From c804507faa104c54059a66037e881e1fd15fd831 Mon Sep 17 00:00:00 2001
From: cpovirk <cpovirk@google.com>
Date: Sun, 14 Jun 2026 20:46:16 -0700
Subject: [PATCH] Add `final` to classes with `private` constructors.

(prompted by https://github.com/google/error-prone/issues/5865)

And suppress some warnings in `Refaster` and `ASTHelpers`.

PiperOrigin-RevId: 932200535
---
 .../src/main/java/com/google/errorprone/BugCheckerInfo.java  | 2 +-
 .../main/java/com/google/errorprone/ErrorProneAnalyzer.java  | 2 +-
 .../src/main/java/com/google/errorprone/ErrorProneFlags.java | 2 +-
 .../main/java/com/google/errorprone/ErrorProneOptions.java   | 2 +-
 .../com/google/errorprone/JavacErrorDescriptionListener.java | 2 +-
 .../java/com/google/errorprone/RefactoringCollection.java    | 2 +-
 .../src/main/java/com/google/errorprone/SuppressionInfo.java | 2 +-
 .../src/main/java/com/google/errorprone/VisitorState.java    | 4 ++--
 .../dataflow/nullnesspropagation/NullnessAnnotations.java    | 2 +-
 .../inference/NullnessQualifierInference.java                | 2 +-
 .../com/google/errorprone/fixes/BranchedSuggestedFixes.java  | 2 +-
 .../java/com/google/errorprone/fixes/SuggestedFixes.java     | 2 +-
 .../google/errorprone/matchers/AnnotationMatcherUtils.java   | 2 +-
 .../java/com/google/errorprone/matchers/Description.java     | 4 ++--
 .../main/java/com/google/errorprone/matchers/Enclosing.java  | 2 +-
 .../main/java/com/google/errorprone/matchers/Matchers.java   | 2 +-
 .../java/com/google/errorprone/matchers/TestNgMatchers.java  | 2 +-
 .../errorprone/matchers/method/MethodInvocationMatcher.java  | 2 +-
 .../com/google/errorprone/names/LevenshteinEditDistance.java | 2 +-
 .../src/main/java/com/google/errorprone/util/ASTHelpers.java | 3 ++-
 .../src/main/java/com/google/errorprone/util/TargetType.java | 2 +-
 .../errorprone/bugpatterns/ByteBufferBackingArray.java       | 4 ++--
 .../google/errorprone/bugpatterns/CanBeStaticAnalyzer.java   | 2 +-
 .../com/google/errorprone/bugpatterns/EqualsGetClass.java    | 2 +-
 .../errorprone/bugpatterns/EqualsIncompatibleType.java       | 2 +-
 .../com/google/errorprone/bugpatterns/FieldCanBeFinal.java   | 2 +-
 .../errorprone/bugpatterns/ImpossibleNullComparison.java     | 2 +-
 .../errorprone/bugpatterns/InconsistentCapitalization.java   | 4 ++--
 .../com/google/errorprone/bugpatterns/MissingSuperCall.java  | 2 +-
 .../google/errorprone/bugpatterns/ModifiedButNotUsed.java    | 2 +-
 .../com/google/errorprone/bugpatterns/UnusedVariable.java    | 2 +-
 .../checkreturnvalue/CanIgnoreReturnValueSuggester.java      | 2 +-
 .../bugpatterns/checkreturnvalue/ErrorMessages.java          | 2 +-
 .../bugpatterns/flogger/FloggerArgumentToString.java         | 2 +-
 .../formatstring/StrictFormatStringValidation.java           | 2 +-
 .../bugpatterns/threadsafety/GuardedByExpression.java        | 2 +-
 .../bugpatterns/threadsafety/GuardedBySymbolResolver.java    | 2 +-
 .../bugpatterns/threadsafety/HeldLockAnalyzer.java           | 4 ++--
 .../errorprone/bugpatterns/threadsafety/HeldLockSet.java     | 2 +-
 .../errorprone/bugpatterns/threadsafety/ThreadSafety.java    | 2 +-
 .../google/errorprone/bugpatterns/time/NearbyCallers.java    | 2 +-
 .../com/google/errorprone/refaster/ControlFlowVisitor.java   | 4 ++--
 .../main/java/com/google/errorprone/refaster/Refaster.java   | 5 ++++-
 .../main/java/com/google/errorprone/refaster/UTypeVar.java   | 2 +-
 .../google/errorprone/scanner/BuiltInCheckerSuppliers.java   | 2 +-
 .../bugpatterns/CompileTimeConstantCheckerTest.java          | 2 +-
 .../bugpatterns/nullness/UnnecessaryCheckNotNullTest.java    | 4 ++--
 .../google/errorprone/BugCheckerRefactoringTestHelper.java   | 4 ++--
 .../java/com/google/errorprone/CompilationTestHelper.java    | 2 +-
 49 files changed, 61 insertions(+), 57 deletions(-)

diff --git a/check_api/src/main/java/com/google/errorprone/BugCheckerInfo.java b/check_api/src/main/java/com/google/errorprone/BugCheckerInfo.java
index 6ebbcfb1c03..60e4eda265b 100644
--- a/check_api/src/main/java/com/google/errorprone/BugCheckerInfo.java
+++ b/check_api/src/main/java/com/google/errorprone/BugCheckerInfo.java
@@ -35,7 +35,7 @@
  * An accessor for information about a single bug checker, including the metadata in the check's
  * {@code @BugPattern} annotation and the class that implements the check.
  */
-public class BugCheckerInfo implements Serializable {
+public final class BugCheckerInfo implements Serializable {
 
   /** The BugChecker class. */
   private final Class<? extends BugChecker> checker;
diff --git a/check_api/src/main/java/com/google/errorprone/ErrorProneAnalyzer.java b/check_api/src/main/java/com/google/errorprone/ErrorProneAnalyzer.java
index fa3ef98d709..a9beac856df 100644
--- a/check_api/src/main/java/com/google/errorprone/ErrorProneAnalyzer.java
+++ b/check_api/src/main/java/com/google/errorprone/ErrorProneAnalyzer.java
@@ -52,7 +52,7 @@
 
 /** A {@link TaskListener} that runs Error Prone over attributed compilation units. */
 @Trusted
-public class ErrorProneAnalyzer implements TaskListener {
+public final class ErrorProneAnalyzer implements TaskListener {
 
   // The set of trees that have already been scanned.
   private final Set<Tree> seen = new HashSet<>();
diff --git a/check_api/src/main/java/com/google/errorprone/ErrorProneFlags.java b/check_api/src/main/java/com/google/errorprone/ErrorProneFlags.java
index 09b3d18b534..144452429d5 100644
--- a/check_api/src/main/java/com/google/errorprone/ErrorProneFlags.java
+++ b/check_api/src/main/java/com/google/errorprone/ErrorProneFlags.java
@@ -191,7 +191,7 @@ public ErrorProneFlags plus(ErrorProneFlags other) {
   }
 
   /** Builder for Error Prone command-line flags object. Parses flags from strings. */
-  public static class Builder {
+  public static final class Builder {
 
     private final HashMap<String, String> flagsMap = new HashMap<>();
 
diff --git a/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java b/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java
index 48632b27696..da631ca6a81 100644
--- a/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java
+++ b/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java
@@ -49,7 +49,7 @@
  *
  * @author eaftan@google.com (Eddie Aftandilian)
  */
-public class ErrorProneOptions {
+public final class ErrorProneOptions {
 
   private static final String PREFIX = "-Xep";
   private static final String SEVERITY_PREFIX = "-Xep:";
diff --git a/check_api/src/main/java/com/google/errorprone/JavacErrorDescriptionListener.java b/check_api/src/main/java/com/google/errorprone/JavacErrorDescriptionListener.java
index 6227bca46dd..6fef73355d9 100644
--- a/check_api/src/main/java/com/google/errorprone/JavacErrorDescriptionListener.java
+++ b/check_api/src/main/java/com/google/errorprone/JavacErrorDescriptionListener.java
@@ -46,7 +46,7 @@
  *
  * @author alexeagle@google.com (Alex Eagle)
  */
-public class JavacErrorDescriptionListener implements DescriptionListener {
+public final class JavacErrorDescriptionListener implements DescriptionListener {
   private final Log log;
   private final JavaFileObject sourceFile;
   private final BiFunction<Description, Fix, AppliedFix> fixToAppliedFix;
diff --git a/check_api/src/main/java/com/google/errorprone/RefactoringCollection.java b/check_api/src/main/java/com/google/errorprone/RefactoringCollection.java
index 479fd90e754..2d5bfc217e0 100644
--- a/check_api/src/main/java/com/google/errorprone/RefactoringCollection.java
+++ b/check_api/src/main/java/com/google/errorprone/RefactoringCollection.java
@@ -49,7 +49,7 @@
 import java.util.logging.Logger;
 
 /** A container of fixes that have been collected during a single compilation phase. */
-public class RefactoringCollection implements DescriptionListener.Factory {
+public final class RefactoringCollection implements DescriptionListener.Factory {
 
   private static final Logger logger = Logger.getLogger(RefactoringCollection.class.getName());
 
diff --git a/check_api/src/main/java/com/google/errorprone/SuppressionInfo.java b/check_api/src/main/java/com/google/errorprone/SuppressionInfo.java
index da48ddffb1c..45d4ef2cd81 100644
--- a/check_api/src/main/java/com/google/errorprone/SuppressionInfo.java
+++ b/check_api/src/main/java/com/google/errorprone/SuppressionInfo.java
@@ -47,7 +47,7 @@
  */
 @Immutable
 @CheckReturnValue
-public class SuppressionInfo {
+public final class SuppressionInfo {
   public static final SuppressionInfo EMPTY =
       new SuppressionInfo(ImmutableSet.of(), ImmutableSet.of(), false);
 
diff --git a/check_api/src/main/java/com/google/errorprone/VisitorState.java b/check_api/src/main/java/com/google/errorprone/VisitorState.java
index 3dd07819aa5..0f4271bcbbb 100644
--- a/check_api/src/main/java/com/google/errorprone/VisitorState.java
+++ b/check_api/src/main/java/com/google/errorprone/VisitorState.java
@@ -71,7 +71,7 @@
 /**
  * @author alexeagle@google.com (Alex Eagle)
  */
-public class VisitorState {
+public /* TODO: cl/931120620 - final */ class VisitorState {
 
   private final SharedState sharedState;
   public final Context context;
@@ -606,7 +606,7 @@ public AutoCloseable timingSpan(Suppressible suppressible) {
     return sharedState.timings.span(suppressible);
   }
 
-  private static class Cache<T> implements Supplier<T> {
+  private static final class Cache<T> implements Supplier<T> {
     private final Supplier<T> impl;
     /* Uses T instead of Optional<T> because we don't want to cache null results
     (b/138753468). These inline caches persist between compilation units, and a type that fails to
diff --git a/check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/NullnessAnnotations.java b/check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/NullnessAnnotations.java
index 1e93d261073..1d12cbb8a5d 100644
--- a/check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/NullnessAnnotations.java
+++ b/check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/NullnessAnnotations.java
@@ -44,7 +44,7 @@
 import org.jspecify.annotations.Nullable;
 
 /** Utilities to extract {@link Nullness} from annotations. */
-public class NullnessAnnotations {
+public final class NullnessAnnotations {
   // TODO(kmb): Correctly handle JSR 305 @Nonnull(NEVER) etc.
   private static final Predicate<String> ANNOTATION_RELEVANT_TO_NULLNESS =
       Pattern.compile(
diff --git a/check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/inference/NullnessQualifierInference.java b/check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/inference/NullnessQualifierInference.java
index deced247508..aa32cdfc567 100644
--- a/check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/inference/NullnessQualifierInference.java
+++ b/check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/inference/NullnessQualifierInference.java
@@ -71,7 +71,7 @@
  *
  * @author bennostein@google.com (Benno Stein)
  */
-public class NullnessQualifierInference extends TreeScanner<Void, Void> {
+public final class NullnessQualifierInference extends TreeScanner<Void, Void> {
 
   private static final LoadingCache<Tree, InferredNullability> inferenceCache =
       Caffeine.newBuilder()
diff --git a/check_api/src/main/java/com/google/errorprone/fixes/BranchedSuggestedFixes.java b/check_api/src/main/java/com/google/errorprone/fixes/BranchedSuggestedFixes.java
index 850bb2d1de5..fd28098deb2 100644
--- a/check_api/src/main/java/com/google/errorprone/fixes/BranchedSuggestedFixes.java
+++ b/check_api/src/main/java/com/google/errorprone/fixes/BranchedSuggestedFixes.java
@@ -43,7 +43,7 @@
  *
  * @author andrewrice@google.com (Andrew Rice)
  */
-public class BranchedSuggestedFixes {
+public final class BranchedSuggestedFixes {
 
   private final ImmutableList<SuggestedFix> fixes;
 
diff --git a/check_api/src/main/java/com/google/errorprone/fixes/SuggestedFixes.java b/check_api/src/main/java/com/google/errorprone/fixes/SuggestedFixes.java
index 7c384c113a3..d5bba61bb5e 100644
--- a/check_api/src/main/java/com/google/errorprone/fixes/SuggestedFixes.java
+++ b/check_api/src/main/java/com/google/errorprone/fixes/SuggestedFixes.java
@@ -1942,7 +1942,7 @@ public static VariableNamer variableNamer(VisitorState state) {
   }
 
   /** Helper class for avoiding variable name shadowing. */
-  public static class VariableNamer {
+  public static final class VariableNamer {
     private final Set<String> idents;
 
     private VariableNamer(VisitorState state) {
diff --git a/check_api/src/main/java/com/google/errorprone/matchers/AnnotationMatcherUtils.java b/check_api/src/main/java/com/google/errorprone/matchers/AnnotationMatcherUtils.java
index 51704364c1d..5635ba67c53 100644
--- a/check_api/src/main/java/com/google/errorprone/matchers/AnnotationMatcherUtils.java
+++ b/check_api/src/main/java/com/google/errorprone/matchers/AnnotationMatcherUtils.java
@@ -26,7 +26,7 @@
  *
  * @author mwacker@google.com (Mike Wacker)
  */
-public class AnnotationMatcherUtils {
+public final class AnnotationMatcherUtils {
 
   /**
    * Gets the value for an argument, or null if the argument does not exist.
diff --git a/check_api/src/main/java/com/google/errorprone/matchers/Description.java b/check_api/src/main/java/com/google/errorprone/matchers/Description.java
index 7247b3dc004..de1828afe3d 100644
--- a/check_api/src/main/java/com/google/errorprone/matchers/Description.java
+++ b/check_api/src/main/java/com/google/errorprone/matchers/Description.java
@@ -42,7 +42,7 @@
  *
  * @author alexeagle@google.com (Alex Eagle)
  */
-public class Description {
+public final class Description {
   /** Describes the sentinel value of the case where the match failed. */
   public static final Description NO_MATCH =
       new Description(
@@ -151,7 +151,7 @@ public static Builder builder(
   }
 
   /** Builder for {@code Description}s. */
-  public static class Builder {
+  public static final class Builder {
     private final ErrorPronePosition position;
     private final String name;
     private String linkUrl;
diff --git a/check_api/src/main/java/com/google/errorprone/matchers/Enclosing.java b/check_api/src/main/java/com/google/errorprone/matchers/Enclosing.java
index c78becb0eef..cf94d284eca 100644
--- a/check_api/src/main/java/com/google/errorprone/matchers/Enclosing.java
+++ b/check_api/src/main/java/com/google/errorprone/matchers/Enclosing.java
@@ -30,7 +30,7 @@
  *
  * @author alexeagle@google.com (Alex Eagle)
  */
-public class Enclosing {
+public final class Enclosing {
   private Enclosing() {}
 
   private abstract static class EnclosingMatcher<T extends Tree, U extends Tree>
diff --git a/check_api/src/main/java/com/google/errorprone/matchers/Matchers.java b/check_api/src/main/java/com/google/errorprone/matchers/Matchers.java
index 02c440b6e47..5cb11478e25 100644
--- a/check_api/src/main/java/com/google/errorprone/matchers/Matchers.java
+++ b/check_api/src/main/java/com/google/errorprone/matchers/Matchers.java
@@ -114,7 +114,7 @@
  *
  * @author alexeagle@google.com (Alex Eagle)
  */
-public class Matchers {
+public final class Matchers {
 
   private Matchers() {}
 
diff --git a/check_api/src/main/java/com/google/errorprone/matchers/TestNgMatchers.java b/check_api/src/main/java/com/google/errorprone/matchers/TestNgMatchers.java
index b5b0f9ca678..89fe8e59609 100644
--- a/check_api/src/main/java/com/google/errorprone/matchers/TestNgMatchers.java
+++ b/check_api/src/main/java/com/google/errorprone/matchers/TestNgMatchers.java
@@ -30,7 +30,7 @@
  *
  * @author bhagwani@google.com (Sumit Bhagwani)
  */
-public class TestNgMatchers {
+public final class TestNgMatchers {
 
   /**
    * Checks if a method, or any overridden method, is annotated with any annotation from the
diff --git a/check_api/src/main/java/com/google/errorprone/matchers/method/MethodInvocationMatcher.java b/check_api/src/main/java/com/google/errorprone/matchers/method/MethodInvocationMatcher.java
index d533678f262..2bbf78f8c8d 100644
--- a/check_api/src/main/java/com/google/errorprone/matchers/method/MethodInvocationMatcher.java
+++ b/check_api/src/main/java/com/google/errorprone/matchers/method/MethodInvocationMatcher.java
@@ -46,7 +46,7 @@
  * The machinery and type definitions necessary to model and compile a single efficient matcher out
  * of a list of {@link com.google.errorprone.matchers.method.MethodMatchers.MethodMatcher}s.
  */
-public class MethodInvocationMatcher {
+public final class MethodInvocationMatcher {
 
   record Context(MethodSymbol sym, ExpressionTree tree) {
     static Optional<Context> create(ExpressionTree tree) {
diff --git a/check_api/src/main/java/com/google/errorprone/names/LevenshteinEditDistance.java b/check_api/src/main/java/com/google/errorprone/names/LevenshteinEditDistance.java
index 40a5dae69b2..9627c0471aa 100644
--- a/check_api/src/main/java/com/google/errorprone/names/LevenshteinEditDistance.java
+++ b/check_api/src/main/java/com/google/errorprone/names/LevenshteinEditDistance.java
@@ -28,7 +28,7 @@
  *
  * @author eaftan@google.com (Eddie Aftandilian)
  */
-public class LevenshteinEditDistance {
+public final class LevenshteinEditDistance {
 
   private LevenshteinEditDistance() {
     /* disallow instantiation */
diff --git a/check_api/src/main/java/com/google/errorprone/util/ASTHelpers.java b/check_api/src/main/java/com/google/errorprone/util/ASTHelpers.java
index 94d3bf53755..a3081fa4bb4 100644
--- a/check_api/src/main/java/com/google/errorprone/util/ASTHelpers.java
+++ b/check_api/src/main/java/com/google/errorprone/util/ASTHelpers.java
@@ -162,7 +162,8 @@
 import org.jspecify.annotations.Nullable;
 
 /** This class contains utility methods to work with the javac AST. */
-public class ASTHelpers {
+@SuppressWarnings("IdentifierName") // should have been "AstHelpers" but too disruptive to change
+public final class ASTHelpers {
   /**
    * Determines whether two expressions refer to the same variable. Note that returning false
    * doesn't necessarily mean the expressions do *not* refer to the same field. We don't attempt to
diff --git a/check_api/src/main/java/com/google/errorprone/util/TargetType.java b/check_api/src/main/java/com/google/errorprone/util/TargetType.java
index c9b8542e7db..7b7350596d6 100644
--- a/check_api/src/main/java/com/google/errorprone/util/TargetType.java
+++ b/check_api/src/main/java/com/google/errorprone/util/TargetType.java
@@ -176,7 +176,7 @@ private static boolean canHaveTargetType(Tree tree) {
   }
 
   @VisibleForTesting
-  static class TargetTypeVisitor extends SimpleTreeVisitor<Type, Void> {
+  static final class TargetTypeVisitor extends SimpleTreeVisitor<Type, Void> {
     private final VisitorState state;
     private final TreePath parent;
     private final ExpressionTree current;
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/ByteBufferBackingArray.java b/core/src/main/java/com/google/errorprone/bugpatterns/ByteBufferBackingArray.java
index c2df097a585..6b176af6de0 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/ByteBufferBackingArray.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/ByteBufferBackingArray.java
@@ -123,7 +123,7 @@ private static boolean isValidInitializerOrNotAByteBuffer(
    * Scan for a call to ByteBuffer.arrayOffset() or check if buffer was initialized with either
    * ByteBuffer.wrap() or ByteBuffer.allocate().
    */
-  private static class ValidByteBufferArrayScanner extends TreeScanner<Void, VisitorState> {
+  private static final class ValidByteBufferArrayScanner extends TreeScanner<Void, VisitorState> {
 
     private final Symbol searchedBufferSymbol;
     private boolean visited;
@@ -185,7 +185,7 @@ private void checkForInitializer(
   }
 
   /** Scan for a call to ByteBuffer.wrap() or ByteBuffer.allocate(). */
-  private static class ValidByteBufferInitializerScanner
+  private static final class ValidByteBufferInitializerScanner
       extends TreeScanner<Boolean, VisitorState> {
 
     static Boolean scan(ExpressionTree tree, VisitorState state) {
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/CanBeStaticAnalyzer.java b/core/src/main/java/com/google/errorprone/bugpatterns/CanBeStaticAnalyzer.java
index 8e6a83da6cf..e17fd573874 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/CanBeStaticAnalyzer.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/CanBeStaticAnalyzer.java
@@ -39,7 +39,7 @@
 import java.util.Set;
 
 /** Analyzes trees for references to their enclosing instance. */
-public class CanBeStaticAnalyzer extends TreeScanner {
+public final class CanBeStaticAnalyzer extends TreeScanner {
 
   /** Returns true if the tree references its enclosing class. */
   public static boolean referencesOuter(Tree tree, Symbol owner, VisitorState state) {
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/EqualsGetClass.java b/core/src/main/java/com/google/errorprone/bugpatterns/EqualsGetClass.java
index b0ebb50c42a..676e511e464 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/EqualsGetClass.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/EqualsGetClass.java
@@ -107,7 +107,7 @@ public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState
     return describeMatch(methodTree, fixer.getFix());
   }
 
-  private static class EqualsFixer extends TreePathScanner<Void, Void> {
+  private static final class EqualsFixer extends TreePathScanner<Void, Void> {
 
     private static final Matcher<ExpressionTree> GET_CLASS =
         instanceMethod().onDescendantOf("java.lang.Object").named("getClass").withNoParameters();
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/EqualsIncompatibleType.java b/core/src/main/java/com/google/errorprone/bugpatterns/EqualsIncompatibleType.java
index cfd1284759c..b0ef8b4d15d 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/EqualsIncompatibleType.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/EqualsIncompatibleType.java
@@ -202,7 +202,7 @@ private static String getMessage(
         + " are incompatible.";
   }
 
-  private static class TypeStringPair {
+  private static final class TypeStringPair {
     private String receiverTypeString;
     private String argumentTypeString;
 
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/FieldCanBeFinal.java b/core/src/main/java/com/google/errorprone/bugpatterns/FieldCanBeFinal.java
index 9654cab479c..c70ba8af508 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/FieldCanBeFinal.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/FieldCanBeFinal.java
@@ -253,7 +253,7 @@ public Description matchCompilationUnit(CompilationUnitTree tree, VisitorState s
   }
 
   /** Record assignments to possibly-final variables in a compilation unit. */
-  private class FinalScanner extends TreePathScanner<Void, InitializationContext> {
+  private final class FinalScanner extends TreePathScanner<Void, InitializationContext> {
 
     private final VariableAssignmentRecords writes;
     private final VisitorState compilationState;
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/ImpossibleNullComparison.java b/core/src/main/java/com/google/errorprone/bugpatterns/ImpossibleNullComparison.java
index b42113e8a30..e9195f102bd 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/ImpossibleNullComparison.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/ImpossibleNullComparison.java
@@ -169,7 +169,7 @@ public Description matchCompilationUnit(CompilationUnitTree tree, VisitorState s
     return Description.NO_MATCH;
   }
 
-  private class NullComparisonScanner extends TreePathScanner<Void, Void> {
+  private final class NullComparisonScanner extends TreePathScanner<Void, Void> {
     private final Map<Symbol, ExpressionTree> effectivelyFinalValues = new HashMap<>();
     private final VisitorState state;
 
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/InconsistentCapitalization.java b/core/src/main/java/com/google/errorprone/bugpatterns/InconsistentCapitalization.java
index f7b0f27be9f..3e1e2c44595 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/InconsistentCapitalization.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/InconsistentCapitalization.java
@@ -142,7 +142,7 @@ private static boolean isUpperCaseAndStatic(Symbol symbol) {
    * Matcher for all fields of the given class node that are either instance members or not all
    * upper case.
    */
-  private static class FieldScanner extends TreeScanner<Void, Void> {
+  private static final class FieldScanner extends TreeScanner<Void, Void> {
 
     static ImmutableSet<Symbol> findFields(ClassTree tree) {
       ImmutableSet.Builder<Symbol> fieldsBuilder = ImmutableSet.builder();
@@ -177,7 +177,7 @@ public Void visitVariable(VariableTree tree, Void unused) {
    * Matcher for all parameters (methods, constructors, lambda expressions) that have the same name
    * as one of the provided fields but with different capitalization.
    */
-  private static class MatchingParametersScanner extends TreePathScanner<Void, Void> {
+  private static final class MatchingParametersScanner extends TreePathScanner<Void, Void> {
 
     static ImmutableMap<TreePath, Symbol> findMatchingParameters(
         ImmutableMap<String, Symbol> fieldNamesMap, TreePath path) {
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/MissingSuperCall.java b/core/src/main/java/com/google/errorprone/bugpatterns/MissingSuperCall.java
index 0a9a37de834..3147a897349 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/MissingSuperCall.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/MissingSuperCall.java
@@ -164,7 +164,7 @@ public Description matchMethod(MethodTree tree, VisitorState state) {
   }
 
   /** Scans a tree looking for calls to a method that is overridden by the given one. */
-  private static class FindSuperTreeScanner extends TreeScanner<Boolean, Void> {
+  private static final class FindSuperTreeScanner extends TreeScanner<Boolean, Void> {
     private final String overridingMethodName;
 
     private FindSuperTreeScanner(String overridingMethodName) {
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/ModifiedButNotUsed.java b/core/src/main/java/com/google/errorprone/bugpatterns/ModifiedButNotUsed.java
index 63d32f7d856..4534894785b 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/ModifiedButNotUsed.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/ModifiedButNotUsed.java
@@ -301,7 +301,7 @@ private static boolean newFluentChain(ExpressionTree tree, VisitorState state) {
         .orElse(false);
   }
 
-  private static class UnusedScanner extends TreePathScanner<Void, Void> {
+  private static final class UnusedScanner extends TreePathScanner<Void, Void> {
     private final Symbol symbol;
     private final VisitorState state;
     private final Matcher<IdentifierTree> matcher;
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/UnusedVariable.java b/core/src/main/java/com/google/errorprone/bugpatterns/UnusedVariable.java
index 0c238cd8ae0..018b85228ac 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/UnusedVariable.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/UnusedVariable.java
@@ -650,7 +650,7 @@ private boolean exemptedByName(Name name) {
         || exemptNames.contains(nameString);
   }
 
-  private class VariableFinder extends TreePathScanner<Void, Void> {
+  private final class VariableFinder extends TreePathScanner<Void, Void> {
     private final Map<Symbol, TreePath> unusedElements = new HashMap<>();
 
     private final Set<Symbol> onlyCheckForReassignments = new HashSet<>();
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/checkreturnvalue/CanIgnoreReturnValueSuggester.java b/core/src/main/java/com/google/errorprone/bugpatterns/checkreturnvalue/CanIgnoreReturnValueSuggester.java
index ad0d2de792f..edb3da5fc3f 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/checkreturnvalue/CanIgnoreReturnValueSuggester.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/checkreturnvalue/CanIgnoreReturnValueSuggester.java
@@ -301,7 +301,7 @@ private static boolean isDefinitionOfZeroArgSelf(MethodSymbol methodSymbol) {
   }
 
   private static boolean methodReturnsIgnorableValues(MethodTree tree, VisitorState state) {
-    class ReturnValuesFromMethodAreIgnorable extends TreeScanner<Void, Void> {
+    final class ReturnValuesFromMethodAreIgnorable extends TreeScanner<Void, Void> {
       private final VisitorState state;
       private final Type enclosingClassType;
       private final Type methodReturnType;
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/checkreturnvalue/ErrorMessages.java b/core/src/main/java/com/google/errorprone/bugpatterns/checkreturnvalue/ErrorMessages.java
index 623926b0727..4b3190a636c 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/checkreturnvalue/ErrorMessages.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/checkreturnvalue/ErrorMessages.java
@@ -21,7 +21,7 @@
 import java.util.List;
 
 /** Error messages used by {@link com.google.errorprone.bugpatterns.CheckReturnValue}. */
-public class ErrorMessages {
+public final class ErrorMessages {
   private ErrorMessages() {}
 
   /**
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/flogger/FloggerArgumentToString.java b/core/src/main/java/com/google/errorprone/bugpatterns/flogger/FloggerArgumentToString.java
index b63c7553a3a..505a9075359 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/flogger/FloggerArgumentToString.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/flogger/FloggerArgumentToString.java
@@ -117,7 +117,7 @@ public class FloggerArgumentToString extends BugChecker implements MethodInvocat
   private static final Character HEX_FORMAT = 'x';
   private static final Character UPPER_HEX_FORMAT = 'X';
 
-  static class Parameter {
+  static final class Parameter {
 
     final Supplier<String> source;
     final Type type;
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/formatstring/StrictFormatStringValidation.java b/core/src/main/java/com/google/errorprone/bugpatterns/formatstring/StrictFormatStringValidation.java
index 1276da1296c..92ccda3f000 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/formatstring/StrictFormatStringValidation.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/formatstring/StrictFormatStringValidation.java
@@ -49,7 +49,7 @@
  * Format string validation utility that fails on more cases than {@link FormatStringValidation} to
  * enforce strict format string checking.
  */
-public class StrictFormatStringValidation {
+public final class StrictFormatStringValidation {
 
   private static final Matcher<ExpressionTree> MOCKITO_MATCHERS =
       staticMethod().onClassAny("org.mockito.Matchers", "org.mockito.ArgumentMatchers");
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/GuardedByExpression.java b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/GuardedByExpression.java
index e41048bf1ec..1d077fa558f 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/GuardedByExpression.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/GuardedByExpression.java
@@ -104,7 +104,7 @@ public String guardString() {
   /** A simple 'this literal. */
   // Don't use AutoValue here, since sym and type need to be 'null'. (And since
   // it's a singleton we don't need to implement equals() or hashCode()).
-  public static class ThisLiteral extends GuardedByExpression {
+  public static final class ThisLiteral extends GuardedByExpression {
 
     static final ThisLiteral INSTANCE = new ThisLiteral();
 
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/GuardedBySymbolResolver.java b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/GuardedBySymbolResolver.java
index 23fba0e4331..ed1aded3e1c 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/GuardedBySymbolResolver.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/GuardedBySymbolResolver.java
@@ -51,7 +51,7 @@
  *
  * @author cushon@google.com (Liam Miller-Cushon)
  */
-public class GuardedBySymbolResolver implements GuardedByBinder.Resolver {
+public final class GuardedBySymbolResolver implements GuardedByBinder.Resolver {
 
   private final ClassSymbol enclosingClass;
   private final MethodInfo method;
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/HeldLockAnalyzer.java b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/HeldLockAnalyzer.java
index bb92c373093..29c79c4b8ed 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/HeldLockAnalyzer.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/HeldLockAnalyzer.java
@@ -133,7 +133,7 @@ private static HeldLockSet handleMonitorGuards(VisitorState state, HeldLockSet l
         .orElse(locks);
   }
 
-  private static class LockScanner extends TreePathScanner<Void, HeldLockSet> {
+  private static final class LockScanner extends TreePathScanner<Void, HeldLockSet> {
 
     private final VisitorState visitorState;
     private final LockEventListener listener;
@@ -306,7 +306,7 @@ static LockResource create(String className, String unlockMethod) {
           LockResource.create("com.google.common.util.concurrent.Monitor", "leave"),
           LockResource.create("java.util.concurrent.Semaphore", "release"));
 
-  private static class LockOperationFinder extends TreeScanner<Void, Void> {
+  private static final class LockOperationFinder extends TreeScanner<Void, Void> {
 
     static Collection<GuardedByExpression> find(
         Tree tree, VisitorState state, Matcher<ExpressionTree> lockOperationMatcher) {
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/HeldLockSet.java b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/HeldLockSet.java
index 53706dadaad..6314df4afcf 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/HeldLockSet.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/HeldLockSet.java
@@ -30,7 +30,7 @@
  *
  * @author cushon@google.com (Liam Miller-Cushon)
  */
-class HeldLockSet {
+final class HeldLockSet {
 
   final PSet<GuardedByExpression> locks;
 
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafety.java b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafety.java
index 0f62569aa04..1c4b4af6fcf 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafety.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/ThreadSafety.java
@@ -421,7 +421,7 @@ private Violation isThreadSafeTypeInternal(
         null);
   }
 
-  private class ThreadSafeTypeVisitor extends Types.SimpleVisitor<Violation, Void> {
+  private final class ThreadSafeTypeVisitor extends Types.SimpleVisitor<Violation, Void> {
 
     private final boolean allowContainerTypeParameters;
     private final Set<String> containerTypeParameters;
diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/time/NearbyCallers.java b/core/src/main/java/com/google/errorprone/bugpatterns/time/NearbyCallers.java
index 22a01972cde..f8875feed17 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/time/NearbyCallers.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/time/NearbyCallers.java
@@ -43,7 +43,7 @@
  *
  * <p>TODO(glorioso): Coalesce this with ByteBufferBackingArray since they have similar aims?
  */
-public class NearbyCallers {
+public final class NearbyCallers {
   private NearbyCallers() {}
 
   // lifted from com.google.devtools.javatools.refactory.refaster.cleanups.proto.ProtoMatchers
diff --git a/core/src/main/java/com/google/errorprone/refaster/ControlFlowVisitor.java b/core/src/main/java/com/google/errorprone/refaster/ControlFlowVisitor.java
index 882038084c3..c5a20a0341e 100644
--- a/core/src/main/java/com/google/errorprone/refaster/ControlFlowVisitor.java
+++ b/core/src/main/java/com/google/errorprone/refaster/ControlFlowVisitor.java
@@ -52,7 +52,7 @@
  *
  * @author lowasser@google.com (Louis Wasserman)
  */
-public class ControlFlowVisitor extends SimpleTreeVisitor<Result, BreakContext> {
+public final class ControlFlowVisitor extends SimpleTreeVisitor<Result, BreakContext> {
   public static final ControlFlowVisitor INSTANCE = new ControlFlowVisitor();
 
   /**
@@ -120,7 +120,7 @@ Result then(Result other) {
     abstract Result then(Result other);
   }
 
-  static class BreakContext {
+  static final class BreakContext {
     final Set<Name> internalLabels;
     int loopDepth;
 
diff --git a/core/src/main/java/com/google/errorprone/refaster/Refaster.java b/core/src/main/java/com/google/errorprone/refaster/Refaster.java
index 30a84ee0684..7e21ca88acb 100644
--- a/core/src/main/java/com/google/errorprone/refaster/Refaster.java
+++ b/core/src/main/java/com/google/errorprone/refaster/Refaster.java
@@ -23,7 +23,9 @@
  *
  * @author lowasser@google.com (Louis Wasserman)
  */
-public class Refaster {
+// We need to call these methods from templates that aren't run as normal Java code.
+@SuppressWarnings("DoNotCallSuggester")
+public final class Refaster {
   private Refaster() {}
 
   /**
@@ -98,6 +100,7 @@ public static <T> T anyOf(T... expressions) {
    *
    * @throws IllegalArgumentException if T is not specified explicitly.
    */
+  @SuppressWarnings("UnusedTypeParameter") // The type parameter supports extralinguistic magic
   public static <T> boolean isInstance(Object o) {
     // real code wouldn't have an unused type parameter (T) or an unused argument (o)
     throw new UnsupportedOperationException(o.toString());
diff --git a/core/src/main/java/com/google/errorprone/refaster/UTypeVar.java b/core/src/main/java/com/google/errorprone/refaster/UTypeVar.java
index 102d779b23f..97c9486eab4 100644
--- a/core/src/main/java/com/google/errorprone/refaster/UTypeVar.java
+++ b/core/src/main/java/com/google/errorprone/refaster/UTypeVar.java
@@ -31,7 +31,7 @@
  *
  * @author Louis Wasserman
  */
-public class UTypeVar extends UType {
+public final class UTypeVar extends UType {
   // This can't be @AutoValue'd, since the fields are mutable.
 
   /** Bindings key linked to a {@code UTypeVar}. */
diff --git a/core/src/main/java/com/google/errorprone/scanner/BuiltInCheckerSuppliers.java b/core/src/main/java/com/google/errorprone/scanner/BuiltInCheckerSuppliers.java
index 809fc65e29a..191262da674 100644
--- a/core/src/main/java/com/google/errorprone/scanner/BuiltInCheckerSuppliers.java
+++ b/core/src/main/java/com/google/errorprone/scanner/BuiltInCheckerSuppliers.java
@@ -671,7 +671,7 @@
  * Static helper class that provides {@link ScannerSupplier}s and {@link BugChecker}s for the
  * built-in Error Prone checks, as opposed to plugin checks or checks used in tests.
  */
-public class BuiltInCheckerSuppliers {
+public final class BuiltInCheckerSuppliers {
   @SafeVarargs
   public static ImmutableSet<BugCheckerInfo> getSuppliers(Class<? extends BugChecker>... checkers) {
     return getSuppliers(Arrays.asList(checkers));
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/CompileTimeConstantCheckerTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/CompileTimeConstantCheckerTest.java
index 7cba8744f22..419eb2878c8 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/CompileTimeConstantCheckerTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/CompileTimeConstantCheckerTest.java
@@ -345,7 +345,7 @@ public static CompileTimeConstantTestCase makeNew(String x) {
   }
 
   /** Holder for a method we wish to reference from a test. */
-  public static class Holder {
+  public static final class Holder {
     public static void m(String s, @CompileTimeConstant String... p) {}
 
     private Holder() {}
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/nullness/UnnecessaryCheckNotNullTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/nullness/UnnecessaryCheckNotNullTest.java
index 1afad3cf771..55c5cdb8cd9 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/nullness/UnnecessaryCheckNotNullTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/nullness/UnnecessaryCheckNotNullTest.java
@@ -517,8 +517,8 @@ void foo(String x, A a) {
   }
 
   // TODO(mdempsky): Make this more reusable.
-  private static class TestScanner extends Scanner {
-    private static class Match {
+  private static final class TestScanner extends Scanner {
+    private static final class Match {
       private final ImmutableList<String> expected;
       private boolean found = false;
 
diff --git a/test_helpers/src/main/java/com/google/errorprone/BugCheckerRefactoringTestHelper.java b/test_helpers/src/main/java/com/google/errorprone/BugCheckerRefactoringTestHelper.java
index 8f1321b3347..de8eb9f22ff 100644
--- a/test_helpers/src/main/java/com/google/errorprone/BugCheckerRefactoringTestHelper.java
+++ b/test_helpers/src/main/java/com/google/errorprone/BugCheckerRefactoringTestHelper.java
@@ -85,7 +85,7 @@
  * @author kurs@google.com (Jan Kurs)
  */
 @CheckReturnValue
-public class BugCheckerRefactoringTestHelper {
+public final class BugCheckerRefactoringTestHelper {
 
   /** Test mode for matching refactored source against expected source. */
   public enum TestMode {
@@ -451,7 +451,7 @@ private static String getFullyQualifiedName(JCCompilationUnit tree) {
   }
 
   /** To assert the proper {@code .addInput().addOutput()} chain. */
-  public class ExpectOutput {
+  public final class ExpectOutput {
     private final JavaFileObject input;
 
     private ExpectOutput(JavaFileObject input) {
diff --git a/test_helpers/src/main/java/com/google/errorprone/CompilationTestHelper.java b/test_helpers/src/main/java/com/google/errorprone/CompilationTestHelper.java
index 45ae57efdcd..05713c0b97c 100644
--- a/test_helpers/src/main/java/com/google/errorprone/CompilationTestHelper.java
+++ b/test_helpers/src/main/java/com/google/errorprone/CompilationTestHelper.java
@@ -59,7 +59,7 @@
 
 /** Helps test Error Prone bug checkers and compilations. */
 @CheckReturnValue
-public class CompilationTestHelper {
+public final class CompilationTestHelper {
   private static final ImmutableList<String> DEFAULT_ARGS =
       ImmutableList.of(
           "-encoding",