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 7b59e3c5bea..9229390258a 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
@@ -140,7 +140,7 @@ 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 fb5ee93c19a..bfd540b45cc 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
@@ -130,7 +130,7 @@ public class InMemoryLevelDBAliasMapClient extends BlockAliasMap<FileRegion>
     }
   }
 
-  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 b940736ccfd..0f0f59866a6 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 @@ import java.util.*;
 @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 @@ public class RamDiskReplicaLruTracker extends RamDiskReplicaTracker {
     }
     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 fa4de38eb75..e0bc0ff0da0 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 @@ public class ReencryptionHandler implements Runnable {
     }
   }
 
-  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 2c327f4ebd6..642bfab4766 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
@@ -64,7 +64,7 @@ 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(),
@@ -74,7 +74,7 @@ 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;
@@ -93,15 +93,15 @@ public class DebugAdmin extends Configured implements Tool {
   /**
    * 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 {
@@ -209,7 +209,7 @@ public class DebugAdmin extends Configured implements Tool {
   /**
    * 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 9834e5c703c..6f8e0cb8422 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
@@ -562,7 +562,7 @@ public class MiniDFSCluster implements AutoCloseable {
                        builder.useConfiguredTopologyMappingClass);
   }
   
-  public class DataNodeProperties {
+  public static class DataNodeProperties {
     final DataNode datanode;
     final Configuration conf;
     String[] dnArgs;