HBASE-27202 Clean up error-prone findings in hbase-balancer (#4623)

Signed-off-by: Duo Zhang <zhangduo@apache.org>

hbase-balancer/src/main/java/org/apache/hadoop/hbase/favored/FavoredNodeAssignmentHelper.java

@@ -111,7 +111,7 @@ public class FavoredNodeAssignmentHelper {
           break;
         }
       }
-      serverList.add((sn));
+      serverList.add(sn);
       this.regionServerToRackMap.put(sn.getHostname(), rackName);
     }
   }
@@ -235,7 +235,7 @@ public class FavoredNodeAssignmentHelper {
           if (numIterations % rackList.size() == 0) {
             if (++serverIndex >= maxRackSize) serverIndex = 0;
           }
-          if ((++rackIndex) >= rackList.size()) {
+          if (++rackIndex >= rackList.size()) {
             rackIndex = 0; // reset the rack index to 0
           }
         } else break;
@@ -259,7 +259,7 @@ public class FavoredNodeAssignmentHelper {
       if (numIterations % rackList.size() == 0) {
         ++serverIndex;
       }
-      if ((++rackIndex) >= rackList.size()) {
+      if (++rackIndex >= rackList.size()) {
         rackIndex = 0; // reset the rack index to 0
       }
     }
@@ -298,7 +298,7 @@ public class FavoredNodeAssignmentHelper {
     if (getTotalNumberOfRacks() == 1) {
       favoredNodes = singleRackCase(regionInfo, primaryRS, primaryRack);
     } else {
-      favoredNodes = multiRackCase(regionInfo, primaryRS, primaryRack);
+      favoredNodes = multiRackCase(primaryRS, primaryRack);
     }
     return favoredNodes;
   }
@@ -483,14 +483,12 @@ public class FavoredNodeAssignmentHelper {
    * has only one region server, then we place primary and tertiary on one rack and secondary on
    * another. The aim is two distribute the three favored nodes on >= 2 racks. TODO: see how we can
    * use generateMissingFavoredNodeMultiRack API here
-   * @param regionInfo  Region for which we are trying to generate FN
    * @param primaryRS   The primary favored node.
    * @param primaryRack The rack of the primary favored node.
    * @return Array containing secondary and tertiary favored nodes.
    * @throws IOException Signals that an I/O exception has occurred.
    */
-  private ServerName[] multiRackCase(RegionInfo regionInfo, ServerName primaryRS,
-    String primaryRack) throws IOException {
+  private ServerName[] multiRackCase(ServerName primaryRS, String primaryRack) throws IOException {
 
     List<ServerName> favoredNodes = Lists.newArrayList(primaryRS);
     // Create the secondary and tertiary pair

hbase-balancer/src/main/java/org/apache/hadoop/hbase/favored/FavoredNodesPlan.java

@@ -99,7 +99,7 @@ public class FavoredNodesPlan {
   }
 
   /**
-   * @return the mapping between each region to its favored region server list
+   * Return the mapping between each region to its favored region server list.
    */
   public Map<String, List<ServerName>> getAssignmentMap() {
     // Make a deep copy so changes don't harm our copy of favoredNodesMap.
@@ -119,7 +119,7 @@ public class FavoredNodesPlan {
     if (o == null) {
       return false;
     }
-    if (getClass() != o.getClass()) {
+    if (!(o instanceof FavoredNodesPlan)) {
       return false;
     }
     // To compare the map from object o is identical to current assignment map.

hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/AssignmentVerificationReport.java

@@ -409,8 +409,8 @@ public class AssignmentVerificationReport {
   }
 
   /**
-   * @return list which contains just 3 elements: average dispersion score, max dispersion score and
-   *         min dispersion score as first, second and third element respectively.
+   * Return a list which contains 3 elements: average dispersion score, max dispersion score and min
+   * dispersion score as first, second and third elements, respectively.
    */
   public List<Float> getDispersionInformation() {
     List<Float> dispersion = new ArrayList<>();
@@ -578,7 +578,7 @@ public class AssignmentVerificationReport {
     }
     int i = 0;
     for (ServerName addr : serverSet) {
-      if ((i++) % 3 == 0) {
+      if (i++ % 3 == 0) {
         System.out.print("\n\t\t\t");
       }
       System.out.print(addr.getAddress() + " ; ");

hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/RegionPlan.java

@@ -148,10 +148,7 @@ public class RegionPlan implements Comparable<RegionPlan> {
     if (this == obj) {
       return true;
     }
-    if (obj == null) {
-      return false;
-    }
-    if (getClass() != obj.getClass()) {
+    if (!(obj instanceof RegionPlan)) {
       return false;
     }
     RegionPlan other = (RegionPlan) obj;

hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/BalancerClusterState.java

@@ -218,7 +218,7 @@ class BalancerClusterState {
     colocatedReplicaCountsPerHost = new Int2IntCounterMap[numHosts];
     colocatedReplicaCountsPerRack = new Int2IntCounterMap[numRacks];
 
-    int tableIndex = 0, regionIndex = 0, regionPerServerIndex = 0;
+    int regionIndex = 0, regionPerServerIndex = 0;
 
     for (Map.Entry<ServerName, List<RegionInfo>> entry : clusterState.entrySet()) {
       if (entry.getKey() == null) {

hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionHDFSBlockLocationFinder.java

@@ -246,6 +246,7 @@ class RegionHDFSBlockLocationFinder extends Configured {
    */
   @RestrictedApi(explanation = "Should only be called in tests", link = "",
       allowedOnPath = ".*/src/test/.*|.*/RegionHDFSBlockLocationFinder.java")
+  @SuppressWarnings("MixedMutabilityReturnType")
   List<ServerName> mapHostNameToServerName(List<String> hosts) {
     if (hosts == null || status == null) {
       if (hosts == null) {