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The following commit(s) were added to refs/heads/master by this push:
     new b70d35ab64 HDDS-12889. Enable AppendCharacterWithChar PMD rule (#8324)
b70d35ab64 is described below

commit b70d35ab64aeba1a772bf2ea5578895a2c911731
Author: Ivan Zlenko <[email protected]>
AuthorDate: Sun Apr 27 00:14:39 2025 +0500

    HDDS-12889. Enable AppendCharacterWithChar PMD rule (#8324)
---
 dev-support/pmd/pmd-ruleset.xml                    |  1 +
 .../java/org/apache/hadoop/hdds/HddsUtils.java     |  2 +-
 .../java/org/apache/hadoop/hdds/NodeDetails.java   |  2 +-
 .../org/apache/hadoop/hdds/scm/ha/SCMNodeInfo.java |  2 +-
 .../hadoop/hdds/scm/net/NetworkTopologyImpl.java   |  6 ++---
 .../apache/hadoop/hdds/scm/pipeline/Pipeline.java  |  6 ++---
 .../apache/hadoop/hdds/tracing/StringCodec.java    |  6 ++---
 .../ozone/container/common/helpers/BlockData.java  |  2 +-
 .../helpers/BlockDeletingServiceMetrics.java       | 30 +++++++++++-----------
 .../helpers/DeletedContainerBlocksSummary.java     |  6 ++---
 .../common/impl/StorageLocationReport.java         |  2 +-
 .../ECReconstructionCoordinator.java               |  2 +-
 .../ozone/container/keyvalue/KeyValueHandler.java  |  2 +-
 .../replication/AbstractReplicationTask.java       |  2 +-
 .../protocol/commands/CloseContainerCommand.java   |  2 +-
 .../protocol/commands/ClosePipelineCommand.java    |  2 +-
 .../protocol/commands/CreatePipelineCommand.java   |  2 +-
 .../protocol/commands/DeleteBlocksCommand.java     |  4 +--
 .../protocol/commands/DeleteContainerCommand.java  |  2 +-
 .../commands/FinalizeNewLayoutVersionCommand.java  |  2 +-
 .../commands/ReconstructECContainersCommand.java   |  4 +--
 .../commands/RefreshVolumeUsageCommand.java        |  2 +-
 .../commands/ReplicateContainerCommand.java        |  2 +-
 .../ozone/protocol/commands/ReregisterCommand.java |  2 +-
 .../commands/SetNodeOperationalStateCommand.java   |  2 +-
 .../container/common/utils/TestHddsVolumeUtil.java |  4 +--
 .../container/common/volume/TestDbVolume.java      |  2 +-
 .../container/ozoneimpl/TestContainerReader.java   |  2 +-
 .../container/ozoneimpl/TestOzoneContainer.java    |  2 +-
 .../apache/ozone/erasurecode/TestCoderBase.java    |  4 +--
 .../rawcoder/RawErasureCoderBenchmark.java         |  2 +-
 .../hadoop/hdds/server/http/HttpServer2.java       |  2 +-
 .../hdds/server/http/PrometheusMetricsSink.java    |  6 ++---
 .../apache/hadoop/hdds/utils/HddsServerUtil.java   |  2 +-
 .../org/apache/hadoop/hdds/utils/SignalLogger.java |  2 +-
 .../rocksdiff/TestRocksDBCheckpointDiffer.java     |  2 +-
 .../scm/block/ScmBlockDeletingServiceMetrics.java  | 16 ++++++------
 .../replication/ContainerHealthResult.java         |  2 +-
 .../replication/ECContainerReplicaCount.java       |  2 +-
 .../hdds/scm/node/DatanodeAdminMonitorImpl.java    |  2 +-
 .../hdds/scm/server/SCMClientProtocolServer.java   |  2 +-
 .../hdds/scm/server/SCMDatanodeProtocolServer.java |  6 ++---
 .../apache/ozone/test/TimedOutTestsListener.java   |  2 +-
 .../hadoop/hdds/scm/cli/TopologySubcommand.java    |  4 +--
 .../hdds/scm/cli/container/InfoSubcommand.java     |  6 ++---
 .../hdds/scm/cli/datanode/ListInfoSubcommand.java  |  6 ++---
 .../scm/cli/container/TestReportSubCommand.java    |  2 +-
 .../hadoop/ozone/client/MockDatanodeStorage.java   |  2 +-
 .../main/java/org/apache/hadoop/ozone/OmUtils.java |  4 +--
 .../ozone/om/helpers/OmKeyLocationInfoGroup.java   |  8 +++---
 .../hadoop/ozone/om/helpers/OzoneFileStatus.java   |  4 +--
 .../ozone/om/helpers/OzoneFileStatusLight.java     |  4 +--
 .../java/org/apache/ozone/lib/lang/XException.java |  2 +-
 .../hadoop/conf/TestConfigurationFieldsBase.java   |  2 +-
 .../fs/contract/AbstractContractSeekTest.java      |  2 +-
 .../hadoop/fs/contract/ContractTestUtils.java      |  4 +--
 .../rpc/TestOzoneClientMultipartUploadWithFSO.java |  2 +-
 .../apache/hadoop/ozone/om/TestKeyManagerImpl.java |  4 +--
 .../apache/hadoop/ozone/MiniOzoneClusterImpl.java  |  4 +--
 .../hadoop/ozone/MiniOzoneHAClusterImpl.java       |  2 +-
 .../org/apache/hadoop/ozone/om/OzoneManager.java   |  2 +-
 .../ozone/om/ratis/OzoneManagerStateMachine.java   |  2 +-
 .../ozone/om/request/key/OMKeysDeleteRequest.java  |  6 ++---
 .../ozone/om/service/OpenKeyCleanupService.java    |  2 +-
 .../hadoop/ozone/om/snapshot/OmSnapshotUtils.java  |  4 +--
 .../request/file/TestOMDirectoryCreateRequest.java |  2 +-
 .../TestRequestFeatureValidatorProcessor.java      |  4 +--
 .../apache/hadoop/fs/ozone/FileStatusAdapter.java  |  4 +--
 .../ozone/s3/signature/StringToSignProducer.java   |  4 +--
 .../hadoop/ozone/s3/endpoint/TestObjectPut.java    |  2 +-
 .../debug/audit/parser/common/DatabaseHelper.java  |  4 +--
 .../hadoop/ozone/freon/OmMetadataGenerator.java    |  2 +-
 .../org/apache/hadoop/ozone/freon/ProgressBar.java |  4 +--
 .../schemaupgrade/ContainerUpgradeResult.java      |  2 +-
 .../schemaupgrade/VolumeUpgradeResult.java         |  2 +-
 .../hadoop/ozone/utils/FormattingCLIUtils.java     | 20 +++++++--------
 76 files changed, 144 insertions(+), 143 deletions(-)

diff --git a/dev-support/pmd/pmd-ruleset.xml b/dev-support/pmd/pmd-ruleset.xml
index 1bdb2be45a..e3af967ff3 100644
--- a/dev-support/pmd/pmd-ruleset.xml
+++ b/dev-support/pmd/pmd-ruleset.xml
@@ -35,6 +35,7 @@
   <rule ref="category/java/bestpractices.xml/SimplifiableTestAssertion" />
 
   <rule ref="category/java/performance.xml/AddEmptyString"/>
+  <rule ref="category/java/performance.xml/AppendCharacterWithChar" />
   <rule ref="category/java/performance.xml/AvoidFileStream"/>
   <rule ref="category/java/performance.xml/InefficientEmptyStringCheck"/>
   <rule ref="category/java/performance.xml/InefficientStringBuffering"/>
diff --git 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/HddsUtils.java 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/HddsUtils.java
index c450e46e8f..690631ca31 100644
--- a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/HddsUtils.java
+++ b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/HddsUtils.java
@@ -845,7 +845,7 @@ public static HddsProtos.UUID toProtobuf(UUID uuid) {
     if (elements != null && elements.length > startIndex) {
       final StringBuilder sb = new StringBuilder();
       for (int line = startIndex; line < elements.length; line++) {
-        sb.append(elements[line]).append("\n");
+        sb.append(elements[line]).append('\n');
       }
       return sb.toString();
     }
diff --git 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/NodeDetails.java 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/NodeDetails.java
index 05e8ecb498..0984048bd5 100644
--- a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/NodeDetails.java
+++ b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/NodeDetails.java
@@ -105,7 +105,7 @@ public String getHostAddress() {
   public String getRatisHostPortStr() {
     StringBuilder hostPort = new StringBuilder();
     hostPort.append(getHostName())
-        .append(":")
+        .append(':')
         .append(ratisPort);
     return hostPort.toString();
   }
diff --git 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/ha/SCMNodeInfo.java
 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/ha/SCMNodeInfo.java
index f3626bfeaf..d0806b34d5 100644
--- 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/ha/SCMNodeInfo.java
+++ 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/ha/SCMNodeInfo.java
@@ -182,7 +182,7 @@ public static List<SCMNodeInfo> 
buildNodeInfo(ConfigurationSource conf) {
   }
 
   private static String buildAddress(String address, int port) {
-    return new StringBuilder().append(address).append(":")
+    return new StringBuilder().append(address).append(':')
         .append(port).toString();
   }
 
diff --git 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/net/NetworkTopologyImpl.java
 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/net/NetworkTopologyImpl.java
index 99e718438d..1e5c57266c 100644
--- 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/net/NetworkTopologyImpl.java
+++ 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/net/NetworkTopologyImpl.java
@@ -893,18 +893,18 @@ public String toString() {
     StringBuilder tree = new StringBuilder();
     tree.append("Level: ");
     tree.append(maxLevel);
-    tree.append("\n");
+    tree.append('\n');
     netlock.readLock().lock();
     try {
       // print the number of leaves
       int numOfLeaves = clusterTree.getNumOfLeaves();
       tree.append("Number of leaves:");
       tree.append(numOfLeaves);
-      tree.append("\n");
+      tree.append('\n');
       // print all nodes
       for (int i = 0; i < numOfLeaves; i++) {
         tree.append(clusterTree.getLeaf(i).getNetworkFullPath());
-        tree.append("\n");
+        tree.append('\n');
       }
     } finally {
       netlock.readLock().unlock();
diff --git 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/pipeline/Pipeline.java
 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/pipeline/Pipeline.java
index 605c3bc254..1549f4f782 100644
--- 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/pipeline/Pipeline.java
+++ 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/pipeline/Pipeline.java
@@ -521,20 +521,20 @@ public int hashCode() {
   @Override
   public String toString() {
     final StringBuilder b =
-        new StringBuilder(getClass().getSimpleName()).append("{");
+        new StringBuilder(getClass().getSimpleName()).append('{');
     b.append(" Id: ").append(id.getId());
     b.append(", Nodes: [");
     for (DatanodeDetails datanodeDetails : nodeStatus.keySet()) {
       b.append(" {").append(datanodeDetails);
       b.append(", ReplicaIndex: 
").append(this.getReplicaIndex(datanodeDetails)).append("},");
     }
-    b.append("]");
+    b.append(']');
     b.append(", ReplicationConfig: ").append(replicationConfig);
     b.append(", State:").append(getPipelineState());
     b.append(", leaderId:").append(leaderId != null ? leaderId.toString() : 
"");
     b.append(", CreationTimestamp").append(getCreationTimestamp()
         .atZone(ZoneId.systemDefault()));
-    b.append("}");
+    b.append('}');
     return b.toString();
   }
 
diff --git 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/tracing/StringCodec.java
 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/tracing/StringCodec.java
index 18f968a9cf..f22393a50d 100644
--- 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/tracing/StringCodec.java
+++ 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/tracing/StringCodec.java
@@ -70,9 +70,9 @@ public JaegerSpanContext extract(StringBuilder s) {
   public void inject(JaegerSpanContext context, StringBuilder string) {
     int intFlag = context.getFlags() & 255;
     string.append(context.getTraceId())
-        .append(":").append(Long.toHexString(context.getSpanId()))
-        .append(":").append(Long.toHexString(context.getParentId()))
-        .append(":").append(Integer.toHexString(intFlag));
+        .append(':').append(Long.toHexString(context.getSpanId()))
+        .append(':').append(Long.toHexString(context.getParentId()))
+        .append(':').append(Integer.toHexString(intFlag));
   }
 
   private static long high(String hexString) {
diff --git 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/ozone/container/common/helpers/BlockData.java
 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/ozone/container/common/helpers/BlockData.java
index b718e80689..eb1a436b67 100644
--- 
a/hadoop-hdds/common/src/main/java/org/apache/hadoop/ozone/container/common/helpers/BlockData.java
+++ 
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/ozone/container/common/helpers/BlockData.java
@@ -279,7 +279,7 @@ public void appendTo(StringBuilder sb) {
     sb.append("[blockId=");
     blockID.appendTo(sb);
     sb.append(", size=").append(size);
-    sb.append("]");
+    sb.append(']');
   }
 
   public long getBlockGroupLength() {
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/helpers/BlockDeletingServiceMetrics.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/helpers/BlockDeletingServiceMetrics.java
index 03f0fec183..6e4d638e6a 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/helpers/BlockDeletingServiceMetrics.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/helpers/BlockDeletingServiceMetrics.java
@@ -206,22 +206,22 @@ public long getProcessedTransactionFailCount() {
   @Override
   public String toString() {
     StringBuilder buffer = new StringBuilder()
-        .append("successCount = ").append(successCount.value()).append("\t")
-        .append("successBytes = ").append(successBytes.value()).append("\t")
-        .append("failureCount = ").append(failureCount.value()).append("\t")
+        .append("successCount = ").append(successCount.value()).append('\t')
+        .append("successBytes = ").append(successBytes.value()).append('\t')
+        .append("failureCount = ").append(failureCount.value()).append('\t')
         .append("outOfOrderDeleteBlockTransactionCount = ")
-        .append(outOfOrderDeleteBlockTransactionCount.value()).append("\t")
-        .append("totalPendingBlockCount = 
").append(totalPendingBlockCount.value()).append("\t")
-        .append("totalBlockChosenCount = 
").append(totalBlockChosenCount.value()).append("\t")
-        .append("totalContainerChosenCount = 
").append(totalContainerChosenCount.value()).append("\t")
-        .append("receivedTransactionCount = 
").append(receivedTransactionCount.value()).append("\t")
-        .append("receivedRetryTransactionCount = 
").append(receivedRetryTransactionCount.value()).append("\t")
-        .append("processedTransactionSuccessCount = 
").append(processedTransactionSuccessCount.value()).append("\t")
-        .append("processedTransactionFailCount = 
").append(processedTransactionFailCount.value()).append("\t")
-        .append("receivedContainerCount = 
").append(receivedContainerCount.value()).append("\t")
-        .append("receivedBlockCount = 
").append(receivedBlockCount.value()).append("\t")
-        .append("markedBlockCount = 
").append(markedBlockCount.value()).append("\t")
-        .append("totalLockTimeoutTransactionCount = 
").append(totalLockTimeoutTransactionCount.value()).append("\t");
+        .append(outOfOrderDeleteBlockTransactionCount.value()).append('\t')
+        .append("totalPendingBlockCount = 
").append(totalPendingBlockCount.value()).append('\t')
+        .append("totalBlockChosenCount = 
").append(totalBlockChosenCount.value()).append('\t')
+        .append("totalContainerChosenCount = 
").append(totalContainerChosenCount.value()).append('\t')
+        .append("receivedTransactionCount = 
").append(receivedTransactionCount.value()).append('\t')
+        .append("receivedRetryTransactionCount = 
").append(receivedRetryTransactionCount.value()).append('\t')
+        .append("processedTransactionSuccessCount = 
").append(processedTransactionSuccessCount.value()).append('\t')
+        .append("processedTransactionFailCount = 
").append(processedTransactionFailCount.value()).append('\t')
+        .append("receivedContainerCount = 
").append(receivedContainerCount.value()).append('\t')
+        .append("receivedBlockCount = 
").append(receivedBlockCount.value()).append('\t')
+        .append("markedBlockCount = 
").append(markedBlockCount.value()).append('\t')
+        .append("totalLockTimeoutTransactionCount = 
").append(totalLockTimeoutTransactionCount.value()).append('\t');
     return buffer.toString();
   }
 }
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/helpers/DeletedContainerBlocksSummary.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/helpers/DeletedContainerBlocksSummary.java
index 638e113756..610e54025b 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/helpers/DeletedContainerBlocksSummary.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/helpers/DeletedContainerBlocksSummary.java
@@ -99,7 +99,7 @@ public String getTxIDSummary() {
   @Override public String toString() {
     StringBuffer sb = new StringBuffer();
     for (DeletedBlocksTransaction blks : blocks) {
-      sb.append(" ")
+      sb.append(' ')
           .append("TXID=")
           .append(blks.getTxID())
           .append(", ")
@@ -108,8 +108,8 @@ public String getTxIDSummary() {
           .append(", ")
           .append(blks.getContainerID())
           .append(" : [")
-          .append(StringUtils.join(',', blks.getLocalIDList())).append("]")
-          .append("\n");
+          .append(StringUtils.join(',', blks.getLocalIDList())).append(']')
+          .append('\n');
     }
     return sb.toString();
   }
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/impl/StorageLocationReport.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/impl/StorageLocationReport.java
index 5f539e121b..d3148df8c8 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/impl/StorageLocationReport.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/impl/StorageLocationReport.java
@@ -235,7 +235,7 @@ public static StorageLocationReport 
getFromProtobuf(StorageReportProto report)
   @Override
   public String toString() {
     StringBuilder sb = new StringBuilder(128)
-        .append("{")
+        .append('{')
         .append(" id=").append(id)
         .append(" dir=").append(storageLocation)
         .append(" type=").append(storageType);
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/ec/reconstruction/ECReconstructionCoordinator.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/ec/reconstruction/ECReconstructionCoordinator.java
index 4694850b93..d8856f081d 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/ec/reconstruction/ECReconstructionCoordinator.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/ec/reconstruction/ECReconstructionCoordinator.java
@@ -373,7 +373,7 @@ private void logBlockGroupDetails(BlockLocationInfo 
blockLocationInfo,
       int cnt = 0;
       for (ContainerProtos.ChunkInfo chunkInfo : data.getChunks()) {
         if (cnt > 0) {
-          sb.append("\n");
+          sb.append('\n');
         }
         sb.append("  chunkNum: ")
             .append(++cnt)
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/keyvalue/KeyValueHandler.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/keyvalue/KeyValueHandler.java
index 408897c6bb..8e1080dc48 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/keyvalue/KeyValueHandler.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/keyvalue/KeyValueHandler.java
@@ -1427,7 +1427,7 @@ private boolean logBlocksFoundOnDisk(Container container) 
throws IOException {
       StringBuilder stringBuilder = new StringBuilder();
       for (Path block : dir) {
         if (notEmpty) {
-          stringBuilder.append(",");
+          stringBuilder.append(',');
         }
         stringBuilder.append(block);
         notEmpty = true;
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/replication/AbstractReplicationTask.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/replication/AbstractReplicationTask.java
index 2ba2b676a9..05932e6edf 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/replication/AbstractReplicationTask.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/replication/AbstractReplicationTask.java
@@ -144,7 +144,7 @@ protected Object getCommandForDebug() {
   @Override
   public String toString() {
     StringBuilder sb = new StringBuilder()
-        .append(getStatus()).append(" ")
+        .append(getStatus()).append(' ')
         .append(getCommandForDebug());
     if (getStatus() == Status.QUEUED) {
       sb.append(", queued at ").append(getQueued());
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/CloseContainerCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/CloseContainerCommand.java
index 8d4b43d1cc..6bd5adb688 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/CloseContainerCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/CloseContainerCommand.java
@@ -90,7 +90,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline())
         .append(", containerID: ").append(getContainerID())
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ClosePipelineCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ClosePipelineCommand.java
index d1c8e9444b..0c1caa3dd6 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ClosePipelineCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ClosePipelineCommand.java
@@ -75,7 +75,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline())
         .append(", pipelineID: ").append(getPipelineID());
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/CreatePipelineCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/CreatePipelineCommand.java
index b6340e86c6..ebd5bcfdcc 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/CreatePipelineCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/CreatePipelineCommand.java
@@ -159,7 +159,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline())
         .append(", pipelineID: ").append(getPipelineID())
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/DeleteBlocksCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/DeleteBlocksCommand.java
index e955cabdfa..e6457d4d25 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/DeleteBlocksCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/DeleteBlocksCommand.java
@@ -69,7 +69,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline())
         .append(", deletedBlocksTransaction: [");
@@ -83,7 +83,7 @@ public String toString() {
     if (!blocksTobeDeleted.isEmpty()) {
       sb.delete(sb.length() - 2, sb.length());
     }
-    sb.append("]");
+    sb.append(']');
     return sb.toString();
   }
 }
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/DeleteContainerCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/DeleteContainerCommand.java
index d142e23c23..193c67576c 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/DeleteContainerCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/DeleteContainerCommand.java
@@ -108,7 +108,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline())
         .append(", containerID: ").append(getContainerID())
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/FinalizeNewLayoutVersionCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/FinalizeNewLayoutVersionCommand.java
index b686db5ef0..0d5c02202d 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/FinalizeNewLayoutVersionCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/FinalizeNewLayoutVersionCommand.java
@@ -78,7 +78,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline())
         .append(", finalizeUpgrade: ").append(finalizeUpgrade)
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReconstructECContainersCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReconstructECContainersCommand.java
index 93bbfd8202..3628c2c9e6 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReconstructECContainersCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReconstructECContainersCommand.java
@@ -131,7 +131,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline())
         .append(", containerID: ").append(containerID)
@@ -139,7 +139,7 @@ public String toString() {
         .append(", sources: [").append(getSources().stream()
             .map(a -> a.dnDetails
                 + " replicaIndex: " + a.getReplicaIndex())
-            .collect(Collectors.joining(", "))).append("]")
+            .collect(Collectors.joining(", "))).append(']')
         .append(", targets: ").append(getTargetDatanodes())
         .append(", missingIndexes: ").append(
             Arrays.toString(missingContainerIndexes.toByteArray()));
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/RefreshVolumeUsageCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/RefreshVolumeUsageCommand.java
index f685a8282b..6872b152e1 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/RefreshVolumeUsageCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/RefreshVolumeUsageCommand.java
@@ -60,7 +60,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline());
     return sb.toString();
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReplicateContainerCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReplicateContainerCommand.java
index d4046bd989..826af4fdd3 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReplicateContainerCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReplicateContainerCommand.java
@@ -159,7 +159,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType());
     sb.append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline());
     sb.append(", containerId=").append(getContainerID());
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReregisterCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReregisterCommand.java
index adb87a3898..82961d994a 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReregisterCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/ReregisterCommand.java
@@ -59,7 +59,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline());
     return sb.toString();
diff --git 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/SetNodeOperationalStateCommand.java
 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/SetNodeOperationalStateCommand.java
index 45e51d00e7..51aaf87ae3 100644
--- 
a/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/SetNodeOperationalStateCommand.java
+++ 
b/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/protocol/commands/SetNodeOperationalStateCommand.java
@@ -91,7 +91,7 @@ public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getType())
         .append(": cmdID: ").append(getId())
-        .append(", encodedToken: \"").append(getEncodedToken()).append("\"")
+        .append(", encodedToken: \"").append(getEncodedToken()).append('"')
         .append(", term: ").append(getTerm())
         .append(", deadlineMsSinceEpoch: ").append(getDeadline())
         .append(", opState: ").append(opState)
diff --git 
a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/utils/TestHddsVolumeUtil.java
 
b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/utils/TestHddsVolumeUtil.java
index 9ec248e383..9cbf95f3ea 100644
--- 
a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/utils/TestHddsVolumeUtil.java
+++ 
b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/utils/TestHddsVolumeUtil.java
@@ -73,7 +73,7 @@ public void setup() throws Exception {
     for (int i = 0; i < VOLUMNE_NUM; i++) {
       hddsVolumeDirs[i] =
           Files.createDirectory(tempDir.resolve("volumeDir" + i)).toFile();
-      hddsDirs.append(hddsVolumeDirs[i]).append(",");
+      hddsDirs.append(hddsVolumeDirs[i]).append(',');
     }
     conf.set(ScmConfigKeys.HDDS_DATANODE_DIR_KEY, hddsDirs.toString());
     hddsVolumeSet = new MutableVolumeSet(datanodeId, clusterId, conf, null,
@@ -85,7 +85,7 @@ public void setup() throws Exception {
     for (int i = 0; i < VOLUMNE_NUM; i++) {
       dbVolumeDirs[i] =
           Files.createDirectory(tempDir.resolve("dbVolumeDir" + i)).toFile();
-      dbDirs.append(dbVolumeDirs[i]).append(",");
+      dbDirs.append(dbVolumeDirs[i]).append(',');
     }
     conf.set(OzoneConfigKeys.HDDS_DATANODE_CONTAINER_DB_DIR,
         dbDirs.toString());
diff --git 
a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/volume/TestDbVolume.java
 
b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/volume/TestDbVolume.java
index 683c2b12b1..280f8597d7 100644
--- 
a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/volume/TestDbVolume.java
+++ 
b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/volume/TestDbVolume.java
@@ -164,7 +164,7 @@ private MutableVolumeSet createHddsVolumeSet(int volumeNum)
     for (int i = 0; i < volumeNum; i++) {
       hddsVolumeDirs[i] =
           Files.createDirectory(folder.resolve("volumeDir" + i)).toFile();
-      hddsDirs.append(hddsVolumeDirs[i]).append(",");
+      hddsDirs.append(hddsVolumeDirs[i]).append(',');
     }
     CONF.set(ScmConfigKeys.HDDS_DATANODE_DIR_KEY, hddsDirs.toString());
     MutableVolumeSet hddsVolumeSet = new MutableVolumeSet(DATANODE_UUID,
diff --git 
a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/ozoneimpl/TestContainerReader.java
 
b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/ozoneimpl/TestContainerReader.java
index dbe6df0c7b..6a48765c1a 100644
--- 
a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/ozoneimpl/TestContainerReader.java
+++ 
b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/ozoneimpl/TestContainerReader.java
@@ -375,7 +375,7 @@ public void 
testMultipleContainerReader(ContainerTestVersionInfo versionInfo)
     for (int i = 0; i < volumeNum; i++) {
       volumeDirs[i] =
           Files.createDirectory(tempDir.resolve("volumeDir" + i)).toFile();
-      datanodeDirs = datanodeDirs.append(volumeDirs[i]).append(",");
+      datanodeDirs = datanodeDirs.append(volumeDirs[i]).append(',');
     }
 
     BlockUtils.shutdownCache(conf);
diff --git 
a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/ozoneimpl/TestOzoneContainer.java
 
b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/ozoneimpl/TestOzoneContainer.java
index 34619c1918..de5b2331f1 100644
--- 
a/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/ozoneimpl/TestOzoneContainer.java
+++ 
b/hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/ozoneimpl/TestOzoneContainer.java
@@ -189,7 +189,7 @@ public void testBuildNodeReport(ContainerTestVersionInfo 
versionInfo)
     for (int i = 0; i < 3; i++) {
       dbPaths[i] =
           Files.createDirectory(folder.resolve(Integer.toString(i))).toFile();
-      dbDirString.append(dbPaths[i]).append(",");
+      dbDirString.append(dbPaths[i]).append(',');
     }
     conf.set(OzoneConfigKeys.HDDS_DATANODE_CONTAINER_DB_DIR,
         dbDirString.toString());
diff --git 
a/hadoop-hdds/erasurecode/src/test/java/org/apache/ozone/erasurecode/TestCoderBase.java
 
b/hadoop-hdds/erasurecode/src/test/java/org/apache/ozone/erasurecode/TestCoderBase.java
index 3f5d66bc14..a6f6dba517 100644
--- 
a/hadoop-hdds/erasurecode/src/test/java/org/apache/ozone/erasurecode/TestCoderBase.java
+++ 
b/hadoop-hdds/erasurecode/src/test/java/org/apache/ozone/erasurecode/TestCoderBase.java
@@ -482,7 +482,7 @@ protected void dumpSetting() {
       StringBuilder sb = new StringBuilder("Erasure coder test settings:\n");
       sb.append(" numDataUnits=").append(numDataUnits);
       sb.append(" numParityUnits=").append(numParityUnits);
-      sb.append(" chunkSize=").append(chunkSize).append("\n");
+      sb.append(" chunkSize=").append(chunkSize).append('\n');
 
       sb.append(" erasedDataIndexes=").
           append(Arrays.toString(erasedDataIndexes));
@@ -490,7 +490,7 @@ protected void dumpSetting() {
           append(Arrays.toString(erasedParityIndexes));
       sb.append(" usingDirectBuffer=").append(usingDirectBuffer);
       sb.append(" allowVerboseDump=").append(allowDump);
-      sb.append("\n");
+      sb.append('\n');
 
       System.out.println(sb.toString());
     }
diff --git 
a/hadoop-hdds/erasurecode/src/test/java/org/apache/ozone/erasurecode/rawcoder/RawErasureCoderBenchmark.java
 
b/hadoop-hdds/erasurecode/src/test/java/org/apache/ozone/erasurecode/rawcoder/RawErasureCoderBenchmark.java
index ef9b59325d..89c15316ef 100644
--- 
a/hadoop-hdds/erasurecode/src/test/java/org/apache/ozone/erasurecode/rawcoder/RawErasureCoderBenchmark.java
+++ 
b/hadoop-hdds/erasurecode/src/test/java/org/apache/ozone/erasurecode/rawcoder/RawErasureCoderBenchmark.java
@@ -85,7 +85,7 @@ private static void printAvailableCoders() {
     StringBuilder sb = new StringBuilder(
         "Available coders with coderIndex:\n");
     for (CODER coder : CODER.values()) {
-      sb.append(coder.ordinal()).append(":").append(coder).append("\n");
+      sb.append(coder.ordinal()).append(':').append(coder).append('\n');
     }
     System.out.println(sb);
   }
diff --git 
a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/server/http/HttpServer2.java
 
b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/server/http/HttpServer2.java
index aa7eb407ae..0e505633dd 100644
--- 
a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/server/http/HttpServer2.java
+++ 
b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/server/http/HttpServer2.java
@@ -1410,7 +1410,7 @@ public String toString() {
             : STATE_DESCRIPTION_NOT_LIVE)
         .append("), listening at:");
     for (ServerConnector l : listeners) {
-      sb.append(l.getHost()).append(":").append(l.getPort()).append("/,");
+      sb.append(l.getHost()).append(':').append(l.getPort()).append("/,");
     }
     return sb.toString();
   }
diff --git 
a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/server/http/PrometheusMetricsSink.java
 
b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/server/http/PrometheusMetricsSink.java
index 6f431bfe89..89cf9adbb6 100644
--- 
a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/server/http/PrometheusMetricsSink.java
+++ 
b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/server/http/PrometheusMetricsSink.java
@@ -90,7 +90,7 @@ private String getPrometheusMetricKeyAsString(MetricsRecord 
metricsRecord,
       String key, String username) {
     StringBuilder prometheusMetricKey = new StringBuilder();
     prometheusMetricKey.append(key)
-        .append("{");
+        .append('{');
     String sep = "";
 
     List<MetricsTag> metricsTags =
@@ -110,10 +110,10 @@ private String 
getPrometheusMetricKeyAsString(MetricsRecord metricsRecord,
           .append(tagName)
           .append("=\"")
           .append(tag.value())
-          .append("\"");
+          .append('"');
       sep = ",";
     }
-    prometheusMetricKey.append("}");
+    prometheusMetricKey.append('}');
 
     return prometheusMetricKey.toString();
   }
diff --git 
a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/utils/HddsServerUtil.java
 
b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/utils/HddsServerUtil.java
index b3e21db17f..9a780be8b3 100644
--- 
a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/utils/HddsServerUtil.java
+++ 
b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/utils/HddsServerUtil.java
@@ -707,7 +707,7 @@ public static String toStartupShutdownString(String prefix, 
String... msg) {
     StringBuilder b = new StringBuilder(prefix);
     
b.append("\n/************************************************************");
     for (String s : msg) {
-      b.append("\n").append(prefix).append(s);
+      b.append('\n').append(prefix).append(s);
     }
     
b.append("\n************************************************************/");
     return b.toString();
diff --git 
a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/utils/SignalLogger.java
 
b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/utils/SignalLogger.java
index 9e5832c9e6..02dcc136c7 100644
--- 
a/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/utils/SignalLogger.java
+++ 
b/hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/utils/SignalLogger.java
@@ -94,7 +94,7 @@ public void register(final Logger log) {
         log.info("Error installing UNIX signal handler for {}", signal, e);
       }
     }
-    bld.append("]");
+    bld.append(']');
     if (log.isInfoEnabled()) {
       log.info(bld.toString());
     }
diff --git 
a/hadoop-hdds/rocksdb-checkpoint-differ/src/test/java/org/apache/ozone/rocksdiff/TestRocksDBCheckpointDiffer.java
 
b/hadoop-hdds/rocksdb-checkpoint-differ/src/test/java/org/apache/ozone/rocksdiff/TestRocksDBCheckpointDiffer.java
index b975ea26dc..2bafef9818 100644
--- 
a/hadoop-hdds/rocksdb-checkpoint-differ/src/test/java/org/apache/ozone/rocksdiff/TestRocksDBCheckpointDiffer.java
+++ 
b/hadoop-hdds/rocksdb-checkpoint-differ/src/test/java/org/apache/ozone/rocksdiff/TestRocksDBCheckpointDiffer.java
@@ -996,7 +996,7 @@ private void printMutableGraphFromAGivenNode(
       for (CompactionNode current : currentLevel) {
         Set<CompactionNode> successors = mutableGraph.successors(current);
         for (CompactionNode succNode : successors) {
-          sb.append(succNode.getFileName()).append(" ");
+          sb.append(succNode.getFileName()).append(' ');
           nextLevel.add(succNode);
         }
       }
diff --git 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/block/ScmBlockDeletingServiceMetrics.java
 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/block/ScmBlockDeletingServiceMetrics.java
index 2f298a5ebc..20293bbd4a 100644
--- 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/block/ScmBlockDeletingServiceMetrics.java
+++ 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/block/ScmBlockDeletingServiceMetrics.java
@@ -334,15 +334,15 @@ public long getNumCommandsDatanodeFailed() {
   @Override
   public String toString() {
     StringBuilder buffer = new StringBuilder()
-        .append("numBlockDeletionTransactionCreated = 
").append(numBlockDeletionTransactionCreated.value()).append("\t")
+        .append("numBlockDeletionTransactionCreated = 
").append(numBlockDeletionTransactionCreated.value()).append('\t')
         .append("numBlockDeletionTransactionCompleted = ")
-        .append(numBlockDeletionTransactionCompleted.value()).append("\t")
-        .append("numBlockDeletionCommandSent = 
").append(numBlockDeletionCommandSent.value()).append("\t")
-        .append("numBlockDeletionCommandSuccess = 
").append(numBlockDeletionCommandSuccess.value()).append("\t")
-        .append("numBlockDeletionCommandFailure = 
").append(numBlockDeletionCommandFailure.value()).append("\t")
-        .append("numBlockDeletionTransactionSent = 
").append(numBlockDeletionTransactionSent.value()).append("\t")
-        .append("numBlockDeletionTransactionSuccess = 
").append(numBlockDeletionTransactionSuccess.value()).append("\t")
-        .append("numBlockDeletionTransactionFailure = 
").append(numBlockDeletionTransactionFailure.value()).append("\t")
+        .append(numBlockDeletionTransactionCompleted.value()).append('\t')
+        .append("numBlockDeletionCommandSent = 
").append(numBlockDeletionCommandSent.value()).append('\t')
+        .append("numBlockDeletionCommandSuccess = 
").append(numBlockDeletionCommandSuccess.value()).append('\t')
+        .append("numBlockDeletionCommandFailure = 
").append(numBlockDeletionCommandFailure.value()).append('\t')
+        .append("numBlockDeletionTransactionSent = 
").append(numBlockDeletionTransactionSent.value()).append('\t')
+        .append("numBlockDeletionTransactionSuccess = 
").append(numBlockDeletionTransactionSuccess.value()).append('\t')
+        .append("numBlockDeletionTransactionFailure = 
").append(numBlockDeletionTransactionFailure.value()).append('\t')
         .append("numDeletionCommandsPerDatanode = 
").append(numCommandsDatanode);
     return buffer.toString();
   }
diff --git 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/ContainerHealthResult.java
 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/ContainerHealthResult.java
index f4489da345..1788bf9f52 100644
--- 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/ContainerHealthResult.java
+++ 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/ContainerHealthResult.java
@@ -294,7 +294,7 @@ public String toString() {
       if (requeueCount > 0) {
         sb.append(" requeued:").append(requeueCount);
       }
-      return sb.append("}").toString();
+      return sb.append('}').toString();
     }
   }
 
diff --git 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/ECContainerReplicaCount.java
 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/ECContainerReplicaCount.java
index 36be55c41b..13ad1d37b4 100644
--- 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/ECContainerReplicaCount.java
+++ 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/ECContainerReplicaCount.java
@@ -569,7 +569,7 @@ public String toString() {
     if (!pendingDelete.isEmpty()) {
       sb.append(", PendingDelete: ").append(pendingDelete.size());
     }
-    sb.append(")")
+    sb.append(')')
         .append(", ReplicationConfig: ").append(repConfig)
         .append(", RemainingMaintenanceRedundancy: ")
         .append(remainingMaintenanceRedundancy);
diff --git 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/node/DatanodeAdminMonitorImpl.java
 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/node/DatanodeAdminMonitorImpl.java
index 4733c0629d..f5bcf6ff63 100644
--- 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/node/DatanodeAdminMonitorImpl.java
+++ 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/node/DatanodeAdminMonitorImpl.java
@@ -499,7 +499,7 @@ private String replicaDetails(Collection<ContainerReplica> 
replicas) {
     sb.append(replicas.stream()
         .map(Object::toString)
         .collect(Collectors.joining(",")));
-    sb.append("}");
+    sb.append('}');
     return sb.toString();
   }
 
diff --git 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMClientProtocolServer.java
 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMClientProtocolServer.java
index 7bc437627a..b945786ac0 100644
--- 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMClientProtocolServer.java
+++ 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMClientProtocolServer.java
@@ -379,7 +379,7 @@ public List<ContainerWithPipeline> 
getContainerWithPipelineBatch(
         ContainerWithPipeline cp = getContainerWithPipelineCommon(containerID);
         cpList.add(cp);
         strContainerIDs.append(ContainerID.valueOf(containerID).toString());
-        strContainerIDs.append(",");
+        strContainerIDs.append(',');
       } catch (IOException ex) {
         AUDIT.logReadFailure(buildAuditMessageForFailure(
             SCMAction.GET_CONTAINER_WITH_PIPELINE_BATCH,
diff --git 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMDatanodeProtocolServer.java
 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMDatanodeProtocolServer.java
index df615eec3b..eb4feec2fc 100644
--- 
a/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMDatanodeProtocolServer.java
+++ 
b/hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMDatanodeProtocolServer.java
@@ -276,14 +276,14 @@ public static SCMRegisteredResponseProto 
getRegisteredResponse(
 
   private String constructCommandAuditMap(List<SCMCommandProto> cmds) {
     StringBuilder auditMap = new StringBuilder();
-    auditMap.append("[");
+    auditMap.append('[');
     for (SCMCommandProto cmd : cmds) {
       if (cmd.getCommandType().equals(deleteBlocksCommand)) {
         auditMap.append("commandType: ").append(cmd.getCommandType());
         auditMap.append(" deleteTransactionsCount: ")
             
.append(cmd.getDeleteBlocksCommandProto().getDeletedBlocksTransactionsCount());
         auditMap.append(" cmdID: 
").append(cmd.getDeleteBlocksCommandProto().getCmdId());
-        auditMap.append(" encodedToken: 
\"").append(cmd.getEncodedToken()).append("\"");
+        auditMap.append(" encodedToken: 
\"").append(cmd.getEncodedToken()).append('"');
         auditMap.append(" deadlineMsSinceEpoch: 
").append(cmd.getDeadlineMsSinceEpoch());
       } else {
         auditMap.append(TextFormat.shortDebugString(cmd));
@@ -294,7 +294,7 @@ private String 
constructCommandAuditMap(List<SCMCommandProto> cmds) {
     if (len > 2) {
       auditMap.delete(len - 2, len);
     }
-    auditMap.append("]");
+    auditMap.append(']');
     return auditMap.toString();
   }
 
diff --git 
a/hadoop-hdds/test-utils/src/test/java/org/apache/ozone/test/TimedOutTestsListener.java
 
b/hadoop-hdds/test-utils/src/test/java/org/apache/ozone/test/TimedOutTestsListener.java
index c2d07137a5..c7a8873c69 100644
--- 
a/hadoop-hdds/test-utils/src/test/java/org/apache/ozone/test/TimedOutTestsListener.java
+++ 
b/hadoop-hdds/test-utils/src/test/java/org/apache/ozone/test/TimedOutTestsListener.java
@@ -96,7 +96,7 @@ private static String buildThreadDump() {
         dump.append("\n        at ");
         dump.append(stackTraceElement);
       }
-      dump.append("\n");
+      dump.append('\n');
     }
     return dump.toString();
   }
diff --git 
a/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/TopologySubcommand.java
 
b/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/TopologySubcommand.java
index b2f7ce1384..5a850551c2 100644
--- 
a/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/TopologySubcommand.java
+++ 
b/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/TopologySubcommand.java
@@ -181,9 +181,9 @@ private String formatPortOutput(List<HddsProtos.Port> 
ports) {
     StringBuilder sb = new StringBuilder();
     for (int i = 0; i < ports.size(); i++) {
       HddsProtos.Port port = ports.get(i);
-      sb.append(port.getName()).append("=").append(port.getValue());
+      sb.append(port.getName()).append('=').append(port.getValue());
       if (i < ports.size() - 1) {
-        sb.append(",");
+        sb.append(',');
       }
     }
     return sb.toString();
diff --git 
a/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/container/InfoSubcommand.java
 
b/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/container/InfoSubcommand.java
index 38df564536..2c3ad44c97 100644
--- 
a/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/container/InfoSubcommand.java
+++ 
b/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/container/InfoSubcommand.java
@@ -195,11 +195,11 @@ private static String 
buildDatanodeDetails(DatanodeDetails details) {
 
   private static String buildReplicaDetails(ContainerReplicaInfo replica) {
     StringBuilder sb = new StringBuilder()
-        .append("State: ").append(replica.getState()).append(";");
+        .append("State: ").append(replica.getState()).append(';');
     if (replica.getReplicaIndex() != -1) {
-      sb.append(" ReplicaIndex: 
").append(replica.getReplicaIndex()).append(";");
+      sb.append(" ReplicaIndex: 
").append(replica.getReplicaIndex()).append(';');
     }
-    sb.append(" Origin: 
").append(replica.getPlaceOfBirth().toString()).append(";")
+    sb.append(" Origin: 
").append(replica.getPlaceOfBirth().toString()).append(';')
         .append(" Location: 
").append(buildDatanodeDetails(replica.getDatanodeDetails()));
     return sb.toString();
   }
diff --git 
a/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/datanode/ListInfoSubcommand.java
 
b/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/datanode/ListInfoSubcommand.java
index 929873c658..90e678f281 100644
--- 
a/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/datanode/ListInfoSubcommand.java
+++ 
b/hadoop-hdds/tools/src/main/java/org/apache/hadoop/hdds/scm/cli/datanode/ListInfoSubcommand.java
@@ -145,9 +145,9 @@ private void printDatanodeInfo(DatanodeWithAttributes dna) {
         relatedPipelineNum = relatedPipelines.size();
         relatedPipelines.forEach(
             p -> pipelineListInfo.append(p.getId().getId().toString())
-                .append("/").append(p.getReplicationConfig().toString())
-                .append("/").append(p.getType().toString())
-                
.append("/").append(p.getPipelineState().toString()).append("/")
+                .append('/').append(p.getReplicationConfig().toString())
+                .append('/').append(p.getType().toString())
+                
.append('/').append(p.getPipelineState().toString()).append('/')
                 .append(datanode.getUuid().equals(p.getLeaderId()) ?
                     "Leader" : "Follower")
                 .append(System.getProperty("line.separator")));
diff --git 
a/hadoop-hdds/tools/src/test/java/org/apache/hadoop/hdds/scm/cli/container/TestReportSubCommand.java
 
b/hadoop-hdds/tools/src/test/java/org/apache/hadoop/hdds/scm/cli/container/TestReportSubCommand.java
index f74850e6c4..ad661ea3c8 100644
--- 
a/hadoop-hdds/tools/src/test/java/org/apache/hadoop/hdds/scm/cli/container/TestReportSubCommand.java
+++ 
b/hadoop-hdds/tools/src/test/java/org/apache/hadoop/hdds/scm/cli/container/TestReportSubCommand.java
@@ -177,7 +177,7 @@ private String containerList(int start, int end) {
       if (i != start) {
         sb.append(", ");
       }
-      sb.append("#").append(i);
+      sb.append('#').append(i);
     }
     return sb.toString();
   }
diff --git 
a/hadoop-ozone/client/src/test/java/org/apache/hadoop/ozone/client/MockDatanodeStorage.java
 
b/hadoop-ozone/client/src/test/java/org/apache/hadoop/ozone/client/MockDatanodeStorage.java
index 92f0b6ea4c..a526cebe2c 100644
--- 
a/hadoop-ozone/client/src/test/java/org/apache/hadoop/ozone/client/MockDatanodeStorage.java
+++ 
b/hadoop-ozone/client/src/test/java/org/apache/hadoop/ozone/client/MockDatanodeStorage.java
@@ -133,7 +133,7 @@ public BlockData getBlock(DatanodeBlockID blockID) {
     if (!blocks.containsKey(id)) {
       StringBuilder sb = new StringBuilder();
       for (BlockID bid : blocks.keySet()) {
-        sb.append(bid).append("\n");
+        sb.append(bid).append('\n');
       }
       throw new AssertionError("blockID " + id +
           " not found in blocks. Available block ID: \n" + sb);
diff --git 
a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/OmUtils.java 
b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/OmUtils.java
index 789d26c888..9ca59b9c38 100644
--- a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/OmUtils.java
+++ b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/OmUtils.java
@@ -919,10 +919,10 @@ public static String 
getOMAddressListPrintString(List<OMNodeDetails> omList) {
     }
     printString.append(omList.get(0).getOMPrintInfo());
     for (int i = 1; i < omList.size(); i++) {
-      printString.append(",")
+      printString.append(',')
           .append(omList.get(i).getOMPrintInfo());
     }
-    printString.append("]");
+    printString.append(']');
     return printString.toString();
   }
 
diff --git 
a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OmKeyLocationInfoGroup.java
 
b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OmKeyLocationInfoGroup.java
index 01d5fbaa70..ddf62a45ed 100644
--- 
a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OmKeyLocationInfoGroup.java
+++ 
b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OmKeyLocationInfoGroup.java
@@ -185,14 +185,14 @@ void addAll(long versionToAdd, List<OmKeyLocationInfo> 
locationInfoList) {
   @Override
   public String toString() {
     StringBuilder sb = new StringBuilder();
-    sb.append("version:").append(version).append(" ");
-    sb.append("isMultipartKey:").append(isMultipartKey).append(" ");
+    sb.append("version:").append(version).append(' ');
+    sb.append("isMultipartKey:").append(isMultipartKey).append(' ');
     for (List<OmKeyLocationInfo> kliList : locationVersionMap.values()) {
       for (OmKeyLocationInfo kli: kliList) {
         sb.append("conID ").append(kli.getContainerID());
-        sb.append(" ");
+        sb.append(' ');
         sb.append("locID ").append(kli.getLocalID());
-        sb.append(" ");
+        sb.append(' ');
         sb.append("bcsID ").append(kli.getBlockCommitSequenceId());
         sb.append(" || ");
       }
diff --git 
a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OzoneFileStatus.java
 
b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OzoneFileStatus.java
index cafffb4809..99ea12b1cd 100644
--- 
a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OzoneFileStatus.java
+++ 
b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OzoneFileStatus.java
@@ -134,7 +134,7 @@ public int hashCode() {
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getClass().getSimpleName());
-    sb.append("{");
+    sb.append('{');
     if (keyInfo == null) {
       sb.append("<root>");
     } else {
@@ -143,7 +143,7 @@ public String toString() {
         sb.append(" (dir)");
       }
     }
-    sb.append("}");
+    sb.append('}');
     return sb.toString();
   }
 
diff --git 
a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OzoneFileStatusLight.java
 
b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OzoneFileStatusLight.java
index 213431188b..5d07f33108 100644
--- 
a/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OzoneFileStatusLight.java
+++ 
b/hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/helpers/OzoneFileStatusLight.java
@@ -132,7 +132,7 @@ public int hashCode() {
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getClass().getSimpleName());
-    sb.append("{");
+    sb.append('{');
     if (keyInfo == null) {
       sb.append("<root>");
     } else {
@@ -141,7 +141,7 @@ public String toString() {
         sb.append(" (dir)");
       }
     }
-    sb.append("}");
+    sb.append('}');
     return sb.toString();
   }
 
diff --git 
a/hadoop-ozone/httpfsgateway/src/main/java/org/apache/ozone/lib/lang/XException.java
 
b/hadoop-ozone/httpfsgateway/src/main/java/org/apache/ozone/lib/lang/XException.java
index b773d2b4db..d9e0147987 100644
--- 
a/hadoop-ozone/httpfsgateway/src/main/java/org/apache/ozone/lib/lang/XException.java
+++ 
b/hadoop-ozone/httpfsgateway/src/main/java/org/apache/ozone/lib/lang/XException.java
@@ -99,7 +99,7 @@ private static String format(ERROR error, Object... args) {
     if (template == null) {
       StringBuilder sb = new StringBuilder();
       for (int i = 0; i < args.length; i++) {
-        sb.append(" {").append(i).append("}");
+        sb.append(" {").append(i).append('}');
       }
       template = sb.deleteCharAt(0).toString();
     }
diff --git 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/conf/TestConfigurationFieldsBase.java
 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/conf/TestConfigurationFieldsBase.java
index 8a1fcb5b55..198874fac8 100644
--- 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/conf/TestConfigurationFieldsBase.java
+++ 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/conf/TestConfigurationFieldsBase.java
@@ -435,7 +435,7 @@ public void testCompareConfigurationClassAgainstXml() {
     StringBuilder xmlErrorMsg = new StringBuilder();
     for (Class c : configurationClasses) {
       xmlErrorMsg.append(c);
-      xmlErrorMsg.append(" ");
+      xmlErrorMsg.append(' ');
     }
     xmlErrorMsg.append("has ");
     xmlErrorMsg.append(missingXmlSize);
diff --git 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/fs/contract/AbstractContractSeekTest.java
 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/fs/contract/AbstractContractSeekTest.java
index ca1450382d..39ecfdda09 100644
--- 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/fs/contract/AbstractContractSeekTest.java
+++ 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/fs/contract/AbstractContractSeekTest.java
@@ -361,7 +361,7 @@ public void testRandomSeeks() throws Throwable {
       sb.append("Sequence of actions:\n");
       for (int j = 0; j < seeks.length; j++) {
         sb.append("seek @ ").append(seeks[j]).append("  ")
-            .append("read ").append(reads[j]).append("\n");
+            .append("read ").append(reads[j]).append('\n');
       }
       LOG.error(sb.toString());
       throw afe;
diff --git 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/fs/contract/ContractTestUtils.java
 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/fs/contract/ContractTestUtils.java
index 1d3fcf4ff5..1ddaa079bb 100644
--- 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/fs/contract/ContractTestUtils.java
+++ 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/fs/contract/ContractTestUtils.java
@@ -1456,9 +1456,9 @@ public static String pathsToString(Collection<Path> 
paths) {
     builder.append(nl);
     for (Path path : paths) {
       builder.append("  \"").append(path.toString())
-          .append("\"").append(nl);
+          .append('"').append(nl);
     }
-    builder.append("]");
+    builder.append(']');
     return builder.toString();
   }
 
diff --git 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/client/rpc/TestOzoneClientMultipartUploadWithFSO.java
 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/client/rpc/TestOzoneClientMultipartUploadWithFSO.java
index f69869c286..1055087d82 100644
--- 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/client/rpc/TestOzoneClientMultipartUploadWithFSO.java
+++ 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/client/rpc/TestOzoneClientMultipartUploadWithFSO.java
@@ -870,7 +870,7 @@ public void testListMultipartUploadsPagination() throws 
Exception {
       StringBuilder key = new StringBuilder();
       int depth = 1 + i % 3; // Creates varying depth (1-3 levels)
       for (int j = 0; j < depth; j++) {
-        key.append("dir").append(j + 1).append("/");
+        key.append("dir").append(j + 1).append('/');
       }
       key.append("file").append(i);
       keys.add(key.toString());
diff --git 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/om/TestKeyManagerImpl.java
 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/om/TestKeyManagerImpl.java
index f1568407a7..0679fcf24f 100644
--- 
a/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/om/TestKeyManagerImpl.java
+++ 
b/hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/om/TestKeyManagerImpl.java
@@ -363,7 +363,7 @@ public void testCreateDirectory() throws IOException {
         .setKeyName(keyNameBuf.toString())
         .build();
     for (int i = 0; i < 5; i++) {
-      
keyNameBuf.append("/").append(RandomStringUtils.secure().nextAlphabetic(5));
+      
keyNameBuf.append('/').append(RandomStringUtils.secure().nextAlphabetic(5));
     }
     String keyName = keyNameBuf.toString();
     writeClient.createDirectory(keyArgs);
@@ -430,7 +430,7 @@ public void testOpenFile() throws IOException {
     StringBuffer keyNameBuf = new StringBuffer();
     keyNameBuf.append(RandomStringUtils.secure().nextAlphabetic(5));
     for (int i = 0; i < 5; i++) {
-      
keyNameBuf.append("/").append(RandomStringUtils.secure().nextAlphabetic(5));
+      
keyNameBuf.append('/').append(RandomStringUtils.secure().nextAlphabetic(5));
     }
     keyName = keyNameBuf.toString();
     keyArgs = createBuilder()
diff --git 
a/hadoop-ozone/mini-cluster/src/main/java/org/apache/hadoop/ozone/MiniOzoneClusterImpl.java
 
b/hadoop-ozone/mini-cluster/src/main/java/org/apache/hadoop/ozone/MiniOzoneClusterImpl.java
index cef2724de2..ef097ab579 100644
--- 
a/hadoop-ozone/mini-cluster/src/main/java/org/apache/hadoop/ozone/MiniOzoneClusterImpl.java
+++ 
b/hadoop-ozone/mini-cluster/src/main/java/org/apache/hadoop/ozone/MiniOzoneClusterImpl.java
@@ -712,10 +712,10 @@ private String 
getSCMAddresses(List<StorageContainerManager> scms) {
       while (iter.hasNext()) {
         StorageContainerManager scm = iter.next();
         stringBuilder.append(scm.getDatanodeRpcAddress().getHostString())
-            .append(":")
+            .append(':')
             .append(scm.getDatanodeRpcAddress().getPort());
         if (iter.hasNext()) {
-          stringBuilder.append(",");
+          stringBuilder.append(',');
         }
 
       }
diff --git 
a/hadoop-ozone/mini-cluster/src/main/java/org/apache/hadoop/ozone/MiniOzoneHAClusterImpl.java
 
b/hadoop-ozone/mini-cluster/src/main/java/org/apache/hadoop/ozone/MiniOzoneHAClusterImpl.java
index e221520333..92e1360732 100644
--- 
a/hadoop-ozone/mini-cluster/src/main/java/org/apache/hadoop/ozone/MiniOzoneHAClusterImpl.java
+++ 
b/hadoop-ozone/mini-cluster/src/main/java/org/apache/hadoop/ozone/MiniOzoneHAClusterImpl.java
@@ -634,7 +634,7 @@ private void initSCMHAConfig() {
         if (i == 1) {
           conf.set(ScmConfigKeys.OZONE_SCM_PRIMORDIAL_NODE_ID_KEY, scmNodeId);
         }
-        scmNodesKeyValue.append(",").append(scmNodeId);
+        scmNodesKeyValue.append(',').append(scmNodeId);
 
         String scmAddrKey = ConfUtils.addKeySuffixes(
             ScmConfigKeys.OZONE_SCM_ADDRESS_KEY, scmServiceId, scmNodeId);
diff --git 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OzoneManager.java
 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OzoneManager.java
index 0624f0ee0e..df3cef96a5 100644
--- 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OzoneManager.java
+++ 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OzoneManager.java
@@ -905,7 +905,7 @@ private void logVersionMismatch(OzoneConfiguration conf, 
ScmInfo scmInfo) {
     StringBuilder scmBlockAddressBuilder = new StringBuilder();
     for (SCMNodeInfo scmNodeInfo : scmNodeInfoList) {
       scmBlockAddressBuilder.append(scmNodeInfo.getBlockClientAddress())
-          .append(",");
+          .append(',');
     }
     String scmBlockAddress = scmBlockAddressBuilder.toString();
     if (!StringUtils.isBlank(scmBlockAddress)) {
diff --git 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/ratis/OzoneManagerStateMachine.java
 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/ratis/OzoneManagerStateMachine.java
index 71e810d78e..8eadd5bff0 100644
--- 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/ratis/OzoneManagerStateMachine.java
+++ 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/ratis/OzoneManagerStateMachine.java
@@ -225,7 +225,7 @@ public void notifyConfigurationChanged(long term, long 
index,
         .append(", index=").append(index)
         .append(", New Peer list: ");
     newPeers.forEach(peer -> logBuilder.append(peer.getId().toStringUtf8())
-        .append("(")
+        .append('(')
         .append(peer.getAddress())
         .append("), "));
     LOG.info(logBuilder.substring(0, logBuilder.length() - 2));
diff --git 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/key/OMKeysDeleteRequest.java
 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/key/OMKeysDeleteRequest.java
index b9a09cbc75..36b61f83e7 100644
--- 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/key/OMKeysDeleteRequest.java
+++ 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/key/OMKeysDeleteRequest.java
@@ -354,9 +354,9 @@ protected static void addDeletedKeys(Map<String, String> 
auditMap,
     StringBuilder keys = new StringBuilder();
     for (int i = 0; i < deletedKeyInfos.size(); i++) {
       OmKeyInfo key = deletedKeyInfos.get(i);
-      
keys.append("{").append(KEY).append("=").append(key.getKeyName()).append(", ");
-      keys.append(DATA_SIZE).append("=").append(key.getDataSize()).append(", 
");
-      
keys.append(REPLICATION_CONFIG).append("=").append(key.getReplicationConfig()).append("}");
+      
keys.append('{').append(KEY).append('=').append(key.getKeyName()).append(", ");
+      keys.append(DATA_SIZE).append('=').append(key.getDataSize()).append(", 
");
+      
keys.append(REPLICATION_CONFIG).append('=').append(key.getReplicationConfig()).append('}');
       if (i < deletedKeyInfos.size() - 1) {
         keys.append(", ");
       }
diff --git 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/service/OpenKeyCleanupService.java
 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/service/OpenKeyCleanupService.java
index 1583f3fef7..d4f97b23ee 100644
--- 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/service/OpenKeyCleanupService.java
+++ 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/service/OpenKeyCleanupService.java
@@ -208,7 +208,7 @@ public BackgroundTaskResult call() throws Exception {
                   .append(": ")
                   
.append(openKey.getKeysList().stream().map(OzoneManagerProtocolProtos.OpenKey::getName)
                       .collect(Collectors.toList()))
-                  .append("\n");
+                  .append('\n');
             }
             LOG.debug("Non-hsync'ed openKeys being deleted in current 
iteration: \n" + sb);
           }
diff --git 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/OmSnapshotUtils.java
 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/OmSnapshotUtils.java
index 8fd47c998e..f5805044b7 100644
--- 
a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/OmSnapshotUtils.java
+++ 
b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/OmSnapshotUtils.java
@@ -92,8 +92,8 @@ public static Path createHardLinkList(int truncateLength,
           fixedFile = f.toString();
         }
       }
-      sb.append(truncateFileName(truncateLength, entry.getKey())).append("\t")
-          .append(fixedFile).append("\n");
+      sb.append(truncateFileName(truncateLength, entry.getKey())).append('\t')
+          .append(fixedFile).append('\n');
     }
     Files.write(data, sb.toString().getBytes(StandardCharsets.UTF_8));
     return data;
diff --git 
a/hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/request/file/TestOMDirectoryCreateRequest.java
 
b/hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/request/file/TestOMDirectoryCreateRequest.java
index 31fb48c57d..65cc1c0d7e 100644
--- 
a/hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/request/file/TestOMDirectoryCreateRequest.java
+++ 
b/hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/request/file/TestOMDirectoryCreateRequest.java
@@ -539,7 +539,7 @@ private String genRandomKeyName() {
     StringBuilder keyNameBuilder = new StringBuilder();
     keyNameBuilder.append(RandomStringUtils.secure().nextAlphabetic(5));
     for (int i = 0; i < 3; i++) {
-      
keyNameBuilder.append("/").append(RandomStringUtils.secure().nextAlphabetic(5));
+      
keyNameBuilder.append('/').append(RandomStringUtils.secure().nextAlphabetic(5));
     }
     return keyNameBuilder.toString();
   }
diff --git 
a/hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/request/validation/TestRequestFeatureValidatorProcessor.java
 
b/hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/request/validation/TestRequestFeatureValidatorProcessor.java
index d55cefc2e7..cb30adaa42 100644
--- 
a/hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/request/validation/TestRequestFeatureValidatorProcessor.java
+++ 
b/hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/request/validation/TestRequestFeatureValidatorProcessor.java
@@ -487,9 +487,9 @@ private StringBuilder buildMethodSignature(
     StringBuilder signature = new StringBuilder();
     signature.append("  ");
     for (String modifier : modifiers) {
-      signature.append(modifier).append(" ");
+      signature.append(modifier).append(' ');
     }
-    signature.append(returnType).append(" ");
+    signature.append(returnType).append(' ');
     signature.append("validatorMethod(");
     signature.append(createParameterList(paramspecs));
     signature.append(") ");
diff --git 
a/hadoop-ozone/ozonefs-common/src/main/java/org/apache/hadoop/fs/ozone/FileStatusAdapter.java
 
b/hadoop-ozone/ozonefs-common/src/main/java/org/apache/hadoop/fs/ozone/FileStatusAdapter.java
index cf858bb335..eba24f88bb 100644
--- 
a/hadoop-ozone/ozonefs-common/src/main/java/org/apache/hadoop/fs/ozone/FileStatusAdapter.java
+++ 
b/hadoop-ozone/ozonefs-common/src/main/java/org/apache/hadoop/fs/ozone/FileStatusAdapter.java
@@ -145,7 +145,7 @@ public BlockLocation[] getBlockLocations() {
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append(getClass().getSimpleName())
-        .append("{")
+        .append('{')
         .append("path=").append(path)
         .append("; isDirectory=").append(isdir);
     if (isFile()) {
@@ -159,7 +159,7 @@ public String toString() {
         .append("; group=").append(group)
         .append("; permission=").append(permission)
         .append("; isSymlink=").append(getSymlink())
-        .append("}");
+        .append('}');
     
     return sb.toString();
   }
diff --git 
a/hadoop-ozone/s3gateway/src/main/java/org/apache/hadoop/ozone/s3/signature/StringToSignProducer.java
 
b/hadoop-ozone/s3gateway/src/main/java/org/apache/hadoop/ozone/s3/signature/StringToSignProducer.java
index a2cb0c6993..5a474a024e 100644
--- 
a/hadoop-ozone/s3gateway/src/main/java/org/apache/hadoop/ozone/s3/signature/StringToSignProducer.java
+++ 
b/hadoop-ozone/s3gateway/src/main/java/org/apache/hadoop/ozone/s3/signature/StringToSignProducer.java
@@ -177,7 +177,7 @@ public static String buildCanonicalRequest(
 
     for (String header : StringUtils.split(signedHeaders, ';')) {
       canonicalHeaders.append(header.toLowerCase());
-      canonicalHeaders.append(":");
+      canonicalHeaders.append(':');
       if (headers.containsKey(header)) {
         String headerValue = headers.get(header);
         canonicalHeaders.append(headerValue);
@@ -291,7 +291,7 @@ private static String getQueryParamString(
     for (String p : params) {
       if (!p.equals("X-Amz-Signature")) {
         if (result.length() > 0) {
-          result.append("&");
+          result.append('&');
         }
         result.append(urlEncode(p));
         result.append('=');
diff --git 
a/hadoop-ozone/s3gateway/src/test/java/org/apache/hadoop/ozone/s3/endpoint/TestObjectPut.java
 
b/hadoop-ozone/s3gateway/src/test/java/org/apache/hadoop/ozone/s3/endpoint/TestObjectPut.java
index 4e8b9b6bad..4f22bd4184 100644
--- 
a/hadoop-ozone/s3gateway/src/test/java/org/apache/hadoop/ozone/s3/endpoint/TestObjectPut.java
+++ 
b/hadoop-ozone/s3gateway/src/test/java/org/apache/hadoop/ozone/s3/endpoint/TestObjectPut.java
@@ -312,7 +312,7 @@ public void testPutObjectWithTooManyTags() throws Exception 
{
     for (int i = 0; i < TAG_NUM_LIMIT + 1; i++) {
       sb.append(String.format("tag%d=value%d", i, i));
       if (i < TAG_NUM_LIMIT) {
-        sb.append("&");
+        sb.append('&');
       }
     }
     
when(headersWithTooManyTags.getHeaderString(TAG_HEADER)).thenReturn(sb.toString());
diff --git 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/debug/audit/parser/common/DatabaseHelper.java
 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/debug/audit/parser/common/DatabaseHelper.java
index 8b68f396f6..7d6271aca3 100644
--- 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/debug/audit/parser/common/DatabaseHelper.java
+++ 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/debug/audit/parser/common/DatabaseHelper.java
@@ -209,9 +209,9 @@ private static String executeStatement(String dbName, 
String sql)
         while (rs.next()) {
           for (int index = 1; index <= cols; index++) {
             result.append(rs.getObject(index));
-            result.append("\t");
+            result.append('\t');
           }
-          result.append("\n");
+          result.append('\n');
         }
       }
     }
diff --git 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/freon/OmMetadataGenerator.java
 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/freon/OmMetadataGenerator.java
index 834eb60b99..e89c71ed11 100644
--- 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/freon/OmMetadataGenerator.java
+++ 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/freon/OmMetadataGenerator.java
@@ -308,7 +308,7 @@ public Supplier<String> realTimeStatusSupplier() {
         maxValueRecorder.put(name, maxValue);
         valueRecorder.put(name, curValue);
         instantsRecorder.put(name, now);
-        sb.append(" ")
+        sb.append(' ')
             .append(name)
             .append(": rate ")
             .append(rate)
diff --git 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/freon/ProgressBar.java
 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/freon/ProgressBar.java
index b578a3430c..4fddb9054b 100644
--- 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/freon/ProgressBar.java
+++ 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/freon/ProgressBar.java
@@ -177,7 +177,7 @@ private void printProgressBar(PrintStream stream, long 
value) {
     if (!realTimeMessage.isEmpty()) {
       shrinkTimes = 3;
     }
-    sb.append(" ").append(String.format("%.2f", percent)).append("% |");
+    sb.append(' ').append(String.format("%.2f", percent)).append("% |");
     for (int i = 0; i <= percent / shrinkTimes; i++) {
       sb.append('█');
     }
@@ -185,7 +185,7 @@ private void printProgressBar(PrintStream stream, long 
value) {
       sb.append(' ');
     }
     sb.append("|  ");
-    sb.append(value).append("/").append(maxValue);
+    sb.append(value).append('/').append(maxValue);
     long timeInSec = TimeUnit.SECONDS.convert(
         System.nanoTime() - startTime, TimeUnit.NANOSECONDS);
     String timeToPrint = String.format("%d:%02d:%02d", timeInSec / 3600,
diff --git 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/repair/datanode/schemaupgrade/ContainerUpgradeResult.java
 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/repair/datanode/schemaupgrade/ContainerUpgradeResult.java
index aa7b3dbb26..83f6c4d552 100644
--- 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/repair/datanode/schemaupgrade/ContainerUpgradeResult.java
+++ 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/repair/datanode/schemaupgrade/ContainerUpgradeResult.java
@@ -113,7 +113,7 @@ public String toString() {
     stringBuilder.append(getCostMs());
     stringBuilder.append(", status=");
     stringBuilder.append(status);
-    stringBuilder.append("}");
+    stringBuilder.append('}');
     return stringBuilder.toString();
   }
 
diff --git 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/repair/datanode/schemaupgrade/VolumeUpgradeResult.java
 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/repair/datanode/schemaupgrade/VolumeUpgradeResult.java
index d7dce31e87..067de25b3b 100644
--- 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/repair/datanode/schemaupgrade/VolumeUpgradeResult.java
+++ 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/repair/datanode/schemaupgrade/VolumeUpgradeResult.java
@@ -94,7 +94,7 @@ public String toString() {
     if (resultMap != null) {
       resultMap.forEach((k, r) -> {
         stringBuilder.append(r.toString());
-        stringBuilder.append("\n");
+        stringBuilder.append('\n');
         total.addAndGet(r.getTotalRow());
       });
     }
diff --git 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/utils/FormattingCLIUtils.java
 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/utils/FormattingCLIUtils.java
index df5844ca08..6bc2284201 100644
--- 
a/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/utils/FormattingCLIUtils.java
+++ 
b/hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/utils/FormattingCLIUtils.java
@@ -133,12 +133,12 @@ private void buildTitle() {
       if (this.title.length() > maxTitleSize) {
         this.title = this.title.substring(0, maxTitleSize);
       }
-      this.join.append("+");
+      this.join.append('+');
       for (int i = 0; i < maxTitleSize + 2; i++) {
-        this.join.append("-");
+        this.join.append('-');
       }
       this.join.append("+\n")
-          .append("|")
+          .append('|')
           .append(StrUtils.center(this.title, maxTitleSize + 2, ' '))
           .append("|\n");
       this.lastTableRowType = TableRowType.TITLE;
@@ -177,14 +177,14 @@ private void buildTable() {
    * @param data dataLine
    */
   private void buildRowBorder(List<String> data) {
-    this.join.append("+");
+    this.join.append('+');
     for (int i = 0, len = data.size(); i < len; i++) {
       for (int j = 0; j < this.maxColMap.get(i) + 2; j++) {
-        this.join.append("-");
+        this.join.append('-');
       }
-      this.join.append("+");
+      this.join.append('+');
     }
-    this.join.append("\n");
+    this.join.append('\n');
   }
 
   /**
@@ -192,12 +192,12 @@ private void buildRowBorder(List<String> data) {
    * @param data dataLine
    */
   private void buildRowLine(List<String> data) {
-    this.join.append("|");
+    this.join.append('|');
     for (int i = 0, len = data.size(); i < len; i++) {
       this.join.append(StrUtils.center(data.get(i), this.maxColMap.get(i) + 2, 
' '))
-          .append("|");
+          .append('|');
     }
-    this.join.append("\n");
+    this.join.append('\n');
   }
 
   /**


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