Make private static classes final

33 files changed, 54 insertions, 54 deletions

diff --git a/src/main/java/org/apache/commons/lang3/CharRange.java b/src/main/java/org/apache/commons/lang3/CharRange.java
index 0437e2d6a..cf90e0950 100644
--- a/src/main/java/org/apache/commons/lang3/CharRange.java
+++ b/src/main/java/org/apache/commons/lang3/CharRange.java
@@ -271,7 +271,7 @@ final class CharRange implements Iterable<Character>, Serializable {
      * Character {@link Iterator}.
      * <p>#NotThreadSafe#</p>
      */
-    private static class CharacterIterator implements Iterator<Character> {
+    private static final class CharacterIterator implements Iterator<Character> {
         /** The current character */
         private char current;
 
diff --git a/src/main/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreaker.java b/src/main/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreaker.java
index 5c9f44b0b..749020ac8 100644
--- a/src/main/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreaker.java
+++ b/src/main/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreaker.java
@@ -433,7 +433,7 @@ public class EventCountCircuitBreaker extends AbstractCircuitBreaker<Integer> {
      * this class. Basically, the number of received events and the start time of the
      * current check interval are stored.
      */
-    private static class CheckIntervalData {
+    private static final class CheckIntervalData {
         /** The counter for events. */
         private final int eventCount;
 
@@ -527,7 +527,7 @@ public class EventCountCircuitBreaker extends AbstractCircuitBreaker<Integer> {
     /**
      * A specialized {@link StateStrategy} implementation for the state closed.
      */
-    private static class StateStrategyClosed extends StateStrategy {
+    private static final class StateStrategyClosed extends StateStrategy {
 
         /**
          * {@inheritDoc}
@@ -550,7 +550,7 @@ public class EventCountCircuitBreaker extends AbstractCircuitBreaker<Integer> {
     /**
      * A specialized {@link StateStrategy} implementation for the state open.
      */
-    private static class StateStrategyOpen extends StateStrategy {
+    private static final class StateStrategyOpen extends StateStrategy {
         /**
          * {@inheritDoc}
          */
diff --git a/src/main/java/org/apache/commons/lang3/event/EventUtils.java b/src/main/java/org/apache/commons/lang3/event/EventUtils.java
index 546c06818..29d6795bb 100644
--- a/src/main/java/org/apache/commons/lang3/event/EventUtils.java
+++ b/src/main/java/org/apache/commons/lang3/event/EventUtils.java
@@ -78,7 +78,7 @@ public class EventUtils {
         addEventListener(eventSource, listenerType, listener);
     }
 
-    private static class EventBindingInvocationHandler implements InvocationHandler {
+    private static final class EventBindingInvocationHandler implements InvocationHandler {
         private final Object target;
         private final String methodName;
         private final Set<String> eventTypes;
diff --git a/src/main/java/org/apache/commons/lang3/stream/LangCollectors.java b/src/main/java/org/apache/commons/lang3/stream/LangCollectors.java
index abd3b10f8..6abc27fdd 100644
--- a/src/main/java/org/apache/commons/lang3/stream/LangCollectors.java
+++ b/src/main/java/org/apache/commons/lang3/stream/LangCollectors.java
@@ -46,7 +46,7 @@ public final class LangCollectors {
      * @param <T> the type of elements to be collected
      * @param <R> the type of the result
      */
-    private static class SimpleCollector<T, A, R> implements Collector<T, A, R> {
+    private static final class SimpleCollector<T, A, R> implements Collector<T, A, R> {
 
         private final BiConsumer<A, T> accumulator;
         private final Set<Characteristics> characteristics;
diff --git a/src/main/java/org/apache/commons/lang3/stream/Streams.java b/src/main/java/org/apache/commons/lang3/stream/Streams.java
index bd5ab630c..fa639ec2a 100644
--- a/src/main/java/org/apache/commons/lang3/stream/Streams.java
+++ b/src/main/java/org/apache/commons/lang3/stream/Streams.java
@@ -133,7 +133,7 @@ public class Streams {
      *
      * @param <T> The element type.
      */
-    private static class EnumerationSpliterator<T> extends AbstractSpliterator<T> {
+    private static final class EnumerationSpliterator<T> extends AbstractSpliterator<T> {
 
         private final Enumeration<T> enumeration;
 
diff --git a/src/main/java/org/apache/commons/lang3/text/StrLookup.java b/src/main/java/org/apache/commons/lang3/text/StrLookup.java
index b28d6db5f..069d68ebf 100644
--- a/src/main/java/org/apache/commons/lang3/text/StrLookup.java
+++ b/src/main/java/org/apache/commons/lang3/text/StrLookup.java
@@ -172,7 +172,7 @@ public abstract class StrLookup<V> {
     /**
      * Lookup implementation based on system properties.
      */
-    private static class SystemPropertiesStrLookup extends StrLookup<String> {
+    private static final class SystemPropertiesStrLookup extends StrLookup<String> {
         /**
          * {@inheritDoc} This implementation directly accesses system properties.
          */
diff --git a/src/main/java/org/apache/commons/lang3/time/FastDateParser.java b/src/main/java/org/apache/commons/lang3/time/FastDateParser.java
index fd59aeb31..07ee62746 100644
--- a/src/main/java/org/apache/commons/lang3/time/FastDateParser.java
+++ b/src/main/java/org/apache/commons/lang3/time/FastDateParser.java
@@ -189,7 +189,7 @@ public class FastDateParser implements DateParser, Serializable {
     /**
      * Holds strategy and field width
      */
-    private static class StrategyAndWidth {
+    private static final class StrategyAndWidth {
 
         final Strategy strategy;
         final int width;
@@ -684,7 +684,7 @@ public class FastDateParser implements DateParser, Serializable {
     /**
      * A strategy that copies the static or quoted field in the parsing pattern
      */
-    private static class CopyQuotedStrategy extends Strategy {
+    private static final class CopyQuotedStrategy extends Strategy {
 
         private final String formatField;
 
@@ -736,7 +736,7 @@ public class FastDateParser implements DateParser, Serializable {
     /**
      * A strategy that handles a text field in the parsing pattern
      */
-    private static class CaseInsensitiveTextStrategy extends PatternStrategy {
+    private static final class CaseInsensitiveTextStrategy extends PatternStrategy {
         private final int field;
         final Locale locale;
         private final Map<String, Integer> lKeyValues;
@@ -894,7 +894,7 @@ public class FastDateParser implements DateParser, Serializable {
         private final Locale locale;
         private final Map<String, TzInfo> tzNames = new HashMap<>();
 
-        private static class TzInfo {
+        private static final class TzInfo {
             final TimeZone zone;
             final int dstOffset;
 
@@ -1017,7 +1017,7 @@ public class FastDateParser implements DateParser, Serializable {
 
     }
 
-    private static class ISO8601TimeZoneStrategy extends PatternStrategy {
+    private static final class ISO8601TimeZoneStrategy extends PatternStrategy {
         // Z, +hh, -hh, +hhmm, -hhmm, +hh:mm or -hh:mm
 
         /**
diff --git a/src/test/java/org/apache/commons/lang3/ClassUtilsTest.java b/src/test/java/org/apache/commons/lang3/ClassUtilsTest.java
index 0050753bd..181975dc2 100644
--- a/src/test/java/org/apache/commons/lang3/ClassUtilsTest.java
+++ b/src/test/java/org/apache/commons/lang3/ClassUtilsTest.java
@@ -59,7 +59,7 @@ public class ClassUtilsTest extends AbstractLangTest {
     }
 
     @SuppressWarnings("unused") // IB is redundant but what a test checks
-    private static class CY extends CX implements IB, IC {
+    private static final class CY extends CX implements IB, IC {
         // empty
     }
 
@@ -87,7 +87,7 @@ public class ClassUtilsTest extends AbstractLangTest {
         // empty
     }
 
-    private static class Inner {
+    private static final class Inner {
         private class DeeplyNested {
             // empty
         }
diff --git a/src/test/java/org/apache/commons/lang3/StringUtilsEqualsIndexOfTest.java b/src/test/java/org/apache/commons/lang3/StringUtilsEqualsIndexOfTest.java
index 456018f0e..db36fd30e 100644
--- a/src/test/java/org/apache/commons/lang3/StringUtilsEqualsIndexOfTest.java
+++ b/src/test/java/org/apache/commons/lang3/StringUtilsEqualsIndexOfTest.java
@@ -46,7 +46,7 @@ public class StringUtilsEqualsIndexOfTest extends AbstractLangTest {
     // with a CharSequence implementation whose equals(Object) override requires that the
     // other object be an instance of CustomCharSequence, even though, as char sequences,
     // `seq` may equal the other object.
-    private static class CustomCharSequence implements CharSequence {
+    private static final class CustomCharSequence implements CharSequence {
         private final CharSequence seq;
 
         CustomCharSequence(final CharSequence seq) {
diff --git a/src/test/java/org/apache/commons/lang3/ThreadUtilsTest.java b/src/test/java/org/apache/commons/lang3/ThreadUtilsTest.java
index 638fb149e..63cb6809d 100644
--- a/src/test/java/org/apache/commons/lang3/ThreadUtilsTest.java
+++ b/src/test/java/org/apache/commons/lang3/ThreadUtilsTest.java
@@ -46,7 +46,7 @@ import org.junit.jupiter.api.Test;
  */
 public class ThreadUtilsTest extends AbstractLangTest {
 
-    private static class TestThread extends Thread {
+    private static final class TestThread extends Thread {
         private final CountDownLatch latch = new CountDownLatch(1);
 
         TestThread(final String name) {
diff --git a/src/test/java/org/apache/commons/lang3/builder/DiffBuilderTest.java b/src/test/java/org/apache/commons/lang3/builder/DiffBuilderTest.java
index 003d2abad..17531ad83 100644
--- a/src/test/java/org/apache/commons/lang3/builder/DiffBuilderTest.java
+++ b/src/test/java/org/apache/commons/lang3/builder/DiffBuilderTest.java
@@ -36,7 +36,7 @@ import org.junit.jupiter.api.Test;
  */
 public class DiffBuilderTest extends AbstractLangTest {
 
-    private static class TypeTestClass implements Diffable<TypeTestClass> {
+    private static final class TypeTestClass implements Diffable<TypeTestClass> {
         private ToStringStyle style = SHORT_STYLE;
         private boolean booleanField = true;
         private boolean[] booleanArrayField = {true};
diff --git a/src/test/java/org/apache/commons/lang3/builder/DiffResultTest.java b/src/test/java/org/apache/commons/lang3/builder/DiffResultTest.java
index a9a9cc19f..014079984 100644
--- a/src/test/java/org/apache/commons/lang3/builder/DiffResultTest.java
+++ b/src/test/java/org/apache/commons/lang3/builder/DiffResultTest.java
@@ -35,7 +35,7 @@ public class DiffResultTest extends AbstractLangTest {
     private static final SimpleClass SIMPLE_TRUE = new SimpleClass(true);
     private static final ToStringStyle SHORT_STYLE = ToStringStyle.SHORT_PREFIX_STYLE;
 
-    private static class SimpleClass implements Diffable<SimpleClass> {
+    private static final class SimpleClass implements Diffable<SimpleClass> {
         private final boolean booleanField;
 
         SimpleClass(final boolean booleanField) {
@@ -54,7 +54,7 @@ public class DiffResultTest extends AbstractLangTest {
         }
     }
 
-    private static class EmptyClass {
+    private static final class EmptyClass {
         // empty
     }
 
diff --git a/src/test/java/org/apache/commons/lang3/builder/DiffTest.java b/src/test/java/org/apache/commons/lang3/builder/DiffTest.java
index 796699395..bd1200848 100644
--- a/src/test/java/org/apache/commons/lang3/builder/DiffTest.java
+++ b/src/test/java/org/apache/commons/lang3/builder/DiffTest.java
@@ -31,7 +31,7 @@ public class DiffTest extends AbstractLangTest {
     private static final String FIELD_NAME = "field";
     private static final Diff<Boolean> booleanDiff = new BooleanDiff(FIELD_NAME);
 
-    private static class BooleanDiff extends Diff<Boolean> {
+    private static final class BooleanDiff extends Diff<Boolean> {
         private static final long serialVersionUID = 1L;
 
         protected BooleanDiff(final String fieldName) {
diff --git a/src/test/java/org/apache/commons/lang3/builder/ReflectionDiffBuilderTest.java b/src/test/java/org/apache/commons/lang3/builder/ReflectionDiffBuilderTest.java
index a1fdce249..754f1edb2 100644
--- a/src/test/java/org/apache/commons/lang3/builder/ReflectionDiffBuilderTest.java
+++ b/src/test/java/org/apache/commons/lang3/builder/ReflectionDiffBuilderTest.java
@@ -71,7 +71,7 @@ public class ReflectionDiffBuilderTest extends AbstractLangTest {
     }
 
     @SuppressWarnings("unused")
-    private static class TypeTestChildClass extends TypeTestClass {
+    private static final class TypeTestChildClass extends TypeTestClass {
         String field = "a";
     }
 
diff --git a/src/test/java/org/apache/commons/lang3/builder/ToStringBuilderTest.java b/src/test/java/org/apache/commons/lang3/builder/ToStringBuilderTest.java
index 0307e702e..a811b538a 100644
--- a/src/test/java/org/apache/commons/lang3/builder/ToStringBuilderTest.java
+++ b/src/test/java/org/apache/commons/lang3/builder/ToStringBuilderTest.java
@@ -471,7 +471,7 @@ public class ToStringBuilderTest extends AbstractLangTest {
         }
     }
 
-    private static class SelfInstanceVarReflectionTestFixture {
+    private static final class SelfInstanceVarReflectionTestFixture {
         @SuppressWarnings("unused")
         private final SelfInstanceVarReflectionTestFixture typeIsSelf;
 
@@ -485,7 +485,7 @@ public class ToStringBuilderTest extends AbstractLangTest {
         }
       }
 
-    private static class SelfInstanceTwoVarsReflectionTestFixture {
+    private static final class SelfInstanceTwoVarsReflectionTestFixture {
         @SuppressWarnings("unused")
         private final SelfInstanceTwoVarsReflectionTestFixture typeIsSelf;
         private final String otherType = "The Other Type";
diff --git a/src/test/java/org/apache/commons/lang3/builder/ToStringStyleTest.java b/src/test/java/org/apache/commons/lang3/builder/ToStringStyleTest.java
index 02399b6db..1f30fbeab 100644
--- a/src/test/java/org/apache/commons/lang3/builder/ToStringStyleTest.java
+++ b/src/test/java/org/apache/commons/lang3/builder/ToStringStyleTest.java
@@ -26,7 +26,7 @@ import org.junit.jupiter.api.Test;
  */
 public class ToStringStyleTest extends AbstractLangTest {
 
-    private static class ToStringStyleImpl extends ToStringStyle {
+    private static final class ToStringStyleImpl extends ToStringStyle {
         private static final long serialVersionUID = 1L;
 
     }
diff --git a/src/test/java/org/apache/commons/lang3/compare/ObjectToStringComparatorTest.java b/src/test/java/org/apache/commons/lang3/compare/ObjectToStringComparatorTest.java
index 984b6a5c3..72cf8f725 100644
--- a/src/test/java/org/apache/commons/lang3/compare/ObjectToStringComparatorTest.java
+++ b/src/test/java/org/apache/commons/lang3/compare/ObjectToStringComparatorTest.java
@@ -31,7 +31,7 @@ import org.junit.jupiter.api.Test;
  */
 public class ObjectToStringComparatorTest extends AbstractLangTest {
 
-    private static class Thing {
+    private static final class Thing {
 
         final String string;
 
diff --git a/src/test/java/org/apache/commons/lang3/concurrent/AtomicSafeInitializerTest.java b/src/test/java/org/apache/commons/lang3/concurrent/AtomicSafeInitializerTest.java
index 3352f99dd..6739ef758 100644
--- a/src/test/java/org/apache/commons/lang3/concurrent/AtomicSafeInitializerTest.java
+++ b/src/test/java/org/apache/commons/lang3/concurrent/AtomicSafeInitializerTest.java
@@ -64,7 +64,7 @@ public class AtomicSafeInitializerTest extends AbstractConcurrentInitializerTest
      * This implementation also counts the number of invocations of the initialize() method.
      * </p>
      */
-    private static class AtomicSafeInitializerTestImpl extends AtomicSafeInitializer<Object> {
+    private static final class AtomicSafeInitializerTestImpl extends AtomicSafeInitializer<Object> {
         /** A counter for initialize() invocations. */
         final AtomicInteger initCounter = new AtomicInteger();
 
diff --git a/src/test/java/org/apache/commons/lang3/concurrent/BackgroundInitializerTest.java b/src/test/java/org/apache/commons/lang3/concurrent/BackgroundInitializerTest.java
index d1a80da81..895a2247c 100644
--- a/src/test/java/org/apache/commons/lang3/concurrent/BackgroundInitializerTest.java
+++ b/src/test/java/org/apache/commons/lang3/concurrent/BackgroundInitializerTest.java
@@ -271,7 +271,7 @@ public class BackgroundInitializerTest extends AbstractLangTest {
      * A concrete implementation of BackgroundInitializer. It also overloads
      * some methods that simplify testing.
      */
-    private static class BackgroundInitializerTestImpl extends
+    private static final class BackgroundInitializerTestImpl extends
             BackgroundInitializer<Integer> {
         /** An exception to be thrown by initialize(). */
         Exception ex;
diff --git a/src/test/java/org/apache/commons/lang3/concurrent/CallableBackgroundInitializerTest.java b/src/test/java/org/apache/commons/lang3/concurrent/CallableBackgroundInitializerTest.java
index 2a2e724ef..59cbb4d2e 100644
--- a/src/test/java/org/apache/commons/lang3/concurrent/CallableBackgroundInitializerTest.java
+++ b/src/test/java/org/apache/commons/lang3/concurrent/CallableBackgroundInitializerTest.java
@@ -91,7 +91,7 @@ public class CallableBackgroundInitializerTest extends AbstractLangTest {
      * A test Callable implementation for checking the initializer's
      * implementation of the initialize() method.
      */
-    private static class TestCallable implements Callable<Integer> {
+    private static final class TestCallable implements Callable<Integer> {
         /** A counter for the number of call() invocations. */
         int callCount;
 
diff --git a/src/test/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreakerTest.java b/src/test/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreakerTest.java
index ef9bf2561..70521c49b 100644
--- a/src/test/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreakerTest.java
+++ b/src/test/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreakerTest.java
@@ -339,7 +339,7 @@ public class EventCountCircuitBreakerTest extends AbstractLangTest {
      * This is useful for the creation of deterministic tests for switching the circuit
      * breaker's state.
      */
-    private static class EventCountCircuitBreakerTestImpl extends EventCountCircuitBreaker {
+    private static final class EventCountCircuitBreakerTestImpl extends EventCountCircuitBreaker {
         /** The current time in nanoseconds. */
         private long currentTime;
 
@@ -374,7 +374,7 @@ public class EventCountCircuitBreakerTest extends AbstractLangTest {
     /**
      * A test change listener for checking whether correct change events are generated.
      */
-    private static class ChangeListener implements PropertyChangeListener {
+    private static final class ChangeListener implements PropertyChangeListener {
         /** The expected event source. */
         private final Object expectedSource;
 
diff --git a/src/test/java/org/apache/commons/lang3/concurrent/LazyInitializerTest.java b/src/test/java/org/apache/commons/lang3/concurrent/LazyInitializerTest.java
index 16eb12451..d9602b069 100644
--- a/src/test/java/org/apache/commons/lang3/concurrent/LazyInitializerTest.java
+++ b/src/test/java/org/apache/commons/lang3/concurrent/LazyInitializerTest.java
@@ -46,7 +46,7 @@ public class LazyInitializerTest extends AbstractConcurrentInitializerTest {
      * Object. As Object does not provide a specific equals() method, it is easy
      * to check whether multiple instances were created.
      */
-    private static class LazyInitializerTestImpl extends
+    private static final class LazyInitializerTestImpl extends
             LazyInitializer<Object> {
         @Override
         protected Object initialize() {
diff --git a/src/test/java/org/apache/commons/lang3/concurrent/MultiBackgroundInitializerTest.java b/src/test/java/org/apache/commons/lang3/concurrent/MultiBackgroundInitializerTest.java
index e5d46a4e7..c054c8396 100644
--- a/src/test/java/org/apache/commons/lang3/concurrent/MultiBackgroundInitializerTest.java
+++ b/src/test/java/org/apache/commons/lang3/concurrent/MultiBackgroundInitializerTest.java
@@ -370,7 +370,7 @@ public class MultiBackgroundInitializerTest extends AbstractLangTest {
      * A concrete implementation of {@code BackgroundInitializer} used for
      * defining background tasks for {@code MultiBackgroundInitializer}.
      */
-    private static class ChildBackgroundInitializer extends
+    private static final class ChildBackgroundInitializer extends
             BackgroundInitializer<Integer> {
         /** Stores the current executor service. */
         volatile ExecutorService currentExecutor;
diff --git a/src/test/java/org/apache/commons/lang3/concurrent/TimedSemaphoreTest.java b/src/test/java/org/apache/commons/lang3/concurrent/TimedSemaphoreTest.java
index 5f158660c..808e605f3 100644
--- a/src/test/java/org/apache/commons/lang3/concurrent/TimedSemaphoreTest.java
+++ b/src/test/java/org/apache/commons/lang3/concurrent/TimedSemaphoreTest.java
@@ -412,7 +412,7 @@ public class TimedSemaphoreTest extends AbstractLangTest {
      * A specialized implementation of {@code TimedSemaphore} that is easier to
      * test.
      */
-    private static class TimedSemaphoreTestImpl extends TimedSemaphore {
+    private static final class TimedSemaphoreTestImpl extends TimedSemaphore {
         /** A mock scheduled future. */
         ScheduledFuture<?> schedFuture;
 
@@ -479,7 +479,7 @@ public class TimedSemaphoreTest extends AbstractLangTest {
      * semaphore. The thread calls the semaphore a configurable number of times.
      * When this is done, it can notify the main thread.
      */
-    private static class SemaphoreThread extends Thread {
+    private static final class SemaphoreThread extends Thread {
         /** The semaphore. */
         private final TimedSemaphore semaphore;
 
@@ -524,7 +524,7 @@ public class TimedSemaphoreTest extends AbstractLangTest {
      * A test thread class which invokes {@code tryAcquire()} on the test semaphore and
      * records the return value.
      */
-    private static class TryAcquireThread extends Thread {
+    private static final class TryAcquireThread extends Thread {
         /** The semaphore. */
         private final TimedSemaphore semaphore;
 
diff --git a/src/test/java/org/apache/commons/lang3/concurrent/UncheckedFutureTest.java b/src/test/java/org/apache/commons/lang3/concurrent/UncheckedFutureTest.java
index d583680be..2a3c9cb72 100644
--- a/src/test/java/org/apache/commons/lang3/concurrent/UncheckedFutureTest.java
+++ b/src/test/java/org/apache/commons/lang3/concurrent/UncheckedFutureTest.java
@@ -37,7 +37,7 @@ import org.junit.jupiter.api.Test;
  */
 public class UncheckedFutureTest extends AbstractLangTest {
 
-    private static class TestFuture<V> extends AbstractFutureProxy<V> {
+    private static final class TestFuture<V> extends AbstractFutureProxy<V> {
 
         private final Exception exception;
 
diff --git a/src/test/java/org/apache/commons/lang3/event/EventUtilsTest.java b/src/test/java/org/apache/commons/lang3/event/EventUtilsTest.java
index 04c110034..0ea2adc95 100644
--- a/src/test/java/org/apache/commons/lang3/event/EventUtilsTest.java
+++ b/src/test/java/org/apache/commons/lang3/event/EventUtilsTest.java
@@ -162,7 +162,7 @@ public class EventUtilsTest extends AbstractLangTest {
     }
 
 
-    private static class EventCountingInvocationHandler implements InvocationHandler {
+    private static final class EventCountingInvocationHandler implements InvocationHandler {
         private final Map<String, Integer> eventCounts = new TreeMap<>();
 
         public <L> L createListener(final Class<L> listenerType) {
diff --git a/src/test/java/org/apache/commons/lang3/exception/ExceptionUtilsTest.java b/src/test/java/org/apache/commons/lang3/exception/ExceptionUtilsTest.java
index c103345ff..4845df492 100644
--- a/src/test/java/org/apache/commons/lang3/exception/ExceptionUtilsTest.java
+++ b/src/test/java/org/apache/commons/lang3/exception/ExceptionUtilsTest.java
@@ -55,7 +55,7 @@ public class ExceptionUtilsTest extends AbstractLangTest {
      * name which matches the full signature (e.g. has a return value
      * of {@code Throwable}).
      */
-    private static class ExceptionWithCause extends Exception {
+    private static final class ExceptionWithCause extends Exception {
         private static final long serialVersionUID = 1L;
 
         private Throwable cause;
@@ -84,7 +84,7 @@ public class ExceptionUtilsTest extends AbstractLangTest {
      * name which does not match the full signature (e.g. lacks a
      * return value of {@code Throwable}).
      */
-    private static class ExceptionWithoutCause extends Exception {
+    private static final class ExceptionWithoutCause extends Exception {
         private static final long serialVersionUID = 1L;
 
         @SuppressWarnings("unused")
@@ -95,7 +95,7 @@ public class ExceptionUtilsTest extends AbstractLangTest {
 
     // Temporary classes to allow the nested exception code to be removed
     // prior to a rewrite of this test class.
-    private static class NestableException extends Exception {
+    private static final class NestableException extends Exception {
         private static final long serialVersionUID = 1L;
 
         @SuppressWarnings("unused")
diff --git a/src/test/java/org/apache/commons/lang3/reflect/ConstructorUtilsTest.java b/src/test/java/org/apache/commons/lang3/reflect/ConstructorUtilsTest.java
index 56871ae48..645fcd7fc 100644
--- a/src/test/java/org/apache/commons/lang3/reflect/ConstructorUtilsTest.java
+++ b/src/test/java/org/apache/commons/lang3/reflect/ConstructorUtilsTest.java
@@ -108,7 +108,7 @@ public class ConstructorUtilsTest extends AbstractLangTest {
 
     private static class BaseClass {}
 
-    private static class SubClass extends BaseClass {}
+    private static final class SubClass extends BaseClass {}
 
     static class PrivateClass {
         @SuppressWarnings("unused")
diff --git a/src/test/java/org/apache/commons/lang3/reflect/MethodUtilsTest.java b/src/test/java/org/apache/commons/lang3/reflect/MethodUtilsTest.java
index c4a9d3031..e2d80d95c 100644
--- a/src/test/java/org/apache/commons/lang3/reflect/MethodUtilsTest.java
+++ b/src/test/java/org/apache/commons/lang3/reflect/MethodUtilsTest.java
@@ -305,7 +305,7 @@ public class MethodUtilsTest extends AbstractLangTest {
 
     }
 
-    private static class TestMutable implements Mutable<Object> {
+    private static final class TestMutable implements Mutable<Object> {
         @Override
         public Object getValue() {
             return null;
@@ -996,7 +996,7 @@ public class MethodUtilsTest extends AbstractLangTest {
     public static class ChildObject extends ParentObject implements ChildInterface {
     }
 
-    private static class MethodDescriptor {
+    private static final class MethodDescriptor {
         final Class<?> declaringClass;
         final String name;
         final Type[] parameterTypes;
@@ -1124,7 +1124,7 @@ public class MethodUtilsTest extends AbstractLangTest {
         public abstract void testMethod5(Exception exception);
     }
 
-    private static class GetMatchingMethodImpl extends AbstractGetMatchingMethod {
+    private static final class GetMatchingMethodImpl extends AbstractGetMatchingMethod {
         @Override
         public void testMethod5(final Exception exception) {
         }
diff --git a/src/test/java/org/apache/commons/lang3/stream/LangCollectorsTest.java b/src/test/java/org/apache/commons/lang3/stream/LangCollectorsTest.java
index e8f408498..b8bdc3355 100644
--- a/src/test/java/org/apache/commons/lang3/stream/LangCollectorsTest.java
+++ b/src/test/java/org/apache/commons/lang3/stream/LangCollectorsTest.java
@@ -32,7 +32,7 @@ import org.junit.jupiter.api.Test;
  */
 public class LangCollectorsTest {
 
-    private static class Fixture {
+    private static final class Fixture {
         int value;
 
         private Fixture(final int value) {
diff --git a/src/test/java/org/apache/commons/lang3/test/NotVisibleExceptionFactory.java b/src/test/java/org/apache/commons/lang3/test/NotVisibleExceptionFactory.java
index 79e077f78..4a1545ed3 100644
--- a/src/test/java/org/apache/commons/lang3/test/NotVisibleExceptionFactory.java
+++ b/src/test/java/org/apache/commons/lang3/test/NotVisibleExceptionFactory.java
@@ -34,7 +34,7 @@ public class NotVisibleExceptionFactory {
     return new NotVisibleException(cause);
   }
 
-  private static class NotVisibleException extends Exception {
+  private static final class NotVisibleException extends Exception {
 
     private static final long serialVersionUID = 1L; // avoid warning
 
diff --git a/src/test/java/org/apache/commons/lang3/text/ExtendedMessageFormatTest.java b/src/test/java/org/apache/commons/lang3/text/ExtendedMessageFormatTest.java
index d8e8f5ff6..eca95151b 100644
--- a/src/test/java/org/apache/commons/lang3/text/ExtendedMessageFormatTest.java
+++ b/src/test/java/org/apache/commons/lang3/text/ExtendedMessageFormatTest.java
@@ -399,7 +399,7 @@ public class ExtendedMessageFormatTest extends AbstractLangTest {
     /**
      * {@link Format} implementation which converts to lower case.
      */
-    private static class LowerCaseFormat extends Format {
+    private static final class LowerCaseFormat extends Format {
         private static final long serialVersionUID = 1L;
 
         @Override
@@ -415,7 +415,7 @@ public class ExtendedMessageFormatTest extends AbstractLangTest {
     /**
      * {@link Format} implementation which converts to upper case.
      */
-    private static class UpperCaseFormat extends Format {
+    private static final class UpperCaseFormat extends Format {
         private static final long serialVersionUID = 1L;
 
         @Override
@@ -434,7 +434,7 @@ public class ExtendedMessageFormatTest extends AbstractLangTest {
     /**
      * {@link FormatFactory} implementation for lower case format.
      */
-    private static class LowerCaseFormatFactory implements FormatFactory {
+    private static final class LowerCaseFormatFactory implements FormatFactory {
         private static final Format LOWER_INSTANCE = new LowerCaseFormat();
 
         @Override
@@ -445,7 +445,7 @@ public class ExtendedMessageFormatTest extends AbstractLangTest {
     /**
      * {@link FormatFactory} implementation for upper case format.
      */
-    private static class UpperCaseFormatFactory implements FormatFactory {
+    private static final class UpperCaseFormatFactory implements FormatFactory {
         private static final Format UPPER_INSTANCE = new UpperCaseFormat();
 
         @Override
@@ -456,7 +456,7 @@ public class ExtendedMessageFormatTest extends AbstractLangTest {
     /**
      * {@link FormatFactory} implementation to override date format "short" to "default".
      */
-    private static class OverrideShortDateFormatFactory implements FormatFactory {
+    private static final class OverrideShortDateFormatFactory implements FormatFactory {
 
         @Override
         public Format getFormat(final String name, final String arguments, final Locale locale) {
@@ -470,7 +470,7 @@ public class ExtendedMessageFormatTest extends AbstractLangTest {
     /**
      * Alternative ExtendedMessageFormat impl.
      */
-    private static class OtherExtendedMessageFormat extends ExtendedMessageFormat {
+    private static final class OtherExtendedMessageFormat extends ExtendedMessageFormat {
         private static final long serialVersionUID = 1L;
 
         OtherExtendedMessageFormat(final String pattern, final Locale locale,
diff --git a/src/test/java/org/apache/commons/lang3/text/StrBuilderTest.java b/src/test/java/org/apache/commons/lang3/text/StrBuilderTest.java
index 0ebf53c21..4eb1a664a 100644
--- a/src/test/java/org/apache/commons/lang3/text/StrBuilderTest.java
+++ b/src/test/java/org/apache/commons/lang3/text/StrBuilderTest.java
@@ -165,7 +165,7 @@ public class StrBuilderTest extends AbstractLangTest {
         assertEquals("Test 123", sb.toString());
     }
 
-    private static class MockReadable implements Readable {
+    private static final class MockReadable implements Readable {
 
         private final CharBuffer src;