YARN-6519. Fix warnings from Spotbugs in hadoop-yarn-server-resourcemanager. Contributed by Weiwei Yang.

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

@@ -393,7 +393,7 @@ public boolean hasApplicationMasterRegistered(
     return hasApplicationMasterRegistered;
   }
 
-  protected final static List<Container> EMPTY_CONTAINER_LIST =
+  private final static List<Container> EMPTY_CONTAINER_LIST =
       new ArrayList<Container>();
   protected static final Allocation EMPTY_ALLOCATION = new Allocation(
       EMPTY_CONTAINER_LIST, Resources.createResource(0), null, null, null);

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

@@ -52,7 +52,6 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
-import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
@@ -306,16 +305,12 @@ private void syncKillableContainersFromScheduler() {
 
   private void cleanupStaledPreemptionCandidates(long currentTime) {
     // Keep the preemptionCandidates list clean
-    for (Iterator<RMContainer> i = preemptionCandidates.keySet().iterator();
-         i.hasNext(); ) {
-      RMContainer id = i.next();
     // garbage collect containers that are irrelevant for preemption
     // And avoid preempt selected containers for *this execution*
     // or within 1 ms
-      if (preemptionCandidates.get(id) + 2 * maxWaitTime < currentTime) {
+    preemptionCandidates.entrySet()
-        i.remove();
+        .removeIf(candidate ->
-      }
+            candidate.getValue() + 2 * maxWaitTime < currentTime);
-    }
   }
 
   private Set<String> getLeafQueueNames(TempQueuePerPartition q) {

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

@@ -1000,9 +1000,11 @@ public void transferStateFromAttempt(RMAppAttempt attempt) {
     // if am crashed and not received this response, we should resend
     // this msg again after am restart
     if (!this.finishedContainersSentToAM.isEmpty()) {
-      for (NodeId nodeId : this.finishedContainersSentToAM.keySet()) {
+      for (Map.Entry<NodeId, List<ContainerStatus>> finishedContainer
+          : this.finishedContainersSentToAM.entrySet()) {
         List<ContainerStatus> containerStatuses =
-            this.finishedContainersSentToAM.get(nodeId);
+            finishedContainer.getValue();
+        NodeId nodeId = finishedContainer.getKey();
         this.justFinishedContainers.putIfAbsent(nodeId, new ArrayList<>());
         this.justFinishedContainers.get(nodeId).addAll(containerStatuses);
       }

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

@@ -152,7 +152,7 @@ public void updateAggregatePreemptedAppResourceUsage(
 
   public void incNumAllocatedContainers(NodeType containerType,
       NodeType requestType) {
-    localityStatistics[containerType.index][requestType.index]++;
+    localityStatistics[containerType.getIndex()][requestType.getIndex()]++;
     totalAllocatedContainers++;
   }
 

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

@@ -132,7 +132,7 @@ public abstract class AbstractYarnScheduler
   protected int nmExpireInterval;
   protected long nmHeartbeatInterval;
 
-  protected final static List<Container> EMPTY_CONTAINER_LIST =
+  private final static List<Container> EMPTY_CONTAINER_LIST =
       new ArrayList<Container>();
   protected static final Allocation EMPTY_ALLOCATION = new Allocation(
     EMPTY_CONTAINER_LIST, Resources.createResource(0), null, null, null);

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

@@ -23,9 +23,17 @@
  */
 public enum NodeType {
   NODE_LOCAL(0), RACK_LOCAL(1), OFF_SWITCH(2);
-  public int index;
 
-  private NodeType(int index) {
+  private final int index;
+
+  NodeType(int index) {
     this.index = index;
   }
+
+  /**
+   * @return the index of the node type
+   */
+  public int getIndex() {
+    return index;
+  }
 }

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

@@ -142,20 +142,29 @@ static QueueMetrics forQueue(String queueName, Queue parent,
    */
   @Private
   public synchronized static void clearQueueMetrics() {
-    queueMetrics.clear();
+    QUEUE_METRICS.clear();
   }
 
   /**
    * Simple metrics cache to help prevent re-registrations.
    */
-  protected final static Map<String, QueueMetrics> queueMetrics =
+  private static final Map<String, QueueMetrics> QUEUE_METRICS =
       new HashMap<String, QueueMetrics>();
 
+  /**
+   * Returns the metrics cache to help prevent re-registrations.
+   *
+   * @return A string to {@link QueueMetrics} map.
+   */
+  protected static Map<String, QueueMetrics> getQueueMetrics() {
+    return QUEUE_METRICS;
+  }
+
   public synchronized 
   static QueueMetrics forQueue(MetricsSystem ms, String queueName,
                                       Queue parent, boolean enableUserMetrics,
 				      Configuration conf) {
-    QueueMetrics metrics = queueMetrics.get(queueName);
+    QueueMetrics metrics = QUEUE_METRICS.get(queueName);
     if (metrics == null) {
       metrics =
           new QueueMetrics(ms, queueName, parent, enableUserMetrics, conf).
@@ -168,7 +177,7 @@ static QueueMetrics forQueue(MetricsSystem ms, String queueName,
                 sourceName(queueName).toString(), 
                 "Metrics for queue: " + queueName, metrics);
       }
-      queueMetrics.put(queueName, metrics);
+      QUEUE_METRICS.put(queueName, metrics);
     }
 
     return metrics;

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/CSQueueMetrics.java

@@ -115,7 +115,7 @@ public void setAbsoluteUsedCapacity(Float absoluteUsedCapacity) {
   public synchronized static CSQueueMetrics forQueue(String queueName,
       Queue parent, boolean enableUserMetrics, Configuration conf) {
     MetricsSystem ms = DefaultMetricsSystem.instance();
-    QueueMetrics metrics = queueMetrics.get(queueName);
+    QueueMetrics metrics = QueueMetrics.getQueueMetrics().get(queueName);
     if (metrics == null) {
       metrics =
           new CSQueueMetrics(ms, queueName, parent, enableUserMetrics, conf)
@@ -127,7 +127,7 @@ public synchronized static CSQueueMetrics forQueue(String queueName,
             ms.register(sourceName(queueName).toString(), "Metrics for queue: "
                 + queueName, metrics);
       }
-      queueMetrics.put(queueName, metrics);
+      QueueMetrics.getQueueMetrics().put(queueName, metrics);
     }
 
     return (CSQueueMetrics) metrics;

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/CapacitySchedulerQueueManager.java

@@ -69,9 +69,11 @@ public class CapacitySchedulerQueueManager implements SchedulerQueueManager<
       new Comparator<CSQueue>() {
     @Override
     public int compare(CSQueue q1, CSQueue q2) {
-      if (q1.getUsedCapacity() < q2.getUsedCapacity()) {
+      int result = Float.compare(q1.getUsedCapacity(),
+          q2.getUsedCapacity());
+      if (result < 0) {
         return -1;
-      } else if (q1.getUsedCapacity() > q2.getUsedCapacity()) {
+      } else if (result > 0) {
         return 1;
       }
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FSQueueMetrics.java

@@ -206,7 +206,7 @@ static FSQueueMetrics forQueue(String queueName, Queue parent,
   public synchronized
   static FSQueueMetrics forQueue(MetricsSystem ms, String queueName,
       Queue parent, boolean enableUserMetrics, Configuration conf) {
-    QueueMetrics metrics = queueMetrics.get(queueName);
+    QueueMetrics metrics = QueueMetrics.getQueueMetrics().get(queueName);
     if (metrics == null) {
       metrics = new FSQueueMetrics(ms, queueName, parent, enableUserMetrics, conf)
           .tag(QUEUE_INFO, queueName);
@@ -217,7 +217,7 @@ static FSQueueMetrics forQueue(MetricsSystem ms, String queueName,
             sourceName(queueName).toString(),
             "Metrics for queue: " + queueName, metrics);
       }
-      queueMetrics.put(queueName, metrics);
+      QueueMetrics.getQueueMetrics().put(queueName, metrics);
     }
 
     return (FSQueueMetrics)metrics;

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FSSchedulerNode.java

@@ -155,10 +155,10 @@ synchronized LinkedHashMap<FSAppAttempt, Resource> getPreemptionList() {
    * Remove apps that have their preemption requests fulfilled.
    */
   private synchronized void cleanupPreemptionList() {
-    Iterator<FSAppAttempt> iterator =
+    Iterator<Map.Entry<FSAppAttempt, Resource>> iterator =
-        resourcesPreemptedForApp.keySet().iterator();
+        resourcesPreemptedForApp.entrySet().iterator();
-    while (iterator.hasNext()) {
+    while(iterator.hasNext()) {
-      FSAppAttempt app = iterator.next();
+      FSAppAttempt app = iterator.next().getKey();
       if (app.isStopped() || !app.isStarved()) {
         // App does not need more resources
         Resources.subtractFrom(totalResourcesPreempted,