Use more immutable collection factory methods

marcphilipp · marcphilipp · commit 6183a6356cd5 · 2025-05-24T19:45:29.000+02:00
diff --git a/documentation/src/test/java/example/ClassTemplateDemo.java b/documentation/src/test/java/example/ClassTemplateDemo.java
@@ -11,11 +11,9 @@
 package example;
 
 import static java.util.Collections.singletonList;
-import static java.util.Collections.unmodifiableList;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
-import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Stream;
 
@@ -36,7 +34,7 @@ class ClassTemplateDemo {
 
 	static final List<String> WELL_KNOWN_FRUITS
 	// tag::custom_line_break[]
-		= unmodifiableList(Arrays.asList("apple", "banana", "lemon"));
+		= List.of("apple", "banana", "lemon");
 
 	//end::user_guide[]
 	@Nullable
diff --git a/documentation/src/test/java/example/ExternalFieldSourceDemo.java b/documentation/src/test/java/example/ExternalFieldSourceDemo.java
@@ -10,8 +10,6 @@
 
 package example;
 
-import java.util.Arrays;
-import java.util.Collections;
 import java.util.List;
 
 import org.junit.jupiter.params.ParameterizedTest;
@@ -30,6 +28,6 @@ void testWithExternalFieldSource(String tropicalFruit) {
 
 class FruitUtils {
 
-	public static final List<String> tropicalFruits = Collections.unmodifiableList(Arrays.asList("pineapple", "kiwi"));
+	public static final List<String> tropicalFruits = List.of("pineapple", "kiwi");
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContext.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContext.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.api.extension;
 
-import static java.util.Collections.unmodifiableList;
 import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
@@ -20,7 +19,6 @@
 import java.lang.reflect.Method;
 import java.nio.file.Path;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -770,13 +768,13 @@ class Namespace {
 		public static Namespace create(Object... parts) {
 			Preconditions.notEmpty(parts, "parts array must not be null or empty");
 			Preconditions.containsNoNullElements(parts, "individual parts must not be null");
-			return new Namespace(new ArrayList<>(Arrays.asList(parts)));
+			return new Namespace(List.of(parts));
 		}
 
 		private final List<Object> parts;
 
 		private Namespace(List<Object> parts) {
-			this.parts = parts;
+			this.parts = List.copyOf(parts);
 		}
 
 		@Override
@@ -815,7 +813,7 @@ public Namespace append(Object... parts) {
 
 		@API(status = INTERNAL, since = "5.13")
 		public List<Object> getParts() {
-			return unmodifiableList(parts);
+			return parts;
 		}
 	}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DisplayNameUtils.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DisplayNameUtils.java
@@ -10,8 +10,6 @@
 
 package org.junit.jupiter.engine.descriptor;
 
-import static java.util.Collections.emptyList;
-import static java.util.Collections.unmodifiableList;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
 
 import java.lang.reflect.AnnotatedElement;
@@ -126,18 +124,14 @@ private static Supplier<String> createDisplayNameSupplier(Supplier<List<Class<?>
 			Class<?> testClass, JupiterConfiguration configuration,
 			BiFunction<DisplayNameGenerator, List<Class<?>>, String> generatorFunction) {
 		return () -> {
-			List<Class<?>> enclosingInstanceTypes = makeUnmodifiable(enclosingInstanceTypesSupplier.get());
+			List<Class<?>> enclosingInstanceTypes = List.copyOf(enclosingInstanceTypesSupplier.get());
 			return findDisplayNameGenerator(enclosingInstanceTypes, testClass) //
 					.map(it -> generatorFunction.apply(it, enclosingInstanceTypes)) //
 					.orElseGet(() -> generatorFunction.apply(configuration.getDefaultDisplayNameGenerator(),
 						enclosingInstanceTypes));
 		};
 	}
 
-	private static <T> List<T> makeUnmodifiable(List<T> list) {
-		return list.isEmpty() ? emptyList() : unmodifiableList(list);
-	}
-
 	private static Optional<DisplayNameGenerator> findDisplayNameGenerator(List<Class<?>> enclosingInstanceTypes,
 			Class<?> testClass) {
 		Preconditions.notNull(testClass, "Test class must not be null");
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ResourceLockAware.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ResourceLockAware.java
@@ -10,8 +10,6 @@
 
 package org.junit.jupiter.engine.descriptor;
 
-import static java.util.Collections.emptyList;
-import static java.util.Collections.unmodifiableList;
 import static org.junit.jupiter.api.parallel.ResourceLockTarget.CHILDREN;
 
 import java.util.ArrayDeque;
@@ -80,14 +78,11 @@ static Function<ResourceLocksProvider, Set<ResourceLocksProvider.Lock>> enclosin
 			@Override
 			public Set<ResourceLocksProvider.Lock> apply(ResourceLocksProvider provider) {
 				if (this.enclosingInstanceTypes == null) {
-					this.enclosingInstanceTypes = makeUnmodifiable(enclosingInstanceTypesSupplier.get());
+					this.enclosingInstanceTypes = List.copyOf(enclosingInstanceTypesSupplier.get());
 				}
 				return evaluator.apply(provider, this.enclosingInstanceTypes);
 			}
 
-			private <T> List<T> makeUnmodifiable(List<T> list) {
-				return list.isEmpty() ? emptyList() : unmodifiableList(list);
-			}
 		};
 	}
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ModuleUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ModuleUtils.java
@@ -25,7 +25,6 @@
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Optional;
@@ -181,7 +180,7 @@ private static List<Class<?>> scan(Set<ModuleReference> references, ClassFilter
 			classes.addAll(scanner.scan(reference));
 		}
 		logger.debug(() -> "Found " + classes.size() + " classes: " + classes);
-		return Collections.unmodifiableList(classes);
+		return List.copyOf(classes);
 	}
 
 	/**
@@ -197,7 +196,7 @@ private static List<Resource> scan(Set<ModuleReference> references, Predicate<Re
 			classes.addAll(scanner.scan(reference));
 		}
 		logger.debug(() -> "Found " + classes.size() + " classes: " + classes);
-		return Collections.unmodifiableList(classes);
+		return List.copyOf(classes);
 	}
 
 	/**
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java
@@ -703,8 +703,7 @@ public static List<Object> readFieldValues(List<Field> fields, @Nullable Object
 		return fields.stream()
 				.filter(predicate)
 				.map(field ->
-					tryToReadFieldValue(field, instance)
-						.getOrThrow(ExceptionUtils::throwAsUncheckedException))
+					tryToReadFieldValue(field, instance).getOrThrow(ExceptionUtils::throwAsUncheckedException))
 				.toList();
 		// @formatter:on
 	}
@@ -1017,14 +1016,14 @@ public static Stream<Class<?>> streamAllClassesInClasspathRoot(URI root, Predica
 	 * @since 1.1
 	 */
 	public static List<Class<?>> findAllClassesInClasspathRoot(URI root, ClassFilter classFilter) {
-		return Collections.unmodifiableList(classpathScanner.scanForClassesInClasspathRoot(root, classFilter));
+		return List.copyOf(classpathScanner.scanForClassesInClasspathRoot(root, classFilter));
 	}
 
 	/**
 	 * @since 1.11
 	 */
 	public static List<Resource> findAllResourcesInClasspathRoot(URI root, Predicate<Resource> resourceFilter) {
-		return Collections.unmodifiableList(classpathScanner.scanForResourcesInClasspathRoot(root, resourceFilter));
+		return List.copyOf(classpathScanner.scanForResourcesInClasspathRoot(root, resourceFilter));
 	}
 
 	/**
@@ -1063,15 +1062,14 @@ public static Stream<Class<?>> streamAllClassesInPackage(String basePackageName,
 	 * @since 1.1
 	 */
 	public static List<Class<?>> findAllClassesInPackage(String basePackageName, ClassFilter classFilter) {
-		return Collections.unmodifiableList(classpathScanner.scanForClassesInPackage(basePackageName, classFilter));
+		return List.copyOf(classpathScanner.scanForClassesInPackage(basePackageName, classFilter));
 	}
 
 	/**
 	 * @since 1.11
 	 */
 	public static List<Resource> findAllResourcesInPackage(String basePackageName, Predicate<Resource> resourceFilter) {
-		return Collections.unmodifiableList(
-			classpathScanner.scanForResourcesInPackage(basePackageName, resourceFilter));
+		return List.copyOf(classpathScanner.scanForResourcesInPackage(basePackageName, resourceFilter));
 	}
 
 	/**
@@ -1112,14 +1110,14 @@ public static Stream<Class<?>> streamAllClassesInModule(String moduleName, Predi
 	 * @since 1.1.1
 	 */
 	public static List<Class<?>> findAllClassesInModule(String moduleName, ClassFilter classFilter) {
-		return Collections.unmodifiableList(ModuleUtils.findAllClassesInModule(moduleName, classFilter));
+		return List.copyOf(ModuleUtils.findAllClassesInModule(moduleName, classFilter));
 	}
 
 	/**
 	 * @since 1.11
 	 */
 	public static List<Resource> findAllResourcesInModule(String moduleName, Predicate<Resource> resourceFilter) {
-		return Collections.unmodifiableList(ModuleUtils.findAllResourcesInModule(moduleName, resourceFilter));
+		return List.copyOf(ModuleUtils.findAllResourcesInModule(moduleName, resourceFilter));
 	}
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueId.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueId.java
@@ -10,8 +10,6 @@
 
 package org.junit.platform.engine;
 
-import static java.util.Collections.singletonList;
-import static java.util.Collections.unmodifiableList;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.io.Serial;
@@ -97,7 +95,7 @@ public static UniqueId root(String segmentType, String value) {
 	private transient SoftReference<String> toString;
 
 	private UniqueId(UniqueIdFormat uniqueIdFormat, Segment segment) {
-		this(uniqueIdFormat, singletonList(segment));
+		this(uniqueIdFormat, List.of(segment));
 	}
 
 	/**
@@ -109,7 +107,7 @@ private UniqueId(UniqueIdFormat uniqueIdFormat, Segment segment) {
 	 */
 	UniqueId(UniqueIdFormat uniqueIdFormat, List<Segment> segments) {
 		this.uniqueIdFormat = uniqueIdFormat;
-		this.segments = segments;
+		this.segments = List.copyOf(segments);
 	}
 
 	final Optional<Segment> getRoot() {
@@ -130,7 +128,7 @@ public final Optional<String> getEngineId() {
 	 * {@code UniqueId}.
 	 */
 	public final List<Segment> getSegments() {
-		return unmodifiableList(this.segments);
+		return this.segments;
 	}
 
 	/**
@@ -218,7 +216,7 @@ public boolean hasPrefix(UniqueId potentialPrefix) {
 	@API(status = STABLE, since = "1.5")
 	public UniqueId removeLastSegment() {
 		Preconditions.condition(this.segments.size() > 1, "Cannot remove last remaining segment");
-		return new UniqueId(uniqueIdFormat, new ArrayList<>(this.segments.subList(0, this.segments.size() - 1)));
+		return new UniqueId(uniqueIdFormat, List.copyOf(this.segments.subList(0, this.segments.size() - 1)));
 	}
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/CompositeLock.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/CompositeLock.java
@@ -10,8 +10,6 @@
 
 package org.junit.platform.engine.support.hierarchical;
 
-import static java.util.Collections.unmodifiableList;
-
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.ForkJoinPool;
@@ -31,7 +29,7 @@ class CompositeLock implements ResourceLock {
 
 	CompositeLock(List<ExclusiveResource> resources, List<Lock> locks) {
 		Preconditions.condition(resources.size() == locks.size(), "Resources and locks must have the same size");
-		this.resources = unmodifiableList(resources);
+		this.resources = List.copyOf(resources);
 		this.locks = Preconditions.notEmpty(locks, "Locks must not be empty");
 		this.exclusive = resources.stream().anyMatch(
 			resource -> resource.getLockMode() == ExclusiveResource.LockMode.READ_WRITE);
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/Namespace.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/Namespace.java
@@ -13,7 +13,6 @@
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
@@ -48,7 +47,7 @@ public class Namespace {
 	public static Namespace create(Object... parts) {
 		Preconditions.notEmpty(parts, "parts array must not be null or empty");
 		Preconditions.containsNoNullElements(parts, "individual parts must not be null");
-		return new Namespace(Arrays.asList(parts));
+		return new Namespace(List.of(parts));
 	}
 
 	/**
@@ -68,7 +67,7 @@ public static Namespace create(List<Object> objects) {
 	private final List<Object> parts;
 
 	private Namespace(List<Object> parts) {
-		this.parts = new ArrayList<>(parts);
+		this.parts = List.copyOf(parts);
 	}
 
 	@Override
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultDiscoveryRequest.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultDiscoveryRequest.java
@@ -10,8 +10,6 @@
 
 package org.junit.platform.launcher.core;
 
-import static java.util.Collections.unmodifiableList;
-
 import java.util.List;
 
 import org.junit.platform.commons.util.Preconditions;
@@ -57,10 +55,10 @@ final class DefaultDiscoveryRequest implements LauncherDiscoveryRequest {
 			List<DiscoveryFilter<?>> discoveryFilters, List<PostDiscoveryFilter> postDiscoveryFilters,
 			LauncherConfigurationParameters configurationParameters, LauncherDiscoveryListener discoveryListener,
 			OutputDirectoryProvider outputDirectoryProvider) {
-		this.selectors = selectors;
-		this.engineFilters = engineFilters;
-		this.discoveryFilters = discoveryFilters;
-		this.postDiscoveryFilters = postDiscoveryFilters;
+		this.selectors = List.copyOf(selectors);
+		this.engineFilters = List.copyOf(engineFilters);
+		this.discoveryFilters = List.copyOf(discoveryFilters);
+		this.postDiscoveryFilters = List.copyOf(postDiscoveryFilters);
 		this.configurationParameters = configurationParameters;
 		this.discoveryListener = discoveryListener;
 		this.outputDirectoryProvider = outputDirectoryProvider;
@@ -74,7 +72,7 @@ public <T extends DiscoverySelector> List<T> getSelectorsByType(Class<T> selecto
 
 	@Override
 	public List<EngineFilter> getEngineFilters() {
-		return unmodifiableList(this.engineFilters);
+		return this.engineFilters;
 	}
 
 	@Override
@@ -85,7 +83,7 @@ public <T extends DiscoveryFilter<?>> List<T> getFiltersByType(Class<T> filterTy
 
 	@Override
 	public List<PostDiscoveryFilter> getPostDiscoveryFilters() {
-		return unmodifiableList(this.postDiscoveryFilters);
+		return this.postDiscoveryFilters;
 	}
 
 	@Override
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueNotifier.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueNotifier.java
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineDiscoveryResults.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineDiscoveryResults.java
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Events.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Events.java
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Executions.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Executions.java

Original file line number	Diff line number	Diff line change
`@@ -10,8 +10,6 @@`
`10`	`10`
`11`	`11`	`package org.junit.jupiter.engine.descriptor;`
`12`	`12`
`13`		`-import static java.util.Collections.emptyList;`
`14`		`-import static java.util.Collections.unmodifiableList;`
`15`	`13`	`import static org.junit.jupiter.api.parallel.ResourceLockTarget.CHILDREN;`
`16`	`14`
`17`	`15`	`import java.util.ArrayDeque;`
`@@ -80,14 +78,11 @@ static Function<ResourceLocksProvider, Set<ResourceLocksProvider.Lock>> enclosin`
`80`	`78`	`@Override`
`81`	`79`	`public Set<ResourceLocksProvider.Lock> apply(ResourceLocksProvider provider) {`
`82`	`80`	`if (this.enclosingInstanceTypes == null) {`
`83`		`- this.enclosingInstanceTypes = makeUnmodifiable(enclosingInstanceTypesSupplier.get());`
	`81`	`+ this.enclosingInstanceTypes = List.copyOf(enclosingInstanceTypesSupplier.get());`
`84`	`82`	`}`
`85`	`83`	`return evaluator.apply(provider, this.enclosingInstanceTypes);`
`86`	`84`	`}`
`87`	`85`
`88`		`- private <T> List<T> makeUnmodifiable(List<T> list) {`
`89`		`- return list.isEmpty() ? emptyList() : unmodifiableList(list);`
`90`		`- }`
`91`	`86`	`};`
`92`	`87`	`}`
`93`	`88`
Original file line number	Diff line number	Diff line change
`@@ -25,7 +25,6 @@`
`25`	`25`	`import java.net.URI;`
`26`	`26`	`import java.net.URISyntaxException;`
`27`	`27`	`import java.util.ArrayList;`
`28`		`-import java.util.Collections;`
`29`	`28`	`import java.util.LinkedHashSet;`
`30`	`29`	`import java.util.List;`
`31`	`30`	`import java.util.Optional;`
`@@ -181,7 +180,7 @@ private static List<Class<?>> scan(Set<ModuleReference> references, ClassFilter`
`181`	`180`	`classes.addAll(scanner.scan(reference));`
`182`	`181`	`}`
`183`	`182`	`logger.debug(() -> "Found " + classes.size() + " classes: " + classes);`
`184`		`- return Collections.unmodifiableList(classes);`
	`183`	`+ return List.copyOf(classes);`
`185`	`184`	`}`
`186`	`185`
`187`	`186`	`/**`
`@@ -197,7 +196,7 @@ private static List<Resource> scan(Set<ModuleReference> references, Predicate<Re`
`197`	`196`	`classes.addAll(scanner.scan(reference));`
`198`	`197`	`}`
`199`	`198`	`logger.debug(() -> "Found " + classes.size() + " classes: " + classes);`
`200`		`- return Collections.unmodifiableList(classes);`
	`199`	`+ return List.copyOf(classes);`
`201`	`200`	`}`
`202`	`201`
`203`	`202`	`/**`