Reuse empty class array constant in ClassUtils

Closes gh-24221

Author: jhoeller

spring-core/src/main/java/org/springframework/util/ClassUtils.java

@@ -65,6 +65,9 @@ public abstract class ClassUtils {
 	/** Prefix for internal non-primitive array class names: {@code "[L"}. */
 	private static final String NON_PRIMITIVE_ARRAY_PREFIX = "[L";
 
+	/** A reusable empty class array constant. */
+	private static final Class<?>[] EMPTY_CLASS_ARRAY = {};
+
 	/** The package separator character: {@code '.'}. */
 	private static final char PACKAGE_SEPARATOR = '.';
 
@@ -543,17 +546,12 @@ public static boolean isAssignable(Class<?> lhsType, Class<?> rhsType) {
 		}
 		if (lhsType.isPrimitive()) {
 			Class<?> resolvedPrimitive = primitiveWrapperTypeMap.get(rhsType);
-			if (lhsType == resolvedPrimitive) {
-				return true;
-			}
+			return (lhsType == resolvedPrimitive);
 		}
 		else {
 			Class<?> resolvedWrapper = primitiveTypeToWrapperMap.get(rhsType);
-			if (resolvedWrapper != null && lhsType.isAssignableFrom(resolvedWrapper)) {
-				return true;
-			}
+			return (resolvedWrapper != null && lhsType.isAssignableFrom(resolvedWrapper));
 		}
-		return false;
 	}
 
 	/**
@@ -681,8 +679,8 @@ public static String classNamesToString(@Nullable Collection<Class<?>> classes)
 	 * @since 3.1
 	 * @see StringUtils#toStringArray
 	 */
-	public static Class<?>[] toClassArray(Collection<Class<?>> collection) {
-		return collection.toArray(new Class<?>[0]);
+	public static Class<?>[] toClassArray(@Nullable Collection<Class<?>> collection) {
+		return (!CollectionUtils.isEmpty(collection) ? collection.toArray(EMPTY_CLASS_ARRAY) : EMPTY_CLASS_ARRAY);
 	}
 
 	/**
@@ -1062,7 +1060,7 @@ public static String getQualifiedMethodName(Method method, @Nullable Class<?> cl
 	 * @param clazz the clazz to analyze
 	 * @param paramTypes the parameter types of the method
 	 * @return whether the class has a corresponding constructor
-	 * @see Class#getMethod
+	 * @see Class#getConstructor
 	 */
 	public static boolean hasConstructor(Class<?> clazz, Class<?>... paramTypes) {
 		return (getConstructorIfAvailable(clazz, paramTypes) != null);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -232,16 +232,15 @@ private static EntityManager createProxy(
 
 		if (emIfc != null) {
 			interfaces = cachedEntityManagerInterfaces.computeIfAbsent(emIfc, key -> {
-				Set<Class<?>> ifcs = new LinkedHashSet<>();
+				Set<Class<?>> ifcs = new LinkedHashSet<>(4);
 				ifcs.add(key);
 				ifcs.add(EntityManagerProxy.class);
 				return ClassUtils.toClassArray(ifcs);
 			});
 		}
 		else {
 			interfaces = cachedEntityManagerInterfaces.computeIfAbsent(rawEm.getClass(), key -> {
-				Set<Class<?>> ifcs = new LinkedHashSet<>(ClassUtils
-						.getAllInterfacesForClassAsSet(key, cl));
+				Set<Class<?>> ifcs = new LinkedHashSet<>(ClassUtils.getAllInterfacesForClassAsSet(key, cl));
 				ifcs.add(EntityManagerProxy.class);
 				return ClassUtils.toClassArray(ifcs);
 			});