Add final to classes with private constructors.

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;

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<>();

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<>();
 

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:";

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;

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());
 

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);
 

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

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(

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()

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;
 

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) {

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.

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;

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>

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() {}
 

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

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) {

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 */

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

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;

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) {

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) {

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();

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;
 

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;

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;
 

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) {

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) {

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;

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<>();

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;

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() {}
 
   /**

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;

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");

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();
 

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;

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) {

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;