or eagerly evaluated based on the
+   * @return all the customers as a stream. The stream may be lazily or eagerly evaluated based 
-   * implementation. The stream must be closed after use.
+   *     on the implementation. The stream must be closed after use.
    * @throws Exception if any error occurs.
    */
   Stream<Customer> getAll() throws Exception;
   
   /**
    * @param id unique identifier of the customer.
-   * @return customer with unique identifier <code>id</code> is found, null otherwise.
+   * @return customer with unique identifier <code>id</code> if found, null otherwise.
    * @throws Exception if any error occurs.
    */
   Customer getById(int id) throws Exception;

dao/src/main/java/com/iluwatar/dao/DbCustomerDao.java

@@ -20,6 +20,7 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+
 package com.iluwatar.dao;
 
 import java.sql.Connection;
@@ -35,27 +36,39 @@ import java.util.stream.StreamSupport;
 import javax.sql.DataSource;
 
 /**
- * 
+ * An implementation of {@link CustomerDao} that persists customers in RDBMS. 
  *
  */
-public class DBCustomerDao implements CustomerDao {
+public class DbCustomerDao implements CustomerDao {
 
   private final DataSource dataSource;
 
-  public DBCustomerDao(DataSource dataSource) {
+  /**
+   * Creates an instance of {@link DbCustomerDao} which uses provided <code>dataSource</code>
+   * to store and retrieve customer information.
+   * 
+   * @param dataSource a non-null dataSource.
+   */
+  public DbCustomerDao(DataSource dataSource) {
     this.dataSource = dataSource;
   }
 
+  /**
+   * @return a lazily populated stream of customers. Note the stream returned must be closed to 
+   *     free all the acquired resources. The stream keeps an open connection to the database till
+   *     it is complete or is closed manually.
+   */
   @Override
   public Stream<Customer> getAll() throws Exception {
-    
+
     Connection connection;
     try {
       connection = getConnection();
       PreparedStatement statement = connection.prepareStatement("SELECT * FROM CUSTOMERS");
       ResultSet resultSet = statement.executeQuery();
-      return StreamSupport.stream(new Spliterators.AbstractSpliterator<Customer>(Long.MAX_VALUE, Spliterator.ORDERED) {
+      return StreamSupport.stream(new Spliterators.AbstractSpliterator<Customer>(Long.MAX_VALUE, 
-        
+          Spliterator.ORDERED) {
+
         @Override
         public boolean tryAdvance(Consumer<? super Customer> action) {
           try {
@@ -65,15 +78,15 @@ public class DBCustomerDao implements CustomerDao {
             action.accept(createCustomer(resultSet));
             return true;
           } catch (SQLException e) {
-            e.printStackTrace();
+            throw new RuntimeException(e);
-            return false;
           }
-        }}, false).onClose(() -> mutedClose(connection));
+        }
+      }, false).onClose(() -> mutedClose(connection));
     } catch (SQLException e) {
       throw new Exception(e.getMessage(), e);
     }
   }
-  
+
   private Connection getConnection() throws SQLException {
     return dataSource.getConnection();
   }
@@ -91,31 +104,40 @@ public class DBCustomerDao implements CustomerDao {
         resultSet.getString("FNAME"), 
         resultSet.getString("LNAME"));
   }
-  
+
+  /**
+   * {@inheritDoc}
+   */
   @Override
   public Customer getById(int id) throws Exception {
     try (Connection connection = getConnection();
-        PreparedStatement statement = connection.prepareStatement("SELECT * FROM CUSTOMERS WHERE ID = ?")) {
+        PreparedStatement statement = 
-        statement.setInt(1, id);
+            connection.prepareStatement("SELECT * FROM CUSTOMERS WHERE ID = ?")) {
-        ResultSet resultSet = statement.executeQuery();
+
-        if (resultSet.next()) {
+      statement.setInt(1, id);
-          return createCustomer(resultSet);
+      ResultSet resultSet = statement.executeQuery();
-        } else {
+      if (resultSet.next()) {
-          return null;
+        return createCustomer(resultSet);
-        }
+      } else {
+        return null;
+      }
     } catch (SQLException ex) {
       throw new Exception(ex.getMessage(), ex);
     }
   }
 
+  /**
+   * {@inheritDoc}
+   */
   @Override
   public boolean add(Customer customer) throws Exception {
     if (getById(customer.getId()) != null) {
       return false;
     }
-    
+
     try (Connection connection = getConnection();
-        PreparedStatement statement = connection.prepareStatement("INSERT INTO CUSTOMERS VALUES (?,?,?)")) {
+        PreparedStatement statement = 
+            connection.prepareStatement("INSERT INTO CUSTOMERS VALUES (?,?,?)")) {
       statement.setInt(1, customer.getId());
       statement.setString(2, customer.getFirstName());
       statement.setString(3, customer.getLastName());
@@ -126,10 +148,14 @@ public class DBCustomerDao implements CustomerDao {
     }
   }
 
+  /**
+   * {@inheritDoc}
+   */
   @Override
   public boolean update(Customer customer) throws Exception {
     try (Connection connection = getConnection();
-        PreparedStatement statement = connection.prepareStatement("UPDATE CUSTOMERS SET FNAME = ?, LNAME = ? WHERE ID = ?")) {
+        PreparedStatement statement = 
+            connection.prepareStatement("UPDATE CUSTOMERS SET FNAME = ?, LNAME = ? WHERE ID = ?")) {
       statement.setString(1, customer.getFirstName());
       statement.setString(2, customer.getLastName());
       statement.setInt(3, customer.getId());
@@ -139,10 +165,14 @@ public class DBCustomerDao implements CustomerDao {
     }
   }
 
+  /**
+   * {@inheritDoc}
+   */
   @Override
   public boolean delete(Customer customer) throws Exception {
     try (Connection connection = getConnection();
-        PreparedStatement statement = connection.prepareStatement("DELETE FROM CUSTOMERS WHERE ID = ?")) {
+        PreparedStatement statement = 
+            connection.prepareStatement("DELETE FROM CUSTOMERS WHERE ID = ?")) {
       statement.setInt(1, customer.getId());
       return statement.executeUpdate() > 0;
     } catch (SQLException ex) {

dao/src/main/java/com/iluwatar/dao/InMemoryCustomerDao.java

@@ -20,6 +20,7 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+
 package com.iluwatar.dao;
 
 import java.util.HashMap;

dao/src/test/java/com/iluwatar/dao/AppTest.java

@@ -20,6 +20,7 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+
 package com.iluwatar.dao;
 
 import org.junit.Test;

dao/src/test/java/com/iluwatar/dao/CustomerTest.java

@@ -20,6 +20,7 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+
 package com.iluwatar.dao;
 
 import static org.junit.Assert.assertEquals;

dao/src/test/java/com/iluwatar/dao/DbCustomerDaoTest.java

@@ -28,33 +28,51 @@ import org.mockito.Mockito;
 
 import de.bechte.junit.runners.context.HierarchicalContextRunner;
 
+/**
+ * Tests {@link DbCustomerDao}.
+ */
 @RunWith(HierarchicalContextRunner.class)
-public class DBCustomerDaoTest {
+public class DbCustomerDaoTest {
 
   private static final String DB_URL = "jdbc:h2:~/dao:customerdb";
-  private DBCustomerDao dao;
+  private DbCustomerDao dao;
   private Customer existingCustomer = new Customer(1, "Freddy", "Krueger");
 
+  /**
+   * Creates customers schema.
+   * @throws SQLException if there is any error while creating schema.
+   */
   @Before
   public void createSchema() throws SQLException {
     try (Connection connection = DriverManager.getConnection(DB_URL);
         Statement statement = connection.createStatement()) {
-      statement.execute("CREATE TABLE CUSTOMERS (ID NUMBER, FNAME VARCHAR(100), LNAME VARCHAR(100))");
+      statement.execute("CREATE TABLE CUSTOMERS (ID NUMBER, FNAME VARCHAR(100),"
+          + " LNAME VARCHAR(100))");
     }
   }
 
+  /**
+   * Represents the scenario where DB connectivity is present.
+   */
   public class ConnectionSuccess {
 
+    /**
+     * Setup for connection success scenario.
+     * @throws Exception if any error occurs.
+     */
     @Before
     public void setUp() throws Exception {
       JdbcDataSource dataSource = new JdbcDataSource();
       dataSource.setURL(DB_URL);
-      dao = new DBCustomerDao(dataSource);
+      dao = new DbCustomerDao(dataSource);
       boolean result = dao.add(existingCustomer);
       assertTrue(result);
     }
 
-    public class NonExistantCustomer {
+    /**
+     * Represents the scenario when DAO operations are being performed on a non existing customer.
+     */
+    public class NonExistingCustomer {
 
       @Test
       public void addingShouldResultInSuccess() throws Exception {
@@ -97,6 +115,11 @@ public class DBCustomerDaoTest {
       }
     }
 
+    /**
+     * Represents a scenario where DAO operations are being performed on an already existing
+     * customer.
+     *
+     */
     public class ExistingCustomer {
 
       @Test
@@ -135,14 +158,23 @@ public class DBCustomerDaoTest {
     }
   }
 
-  public class DBConnectivityIssue {
+  /**
+   * Represents a scenario where DB connectivity is not present due to network issue, or
+   * DB service unavailable.
+   * 
+   */
+  public class ConnectivityIssue {
     
     private static final String EXCEPTION_CAUSE = "Connection not available";
     @Rule public ExpectedException exception = ExpectedException.none();
     
+    /**
+     * setup a connection failure scenario.
+     * @throws SQLException if any error occurs.
+     */
     @Before
     public void setUp() throws SQLException {
-      dao = new DBCustomerDao(mockedDatasource());
+      dao = new DbCustomerDao(mockedDatasource());
       exception.expect(Exception.class);
       exception.expectMessage(EXCEPTION_CAUSE);
     }
@@ -186,6 +218,10 @@ public class DBCustomerDaoTest {
 
   }
 
+  /**
+   * Delete customer schema for fresh setup per test.
+   * @throws SQLException if any error occurs.
+   */
   @After
   public void deleteSchema() throws SQLException {
     try (Connection connection = DriverManager.getConnection(DB_URL);

dao/src/test/java/com/iluwatar/dao/InMemoryCustomerDaoTest.java

@@ -20,6 +20,7 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+
 package com.iluwatar.dao;
 
 import static org.junit.Assert.assertEquals;
@@ -36,6 +37,9 @@ import org.junit.runner.RunWith;
 
 import de.bechte.junit.runners.context.HierarchicalContextRunner;
 
+/**
+ * Tests {@link InMemoryCustomerDao}.
+ */
 @RunWith(HierarchicalContextRunner.class)
 public class InMemoryCustomerDaoTest {
 
@@ -47,8 +51,12 @@ public class InMemoryCustomerDaoTest {
     dao = new InMemoryCustomerDao();
     dao.add(CUSTOMER);
   }
-  
+
-  public class NonExistantCustomer {
+  /**
+   * Represents the scenario when the DAO operations are being performed on a non existent 
+   * customer.  
+   */
+  public class NonExistingCustomer {
 
     @Test
     public void addingShouldResultInSuccess() throws Exception {
@@ -91,6 +99,10 @@ public class InMemoryCustomerDaoTest {
     }
   }
 
+  /**
+   * Represents the scenario when the DAO operations are being performed on an already existing
+   * customer.
+   */
   public class ExistingCustomer {
 
     @Test