HADOOP-15223. Replace Collections.EMPTY* with empty* when available

Signed-off-by: Akira Ajisaka <aajisaka@apache.org>

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/crypto/key/KeyProvider.java

@@ -199,9 +199,8 @@ public abstract class KeyProvider {
       return cipher;
     }
 
-    @SuppressWarnings("unchecked")
     public Map<String, String> getAttributes() {
-      return (attributes == null) ? Collections.EMPTY_MAP : attributes;
+      return (attributes == null) ? Collections.emptyMap() : attributes;
     }
 
     /**
@@ -370,9 +369,8 @@ public abstract class KeyProvider {
       return description;
     }
 
-    @SuppressWarnings("unchecked")
     public Map<String, String> getAttributes() {
-      return (attributes == null) ? Collections.EMPTY_MAP : attributes;
+      return (attributes == null) ? Collections.emptyMap() : attributes;
     }
 
     @Override

hadoop-hdfs-project/hadoop-hdfs-client/src/test/java/org/apache/hadoop/hdfs/protocol/TestHdfsFileStatusMethods.java

@@ -54,7 +54,7 @@ public class TestHdfsFileStatusMethods {
     assertEquals(fsM.stream()
             .map(MethodSignature::toString)
             .collect(joining("\n")),
-        Collections.EMPTY_SET, fsM);
+        Collections.emptySet(), fsM);
   }
 
   /** Map non-static, declared methods for this class to signatures. */

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/lib/service/security/DummyGroupMapping.java

@@ -28,7 +28,6 @@ import org.apache.hadoop.test.HadoopUsersConfTestHelper;
 public class DummyGroupMapping implements GroupMappingServiceProvider {
 
   @Override
-  @SuppressWarnings("unchecked")
   public List<String> getGroups(String user) throws IOException {
     if (user.equals("root")) {
       return Arrays.asList("admin");
@@ -37,7 +36,7 @@ public class DummyGroupMapping implements GroupMappingServiceProvider {
       return Arrays.asList("nobody");
     } else {
       String[] groups = HadoopUsersConfTestHelper.getHadoopUserGroups(user);
-      return (groups != null) ? Arrays.asList(groups) : Collections.EMPTY_LIST;
+      return (groups != null) ? Arrays.asList(groups) : Collections.emptyList();
     }
   }
 

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/Listing.java

@@ -723,7 +723,7 @@ public class Listing {
       if (tombstones != null) {
         this.tombstones = tombstones;
       } else {
-        this.tombstones = Collections.EMPTY_SET;
+        this.tombstones = Collections.emptySet();
       }
     }
 

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java

@@ -2099,7 +2099,7 @@ public class S3AFileSystem extends FileSystem implements StreamCapabilities {
 
     // Check MetadataStore, if any.
     PathMetadata pm = metadataStore.get(path, needEmptyDirectoryFlag);
-    Set<Path> tombstones = Collections.EMPTY_SET;
+    Set<Path> tombstones = Collections.emptySet();
     if (pm != null) {
       if (pm.isDeleted()) {
         throw new FileNotFoundException("Path " + f + " is recorded as " +

hadoop-tools/hadoop-distcp/src/test/java/org/apache/hadoop/tools/mapred/TestCopyCommitter.java

@@ -415,7 +415,7 @@ public class TestCopyCommitter {
     @Override
     public List getSplits(JobContext context)
         throws IOException, InterruptedException {
-      return Collections.EMPTY_LIST;
+      return Collections.emptyList();
     }
 
     @Override

hadoop-tools/hadoop-sls/src/main/java/org/apache/hadoop/yarn/sls/scheduler/RMNodeWrapper.java

@@ -144,9 +144,8 @@ public class RMNodeWrapper implements RMNode {
   }
 
   @Override
-  @SuppressWarnings("unchecked")
   public List<UpdatedContainerInfo> pullContainerUpdates() {
-    List<UpdatedContainerInfo> list = Collections.EMPTY_LIST;
+    List<UpdatedContainerInfo> list = Collections.emptyList();
     if (! pulled) {
       list = updates;
       pulled = true;
@@ -168,11 +167,10 @@ public class RMNodeWrapper implements RMNode {
     return RMNodeLabelsManager.EMPTY_STRING_SET;
   }
 
-  @SuppressWarnings("unchecked")
   @Override
   public List<Container> pullNewlyIncreasedContainers() {
     // TODO Auto-generated method stub
-    return Collections.EMPTY_LIST;
+    return Collections.emptyList();
   }
 
   public OpportunisticContainersStatus getOpportunisticContainersStatus() {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/api/protocolrecords/AllocateRequest.java

@@ -223,7 +223,7 @@ public abstract class AllocateRequest {
   @Public
   @Unstable
   public List<SchedulingRequest> getSchedulingRequests() {
-    return Collections.EMPTY_LIST;
+    return Collections.emptyList();
   }
 
   /**

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/api/protocolrecords/AllocateResponse.java

@@ -420,7 +420,7 @@ public abstract class AllocateResponse {
   @Public
   @Unstable
   public List<RejectedSchedulingRequest> getRejectedSchedulingRequests() {
-    return Collections.EMPTY_LIST;
+    return Collections.emptyList();
   }
 
   /**

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-api/src/main/java/org/apache/hadoop/yarn/api/records/Container.java

@@ -263,7 +263,7 @@ public abstract class Container implements Comparable<Container> {
   @Private
   @Unstable
   public Set<String> getAllocationTags() {
-    return Collections.EMPTY_SET;
+    return Collections.emptySet();
   }
 
   @Private

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/security/ContainerTokenIdentifier.java

@@ -368,7 +368,7 @@ public class ContainerTokenIdentifier extends TokenIdentifier {
     if (proto.getAllocationTagsList() != null) {
       return new HashSet<>(proto.getAllocationTagsList());
     }
-    return Collections.EMPTY_SET;
+    return Collections.emptySet();
   }
 
   // TODO: Needed?

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-common/src/main/java/org/apache/hadoop/yarn/server/api/protocolrecords/NMContainerStatus.java

@@ -169,7 +169,7 @@ public abstract class NMContainerStatus {
    * Get and set the Allocation tags associated with the container.
    */
   public Set<String> getAllocationTags() {
-    return Collections.EMPTY_SET;
+    return Collections.emptySet();
   }
 
   public void setAllocationTags(Set<String> allocationTags) {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/resourceplugin/ResourcePluginManager.java

@@ -46,7 +46,8 @@ public class ResourcePluginManager {
   private static final Set<String> SUPPORTED_RESOURCE_PLUGINS = ImmutableSet.of(
       GPU_URI, FPGA_URI);
 
-  private Map<String, ResourcePlugin> configuredPlugins = Collections.EMPTY_MAP;
+  private Map<String, ResourcePlugin> configuredPlugins =
+          Collections.emptyMap();
 
   public synchronized void initialize(Context context)
       throws YarnException {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/DefaultAMSProcessor.java

@@ -207,10 +207,10 @@ final class DefaultAMSProcessor implements ApplicationMasterServiceProcessor {
         request.getResourceBlacklistRequest();
     List<String> blacklistAdditions =
         (blacklistRequest != null) ?
-            blacklistRequest.getBlacklistAdditions() : Collections.EMPTY_LIST;
+            blacklistRequest.getBlacklistAdditions() : Collections.emptyList();
     List<String> blacklistRemovals =
         (blacklistRequest != null) ?
-            blacklistRequest.getBlacklistRemovals() : Collections.EMPTY_LIST;
+            blacklistRequest.getBlacklistRemovals() : Collections.emptyList();
     RMApp app =
         getRmContext().getRMApps().get(appAttemptId.getApplicationId());
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/monitor/capacity/ProportionalCapacityPreemptionPolicy.java

@@ -136,23 +136,21 @@ public class ProportionalCapacityPreemptionPolicy
   private Map<String, PreemptableQueue> preemptableQueues;
   private Set<ContainerId> killableContainers;
 
-  @SuppressWarnings("unchecked")
   public ProportionalCapacityPreemptionPolicy() {
     clock = SystemClock.getInstance();
-    allPartitions = Collections.EMPTY_SET;
-    leafQueueNames = Collections.EMPTY_SET;
-    preemptableQueues = Collections.EMPTY_MAP;
+    allPartitions = Collections.emptySet();
+    leafQueueNames = Collections.emptySet();
+    preemptableQueues = Collections.emptyMap();
   }
 
-  @SuppressWarnings("unchecked")
   @VisibleForTesting
   public ProportionalCapacityPreemptionPolicy(RMContext context,
       CapacityScheduler scheduler, Clock clock) {
     init(context.getYarnConfiguration(), context, scheduler);
     this.clock = clock;
-    allPartitions = Collections.EMPTY_SET;
-    leafQueueNames = Collections.EMPTY_SET;
-    preemptableQueues = Collections.EMPTY_MAP;
+    allPartitions = Collections.emptySet();
+    leafQueueNames = Collections.emptySet();
+    preemptableQueues = Collections.emptyMap();
   }
 
   public void init(Configuration config, RMContext context,

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/rmapp/attempt/RMAppAttemptImpl.java

@@ -2237,7 +2237,7 @@ public class RMAppAttemptImpl implements RMAppAttempt, Recoverable {
         return attempt.getBlacklistedNodes();
       }
     }
-    return Collections.EMPTY_SET;
+    return Collections.emptySet();
   }
 
   protected void onInvalidTranstion(RMAppAttemptEventType rmAppAttemptEventType,

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/rmnode/RMNodeImpl.java

@@ -1477,7 +1477,7 @@ public class RMNodeImpl implements RMNode, EventHandler<RMNodeEvent> {
       writeLock.lock();
 
       if (nmReportedIncreasedContainers.isEmpty()) {
-        return Collections.EMPTY_LIST;
+        return Collections.emptyList();
       } else {
         List<Container> container =
             new ArrayList<Container>(nmReportedIncreasedContainers.values());

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/rmnode/RMNodeStatusEvent.java

@@ -80,10 +80,9 @@ public class RMNodeStatusEvent extends RMNodeEvent {
     this.logAggregationReportsForApps = logAggregationReportsForApps;
   }
   
-  @SuppressWarnings("unchecked")
   public List<Container> getNMReportedIncreasedContainers() {
     return this.nodeStatus.getIncreasedContainers() == null ?
-        Collections.EMPTY_LIST : this.nodeStatus.getIncreasedContainers();
+        Collections.emptyList() : this.nodeStatus.getIncreasedContainers();
   }
 
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/constraint/processor/BatchedRequests.java

@@ -131,7 +131,7 @@ public class BatchedRequests
    * @return Set of blacklisted Nodes.
    */
   public Set<NodeId> getBlacklist(String tag) {
-    return blacklist.getOrDefault(tag, Collections.EMPTY_SET);
+    return blacklist.getOrDefault(tag, Collections.emptySet());
   }
 
   /**

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/constraint/processor/PlacementDispatcher.java

@@ -87,7 +87,7 @@ class PlacementDispatcher implements
       }
       return retList;
     }
-    return Collections.EMPTY_LIST;
+    return Collections.emptyList();
   }
 
   public List<SchedulingRequestWithPlacementAttempt> pullRejectedRequests(
@@ -104,7 +104,7 @@ class PlacementDispatcher implements
       }
       return retList;
     }
-    return Collections.EMPTY_LIST;
+    return Collections.emptyList();
   }
 
   void clearApplicationState(ApplicationId applicationId) {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/placement/SingleConstraintAppPlacementAllocator.java

@@ -373,9 +373,8 @@ public class SingleConstraintAppPlacementAllocator<N extends SchedulerNode>
   }
 
   @Override
-  @SuppressWarnings("unchecked")
   public Map<String, ResourceRequest> getResourceRequests() {
-    return Collections.EMPTY_MAP;
+    return Collections.emptyMap();
   }
 
   @Override

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/TestResourceTrackerService.java

@@ -723,13 +723,12 @@ public class TestResourceTrackerService extends NodeLabelTestBase {
     }
   }
 
-  @SuppressWarnings("unchecked")
   private NodeStatus getNodeStatusObject(NodeId nodeId) {
     NodeStatus status = Records.newRecord(NodeStatus.class);
     status.setNodeId(nodeId);
     status.setResponseId(0);
-    status.setContainersStatuses(Collections.EMPTY_LIST);
-    status.setKeepAliveApplications(Collections.EMPTY_LIST);
+    status.setContainersStatuses(Collections.emptyList());
+    status.setKeepAliveApplications(Collections.emptyList());
     return status;
   }
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/monitor/capacity/ProportionalCapacityPreemptionPolicyMockFramework.java

@@ -781,7 +781,7 @@ public class ProportionalCapacityPreemptionPolicyMockFramework {
       }
     }
 
-    return Collections.EMPTY_MAP;
+    return Collections.emptyMap();
   }
 
   /**