diff --git a/zeppelin-server/src/main/java/org/apache/zeppelin/realm/ActiveDirectoryGroupRealm.java b/zeppelin-server/src/main/java/org/apache/zeppelin/realm/ActiveDirectoryGroupRealm.java
index 6d461d2da4c..2c2594d90e0 100644
--- a/zeppelin-server/src/main/java/org/apache/zeppelin/realm/ActiveDirectoryGroupRealm.java
+++ b/zeppelin-server/src/main/java/org/apache/zeppelin/realm/ActiveDirectoryGroupRealm.java
@@ -97,6 +97,7 @@ public void setGroupRolesMap(Map<String, String> groupRolesMap) {
 
   LdapContextFactory ldapContextFactory;
 
+  @Override
   protected void onInit() {
     super.onInit();
     this.getLdapContextFactory();
@@ -120,6 +121,7 @@ public LdapContextFactory getLdapContextFactory() {
     return this.ldapContextFactory;
   }
 
+  @Override
   protected AuthenticationInfo doGetAuthenticationInfo(AuthenticationToken token)
           throws AuthenticationException {
     try {
@@ -134,6 +136,8 @@ protected AuthenticationInfo doGetAuthenticationInfo(AuthenticationToken token)
     }
   }
 
+  
+  @Override
   protected AuthorizationInfo doGetAuthorizationInfo(PrincipalCollection principals) {
     try {
       AuthorizationInfo info = this.queryForAuthorizationInfo(principals,
@@ -168,6 +172,7 @@ private String getSystemPassword() {
    * @return an {@link AuthenticationInfo} instance containing information retrieved from LDAP.
    * @throws NamingException if any LDAP errors occur during the search.
    */
+  @Override
   protected AuthenticationInfo queryForAuthenticationInfo(AuthenticationToken token,
           LdapContextFactory ldapContextFactory) throws NamingException {
     UsernamePasswordToken upToken = (UsernamePasswordToken) token;
@@ -228,6 +233,8 @@ protected AuthenticationInfo buildAuthenticationInfo(String username, char[] pas
    * @return the AuthorizationInfo for the given Subject principal.
    * @throws NamingException if an error occurs when searching the LDAP server.
    */
+  
+  @Override
   protected AuthorizationInfo queryForAuthorizationInfo(PrincipalCollection principals,
           LdapContextFactory ldapContextFactory) throws NamingException {
     String username = (String) getAvailablePrincipal(principals);
diff --git a/zeppelin-server/src/main/java/org/apache/zeppelin/realm/ZeppelinHubRealm.java b/zeppelin-server/src/main/java/org/apache/zeppelin/realm/ZeppelinHubRealm.java
index 94d8126bef4..b0b5837dcce 100644
--- a/zeppelin-server/src/main/java/org/apache/zeppelin/realm/ZeppelinHubRealm.java
+++ b/zeppelin-server/src/main/java/org/apache/zeppelin/realm/ZeppelinHubRealm.java
@@ -173,7 +173,7 @@ protected User authenticateUser(String requestBody) {
    * @param pwd
    * @return
    */
-  protected String createLoginPayload(String login, char[] pwd) {
+  protected String createLoginPayload(String login, char ... pwd) {
     StringBuilder sb = new StringBuilder("{\"login\":\"");
     return sb.append(login).append("\", \"password\":\"").append(pwd).append("\"}").toString();
   }
diff --git a/zeppelin-server/src/main/java/org/apache/zeppelin/realm/jwt/SimplePrincipalMapper.java b/zeppelin-server/src/main/java/org/apache/zeppelin/realm/jwt/SimplePrincipalMapper.java
index b1948102e60..ba7aec1b263 100644
--- a/zeppelin-server/src/main/java/org/apache/zeppelin/realm/jwt/SimplePrincipalMapper.java
+++ b/zeppelin-server/src/main/java/org/apache/zeppelin/realm/jwt/SimplePrincipalMapper.java
@@ -60,8 +60,8 @@ private HashMap<String, String[]> parseMapping(String mappings)
           String value = mapping.substring(mapping.indexOf('=') + 1);
           String[] v = value.split(",");
           String[] p = principals.split(",");
-          for (int i = 0; i < p.length; i++) {
-            table.put(p[i], v);
+          for (String s : p) {
+            table.put(s, v);
           }
         } while (t.hasMoreTokens());
       }
@@ -98,7 +98,7 @@ public String mapUserPrincipal(String principalName) {
   @Override
   public String[] mapGroupPrincipal(String principalName) {
     String[] groups = null;
-    String[] wildCardGroups = null;
+    String[] wildCardGroups;
 
     if (groupMappings != null) {
       groups = groupMappings.get(principalName);
@@ -112,13 +112,15 @@ public String[] mapGroupPrincipal(String principalName) {
 
     return groups;
   }
-
+  
   /**
+   *
    * @param groups
    * @param wildCardGroups
+   * @param <T>
    * @return
    */
-  public static <T> T[] concat(T[] groups, T[] wildCardGroups) {
+  public static <T> T[] concat(T[] groups, T ... wildCardGroups) {
     T[] result = Arrays.copyOf(groups, groups.length + wildCardGroups.length);
     System.arraycopy(wildCardGroups, 0, result, groups.length, wildCardGroups.length);
     return result;
diff --git a/zeppelin-server/src/main/java/org/apache/zeppelin/realm/kerberos/KerberosRealm.java b/zeppelin-server/src/main/java/org/apache/zeppelin/realm/kerberos/KerberosRealm.java
index c2a88f7fe16..513c156677a 100644
--- a/zeppelin-server/src/main/java/org/apache/zeppelin/realm/kerberos/KerberosRealm.java
+++ b/zeppelin-server/src/main/java/org/apache/zeppelin/realm/kerberos/KerberosRealm.java
@@ -699,7 +699,7 @@ private AuthenticationToken getToken(HttpServletRequest request)
     return token;
   }
 
-  private static AuthenticationToken getTokenFromCookies(Cookie[] cookies)
+  private static AuthenticationToken getTokenFromCookies(Cookie ... cookies)
       throws AuthenticationException {
     AuthenticationToken token = null;
     String tokenStr = null;
diff --git a/zeppelin-server/src/main/java/org/apache/zeppelin/socket/NotebookServer.java b/zeppelin-server/src/main/java/org/apache/zeppelin/socket/NotebookServer.java
index ad06e020ae7..9e5ea3a7b5b 100644
--- a/zeppelin-server/src/main/java/org/apache/zeppelin/socket/NotebookServer.java
+++ b/zeppelin-server/src/main/java/org/apache/zeppelin/socket/NotebookServer.java
@@ -2111,8 +2111,7 @@ public List<ParagraphInfo> getParagraphList(String user, String noteId)
     // Convert Paragraph to ParagraphInfo
     List<ParagraphInfo> paragraphInfos = new ArrayList();
     List<Paragraph> paragraphs = note.getParagraphs();
-    for (Iterator<Paragraph> iter = paragraphs.iterator(); iter.hasNext();) {
-      Paragraph paragraph = iter.next();
+    for (Paragraph paragraph : paragraphs) {
       ParagraphInfo paraInfo = new ParagraphInfo();
       paraInfo.setNoteId(noteId);
       paraInfo.setParagraphId(paragraph.getId());
diff --git a/zeppelin-server/src/test/java/org/apache/zeppelin/cluster/ClusterEventTest.java b/zeppelin-server/src/test/java/org/apache/zeppelin/cluster/ClusterEventTest.java
index 90ba1345b5e..a5dc021c232 100644
--- a/zeppelin-server/src/test/java/org/apache/zeppelin/cluster/ClusterEventTest.java
+++ b/zeppelin-server/src/test/java/org/apache/zeppelin/cluster/ClusterEventTest.java
@@ -66,9 +66,7 @@
 import java.util.Map;
 import java.util.Set;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertThat;
+import static org.junit.Assert.*;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.when;
@@ -134,7 +132,7 @@ public static void init() throws Exception {
     }
 
     Thread.sleep(3000);
-    assertEquals(true, clusterIsStartup());
+    assertTrue(clusterIsStartup());
 
     getClusterServerMeta();
   }
@@ -282,7 +280,7 @@ public static void getClusterServerMeta() {
     LOGGER.info(intpMeta.toString());
 
     assertNotNull(srvMeta);
-    assertEquals(true, (srvMeta instanceof HashMap));
+    assertTrue((srvMeta instanceof HashMap));
     HashMap hashMap = (HashMap) srvMeta;
 
     assertEquals(hashMap.size(), 3);
@@ -406,8 +404,9 @@ public void testClusterAuthEvent() throws IOException {
       notebookServer.getNotebook().saveNote(note, anonymous);
 
       String noteId = note.getId();
-      String user1Id = "user1", user2Id = "user2";
-
+      String user1Id = "user1";
+      String user2Id = "user2";
+  
       // test user1 can get anonymous's note
       List<ParagraphInfo> paragraphList0 = null;
       try {
diff --git a/zeppelin-server/src/test/java/org/apache/zeppelin/realm/PamRealmTest.java b/zeppelin-server/src/test/java/org/apache/zeppelin/realm/PamRealmTest.java
index f328407c78c..81850830af0 100644
--- a/zeppelin-server/src/test/java/org/apache/zeppelin/realm/PamRealmTest.java
+++ b/zeppelin-server/src/test/java/org/apache/zeppelin/realm/PamRealmTest.java
@@ -16,6 +16,7 @@
  */
 package org.apache.zeppelin.realm;
 
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assume.assumeTrue;
 import static org.mockito.Mockito.mock;
@@ -55,8 +56,8 @@ public void testDoGetAuthenticationInfo() {
     when(authToken.getCredentials()).thenReturn(pamPass);
 
     AuthenticationInfo authInfo = realm.doGetAuthenticationInfo(authToken);
-
-    assertTrue(authInfo.getCredentials() != null);
+  
+    assertNotNull(authInfo.getCredentials());
   }
 
   public static void main(String[] args) {
diff --git a/zeppelin-server/src/test/java/org/apache/zeppelin/rest/CredentialsRestApiTest.java b/zeppelin-server/src/test/java/org/apache/zeppelin/rest/CredentialsRestApiTest.java
index f6f00a170b9..9a8ec1ad763 100644
--- a/zeppelin-server/src/test/java/org/apache/zeppelin/rest/CredentialsRestApiTest.java
+++ b/zeppelin-server/src/test/java/org/apache/zeppelin/rest/CredentialsRestApiTest.java
@@ -43,14 +43,14 @@ public class CredentialsRestApiTest {
   private AuthenticationService authenticationService;
 
   @Before
-  public void setUp() throws IOException {
+  public void setUp() {
     credentials = new Credentials();
     authenticationService = new NoAuthenticationService();
     credentialRestApi = new CredentialRestApi(credentials, authenticationService);
   }
 
   @Test
-  public void testInvalidRequest() throws IOException {
+  public void testInvalidRequest() {
     String jsonInvalidRequestEntityNull =
         "{\"entity\" : null, \"username\" : \"test\", " + "\"password\" : \"testpass\"}";
     String jsonInvalidRequestNameNull =
@@ -73,19 +73,18 @@ public void testInvalidRequest() throws IOException {
     assertEquals(Status.BAD_REQUEST, response.getStatusInfo().toEnum());
   }
 
-  public Map<String, UserCredentials> testGetUserCredentials() throws IOException {
+  @Test
+  public Map<String, UserCredentials> testGetUserCredentials() {
     Response response = credentialRestApi.getCredentials();
     Map<String, Object> resp =
         gson.fromJson(
             response.getEntity().toString(), new TypeToken<Map<String, Object>>() {}.getType());
     Map<String, Object> body = (Map<String, Object>) resp.get("body");
-    Map<String, UserCredentials> credentialMap =
-        (Map<String, UserCredentials>) body.get("userCredentials");
-    return credentialMap;
+    return (Map<String, UserCredentials>) body.get("userCredentials");
   }
 
   @Test
-  public void testCredentialsAPIs() throws IOException {
+  public void testCredentialsAPIs() {
     String requestData1 =
         "{\"entity\" : \"entityname\", \"username\" : \"myuser\", \"password\" " + ": \"mypass\"}";
     String entity = "entityname";
diff --git a/zeppelin-server/src/test/java/org/apache/zeppelin/rest/InterpreterRestApiTest.java b/zeppelin-server/src/test/java/org/apache/zeppelin/rest/InterpreterRestApiTest.java
index 48d6c515d7f..1bd62c08deb 100644
--- a/zeppelin-server/src/test/java/org/apache/zeppelin/rest/InterpreterRestApiTest.java
+++ b/zeppelin-server/src/test/java/org/apache/zeppelin/rest/InterpreterRestApiTest.java
@@ -291,6 +291,7 @@ public void testSettingsCreateWithInvalidName() throws IOException {
 
   }
 
+  @Test
   public void testInterpreterRestart() throws IOException, InterruptedException {
     Note note = null;
     try {
diff --git a/zeppelin-server/src/test/java/org/apache/zeppelin/rest/NotebookRepoRestApiTest.java b/zeppelin-server/src/test/java/org/apache/zeppelin/rest/NotebookRepoRestApiTest.java
index 46ea7122fcc..2450686ceb5 100644
--- a/zeppelin-server/src/test/java/org/apache/zeppelin/rest/NotebookRepoRestApiTest.java
+++ b/zeppelin-server/src/test/java/org/apache/zeppelin/rest/NotebookRepoRestApiTest.java
@@ -97,13 +97,13 @@ public void setNewDirectoryForLocalDirectory() throws IOException {
     List<Map<String, Object>> listOfRepositories = getListOfReposotiry();
     String localVfs = StringUtils.EMPTY;
     String className = StringUtils.EMPTY;
-
-    for (int i = 0; i < listOfRepositories.size(); i++) {
-      if (listOfRepositories.get(i).get("name").equals("VFSNotebookRepo")) {
+  
+    for (Map<String, Object> listOfRepository : listOfRepositories) {
+      if (listOfRepository.get("name").equals("VFSNotebookRepo")) {
         localVfs =
-                (String) ((List<Map<String, Object>>) listOfRepositories.get(i).get("settings"))
-                        .get(0).get("selected");
-        className = (String) listOfRepositories.get(i).get("className");
+                (String) ((List<Map<String, Object>>) listOfRepository.get("settings"))
+                                 .get(0).get("selected");
+        className = (String) listOfRepository.get("className");
         break;
       }
     }
@@ -120,11 +120,11 @@ public void setNewDirectoryForLocalDirectory() throws IOException {
     // Verify
     listOfRepositories = getListOfReposotiry();
     String updatedPath = StringUtils.EMPTY;
-    for (int i = 0; i < listOfRepositories.size(); i++) {
-      if (listOfRepositories.get(i).get("name").equals("VFSNotebookRepo")) {
+    for (Map<String, Object> listOfRepository : listOfRepositories) {
+      if (listOfRepository.get("name").equals("VFSNotebookRepo")) {
         updatedPath =
-                (String) ((List<Map<String, Object>>) listOfRepositories.get(i).get("settings"))
-                        .get(0).get("selected");
+                (String) ((List<Map<String, Object>>) listOfRepository.get("settings"))
+                                 .get(0).get("selected");
         break;
       }
     }
diff --git a/zeppelin-server/src/test/java/org/apache/zeppelin/rest/ZeppelinRestApiTest.java b/zeppelin-server/src/test/java/org/apache/zeppelin/rest/ZeppelinRestApiTest.java
index f353429848b..9a2a031d5b6 100644
--- a/zeppelin-server/src/test/java/org/apache/zeppelin/rest/ZeppelinRestApiTest.java
+++ b/zeppelin-server/src/test/java/org/apache/zeppelin/rest/ZeppelinRestApiTest.java
@@ -367,7 +367,8 @@ private void testDeleteNotExistNote(String noteId) throws IOException {
   @Test
   public void testCloneNote() throws IOException, IllegalArgumentException {
     LOG.info("testCloneNote");
-    Note note = null, newNote = null;
+    Note note = null;
+    Note newNote = null;
     try {
       // Create note to clone
       note = TestUtils.getInstance(Notebook.class).createNote("note1_testCloneNote", anonymous);
@@ -948,13 +949,13 @@ public void testTitleSearch() throws IOException, InterruptedException {
       ArrayList searchBody = (ArrayList) respSearchResult.get("body");
 
       int numberOfTitleHits = 0;
-      for (int i = 0; i < searchBody.size(); i++) {
-        Map<String, String> searchResult = (Map<String, String>) searchBody.get(i);
+      for (Object o : searchBody) {
+        Map<String, String> searchResult = (Map<String, String>) o;
         if (searchResult.get("header").contains("testTitleSearchOfParagraph")) {
           numberOfTitleHits++;
         }
       }
-      assertEquals("Paragraph title hits must be at-least one", true, numberOfTitleHits >= 1);
+      assertTrue("Paragraph title hits must be at-least one", numberOfTitleHits >= 1);
       searchNote.releaseConnection();
     } finally {
       //cleanup
diff --git a/zeppelin-server/src/test/java/org/apache/zeppelin/socket/NotebookServerTest.java b/zeppelin-server/src/test/java/org/apache/zeppelin/socket/NotebookServerTest.java
index 185de1f8d98..3a42323fe74 100644
--- a/zeppelin-server/src/test/java/org/apache/zeppelin/socket/NotebookServerTest.java
+++ b/zeppelin-server/src/test/java/org/apache/zeppelin/socket/NotebookServerTest.java
@@ -698,14 +698,13 @@ public void testGetParagraphList() throws IOException {
       notebook.saveNote(note, anonymous);
 
       String noteId = note.getId();
-      String user1Id = "user1", user2Id = "user2";
-
+      String user1Id = "user1";
+      String user2Id = "user2";
+  
       // test user1 can get anonymous's note
       List<ParagraphInfo> paragraphList0 = null;
       try {
         paragraphList0 = notebookServer.getParagraphList(user1Id, noteId);
-      } catch (ServiceException e) {
-        e.printStackTrace();
       } catch (TException e) {
         e.printStackTrace();
       }