Use Set.of() for constant sets where appropriate

spring-aop/src/main/java/org/springframework/aop/aspectj/AspectJAdviceParameterNameDiscoverer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -132,17 +132,17 @@ public class AspectJAdviceParameterNameDiscoverer implements ParameterNameDiscov
 	private static final int STEP_REFERENCE_PCUT_BINDING = 7;
 	private static final int STEP_FINISHED = 8;
 
-	private static final Set<String> singleValuedAnnotationPcds = new HashSet<>();
+	private static final Set<String> singleValuedAnnotationPcds = Set.of(
+			"@this",
+			"@target",
+			"@within",
+			"@withincode",
+			"@annotation");
+
 	private static final Set<String> nonReferencePointcutTokens = new HashSet<>();
 
 
 	static {
-		singleValuedAnnotationPcds.add("@this");
-		singleValuedAnnotationPcds.add("@target");
-		singleValuedAnnotationPcds.add("@within");
-		singleValuedAnnotationPcds.add("@withincode");
-		singleValuedAnnotationPcds.add("@annotation");
-
 		Set<PointcutPrimitive> pointcutPrimitives = PointcutParser.getAllSupportedPointcutPrimitives();
 		for (PointcutPrimitive primitive : pointcutPrimitives) {
 			nonReferencePointcutTokens.add(primitive.getName());

spring-aop/src/main/java/org/springframework/aop/aspectj/AspectJExpressionPointcut.java

@@ -21,7 +21,6 @@ import java.io.ObjectInputStream;
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
 import java.util.Arrays;
-import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
@@ -85,21 +84,17 @@ import org.springframework.util.StringUtils;
 public class AspectJExpressionPointcut extends AbstractExpressionPointcut
 		implements ClassFilter, IntroductionAwareMethodMatcher, BeanFactoryAware {
 
-	private static final Set<PointcutPrimitive> SUPPORTED_PRIMITIVES = new HashSet<>();
-
-	static {
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.EXECUTION);
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.ARGS);
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.REFERENCE);
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.THIS);
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.TARGET);
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.WITHIN);
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.AT_ANNOTATION);
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.AT_WITHIN);
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.AT_ARGS);
-		SUPPORTED_PRIMITIVES.add(PointcutPrimitive.AT_TARGET);
-	}
-
+	private static final Set<PointcutPrimitive> SUPPORTED_PRIMITIVES = Set.of(
+			PointcutPrimitive.EXECUTION,
+			PointcutPrimitive.ARGS,
+			PointcutPrimitive.REFERENCE,
+			PointcutPrimitive.THIS,
+			PointcutPrimitive.TARGET,
+			PointcutPrimitive.WITHIN,
+			PointcutPrimitive.AT_ANNOTATION,
+			PointcutPrimitive.AT_WITHIN,
+			PointcutPrimitive.AT_ARGS,
+			PointcutPrimitive.AT_TARGET);
 
 	private static final Log logger = LogFactory.getLog(AspectJExpressionPointcut.class);
 

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassUtils.java

@@ -17,7 +17,6 @@
 package org.springframework.context.annotation;
 
 import java.io.IOException;
-import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 
@@ -66,14 +65,12 @@ public abstract class ConfigurationClassUtils {
 
 	private static final Log logger = LogFactory.getLog(ConfigurationClassUtils.class);
 
-	private static final Set<String> candidateIndicators = new HashSet<>(8);
+	private static final Set<String> candidateIndicators = Set.of(
+			Component.class.getName(),
+			ComponentScan.class.getName(),
+			Import.class.getName(),
+			ImportResource.class.getName());
 
-	static {
-		candidateIndicators.add(Component.class.getName());
-		candidateIndicators.add(ComponentScan.class.getName());
-		candidateIndicators.add(Import.class.getName());
-		candidateIndicators.add(ImportResource.class.getName());
-	}
 
 	/**
 	 * Initialize a configuration class proxy for the specified class.

spring-context/src/main/java/org/springframework/validation/beanvalidation/SpringValidatorAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,7 +18,6 @@ package org.springframework.validation.beanvalidation;
 
 import java.io.Serializable;
 import java.util.ArrayList;
-import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
@@ -66,13 +65,8 @@ import org.springframework.validation.SmartValidator;
  */
 public class SpringValidatorAdapter implements SmartValidator, jakarta.validation.Validator {
 
-	private static final Set<String> internalAnnotationAttributes = new HashSet<>(4);
+	private static final Set<String> internalAnnotationAttributes = Set.of("message", "groups", "payload");
 
-	static {
-		internalAnnotationAttributes.add("message");
-		internalAnnotationAttributes.add("groups");
-		internalAnnotationAttributes.add("payload");
-	}
 
 	@Nullable
 	private jakarta.validation.Validator targetValidator;

spring-core/src/main/java/org/springframework/core/CollectionFactory.java

@@ -55,34 +55,31 @@ import org.springframework.util.ReflectionUtils;
  */
 public final class CollectionFactory {
 
-	private static final Set<Class<?>> approximableCollectionTypes = new HashSet<>();
+	private static final Set<Class<?>> approximableCollectionTypes = Set.of(
+			// Standard collection interfaces
+			Collection.class,
+			List.class,
+			Set.class,
+			SortedSet.class,
+			NavigableSet.class,
+			// Common concrete collection classes
+			ArrayList.class,
+			LinkedList.class,
+			HashSet.class,
+			LinkedHashSet.class,
+			TreeSet.class,
+			EnumSet.class);
 
-	private static final Set<Class<?>> approximableMapTypes = new HashSet<>();
-
-
-	static {
-		// Standard collection interfaces
-		approximableCollectionTypes.add(Collection.class);
-		approximableCollectionTypes.add(List.class);
-		approximableCollectionTypes.add(Set.class);
-		approximableCollectionTypes.add(SortedSet.class);
-		approximableCollectionTypes.add(NavigableSet.class);
-		approximableMapTypes.add(Map.class);
-		approximableMapTypes.add(SortedMap.class);
-		approximableMapTypes.add(NavigableMap.class);
-
-		// Common concrete collection classes
-		approximableCollectionTypes.add(ArrayList.class);
-		approximableCollectionTypes.add(LinkedList.class);
-		approximableCollectionTypes.add(HashSet.class);
-		approximableCollectionTypes.add(LinkedHashSet.class);
-		approximableCollectionTypes.add(TreeSet.class);
-		approximableCollectionTypes.add(EnumSet.class);
-		approximableMapTypes.add(HashMap.class);
-		approximableMapTypes.add(LinkedHashMap.class);
-		approximableMapTypes.add(TreeMap.class);
-		approximableMapTypes.add(EnumMap.class);
-	}
+	private static final Set<Class<?>> approximableMapTypes = Set.of(
+			// Standard map interfaces
+			Map.class,
+			SortedMap.class,
+			NavigableMap.class,
+			// Common concrete map classes
+			HashMap.class,
+			LinkedHashMap.class,
+			TreeMap.class,
+			EnumMap.class);
 
 
 	private CollectionFactory() {

spring-jdbc/src/main/java/org/springframework/jdbc/support/SQLStateSQLExceptionTranslator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,7 +17,6 @@
 package org.springframework.jdbc.support;
 
 import java.sql.SQLException;
-import java.util.HashSet;
 import java.util.Set;
 
 import org.springframework.dao.ConcurrencyFailureException;
@@ -46,45 +45,42 @@ import org.springframework.lang.Nullable;
  */
 public class SQLStateSQLExceptionTranslator extends AbstractFallbackSQLExceptionTranslator {
 
-	private static final Set<String> BAD_SQL_GRAMMAR_CODES = new HashSet<>(8);
-
-	private static final Set<String> DATA_INTEGRITY_VIOLATION_CODES = new HashSet<>(8);
-
-	private static final Set<String> DATA_ACCESS_RESOURCE_FAILURE_CODES = new HashSet<>(8);
-
-	private static final Set<String> TRANSIENT_DATA_ACCESS_RESOURCE_CODES = new HashSet<>(8);
-
-	private static final Set<String> CONCURRENCY_FAILURE_CODES = new HashSet<>(4);
-
-
-	static {
-		BAD_SQL_GRAMMAR_CODES.add("07");  // Dynamic SQL error
-		BAD_SQL_GRAMMAR_CODES.add("21");  // Cardinality violation
-		BAD_SQL_GRAMMAR_CODES.add("2A");  // Syntax error direct SQL
-		BAD_SQL_GRAMMAR_CODES.add("37");  // Syntax error dynamic SQL
-		BAD_SQL_GRAMMAR_CODES.add("42");  // General SQL syntax error
-		BAD_SQL_GRAMMAR_CODES.add("65");  // Oracle: unknown identifier
-
-		DATA_INTEGRITY_VIOLATION_CODES.add("01");  // Data truncation
-		DATA_INTEGRITY_VIOLATION_CODES.add("02");  // No data found
-		DATA_INTEGRITY_VIOLATION_CODES.add("22");  // Value out of range
-		DATA_INTEGRITY_VIOLATION_CODES.add("23");  // Integrity constraint violation
-		DATA_INTEGRITY_VIOLATION_CODES.add("27");  // Triggered data change violation
-		DATA_INTEGRITY_VIOLATION_CODES.add("44");  // With check violation
-
-		DATA_ACCESS_RESOURCE_FAILURE_CODES.add("08");  // Connection exception
-		DATA_ACCESS_RESOURCE_FAILURE_CODES.add("53");  // PostgreSQL: insufficient resources (e.g. disk full)
-		DATA_ACCESS_RESOURCE_FAILURE_CODES.add("54");  // PostgreSQL: program limit exceeded (e.g. statement too complex)
-		DATA_ACCESS_RESOURCE_FAILURE_CODES.add("57");  // DB2: out-of-memory exception / database not started
-		DATA_ACCESS_RESOURCE_FAILURE_CODES.add("58");  // DB2: unexpected system error
-
-		TRANSIENT_DATA_ACCESS_RESOURCE_CODES.add("JW");  // Sybase: internal I/O error
-		TRANSIENT_DATA_ACCESS_RESOURCE_CODES.add("JZ");  // Sybase: unexpected I/O error
-		TRANSIENT_DATA_ACCESS_RESOURCE_CODES.add("S1");  // DB2: communication failure
-
-		CONCURRENCY_FAILURE_CODES.add("40");  // Transaction rollback
-		CONCURRENCY_FAILURE_CODES.add("61");  // Oracle: deadlock
-	}
+	private static final Set<String> BAD_SQL_GRAMMAR_CODES = Set.of(
+			"07",  // Dynamic SQL error
+			"21",  // Cardinality violation
+			"2A",  // Syntax error direct SQL
+			"37",  // Syntax error dynamic SQL
+			"42",  // General SQL syntax error
+			"65"   // Oracle: unknown identifier
+		);
+
+	private static final Set<String> DATA_INTEGRITY_VIOLATION_CODES = Set.of(
+			"01",  // Data truncation
+			"02",  // No data found
+			"22",  // Value out of range
+			"23",  // Integrity constraint violation
+			"27",  // Triggered data change violation
+			"44"   // With check violation
+		);
+
+	private static final Set<String> DATA_ACCESS_RESOURCE_FAILURE_CODES = Set.of(
+			"08",  // Connection exception
+			"53",  // PostgreSQL: insufficient resources (e.g. disk full)
+			"54",  // PostgreSQL: program limit exceeded (e.g. statement too complex)
+			"57",  // DB2: out-of-memory exception / database not started
+			"58"   // DB2: unexpected system error
+		);
+
+	private static final Set<String> TRANSIENT_DATA_ACCESS_RESOURCE_CODES = Set.of(
+			"JW",  // Sybase: internal I/O error
+			"JZ",  // Sybase: unexpected I/O error
+			"S1"   // DB2: communication failure
+		);
+
+	private static final Set<String> CONCURRENCY_FAILURE_CODES = Set.of(
+			"40",  // Transaction rollback
+			"61"   // Oracle: deadlock
+		);
 
 
 	@Override

spring-orm/src/main/java/org/springframework/orm/jpa/SharedEntityManagerCreator.java

@@ -23,7 +23,6 @@ import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
-import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Set;
@@ -73,25 +72,22 @@ public abstract class SharedEntityManagerCreator {
 
 	private static final Map<Class<?>, Class<?>[]> cachedQueryInterfaces = new ConcurrentReferenceHashMap<>(4);
 
-	private static final Set<String> transactionRequiringMethods = new HashSet<>(8);
-
-	private static final Set<String> queryTerminatingMethods = new HashSet<>(8);
-
-	static {
-		transactionRequiringMethods.add("joinTransaction");
-		transactionRequiringMethods.add("flush");
-		transactionRequiringMethods.add("persist");
-		transactionRequiringMethods.add("merge");
-		transactionRequiringMethods.add("remove");
-		transactionRequiringMethods.add("refresh");
-
-		queryTerminatingMethods.add("execute");  // JPA 2.1 StoredProcedureQuery
-		queryTerminatingMethods.add("executeUpdate");
-		queryTerminatingMethods.add("getSingleResult");
-		queryTerminatingMethods.add("getResultStream");
-		queryTerminatingMethods.add("getResultList");
-		queryTerminatingMethods.add("list");  // Hibernate Query.list() method
-	}
+	private static final Set<String> transactionRequiringMethods = Set.of(
+			"joinTransaction",
+			"flush",
+			"persist",
+			"merge",
+			"remove",
+			"refresh");
+
+	private static final Set<String> queryTerminatingMethods = Set.of(
+			"execute",  // JPA 2.1 StoredProcedureQuery
+			"executeUpdate",
+			"getSingleResult",
+			"getResultStream",
+			"getResultList",
+			"list"  // Hibernate Query.list() method
+		);
 
 
 	/**

spring-orm/src/main/java/org/springframework/orm/jpa/persistenceunit/PersistenceManagedTypesScanner.java

@@ -58,10 +58,9 @@ public final class PersistenceManagedTypesScanner {
 
 	private static final String PACKAGE_INFO_SUFFIX = ".package-info";
 
-	private static final Set<AnnotationTypeFilter> entityTypeFilters;
+	private static final Set<AnnotationTypeFilter> entityTypeFilters = new LinkedHashSet<>(4);
 
 	static {
-		entityTypeFilters = new LinkedHashSet<>(8);
 		entityTypeFilters.add(new AnnotationTypeFilter(Entity.class, false));
 		entityTypeFilters.add(new AnnotationTypeFilter(Embeddable.class, false));
 		entityTypeFilters.add(new AnnotationTypeFilter(MappedSuperclass.class, false));

spring-test/src/main/java/org/springframework/test/context/MergedContextConfiguration.java

@@ -75,9 +75,9 @@ public class MergedContextConfiguration implements Serializable {
 	private static final Class<?>[] EMPTY_CLASS_ARRAY = new Class<?>[0];
 
 	private static final Set<Class<? extends ApplicationContextInitializer<?>>> EMPTY_INITIALIZER_CLASSES =
-			Collections.<Class<? extends ApplicationContextInitializer<?>>> emptySet();
+			Collections.emptySet();
 
-	private static final Set<ContextCustomizer> EMPTY_CONTEXT_CUSTOMIZERS = Collections.<ContextCustomizer> emptySet();
+	private static final Set<ContextCustomizer> EMPTY_CONTEXT_CUSTOMIZERS = Collections.emptySet();
 
 
 	private final Class<?> testClass;

spring-web/src/main/java/org/springframework/http/converter/xml/SourceHttpMessageConverter.java

@@ -21,7 +21,6 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.StringReader;
-import java.util.HashSet;
 import java.util.Set;
 
 import javax.xml.parsers.DocumentBuilder;
@@ -75,15 +74,12 @@ public class SourceHttpMessageConverter<T extends Source> extends AbstractHttpMe
 	private static final XMLResolver NO_OP_XML_RESOLVER =
 			(publicID, systemID, base, ns) -> InputStream.nullInputStream();
 
-	private static final Set<Class<?>> SUPPORTED_CLASSES = new HashSet<>(8);
-
-	static {
-		SUPPORTED_CLASSES.add(DOMSource.class);
-		SUPPORTED_CLASSES.add(SAXSource.class);
-		SUPPORTED_CLASSES.add(StAXSource.class);
-		SUPPORTED_CLASSES.add(StreamSource.class);
-		SUPPORTED_CLASSES.add(Source.class);
-	}
+	private static final Set<Class<?>> SUPPORTED_CLASSES = Set.of(
+			DOMSource.class,
+			SAXSource.class,
+			StAXSource.class,
+			StreamSource.class,
+			Source.class);
 
 
 	private final TransformerFactory transformerFactory = TransformerFactory.newInstance();

spring-web/src/main/java/org/springframework/web/server/adapter/HttpWebHandlerAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,8 +16,6 @@
 
 package org.springframework.web.server.adapter;
 
-import java.util.Arrays;
-import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
@@ -73,9 +71,9 @@ public class HttpWebHandlerAdapter extends WebHandlerDecorator implements HttpHa
 	private static final String DISCONNECTED_CLIENT_LOG_CATEGORY =
 			"org.springframework.web.server.DisconnectedClient";
 
-	 // Similar declaration exists in AbstractSockJsSession..
-	private static final Set<String> DISCONNECTED_CLIENT_EXCEPTIONS = new HashSet<>(
-			Arrays.asList("AbortedException", "ClientAbortException", "EOFException", "EofException"));
+	 // Similar declaration exists in AbstractSockJsSession.
+	private static final Set<String> DISCONNECTED_CLIENT_EXCEPTIONS =
+			Set.of("AbortedException", "ClientAbortException", "EOFException", "EofException");
 
 
 	private static final Log logger = LogFactory.getLog(HttpWebHandlerAdapter.class);

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/client/SockJsClient.java

@@ -19,7 +19,6 @@ package org.springframework.web.socket.sockjs.client;
 import java.net.URI;
 import java.security.Principal;
 import java.util.ArrayList;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -67,14 +66,7 @@ public class SockJsClient implements WebSocketClient, Lifecycle {
 
 	private static final Log logger = LogFactory.getLog(SockJsClient.class);
 
-	private static final Set<String> supportedProtocols = new HashSet<>(4);
-
-	static {
-		supportedProtocols.add("ws");
-		supportedProtocols.add("wss");
-		supportedProtocols.add("http");
-		supportedProtocols.add("https");
-	}
+	private static final Set<String> supportedProtocols = Set.of("ws", "wss", "http", "https");
 
 
 	private final List<Transport> transports;