diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index a1d945f9d9b..d2b276187ba 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -346,6 +346,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-8623. Refactor NameNode handling of invalid, corrupt, and under-recovery
     blocks. (Zhe Zhang via jing9)
 
+    HDFS-8653. Code cleanup for DatanodeManager, DatanodeDescriptor and
+    DatanodeStorageInfo. (Zhe Zhang via wang)
+
   OPTIMIZATIONS
 
     HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CacheReplicationMonitor.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CacheReplicationMonitor.java
index a0f35039e47..2f81ddfad74 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CacheReplicationMonitor.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CacheReplicationMonitor.java
@@ -452,8 +452,8 @@ public class CacheReplicationMonitor extends Thread implements Closeable {
         file.getFullPathName(), cachedTotal, neededTotal);
   }
 
-  private String findReasonForNotCaching(CachedBlock cblock, 
-          BlockInfo blockInfo) {
+  private String findReasonForNotCaching(CachedBlock cblock,
+      BlockInfo blockInfo) {
     if (blockInfo == null) {
       // Somehow, a cache report with the block arrived, but the block
       // reports from the DataNode haven't (yet?) described such a block.
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeDescriptor.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeDescriptor.java
index 846ca338443..45a56b5730c 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeDescriptor.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeDescriptor.java
@@ -66,7 +66,8 @@ public class DatanodeDescriptor extends DatanodeInfo {
 
   // Stores status of decommissioning.
   // If node is not decommissioning, do not use this object for anything.
-  public final DecommissioningStatus decommissioningStatus = new DecommissioningStatus();
+  public final DecommissioningStatus decommissioningStatus =
+      new DecommissioningStatus();
 
   private long curBlockReportId = 0;
 
@@ -117,7 +118,7 @@ public class DatanodeDescriptor extends DatanodeInfo {
         return null;
       }
 
-      List<E> results = new ArrayList<E>();
+      List<E> results = new ArrayList<>();
       for(; !blockq.isEmpty() && numBlocks > 0; numBlocks--) {
         results.add(blockq.poll());
       }
@@ -137,7 +138,7 @@ public class DatanodeDescriptor extends DatanodeInfo {
   }
 
   private final Map<String, DatanodeStorageInfo> storageMap = 
-      new HashMap<String, DatanodeStorageInfo>();
+      new HashMap<>();
 
   /**
    * A list of CachedBlock objects on this datanode.
@@ -219,12 +220,14 @@ public class DatanodeDescriptor extends DatanodeInfo {
   private long bandwidth;
 
   /** A queue of blocks to be replicated by this datanode */
-  private final BlockQueue<BlockTargetPair> replicateBlocks = new BlockQueue<BlockTargetPair>();
+  private final BlockQueue<BlockTargetPair> replicateBlocks =
+      new BlockQueue<>();
   /** A queue of blocks to be recovered by this datanode */
   private final BlockQueue<BlockInfoUnderConstruction> recoverBlocks =
-                                new BlockQueue<BlockInfoUnderConstruction>();
+      new BlockQueue<>();
   /** A set of blocks to be invalidated by this datanode */
-  private final LightWeightHashSet<Block> invalidateBlocks = new LightWeightHashSet<Block>();
+  private final LightWeightHashSet<Block> invalidateBlocks =
+      new LightWeightHashSet<>();
 
   /* Variables for maintaining number of blocks scheduled to be written to
    * this storage. This count is approximate and might be slightly bigger
@@ -232,9 +235,9 @@ public class DatanodeDescriptor extends DatanodeInfo {
    * while writing the block).
    */
   private EnumCounters<StorageType> currApproxBlocksScheduled
-      = new EnumCounters<StorageType>(StorageType.class);
+      = new EnumCounters<>(StorageType.class);
   private EnumCounters<StorageType> prevApproxBlocksScheduled
-      = new EnumCounters<StorageType>(StorageType.class);
+      = new EnumCounters<>(StorageType.class);
   private long lastBlocksScheduledRollTime = 0;
   private static final int BLOCKS_SCHEDULED_ROLL_INTERVAL = 600*1000; //10min
   private int volumeFailures = 0;
@@ -278,6 +281,7 @@ public class DatanodeDescriptor extends DatanodeInfo {
       return storageMap.get(storageID);
     }
   }
+
   DatanodeStorageInfo[] getStorageInfos() {
     synchronized (storageMap) {
       final Collection<DatanodeStorageInfo> storages = storageMap.values();
@@ -323,7 +327,7 @@ public class DatanodeDescriptor extends DatanodeInfo {
               Long.toHexString(curBlockReportId));
           iter.remove();
           if (zombies == null) {
-            zombies = new LinkedList<DatanodeStorageInfo>();
+            zombies = new LinkedList<>();
           }
           zombies.add(storageInfo);
         }
@@ -352,10 +356,7 @@ public class DatanodeDescriptor extends DatanodeInfo {
    */
   boolean removeBlock(String storageID, BlockInfo b) {
     DatanodeStorageInfo s = getStorageInfo(storageID);
-    if (s != null) {
-      return s.removeBlock(b);
-    }
-    return false;
+    return s != null && s.removeBlock(b);
   }
 
   public void resetBlocks() {
@@ -451,7 +452,7 @@ public class DatanodeDescriptor extends DatanodeInfo {
           + this.volumeFailures + " to " + volFailures);
       synchronized (storageMap) {
         failedStorageInfos =
-            new HashSet<DatanodeStorageInfo>(storageMap.values());
+            new HashSet<>(storageMap.values());
       }
     }
 
@@ -507,7 +508,7 @@ public class DatanodeDescriptor extends DatanodeInfo {
       HashMap<String, DatanodeStorageInfo> excessStorages;
 
       // Init excessStorages with all known storages.
-      excessStorages = new HashMap<String, DatanodeStorageInfo>(storageMap);
+      excessStorages = new HashMap<>(storageMap);
 
       // Remove storages that the DN reported in the heartbeat.
       for (final StorageReport report : reports) {
@@ -544,7 +545,7 @@ public class DatanodeDescriptor extends DatanodeInfo {
     private final List<Iterator<BlockInfo>> iterators;
     
     private BlockIterator(final DatanodeStorageInfo... storages) {
-      List<Iterator<BlockInfo>> iterators = new ArrayList<Iterator<BlockInfo>>();
+      List<Iterator<BlockInfo>> iterators = new ArrayList<>();
       for (DatanodeStorageInfo e : storages) {
         iterators.add(e.getBlockIterator());
       }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeManager.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeManager.java
index c26d31019e1..90b173a7136 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeManager.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeManager.java
@@ -85,7 +85,7 @@ public class DatanodeManager {
    * Mapping: StorageID -> DatanodeDescriptor
    */
   private final Map<String, DatanodeDescriptor> datanodeMap
-      = new HashMap<String, DatanodeDescriptor>();
+      = new HashMap<>();
 
   /** Cluster network topology */
   private final NetworkTopology networktopology;
@@ -162,7 +162,7 @@ public class DatanodeManager {
    * Software version -> Number of datanodes with this version
    */
   private HashMap<String, Integer> datanodesSoftwareVersions =
-    new HashMap<String, Integer>(4, 0.75f);
+    new HashMap<>(4, 0.75f);
   
   /**
    * The minimum time between resending caching directives to Datanodes,
@@ -217,7 +217,7 @@ public class DatanodeManager {
     // locations of those hosts in the include list and store the mapping
     // in the cache; so future calls to resolve will be fast.
     if (dnsToSwitchMapping instanceof CachedDNSToSwitchMapping) {
-      final ArrayList<String> locations = new ArrayList<String>();
+      final ArrayList<String> locations = new ArrayList<>();
       for (InetSocketAddress addr : hostFileManager.getIncludes()) {
         locations.add(addr.getAddress().getHostAddress());
       }
@@ -370,7 +370,7 @@ public class DatanodeManager {
     // here we should get node but not datanode only .
     Node client = getDatanodeByHost(targethost);
     if (client == null) {
-      List<String> hosts = new ArrayList<String> (1);
+      List<String> hosts = new ArrayList<> (1);
       hosts.add(targethost);
       List<String> resolvedHosts = dnsToSwitchMapping.resolve(hosts);
       if (resolvedHosts != null && !resolvedHosts.isEmpty()) {
@@ -522,7 +522,7 @@ public class DatanodeManager {
   void datanodeDump(final PrintWriter out) {
     synchronized (datanodeMap) {
       Map<String,DatanodeDescriptor> sortedDatanodeMap =
-          new TreeMap<String,DatanodeDescriptor>(datanodeMap);
+          new TreeMap<>(datanodeMap);
       out.println("Metasave: Number of datanodes: " + datanodeMap.size());
       for (DatanodeDescriptor node : sortedDatanodeMap.values()) {
         out.println(node.dumpDatanode());
@@ -660,7 +660,7 @@ public class DatanodeManager {
 
   private void countSoftwareVersions() {
     synchronized(datanodeMap) {
-      HashMap<String, Integer> versionCount = new HashMap<String, Integer>();
+      HashMap<String, Integer> versionCount = new HashMap<>();
       for(DatanodeDescriptor dn: datanodeMap.values()) {
         // Check isAlive too because right after removeDatanode(),
         // isDatanodeDead() is still true 
@@ -677,7 +677,7 @@ public class DatanodeManager {
 
   public HashMap<String, Integer> getDatanodesSoftwareVersions() {
     synchronized(datanodeMap) {
-      return new HashMap<String, Integer> (this.datanodesSoftwareVersions);
+      return new HashMap<> (this.datanodesSoftwareVersions);
     }
   }
   
@@ -710,7 +710,7 @@ public class DatanodeManager {
    */
   private String resolveNetworkLocation (DatanodeID node) 
       throws UnresolvedTopologyException {
-    List<String> names = new ArrayList<String>(1);
+    List<String> names = new ArrayList<>(1);
     if (dnsToSwitchMapping instanceof CachedDNSToSwitchMapping) {
       names.add(node.getIpAddr());
     } else {
@@ -999,7 +999,7 @@ public class DatanodeManager {
       // If the network location is invalid, clear the cached mappings
       // so that we have a chance to re-add this DataNode with the
       // correct network location later.
-      List<String> invalidNodeNames = new ArrayList<String>(3);
+      List<String> invalidNodeNames = new ArrayList<>(3);
       // clear cache for nodes in IP or Hostname
       invalidNodeNames.add(nodeReg.getIpAddr());
       invalidNodeNames.add(nodeReg.getHostName());
@@ -1274,7 +1274,7 @@ public class DatanodeManager {
     final HostFileManager.HostSet excludedNodes = hostFileManager.getExcludes();
 
     synchronized(datanodeMap) {
-      nodes = new ArrayList<DatanodeDescriptor>(datanodeMap.size());
+      nodes = new ArrayList<>(datanodeMap.size());
       for (DatanodeDescriptor dn : datanodeMap.values()) {
         final boolean isDead = isDatanodeDead(dn);
         final boolean isDecommissioning = dn.isDecommissionInProgress();
@@ -1350,7 +1350,7 @@ public class DatanodeManager {
       VolumeFailureSummary volumeFailureSummary) throws IOException {
     synchronized (heartbeatManager) {
       synchronized (datanodeMap) {
-        DatanodeDescriptor nodeinfo = null;
+        DatanodeDescriptor nodeinfo;
         try {
           nodeinfo = getDatanode(nodeReg);
         } catch(UnregisteredNodeException e) {
@@ -1388,7 +1388,7 @@ public class DatanodeManager {
             final DatanodeStorageInfo[] storages = b.getExpectedStorageLocations();
             // Skip stale nodes during recovery - not heart beated for some time (30s by default).
             final List<DatanodeStorageInfo> recoveryLocations =
-                new ArrayList<DatanodeStorageInfo>(storages.length);
+                new ArrayList<>(storages.length);
             for (int i = 0; i < storages.length; i++) {
               if (!storages[i].getDatanodeDescriptor().isStale(staleInterval)) {
                 recoveryLocations.add(storages[i]);
@@ -1430,7 +1430,7 @@ public class DatanodeManager {
           return new DatanodeCommand[] { brCommand };
         }
 
-        final List<DatanodeCommand> cmds = new ArrayList<DatanodeCommand>();
+        final List<DatanodeCommand> cmds = new ArrayList<>();
         //check pending replication
         List<BlockTargetPair> pendingList = nodeinfo.getReplicationCommand(
               maxTransfers);
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeStorageInfo.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeStorageInfo.java
index 65b83e1a247..92841a634cb 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeStorageInfo.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeStorageInfo.java
@@ -37,8 +37,9 @@ import org.apache.hadoop.hdfs.server.protocol.StorageReport;
 public class DatanodeStorageInfo {
   public static final DatanodeStorageInfo[] EMPTY_ARRAY = {};
 
-  public static DatanodeInfo[] toDatanodeInfos(DatanodeStorageInfo[] storages) {
-    return toDatanodeInfos(Arrays.asList(storages));
+  public static DatanodeInfo[] toDatanodeInfos(
+      DatanodeStorageInfo[] storages) {
+    return storages == null ? null: toDatanodeInfos(Arrays.asList(storages));
   }
   static DatanodeInfo[] toDatanodeInfos(List<DatanodeStorageInfo> storages) {
     final DatanodeInfo[] datanodes = new DatanodeInfo[storages.size()];
@@ -58,6 +59,9 @@ public class DatanodeStorageInfo {
   }
 
   public static String[] toStorageIDs(DatanodeStorageInfo[] storages) {
+    if (storages == null) {
+      return null;
+    }
     String[] storageIDs = new String[storages.length];
     for(int i = 0; i < storageIDs.length; i++) {
       storageIDs[i] = storages[i].getStorageID();
@@ -66,6 +70,9 @@ public class DatanodeStorageInfo {
   }
 
   public static StorageType[] toStorageTypes(DatanodeStorageInfo[] storages) {
+    if (storages == null) {
+      return null;
+    }
     StorageType[] storageTypes = new StorageType[storages.length];
     for(int i = 0; i < storageTypes.length; i++) {
       storageTypes[i] = storages[i].getStorageType();
@@ -380,6 +387,6 @@ public class DatanodeStorageInfo {
   }
 
   static enum AddBlockResult {
-    ADDED, REPLACED, ALREADY_EXIST;
+    ADDED, REPLACED, ALREADY_EXIST
   }
 }