diff --git a/hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/MiniRouterDFSCluster.java b/hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/MiniRouterDFSCluster.java
index 0c9a2e0046c..896d08f2c49 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/MiniRouterDFSCluster.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/MiniRouterDFSCluster.java
@@ -152,7 +152,7 @@ public class MiniRouterDFSCluster {
   /**
    * Router context.
    */
-  public class RouterContext {
+  public static class RouterContext {
     private Router router;
     private FileContext fileContext;
     private String nameserviceId;
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/blockaliasmap/impl/InMemoryLevelDBAliasMapClient.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/blockaliasmap/impl/InMemoryLevelDBAliasMapClient.java
index cacf8f102fa..6cac72af82c 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/blockaliasmap/impl/InMemoryLevelDBAliasMapClient.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/blockaliasmap/impl/InMemoryLevelDBAliasMapClient.java
@@ -129,7 +129,7 @@ public Iterator<FileRegion> iterator() {
     }
   }
 
-  class LevelDbWriter extends BlockAliasMap.Writer<FileRegion> {
+  static class LevelDbWriter extends BlockAliasMap.Writer<FileRegion> {
 
     private InMemoryAliasMapProtocol aliasMap;
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/RamDiskReplicaLruTracker.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/RamDiskReplicaLruTracker.java
index 31e9ebe0b8c..aebedaab0ef 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/RamDiskReplicaLruTracker.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/RamDiskReplicaLruTracker.java
@@ -35,7 +35,7 @@
 @InterfaceStability.Unstable
 public class RamDiskReplicaLruTracker extends RamDiskReplicaTracker {
 
-  private class RamDiskReplicaLru extends RamDiskReplica {
+  private static class RamDiskReplicaLru extends RamDiskReplica {
     long lastUsedTime;
 
     private RamDiskReplicaLru(String bpid, long blockId,
@@ -88,7 +88,7 @@ synchronized void addReplica(final String bpid, final long blockId,
     }
     RamDiskReplicaLru ramDiskReplicaLru =
         new RamDiskReplicaLru(bpid, blockId, transientVolume,
-                              lockedBytesReserved);
+            lockedBytesReserved);
     map.put(blockId, ramDiskReplicaLru);
     replicasNotPersisted.add(ramDiskReplicaLru);
   }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ReencryptionHandler.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ReencryptionHandler.java
index ea38da6021c..b1c5928f857 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ReencryptionHandler.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ReencryptionHandler.java
@@ -835,7 +835,7 @@ protected void readUnlock() {
     }
   }
 
-  private class ZoneTraverseInfo extends TraverseInfo {
+  private static class ZoneTraverseInfo extends TraverseInfo {
     private String ezKeyVerName;
 
     ZoneTraverseInfo(String ezKeyVerName) {
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DebugAdmin.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DebugAdmin.java
index 89389a09468..1784ea2accf 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DebugAdmin.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DebugAdmin.java
@@ -65,7 +65,7 @@ public class DebugAdmin extends Configured implements Tool {
   /**
    * All the debug commands we can run.
    */
-  private DebugCommand DEBUG_COMMANDS[] = {
+  private final DebugCommand[] DEBUG_COMMANDS = {
       new VerifyMetaCommand(),
       new ComputeMetaCommand(),
       new RecoverLeaseCommand(),
@@ -75,7 +75,7 @@ public class DebugAdmin extends Configured implements Tool {
   /**
    * The base class for debug commands.
    */
-  private abstract class DebugCommand {
+  private abstract static class DebugCommand {
     final String name;
     final String usageText;
     final String helpText;
@@ -94,15 +94,15 @@ private abstract class DebugCommand {
   /**
    * The command for verifying a block metadata file and possibly block file.
    */
-  private class VerifyMetaCommand extends DebugCommand {
+  private static class VerifyMetaCommand extends DebugCommand {
     VerifyMetaCommand() {
       super("verifyMeta",
-"verifyMeta -meta <metadata-file> [-block <block-file>]",
-"  Verify HDFS metadata and block files.  If a block file is specified, we" +
-    System.lineSeparator() +
-"  will verify that the checksums in the metadata file match the block" +
-    System.lineSeparator() +
-"  file.");
+          "verifyMeta -meta <metadata-file> [-block <block-file>]",
+          "  Verify HDFS metadata and block files.  If a block file is specified, we" +
+              System.lineSeparator() +
+              "  will verify that the checksums in the metadata file match the block" +
+              System.lineSeparator() +
+              "  file.");
     }
 
     int run(List<String> args) throws IOException {
@@ -210,7 +210,7 @@ int run(List<String> args) throws IOException {
   /**
    * The command for verifying a block metadata file and possibly block file.
    */
-  private class ComputeMetaCommand extends DebugCommand {
+  private static class ComputeMetaCommand extends DebugCommand {
     ComputeMetaCommand() {
       super("computeMeta",
           "computeMeta -block <block-file> -out <output-metadata-file>",
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java
index 2faca69a564..aec5afc37b3 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java
@@ -599,7 +599,7 @@ protected MiniDFSCluster(Builder builder) throws IOException {
                        builder.useConfiguredTopologyMappingClass);
   }
   
-  public class DataNodeProperties {
+  public static class DataNodeProperties {
     final DataNode datanode;
     final Configuration conf;
     String[] dnArgs;