[Java] Fix Checkstyle warnings.

aeron-archive/src/test/java/io/aeron/archive/ArchiveToolCliTest.java

@@ -184,7 +184,7 @@ private static boolean outputMatches(final OutputConsole console, final String e
             .count() == 1;
     }
 
-    private static class OutputConsole
+    private static final class OutputConsole
     {
         private final OutputStream outputBytes = new ByteArrayOutputStream();
         private final PrintStream sysOut = new PrintStream(outputBytes);

aeron-cluster/src/test/java/io/aeron/cluster/PriorityHeapTimerServiceTest.java

@@ -513,7 +513,7 @@ void manyRandomOperations()
         }
     }
 
-    private static class TestHarness
+    private static final class TestHarness
     {
         final PriorityHeapTimerService timerService = new PriorityHeapTimerService(this::onTimerEvent);
         final Long2LongHashMap timerDeadlines = new Long2LongHashMap(-1);

aeron-samples/src/main/java/io/aeron/samples/echo/EchoPair.java

@@ -132,7 +132,7 @@ public void close()
         CloseHelper.quietCloseAll(publication, subscription);
     }
 
-    private class EchoMonitor implements EchoMonitorMBean
+    private final class EchoMonitor implements EchoMonitorMBean
     {
         /**
          * Get the correaltionId

aeron-system-tests/src/test/java/io/aeron/TaggedFlowControlSystemTest.java

@@ -131,7 +131,7 @@ private static Stream<Arguments> strategyConfigurations()
             Arguments.of(null, null, null, "|fc=tagged,g:123", "|gtag=123"));
     }
 
-    private static class State
+    private static final class State
     {
         private int numMessagesToSend;
         private int numMessagesLeftToSend;

aeron-system-tests/src/test/java/io/aeron/archive/MigrateSegmentsTest.java

@@ -843,7 +843,7 @@ private static FailureCaseParams appendOverPreexistingSegmentFile()
     }
 
     @SuppressWarnings("UnusedReturnValue")
-    private static class StreamParams
+    private static final class StreamParams
     {
         private String endpoint;
         private int initialTermId = 1337;
@@ -933,7 +933,7 @@ private enum RecordingState
     }
 
     @SuppressWarnings("UnusedReturnValue")
-    private static class RecordingParams
+    private static final class RecordingParams
     {
         private final StreamParams stream = new StreamParams();
         private long startPosition;
@@ -1031,7 +1031,7 @@ private interface SegmentFileExpectation
     }
 
     @SuppressWarnings("UnusedReturnValue")
-    private static class TestCaseParams
+    private static final class TestCaseParams
     {
         private final RecordingParams source = new RecordingParams();
         private final RecordingParams destination = new RecordingParams();
@@ -1154,7 +1154,7 @@ public String toString()
     }
 
     @SuppressWarnings("UnusedReturnValue")
-    private static class FailureCaseParams
+    private static final class FailureCaseParams
     {
         private final RecordingParams source = new RecordingParams();
         private final RecordingParams destination = new RecordingParams();

aeron-test-support/src/main/java/io/aeron/test/SystemTestWatcher.java

@@ -563,7 +563,7 @@ void filterErrors(List<Path> paths, MutableInteger count, StringBuilder errors,
             throws IOException;
     }
 
-    private static class ArchiveMarkFileDissector implements MarkFileDissector
+    private static final class ArchiveMarkFileDissector implements MarkFileDissector
     {
         public String filename()
         {

aeron-test-support/src/main/java/io/aeron/test/cluster/TestCluster.java

@@ -2162,7 +2162,7 @@ public byte[] onChallenge(final byte[] encodedChallenge)
         }
     };
 
-    private class KeepAlive implements Runnable
+    private final class KeepAlive implements Runnable
     {
         private long keepAliveDeadlineMs;
         private EpochClock epochClock;
@@ -2243,7 +2243,7 @@ int newLeaderEvent()
         }
     }
 
-    private static class BackupListener implements ClusterBackupEventsListener
+    private static final class BackupListener implements ClusterBackupEventsListener
     {
         public void onBackupQuery()
         {