Unify on Set.of

30 files changed, 152 insertions, 182 deletions

diff --git a/abi-check-plugin/src/test/java/com/yahoo/abicheck/mojo/AbiCheckTest.java b/abi-check-plugin/src/test/java/com/yahoo/abicheck/mojo/AbiCheckTest.java
index 6821a03818e..8782e6a6c03 100644
--- a/abi-check-plugin/src/test/java/com/yahoo/abicheck/mojo/AbiCheckTest.java
+++ b/abi-check-plugin/src/test/java/com/yahoo/abicheck/mojo/AbiCheckTest.java
@@ -13,8 +13,9 @@ import com.yahoo.abicheck.classtree.ClassFileTree;
 import com.yahoo.abicheck.signature.JavaClassSignature;
 import java.io.IOException;
 import java.util.Arrays;
-import java.util.Collections;
+import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import org.apache.maven.plugin.logging.Log;
 import org.junit.jupiter.api.Test;
 import root.Root;
@@ -30,9 +31,9 @@ public class AbiCheckTest {
     ClassFileTree.ClassFile rootPkgClass = mock(ClassFileTree.ClassFile.class);
     ClassFileTree.ClassFile subPkgClass = mock(ClassFileTree.ClassFile.class);
 
-    when(rootPkg.getSubPackages()).thenReturn(Collections.singleton(subPkg));
+    when(rootPkg.getSubPackages()).thenReturn(Set.of(subPkg));
     when(rootPkg.getClassFiles()).thenReturn(Arrays.asList(rootPkgClass, rootPkgInfoClass));
-    when(subPkg.getClassFiles()).thenReturn(Collections.singleton(subPkgClass));
+    when(subPkg.getClassFiles()).thenReturn(Set.of(subPkgClass));
 
     when(rootPkgInfoClass.getName()).thenReturn("package-info.class");
     when(rootPkgInfoClass.getInputStream())
@@ -68,16 +69,16 @@ public class AbiCheckTest {
 
     JavaClassSignature signatureA = new JavaClassSignature(
         "java.lang.Object",
-        Collections.emptySet(),
-        Collections.singletonList("public"),
-        Collections.singleton("public void foo()"),
-        Collections.singleton("public int bar"));
+        Set.of(),
+        List.of("public"),
+        Set.of("public void foo()"),
+        Set.of("public int bar"));
     JavaClassSignature signatureB = new JavaClassSignature(
         "java.lang.Exception",
-        Collections.singleton("java.lang.Runnable"),
-        Collections.singletonList("protected"),
-        Collections.singleton("public void foo(int)"),
-        Collections.singleton("public boolean bar"));
+        Set.of("java.lang.Runnable"),
+        List.of("protected"),
+        Set.of("public void foo(int)"),
+        Set.of("public boolean bar"));
 
     Map<String, JavaClassSignature> expected = ImmutableMap.<String, JavaClassSignature>builder()
         .put("test.Missing", signatureA)
diff --git a/application/src/test/java/com/yahoo/application/container/handler/HeadersTestCase.java b/application/src/test/java/com/yahoo/application/container/handler/HeadersTestCase.java
index 9514749138c..4079fc377d6 100644
--- a/application/src/test/java/com/yahoo/application/container/handler/HeadersTestCase.java
+++ b/application/src/test/java/com/yahoo/application/container/handler/HeadersTestCase.java
@@ -3,11 +3,7 @@ package com.yahoo.application.container.handler;
 
 import org.junit.jupiter.api.Test;
 
-import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -66,9 +62,9 @@ public class HeadersTestCase {
     @Test
     void requireThatContainsValueWorksAsExpected() {
         Headers headers = new Headers();
-        assertFalse(headers.containsValue(Arrays.asList("bar")));
+        assertFalse(headers.containsValue(List.of("bar")));
         headers.add("foo", "bar");
-        assertTrue(headers.containsValue(Arrays.asList("bar")));
+        assertTrue(headers.containsValue(List.of("bar")));
     }
 
     @Test
@@ -104,19 +100,19 @@ public class HeadersTestCase {
         Headers headers = new Headers();
         assertNull(headers.get("foo"));
         headers.add("foo", "bar");
-        assertEquals(Arrays.asList("bar"), headers.get("foo"));
+        assertEquals(List.of("bar"), headers.get("foo"));
         headers.add("foo", "baz");
-        assertEquals(Arrays.asList("bar", "baz"), headers.get("foo"));
+        assertEquals(List.of("bar", "baz"), headers.get("foo"));
     }
 
     @Test
     void requireThatAddListWorksAsExpected() {
         Headers headers = new Headers();
         assertNull(headers.get("foo"));
-        headers.add("foo", Arrays.asList("bar"));
-        assertEquals(Arrays.asList("bar"), headers.get("foo"));
-        headers.add("foo", Arrays.asList("baz", "cox"));
-        assertEquals(Arrays.asList("bar", "baz", "cox"), headers.get("foo"));
+        headers.add("foo", List.of("bar"));
+        assertEquals(List.of("bar"), headers.get("foo"));
+        headers.add("foo", List.of("baz", "cox"));
+        assertEquals(List.of("bar", "baz", "cox"), headers.get("foo"));
     }
 
     @Test
@@ -124,16 +120,14 @@ public class HeadersTestCase {
         Headers headers = new Headers();
         headers.add("foo", "bar");
         headers.add("bar", "baz");
-        assertEquals(Arrays.asList("bar"), headers.get("foo"));
-        assertEquals(Arrays.asList("baz"), headers.get("bar"));
+        assertEquals(List.of("bar"), headers.get("foo"));
+        assertEquals(List.of("baz"), headers.get("bar"));
 
-        Map<String, List<String>> map = new HashMap<>();
-        map.put("foo", Arrays.asList("baz", "cox"));
-        map.put("bar", Arrays.asList("cox"));
+        Map<String, List<String>> map = Map.of("foo", List.of("baz", "cox"), "bar", List.of("cox"));
         headers.addAll(map);
 
-        assertEquals(Arrays.asList("bar", "baz", "cox"), headers.get("foo"));
-        assertEquals(Arrays.asList("baz", "cox"), headers.get("bar"));
+        assertEquals(List.of("bar", "baz", "cox"), headers.get("foo"));
+        assertEquals(List.of("baz", "cox"), headers.get("bar"));
     }
 
     @Test
@@ -141,19 +135,19 @@ public class HeadersTestCase {
         Headers headers = new Headers();
         assertNull(headers.get("foo"));
         headers.put("foo", "bar");
-        assertEquals(Arrays.asList("bar"), headers.get("foo"));
+        assertEquals(List.of("bar"), headers.get("foo"));
         headers.put("foo", "baz");
-        assertEquals(Arrays.asList("baz"), headers.get("foo"));
+        assertEquals(List.of("baz"), headers.get("foo"));
     }
 
     @Test
     void requireThatPutListWorksAsExpected() {
         Headers headers = new Headers();
         assertNull(headers.get("foo"));
-        headers.put("foo", Arrays.asList("bar"));
-        assertEquals(Arrays.asList("bar"), headers.get("foo"));
-        headers.put("foo", Arrays.asList("baz", "cox"));
-        assertEquals(Arrays.asList("baz", "cox"), headers.get("foo"));
+        headers.put("foo", List.of("bar"));
+        assertEquals(List.of("bar"), headers.get("foo"));
+        headers.put("foo", List.of("baz", "cox"));
+        assertEquals(List.of("baz", "cox"), headers.get("foo"));
     }
 
     @Test
@@ -161,24 +155,22 @@ public class HeadersTestCase {
         Headers headers = new Headers();
         headers.add("foo", "bar");
         headers.add("bar", "baz");
-        assertEquals(Arrays.asList("bar"), headers.get("foo"));
-        assertEquals(Arrays.asList("baz"), headers.get("bar"));
+        assertEquals(List.of("bar"), headers.get("foo"));
+        assertEquals(List.of("baz"), headers.get("bar"));
 
-        Map<String, List<String>> map = new HashMap<>();
-        map.put("foo", Arrays.asList("baz", "cox"));
-        map.put("bar", Arrays.asList("cox"));
+        Map<String, List<String>> map = Map.of("foo", List.of("baz", "cox"), "bar", List.of("cox"));
         headers.putAll(map);
 
-        assertEquals(Arrays.asList("baz", "cox"), headers.get("foo"));
-        assertEquals(Arrays.asList("cox"), headers.get("bar"));
+        assertEquals(List.of("baz", "cox"), headers.get("foo"));
+        assertEquals(List.of("cox"), headers.get("bar"));
     }
 
     @Test
     void requireThatRemoveWorksAsExpected() {
         Headers headers = new Headers();
-        headers.put("foo", Arrays.asList("bar", "baz"));
-        assertEquals(Arrays.asList("bar", "baz"), headers.get("foo"));
-        assertEquals(Arrays.asList("bar", "baz"), headers.remove("foo"));
+        headers.put("foo", List.of("bar", "baz"));
+        assertEquals(List.of("bar", "baz"), headers.get("foo"));
+        assertEquals(List.of("bar", "baz"), headers.remove("foo"));
         assertNull(headers.get("foo"));
         assertNull(headers.remove("foo"));
     }
@@ -186,11 +178,11 @@ public class HeadersTestCase {
     @Test
     void requireThatRemoveStringWorksAsExpected() {
         Headers headers = new Headers();
-        headers.put("foo", Arrays.asList("bar", "baz"));
-        assertEquals(Arrays.asList("bar", "baz"), headers.get("foo"));
+        headers.put("foo", List.of("bar", "baz"));
+        assertEquals(List.of("bar", "baz"), headers.get("foo"));
         assertTrue(headers.remove("foo", "bar"));
         assertFalse(headers.remove("foo", "cox"));
-        assertEquals(Arrays.asList("baz"), headers.get("foo"));
+        assertEquals(List.of("baz"), headers.get("foo"));
         assertTrue(headers.remove("foo", "baz"));
         assertFalse(headers.remove("foo", "cox"));
         assertNull(headers.get("foo"));
@@ -201,8 +193,8 @@ public class HeadersTestCase {
         Headers headers = new Headers();
         headers.add("foo", "bar");
         headers.add("bar", "baz");
-        assertEquals(Arrays.asList("bar"), headers.get("foo"));
-        assertEquals(Arrays.asList("baz"), headers.get("bar"));
+        assertEquals(List.of("bar"), headers.get("foo"));
+        assertEquals(List.of("baz"), headers.get("bar"));
         headers.clear();
         assertNull(headers.get("foo"));
         assertNull(headers.get("bar"));
@@ -213,14 +205,14 @@ public class HeadersTestCase {
         Headers headers = new Headers();
         assertNull(headers.get("foo"));
         headers.add("foo", "bar");
-        assertEquals(Arrays.asList("bar"), headers.get("foo"));
+        assertEquals(List.of("bar"), headers.get("foo"));
     }
 
     @Test
     void requireThatGetFirstWorksAsExpected() {
         Headers headers = new Headers();
         assertNull(headers.getFirst("foo"));
-        headers.add("foo", Arrays.asList("bar", "baz"));
+        headers.add("foo", List.of("bar", "baz"));
         assertEquals("bar", headers.getFirst("foo"));
     }
 
@@ -228,28 +220,28 @@ public class HeadersTestCase {
     void requireThatIsTrueWorksAsExpected() {
         Headers headers = new Headers();
         assertFalse(headers.isTrue("foo"));
-        headers.put("foo", Arrays.asList("true"));
+        headers.put("foo", List.of("true"));
         assertTrue(headers.isTrue("foo"));
-        headers.put("foo", Arrays.asList("true", "true"));
+        headers.put("foo", List.of("true", "true"));
         assertTrue(headers.isTrue("foo"));
-        headers.put("foo", Arrays.asList("true", "false"));
+        headers.put("foo", List.of("true", "false"));
         assertFalse(headers.isTrue("foo"));
-        headers.put("foo", Arrays.asList("false", "true"));
+        headers.put("foo", List.of("false", "true"));
         assertFalse(headers.isTrue("foo"));
-        headers.put("foo", Arrays.asList("false", "false"));
+        headers.put("foo", List.of("false", "false"));
         assertFalse(headers.isTrue("foo"));
-        headers.put("foo", Arrays.asList("false"));
+        headers.put("foo", List.of("false"));
         assertFalse(headers.isTrue("foo"));
     }
 
     @Test
     void requireThatKeySetWorksAsExpected() {
         Headers headers = new Headers();
-        assertEquals(Collections.<Set<String>>emptySet(), headers.keySet());
+        assertEquals(Set.of(), headers.keySet());
         headers.add("foo", "bar");
-        assertEquals(new HashSet<>(Arrays.asList("foo")), headers.keySet());
+        assertEquals(Set.of("foo"), headers.keySet());
         headers.add("bar", "baz");
-        assertEquals(new HashSet<>(Arrays.asList("foo", "bar")), headers.keySet());
+        assertEquals(Set.of("foo", "bar"), headers.keySet());
     }
 
     @Test
@@ -259,34 +251,34 @@ public class HeadersTestCase {
         headers.add("foo", "bar");
         Collection<List<String>> values = headers.values();
         assertEquals(1, values.size());
-        assertTrue(values.contains(Arrays.asList("bar")));
+        assertTrue(values.contains(List.of("bar")));
 
         headers.add("bar", "baz");
         values = headers.values();
         assertEquals(2, values.size());
-        assertTrue(values.contains(Arrays.asList("bar")));
-        assertTrue(values.contains(Arrays.asList("baz")));
+        assertTrue(values.contains(List.of("bar")));
+        assertTrue(values.contains(List.of("baz")));
     }
 
     @Test
     void requireThatEntrySetWorksAsExpected() {
         Headers headers = new Headers();
-        assertEquals(Collections.emptySet(), headers.entrySet());
-        headers.put("foo", Arrays.asList("bar", "baz"));
+        assertEquals(Set.of(), headers.entrySet());
+        headers.put("foo", List.of("bar", "baz"));
 
         Set<Map.Entry<String, List<String>>> entries = headers.entrySet();
         assertEquals(1, entries.size());
         Map.Entry<String, List<String>> entry = entries.iterator().next();
         assertNotNull(entry);
         assertEquals("foo", entry.getKey());
-        assertEquals(Arrays.asList("bar", "baz"), entry.getValue());
+        assertEquals(List.of("bar", "baz"), entry.getValue());
     }
 
     @Test
     void requireThatEntriesWorksAsExpected() {
         Headers headers = new Headers();
-        assertEquals(Collections.emptyList(), headers.entries());
-        headers.put("foo", Arrays.asList("bar", "baz"));
+        assertEquals(List.of(), headers.entries());
+        headers.put("foo", List.of("bar", "baz"));
 
         List<Map.Entry<String, String>> entries = headers.entries();
         assertEquals(2, entries.size());
diff --git a/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/EventDiffCalculator.java b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/EventDiffCalculator.java
index 5c29228b858..d57f32ee3cb 100644
--- a/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/EventDiffCalculator.java
+++ b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/EventDiffCalculator.java
@@ -9,7 +9,6 @@ import com.yahoo.vdslib.state.NodeType;
 import com.yahoo.vdslib.state.State;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
@@ -174,8 +173,8 @@ public class EventDiffCalculator {
 
     private static void emitNodeResourceExhaustionEvents(PerStateParams params, List<Event> events, ContentCluster cluster) {
         // Feed block events are not ordered by node
-        Set<NodeResourceExhaustion> fromBlockSet = params.feedBlockFrom != null ? params.feedBlockFrom.getConcreteExhaustions() : Collections.emptySet();
-        Set<NodeResourceExhaustion> toBlockSet   = params.feedBlockTo   != null ? params.feedBlockTo.getConcreteExhaustions()   : Collections.emptySet();
+        Set<NodeResourceExhaustion> fromBlockSet = params.feedBlockFrom != null ? params.feedBlockFrom.getConcreteExhaustions() : Set.of();
+        Set<NodeResourceExhaustion> toBlockSet   = params.feedBlockTo   != null ? params.feedBlockTo.getConcreteExhaustions()   : Set.of();
 
         for (var ex : setSubtraction(fromBlockSet, toBlockSet)) {
             var info = cluster.getNodeInfo(ex.node);
diff --git a/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/ResourceExhaustionCalculator.java b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/ResourceExhaustionCalculator.java
index 200a5564c64..4ed1ab967fd 100644
--- a/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/ResourceExhaustionCalculator.java
+++ b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/ResourceExhaustionCalculator.java
@@ -4,7 +4,6 @@ package com.yahoo.vespa.clustercontroller.core;
 import com.yahoo.vespa.clustercontroller.core.hostinfo.HostInfo;
 
 import java.util.Collection;
-import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Objects;
@@ -60,7 +59,7 @@ public class ResourceExhaustionCalculator {
         this.feedBlockEnabled = feedBlockEnabled;
         this.feedBlockLimits = feedBlockLimits;
         this.feedBlockNoiseLevel = 0.0;
-        this.previouslyBlockedNodeResources = Collections.emptySet();
+        this.previouslyBlockedNodeResources = Set.of();
     }
 
     public ResourceExhaustionCalculator(boolean feedBlockEnabled, Map<String, Double> feedBlockLimits,
@@ -74,7 +73,7 @@ public class ResourceExhaustionCalculator {
                     .map(ex -> NodeAndResourceType.of(ex.node.getIndex(), ex.resourceType))
                     .collect(Collectors.toSet());
         } else {
-            this.previouslyBlockedNodeResources = Collections.emptySet();
+            this.previouslyBlockedNodeResources = Set.of();
         }
     }
 
@@ -124,12 +123,12 @@ public class ResourceExhaustionCalculator {
                                                               effectiveLimit, nodeInfo.getRpcAddress()));
             }
         }
-        return (exceedingLimit != null) ? exceedingLimit : Collections.emptySet();
+        return (exceedingLimit != null) ? exceedingLimit : Set.of();
     }
 
     public Set<NodeResourceExhaustion> enumerateNodeResourceExhaustions(NodeInfo nodeInfo) {
         if (!nodeInfo.isStorage()) {
-            return Collections.emptySet();
+            return Set.of();
         }
         return resourceExhaustionsFromHostInfo(nodeInfo, nodeInfo.getHostInfo());
     }
diff --git a/clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/testutils/Waiter.java b/clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/testutils/Waiter.java
index 9e7665e65ee..bf8ba7756e2 100644
--- a/clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/testutils/Waiter.java
+++ b/clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/testutils/Waiter.java
@@ -8,7 +8,6 @@ import com.yahoo.vespa.clustercontroller.core.DummyVdsNode;
 import com.yahoo.vespa.clustercontroller.core.FleetController;
 import java.time.Duration;
 import java.time.Instant;
-import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Objects;
@@ -62,13 +61,13 @@ public interface Waiter {
             return waitForState(state, data.getTimeout());
         }
         public ClusterState waitForStateInAllSpaces(String state) {
-            return waitForState(state, data.getTimeout(), true, Collections.emptySet());
+            return waitForState(state, data.getTimeout(), true, Set.of());
         }
         public ClusterState waitForStateInSpace(String space, String state) {
-            return waitForState(state, data.getTimeout(), false, Collections.singleton(space));
+            return waitForState(state, data.getTimeout(), false, Set.of(space));
         }
         public ClusterState waitForState(String state, Duration timeoutMS) {
-            return waitForState(state, timeoutMS, false, Collections.emptySet());
+            return waitForState(state, timeoutMS, false, Set.of());
         }
         public ClusterState waitForStableSystem() {
             return waitForStableSystem(data.getDummyNodes().size() / 2);
diff --git a/config-provisioning/src/main/java/com/yahoo/config/provision/HostFilter.java b/config-provisioning/src/main/java/com/yahoo/config/provision/HostFilter.java
index 4fe6f8453de..f79fee08bc4 100644
--- a/config-provisioning/src/main/java/com/yahoo/config/provision/HostFilter.java
+++ b/config-provisioning/src/main/java/com/yahoo/config/provision/HostFilter.java
@@ -4,7 +4,6 @@ package com.yahoo.config.provision;
 import com.yahoo.text.StringUtilities;
 
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
@@ -44,27 +43,27 @@ public class HostFilter {
 
     /** Returns a filter which matches all hosts */
     public static HostFilter all() {
-        return new HostFilter(Collections.emptySet(), Collections.emptySet(), Collections.emptySet(), Collections.emptySet());
+        return new HostFilter(Set.of(), Set.of(), Set.of(), Set.of());
     }
 
     /** Returns a filter which matches a given host only */
     public static HostFilter hostname(String hostname) {
-        return new HostFilter(Collections.singleton(hostname), Collections.emptySet(), Collections.emptySet(), Collections.emptySet());
+        return new HostFilter(Set.of(hostname), Set.of(), Set.of(), Set.of());
     }
 
     /** Returns a filter which matches a given flavor only */
     public static HostFilter flavor(String flavor) {
-        return new HostFilter(Collections.emptySet(), Collections.singleton(flavor), Collections.emptySet(), Collections.emptySet());
+        return new HostFilter(Set.of(), Set.of(flavor), Set.of(), Set.of());
     }
 
     /** Returns a filter which matches a given cluster type only */
     public static HostFilter clusterType(ClusterSpec.Type clusterType) {
-        return new HostFilter(Collections.emptySet(), Collections.emptySet(), Collections.singleton(clusterType), Collections.emptySet());
+        return new HostFilter(Set.of(), Set.of(), Set.of(clusterType), Set.of());
     }
 
     /** Returns a filter which matches a given cluster id only */
     public static HostFilter clusterId(ClusterSpec.Id clusterId) {
-        return new HostFilter(Collections.emptySet(), Collections.emptySet(), Collections.emptySet(), Collections.singleton(clusterId));
+        return new HostFilter(Set.of(), Set.of(), Set.of(), Set.of(clusterId));
     }
 
     /** Returns a host filter from three optional conditions */
diff --git a/container-core/src/main/java/com/yahoo/container/di/ConfigRetriever.java b/container-core/src/main/java/com/yahoo/container/di/ConfigRetriever.java
index fcccc02d143..5a04bd8eae1 100644
--- a/container-core/src/main/java/com/yahoo/container/di/ConfigRetriever.java
+++ b/container-core/src/main/java/com/yahoo/container/di/ConfigRetriever.java
@@ -8,7 +8,6 @@ import com.yahoo.container.di.config.Subscriber;
 import com.yahoo.container.di.config.SubscriberFactory;
 import com.yahoo.vespa.config.ConfigKey;
 
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Optional;
@@ -135,7 +134,7 @@ public final class ConfigRetriever {
 
     private void resetComponentSubscriberIfBootstrap(ConfigSnapshot configSnapshot) {
         if (configSnapshot instanceof BootstrapConfigs) {
-            setupComponentSubscriber(Collections.emptySet());
+            setupComponentSubscriber(Set.of());
         }
     }
 
diff --git a/container-core/src/main/java/com/yahoo/container/di/Osgi.java b/container-core/src/main/java/com/yahoo/container/di/Osgi.java
index 0ff640031fc..7bab8605a3e 100644
--- a/container-core/src/main/java/com/yahoo/container/di/Osgi.java
+++ b/container-core/src/main/java/com/yahoo/container/di/Osgi.java
@@ -10,8 +10,6 @@ import org.osgi.framework.Bundle;
 import java.util.Collection;
 import java.util.Set;
 
-import static java.util.Collections.emptySet;
-
 /**
  * This interface has default implementations of all methods, to allow using it
  * for testing, instead of mocking or a test implementation.
@@ -49,7 +47,7 @@ public interface Osgi {
      * @return The set of bundles that are no longer needed by the new or latest good generation.
      */
     default Set<Bundle> completeBundleGeneration(GenerationStatus status) {
-        return emptySet();
+        return Set.of();
     }
 
     default Class<?> resolveClass(BundleInstantiationSpecification spec) {
diff --git a/container-core/src/main/java/com/yahoo/container/di/componentgraph/core/ComponentRegistryNode.java b/container-core/src/main/java/com/yahoo/container/di/componentgraph/core/ComponentRegistryNode.java
index ca10072c6c9..8b5fb128e2b 100644
--- a/container-core/src/main/java/com/yahoo/container/di/componentgraph/core/ComponentRegistryNode.java
+++ b/container-core/src/main/java/com/yahoo/container/di/componentgraph/core/ComponentRegistryNode.java
@@ -8,10 +8,8 @@ import com.yahoo.component.provider.ComponentRegistry;
 import com.yahoo.config.ConfigInstance;
 import com.yahoo.vespa.config.ConfigKey;
 
-import java.util.Collections;
 import java.util.List;
 import java.util.Set;
-import java.util.stream.Collectors;
 
 /**
  * @author Tony Vaagenes
@@ -20,7 +18,7 @@ import java.util.stream.Collectors;
  */
 public class ComponentRegistryNode extends Node {
 
-    private static ComponentId componentRegistryNamespace = ComponentId.fromString("ComponentRegistry");
+    private static final ComponentId componentRegistryNamespace = ComponentId.fromString("ComponentRegistry");
 
     private final Class<?> componentClass;
 
@@ -63,7 +61,7 @@ public class ComponentRegistryNode extends Node {
 
     @Override
     public Set<ConfigKey<ConfigInstance>> configKeys() {
-        return Collections.emptySet();
+        return Set.of();
     }
 
     @Override
@@ -76,8 +74,7 @@ public class ComponentRegistryNode extends Node {
 
     @Override
     public boolean equals(Object other) {
-        if (other instanceof ComponentRegistryNode) {
-            ComponentRegistryNode that = (ComponentRegistryNode) other;
+        if (other instanceof ComponentRegistryNode that) {
             return this.componentId().equals(that.componentId()) && this.instanceType().equals(that.instanceType())
                     && equalNodeEdges(this.usedComponents(), that.usedComponents());
         } else {
diff --git a/container-core/src/main/java/com/yahoo/container/di/componentgraph/core/GuiceNode.java b/container-core/src/main/java/com/yahoo/container/di/componentgraph/core/GuiceNode.java
index 936eadb0b3c..8e6a39a4921 100644
--- a/container-core/src/main/java/com/yahoo/container/di/componentgraph/core/GuiceNode.java
+++ b/container-core/src/main/java/com/yahoo/container/di/componentgraph/core/GuiceNode.java
@@ -7,7 +7,6 @@ import com.yahoo.config.ConfigInstance;
 import com.yahoo.vespa.config.ConfigKey;
 
 import java.lang.annotation.Annotation;
-import java.util.Collections;
 import java.util.List;
 import java.util.Set;
 
@@ -24,8 +23,7 @@ public final class GuiceNode extends Node {
     private final Object myInstance;
     private final Annotation annotation;
 
-    public GuiceNode(Object myInstance,
-                     Annotation annotation) {
+    public GuiceNode(Object myInstance, Annotation annotation) {
         super(componentId(myInstance));
         this.myInstance = myInstance;
         this.annotation = annotation;
@@ -33,7 +31,7 @@ public final class GuiceNode extends Node {
 
     @Override
     public Set<ConfigKey<ConfigInstance>> configKeys() {
-        return Collections.emptySet();
+        return Set.of();
     }
 
     @Override
@@ -54,7 +52,7 @@ public final class GuiceNode extends Node {
 
     @Override
     public List<Node> usedComponents() {
-        return Collections.emptyList();
+        return List.of();
     }
 
     @Override
diff --git a/container-core/src/main/java/com/yahoo/container/jdisc/state/MetricsPacketsHandler.java b/container-core/src/main/java/com/yahoo/container/jdisc/state/MetricsPacketsHandler.java
index 165330662a9..894a231f9be 100644
--- a/container-core/src/main/java/com/yahoo/container/jdisc/state/MetricsPacketsHandler.java
+++ b/container-core/src/main/java/com/yahoo/container/jdisc/state/MetricsPacketsHandler.java
@@ -25,7 +25,6 @@ import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -91,7 +90,7 @@ public class MetricsPacketsHandler extends AbstractRequestHandler {
 
             @Override
             protected Iterable<ByteBuffer> responseContent() {
-                return Collections.singleton(ByteBuffer.wrap(buildMetricOutput(request.getUri().getQuery())));
+                return Set.of(ByteBuffer.wrap(buildMetricOutput(request.getUri().getQuery())));
             }
         }.dispatch(handler);
 
@@ -160,7 +159,7 @@ public class MetricsPacketsHandler extends AbstractRequestHandler {
     }
 
     private List<JsonNode> getPacketsForSnapshot(MetricSnapshot metricSnapshot, String application, long timestamp) {
-        if (metricSnapshot == null) return Collections.emptyList();
+        if (metricSnapshot == null) return List.of();
 
         List<JsonNode> packets = new ArrayList<>();
 
@@ -178,9 +177,9 @@ public class MetricsPacketsHandler extends AbstractRequestHandler {
     }
 
     private List<JsonNode> getPacketsForSnapshot(MetricSnapshot metricSnapshot, String metricSetId, String application, long timestamp) {
-        if (metricSnapshot == null) return Collections.emptyList();
+        if (metricSnapshot == null) return List.of();
         if (metricSetId == null) return getPacketsForSnapshot(metricSnapshot, application, timestamp);
-        Set<String> configuredMetrics = metricSets.getOrDefault(metricSetId, Collections.emptySet());
+        Set<String> configuredMetrics = metricSets.getOrDefault(metricSetId, Set.of());
         List<JsonNode> packets = new ArrayList<>();
 
         for (Map.Entry<MetricDimensions, MetricSet> snapshotEntry : metricSnapshot) {
diff --git a/container-core/src/test/java/com/yahoo/component/chain/dependencies/ordering/ChainBuilderTest.java b/container-core/src/test/java/com/yahoo/component/chain/dependencies/ordering/ChainBuilderTest.java
index 8c94b5f9a93..7e5cc5187ba 100644
--- a/container-core/src/test/java/com/yahoo/component/chain/dependencies/ordering/ChainBuilderTest.java
+++ b/container-core/src/test/java/com/yahoo/component/chain/dependencies/ordering/ChainBuilderTest.java
@@ -12,7 +12,6 @@ import org.junit.jupiter.api.Test;
 
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
@@ -90,9 +89,9 @@ public class ChainBuilderTest {
     @Test
     void testPhaseAndSearcher() {
         ChainBuilder depHandler = newChainBuilder();
-        depHandler.addPhase(new Phase("phase1", set("phase2"), Collections.<String>emptySet()));
+        depHandler.addPhase(new Phase("phase1", set("phase2"), Set.of()));
         depHandler.addPhase(new Phase("phase2", set("phase3"), set("phase1")));
-        depHandler.addPhase(new Phase("phase3", Collections.<String>emptySet(), set("phase2", "phase1")));
+        depHandler.addPhase(new Phase("phase3", Set.of(), set("phase2", "phase1")));
         ChainedComponent first = new First();
         ChainedComponent second = new Second();
 
@@ -172,9 +171,9 @@ public class ChainBuilderTest {
 
     private ChainBuilder createDependencyHandler() {
         ChainBuilder chainBuilder = newChainBuilder();
-        chainBuilder.addPhase(new Phase("phase1", Collections.<String>emptySet(), Collections.<String>emptySet()));
-        chainBuilder.addPhase(new Phase("phase2", Collections.<String>emptySet(), Collections.<String>emptySet()));
-        chainBuilder.addPhase(new Phase("phase3", Collections.<String>emptySet(), Collections.<String>emptySet()));
+        chainBuilder.addPhase(new Phase("phase1", Set.of(), Set.of()));
+        chainBuilder.addPhase(new Phase("phase2", Set.of(), Set.of()));
+        chainBuilder.addPhase(new Phase("phase3", Set.of(), Set.of()));
         return chainBuilder;
     }
 
diff --git a/container-core/src/test/java/com/yahoo/container/di/ConfigRetrieverTest.java b/container-core/src/test/java/com/yahoo/container/di/ConfigRetrieverTest.java
index 14349d4cd51..7240b6510c5 100644
--- a/container-core/src/test/java/com/yahoo/container/di/ConfigRetrieverTest.java
+++ b/container-core/src/test/java/com/yahoo/container/di/ConfigRetrieverTest.java
@@ -15,7 +15,6 @@ import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
 import java.io.File;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
 
@@ -45,7 +44,7 @@ public class ConfigRetrieverTest {
     void require_that_bootstrap_configs_come_first() {
         writeConfigs();
         ConfigRetriever retriever = createConfigRetriever();
-        ConfigSnapshot bootstrapConfigs = retriever.getConfigs(Collections.emptySet(), 0, true);
+        ConfigSnapshot bootstrapConfigs = retriever.getConfigs(Set.of(), 0, true);
 
         assertTrue(bootstrapConfigs instanceof BootstrapConfigs);
         retriever.shutdown();
@@ -56,10 +55,10 @@ public class ConfigRetrieverTest {
     void require_that_components_comes_after_bootstrap() {
         writeConfigs();
         ConfigRetriever retriever = createConfigRetriever();
-        ConfigSnapshot bootstrapConfigs = retriever.getConfigs(Collections.emptySet(), 0, true);
+        ConfigSnapshot bootstrapConfigs = retriever.getConfigs(Set.of(), 0, true);
 
         ConfigKey<? extends ConfigInstance> testConfigKey = new ConfigKey<>(TestConfig.class, dirConfigSource.configId());
-        ConfigSnapshot componentsConfigs = retriever.getConfigs(Collections.singleton(testConfigKey), 0, true);
+        ConfigSnapshot componentsConfigs = retriever.getConfigs(Set.of(testConfigKey), 0, true);
 
         if (componentsConfigs instanceof ComponentsConfigs) {
             assertEquals(3, componentsConfigs.size());
@@ -75,8 +74,8 @@ public class ConfigRetrieverTest {
         writeConfigs();
         ConfigRetriever retriever = createConfigRetriever();
         ConfigKey<? extends ConfigInstance> testConfigKey = new ConfigKey<>(TestConfig.class, dirConfigSource.configId());
-        ConfigSnapshot bootstrapConfigs = retriever.getConfigs(Collections.emptySet(), 0, true);
-        ConfigSnapshot componentsConfigs = retriever.getConfigs(Collections.singleton(testConfigKey), 0, true);
+        ConfigSnapshot bootstrapConfigs = retriever.getConfigs(Set.of(), 0, true);
+        ConfigSnapshot componentsConfigs = retriever.getConfigs(Set.of(testConfigKey), 0, true);
         Set<ConfigKey<? extends ConfigInstance>> keys = new HashSet<>();
         keys.add(testConfigKey);
         keys.add(new ConfigKey<>(TestConfig.class, ""));
@@ -92,8 +91,8 @@ public class ConfigRetrieverTest {
     void require_that_empty_components_keys_after_bootstrap_returns_components_configs() {
         writeConfigs();
         ConfigRetriever retriever = createConfigRetriever();
-        assertTrue(retriever.getConfigs(Collections.emptySet(), 0, true) instanceof BootstrapConfigs);
-        assertTrue(retriever.getConfigs(Collections.emptySet(), 0, true) instanceof ComponentsConfigs);
+        assertTrue(retriever.getConfigs(Set.of(), 0, true) instanceof BootstrapConfigs);
+        assertTrue(retriever.getConfigs(Set.of(), 0, true) instanceof ComponentsConfigs);
         retriever.shutdown();
     }
 
diff --git a/container-core/src/test/java/com/yahoo/container/handler/threadpool/ContainerThreadPoolImplTest.java b/container-core/src/test/java/com/yahoo/container/handler/threadpool/ContainerThreadPoolImplTest.java
index 3d5375a9740..11de808a415 100644
--- a/container-core/src/test/java/com/yahoo/container/handler/threadpool/ContainerThreadPoolImplTest.java
+++ b/container-core/src/test/java/com/yahoo/container/handler/threadpool/ContainerThreadPoolImplTest.java
@@ -116,7 +116,7 @@ public class ContainerThreadPoolImplTest {
         assertEquals(CPUS * 4 * 100, executor.getQueue().remainingCapacity());
     }
 
-    private class FlipIt implements Runnable {
+    private static class FlipIt implements Runnable {
         public final Receiver<Boolean> didItRun = new Receiver<>();
 
         @Override
@@ -176,7 +176,7 @@ public class ContainerThreadPoolImplTest {
         }
     }
 
-    private class Hang implements Runnable {
+    private static class Hang implements Runnable {
 
         private final long hangMillis;
 
diff --git a/container-search/src/main/java/com/yahoo/prelude/fastsearch/FastHit.java b/container-search/src/main/java/com/yahoo/prelude/fastsearch/FastHit.java
index b5e5ed9ed8f..25aebfb5a00 100644
--- a/container-search/src/main/java/com/yahoo/prelude/fastsearch/FastHit.java
+++ b/container-search/src/main/java/com/yahoo/prelude/fastsearch/FastHit.java
@@ -13,7 +13,6 @@ import com.yahoo.data.access.Inspector;
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -62,7 +61,7 @@ public class FastHit extends Hit {
      * that most fields passes through the container with no processing most
      * of the time.
      */
-    private List<SummaryData> summaries = Collections.emptyList();
+    private List<SummaryData> summaries = List.of();
 
     /** Removed field values, which should therefore not be returned if present in summary data */
     private Set<String> removedFields = null;
@@ -481,7 +480,7 @@ public class FastHit extends Hit {
 
         private Set<String> createSet() {
             if (this.fieldSet != null) return this.fieldSet;
-            if ( ! hit.hasFields() && hit.summaries.isEmpty()) return Collections.emptySet(); // shortcut
+            if ( ! hit.hasFields() && hit.summaries.isEmpty()) return Set.of(); // shortcut
 
             Set<String> fields = new HashSet<>();
             if (hit.hasFields())
diff --git a/container-search/src/main/java/com/yahoo/prelude/query/parser/CustomParser.java b/container-search/src/main/java/com/yahoo/prelude/query/parser/CustomParser.java
index 44c0cb45732..520879be928 100644
--- a/container-search/src/main/java/com/yahoo/prelude/query/parser/CustomParser.java
+++ b/container-search/src/main/java/com/yahoo/prelude/query/parser/CustomParser.java
@@ -6,7 +6,6 @@ import com.yahoo.prelude.IndexFacts;
 import com.yahoo.prelude.query.Item;
 import com.yahoo.search.query.parser.Parser;
 
-import java.util.Collections;
 import java.util.Set;
 
 /**
@@ -23,7 +22,7 @@ public interface CustomParser extends Parser {
                        Set<String> toSearch, IndexFacts indexFacts, String defaultIndexName) {
         if (indexFacts == null)
             indexFacts = new IndexFacts();
-        return parse(queryToParse, filterToParse, parsingLanguage, indexFacts.newSession(toSearch, Collections.emptySet()), defaultIndexName);
+        return parse(queryToParse, filterToParse, parsingLanguage, indexFacts.newSession(toSearch, Set.of()), defaultIndexName);
     }
 
     Item parse(String queryToParse, String filterToParse, Language parsingLanguage,
diff --git a/container-search/src/main/java/com/yahoo/prelude/query/parser/Tokenizer.java b/container-search/src/main/java/com/yahoo/prelude/query/parser/Tokenizer.java
index 1c0d3ea2ee9..5a42efaaea0 100644
--- a/container-search/src/main/java/com/yahoo/prelude/query/parser/Tokenizer.java
+++ b/container-search/src/main/java/com/yahoo/prelude/query/parser/Tokenizer.java
@@ -8,8 +8,8 @@ import com.yahoo.prelude.Index;
 import com.yahoo.prelude.IndexFacts;
 import com.yahoo.prelude.query.Substring;
 
-import java.util.Collections;
 import java.util.List;
+import java.util.Set;
 
 import static com.yahoo.prelude.query.parser.Token.Kind.*;
 
@@ -63,7 +63,7 @@ public final class Tokenizer {
      * @return a read-only list of tokens. This list can only be used by this thread
      */
     public List<Token> tokenize(String string) {
-        return tokenize(string, new IndexFacts().newSession(Collections.emptySet(), Collections.emptySet()));
+        return tokenize(string, new IndexFacts().newSession(Set.of(), Set.of()));
     }
 
     /**
diff --git a/container-search/src/main/java/com/yahoo/search/handler/SearchHandler.java b/container-search/src/main/java/com/yahoo/search/handler/SearchHandler.java
index c1eff1eec67..c2a5ad0222d 100644
--- a/container-search/src/main/java/com/yahoo/search/handler/SearchHandler.java
+++ b/container-search/src/main/java/com/yahoo/search/handler/SearchHandler.java
@@ -3,7 +3,6 @@ package com.yahoo.search.handler;
 
 import ai.vespa.metrics.ContainerMetrics;
 import ai.vespa.cloud.ZoneInfo;
-import ai.vespa.metrics.ContainerMetrics;
 import com.yahoo.collections.Tuple2;
 import com.yahoo.component.ComponentSpecification;
 import com.yahoo.component.Vtag;
@@ -117,7 +116,7 @@ public class SearchHandler extends LoggingRequestHandler {
                          ZoneInfo zoneInfo) {
         this(metric, threadpool.executor(), queryProfileRegistry, embedders, executionFactory,
              config.numQueriesToTraceOnDebugAfterConstruction(),
-             config.hostResponseHeaderKey().equals("") ? Optional.empty() : Optional.of(config.hostResponseHeaderKey()),
+                config.hostResponseHeaderKey().isEmpty() ? Optional.empty() : Optional.of(config.hostResponseHeaderKey()),
              zoneInfo);
     }
 
diff --git a/container-search/src/main/java/com/yahoo/search/result/FeatureData.java b/container-search/src/main/java/com/yahoo/search/result/FeatureData.java
index 0f26ecdcce7..55a4c6c11f2 100644
--- a/container-search/src/main/java/com/yahoo/search/result/FeatureData.java
+++ b/container-search/src/main/java/com/yahoo/search/result/FeatureData.java
@@ -14,7 +14,6 @@ import com.yahoo.tensor.serialization.TypedBinaryFormat;
 import static com.yahoo.searchlib.rankingexpression.Reference.wrapInRankingExpression;
 
 import java.nio.charset.StandardCharsets;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
@@ -150,7 +149,7 @@ public class FeatureData implements Inspectable, JsonProducer {
 
     /** Returns the names of the features available in this */
     public Set<String> featureNames() {
-        if (this == empty) return Collections.emptySet();
+        if (this == empty) return Set.of();
         if (featureNames != null) return featureNames;
 
         featureNames = new HashSet<>();
diff --git a/container-search/src/main/java/com/yahoo/search/result/HitGroup.java b/container-search/src/main/java/com/yahoo/search/result/HitGroup.java
index 51c0caf38a9..ce403861014 100644
--- a/container-search/src/main/java/com/yahoo/search/result/HitGroup.java
+++ b/container-search/src/main/java/com/yahoo/search/result/HitGroup.java
@@ -718,7 +718,7 @@ public class HitGroup extends Hit implements DataList<Hit>, Cloneable, Iterable<
                 if (hitFilled.isEmpty()) {
                     filled = null;
                 } else if (hitFilled.size() == 1) {
-                    filled = Collections.singleton(hitFilled.iterator().next());
+                    filled = Set.of(hitFilled.iterator().next());
                 } else {
                     filled = new HashSet<>(hitFilled);
                 }
@@ -800,7 +800,7 @@ public class HitGroup extends Hit implements DataList<Hit>, Cloneable, Iterable<
             Set<String> hitFilled = hit.getFilled();
             if (hitFilled != null) {
                 filled = (hitFilled.size() == 1)
-                        ? Collections.singleton(hitFilled.iterator().next())
+                        ? Set.of(hitFilled.iterator().next())
                         : hitFilled.isEmpty() ? null : new HashSet<>(hitFilled);
                 setFilledInternal(filled);
             }
@@ -931,9 +931,9 @@ public class HitGroup extends Hit implements DataList<Hit>, Cloneable, Iterable<
     private Set<String> getFilledSingle(String summaryName, Set<String> summaryNames, Iterator<Hit> iterator) {
         while (true) {
             if (summaryNames == null) {
-                return Collections.singleton(summaryName);
+                return Set.of(summaryName);
             } else if (!summaryNames.contains(summaryName)) {
-                return Collections.emptySet();
+                return Set.of();
             }
             summaryNames = getSummaryNamesNextFilledHit(iterator);
         }
diff --git a/container-search/src/test/java/com/yahoo/prelude/query/parser/test/TokenizerTestCase.java b/container-search/src/test/java/com/yahoo/prelude/query/parser/test/TokenizerTestCase.java
index fbede4613da..0b12cf99396 100644
--- a/container-search/src/test/java/com/yahoo/prelude/query/parser/test/TokenizerTestCase.java
+++ b/container-search/src/test/java/com/yahoo/prelude/query/parser/test/TokenizerTestCase.java
@@ -13,8 +13,8 @@ import com.yahoo.prelude.query.parser.Tokenizer;
 import org.junit.jupiter.api.Test;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
+import java.util.Set;
 
 import static com.yahoo.prelude.query.parser.Token.Kind.COLON;
 import static com.yahoo.prelude.query.parser.Token.Kind.COMMA;
@@ -283,7 +283,7 @@ public class TokenizerTestCase {
         sd.addIndex(index2);
 
         IndexFacts facts = new IndexFacts(new IndexModel(sd));
-        IndexFacts.Session session = facts.newSession(Collections.emptySet(), Collections.emptySet());
+        IndexFacts.Session session = facts.newSession(Set.of(), Set.of());
         Tokenizer tokenizer = new Tokenizer(new SimpleLinguistics());
         List<?> tokens = tokenizer.tokenize("normal a:b (normal testexact1:/,%#%&+-+ ) testexact2:ho_/&%&/()/aa*::*& b:c", "default", session);
         // tokenizer.print();
@@ -328,7 +328,7 @@ public class TokenizerTestCase {
 
         IndexFacts facts = new IndexFacts(new IndexModel(sd));
         Tokenizer tokenizer = new Tokenizer(new SimpleLinguistics());
-        IndexFacts.Session session = facts.newSession(Collections.emptySet(), Collections.emptySet());
+        IndexFacts.Session session = facts.newSession(Set.of(), Set.of());
         List<?> tokens = tokenizer.tokenize("normal a:b (normal testexact1:/,%#%&+-+ ) testexact2:ho_/&%&/()/aa*::*&", session);
         assertEquals(new Token(WORD, "normal"), tokens.get(0));
         assertEquals(new Token(SPACE, " "), tokens.get(1));
@@ -365,7 +365,7 @@ public class TokenizerTestCase {
 
         IndexFacts facts = new IndexFacts(new IndexModel(sd));
         Tokenizer tokenizer = new Tokenizer(new SimpleLinguistics());
-        IndexFacts.Session session = facts.newSession(Collections.emptySet(), Collections.emptySet());
+        IndexFacts.Session session = facts.newSession(Set.of(), Set.of());
         List<?> tokens = tokenizer.tokenize("normal a:b (normal testexact1:/,%#%&+-+ ) testexact2:ho_/&%&/()/aa*::*", session);
         assertEquals(new Token(WORD, "normal"), tokens.get(0));
         assertEquals(new Token(SPACE, " "), tokens.get(1));
@@ -402,7 +402,7 @@ public class TokenizerTestCase {
 
         IndexFacts facts = new IndexFacts(new IndexModel(sd));
         Tokenizer tokenizer = new Tokenizer(new SimpleLinguistics());
-        IndexFacts.Session session = facts.newSession(Collections.emptySet(), Collections.emptySet());
+        IndexFacts.Session session = facts.newSession(Set.of(), Set.of());
         List<?> tokens = tokenizer.tokenize("normal a:b (normal testexact1:!/%#%&+-+ ) testexact2:ho_/&%&/()/aa*::*&b:", session);
         assertEquals(new Token(WORD, "normal"), tokens.get(0));
         assertEquals(new Token(SPACE, " "), tokens.get(1));
@@ -439,7 +439,7 @@ public class TokenizerTestCase {
         sd.addIndex(index2);
 
         IndexFacts indexFacts = new IndexFacts(new IndexModel(sd));
-        IndexFacts.Session facts = indexFacts.newSession(Collections.emptySet(), Collections.emptySet());
+        IndexFacts.Session facts = indexFacts.newSession(Set.of(), Set.of());
 
         Tokenizer tokenizer = new Tokenizer(new SimpleLinguistics());
         List<?> tokens = tokenizer.tokenize("normal a:b (normal testexact1:foo) testexact2:bar", facts);
diff --git a/container-search/src/test/java/com/yahoo/search/dispatch/InterleavedSearchInvokerTest.java b/container-search/src/test/java/com/yahoo/search/dispatch/InterleavedSearchInvokerTest.java
index 8ced7d3895e..c59dbc3421e 100644
--- a/container-search/src/test/java/com/yahoo/search/dispatch/InterleavedSearchInvokerTest.java
+++ b/container-search/src/test/java/com/yahoo/search/dispatch/InterleavedSearchInvokerTest.java
@@ -29,10 +29,10 @@ import java.time.Duration;
 import java.time.Instant;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Optional;
+import java.util.Set;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.StreamSupport;
@@ -356,7 +356,7 @@ public class InterleavedSearchInvokerTest {
                         .addAggregationResult(new MinAggregationResult().setMin(new IntegerResultNode(6)).setTag(3))));
         invokers.add(new MockInvoker(0).setHits(List.of(new GroupingListHit(List.of(grouping2)))));
 
-        try (InterleavedSearchInvoker invoker = new InterleavedSearchInvoker(Timer.monotonic, invokers, hitEstimator, dispatchConfig, new Group(0, List.of()), Collections.emptySet())) {
+        try (InterleavedSearchInvoker invoker = new InterleavedSearchInvoker(Timer.monotonic, invokers, hitEstimator, dispatchConfig, new Group(0, List.of()), Set.of())) {
             invoker.responseAvailable(invokers.get(0));
             invoker.responseAvailable(invokers.get(1));
             Result result = invoker.search(query);
@@ -373,7 +373,7 @@ public class InterleavedSearchInvokerTest {
         List<SearchInvoker> invokers = new ArrayList<>();
         invokers.add(createInvoker(a, 0));
         invokers.add(createInvoker(b, 1));
-        InterleavedSearchInvoker invoker = new InterleavedSearchInvoker(Timer.monotonic, invokers, hitEstimator, dispatchConfig, group, Collections.emptySet());
+        InterleavedSearchInvoker invoker = new InterleavedSearchInvoker(Timer.monotonic, invokers, hitEstimator, dispatchConfig, group, Set.of());
         invoker.responseAvailable(invokers.get(0));
         invoker.responseAvailable(invokers.get(1));
         return invoker;
diff --git a/container-search/src/test/java/com/yahoo/search/result/test/FillingTestCase.java b/container-search/src/test/java/com/yahoo/search/result/test/FillingTestCase.java
index 298673a1ae7..d8f4f39c5b8 100644
--- a/container-search/src/test/java/com/yahoo/search/result/test/FillingTestCase.java
+++ b/container-search/src/test/java/com/yahoo/search/result/test/FillingTestCase.java
@@ -5,7 +5,8 @@ import com.yahoo.search.result.Hit;
 import com.yahoo.search.result.HitGroup;
 import org.junit.jupiter.api.Test;
 
-import java.util.Collections;
+
+import java.util.Set;
 
 import static org.junit.jupiter.api.Assertions.*;
 
@@ -63,7 +64,7 @@ public class FillingTestCase {
         hits.add(hit1);
         hits.add(hit2);
 
-        assertEquals(Collections.emptySet(), hits.getFilled());
+        assertEquals(Set.of(), hits.getFilled());
     }
 
     @Test
@@ -82,7 +83,7 @@ public class FillingTestCase {
         hits.add(hit2);
         hits.add(hit3);
 
-        assertEquals(Collections.singleton("summary1"), hits.getFilled());
+        assertEquals(Set.of("summary1"), hits.getFilled());
     }
 
     private Hit createNonFilled(String id) {
diff --git a/document/src/main/java/com/yahoo/document/DocumentType.java b/document/src/main/java/com/yahoo/document/DocumentType.java
index 38bd3bfdeca..3b58b50dc4f 100644
--- a/document/src/main/java/com/yahoo/document/DocumentType.java
+++ b/document/src/main/java/com/yahoo/document/DocumentType.java
@@ -62,13 +62,13 @@ public class DocumentType extends StructuredDataType {
      * @param contentStructType The type of the content struct
      */
     public DocumentType(String name, StructDataType contentStructType) {
-        this(name, contentStructType, Collections.emptySet());
+        this(name, contentStructType, Set.of());
     }
 
     public DocumentType(String name, StructDataType contentStructType, Set<String> importedFieldNames) {
         super(name);
         this.contentStructType = contentStructType;
-        this.importedFieldNames = Collections.unmodifiableSet(importedFieldNames);
+        this.importedFieldNames = Set.copyOf(importedFieldNames);
     }
 
     public DocumentType(String name, Set<String> importedFieldNames) {
diff --git a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/metric/model/MetricsPacket.java b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/metric/model/MetricsPacket.java
index 53c6c533518..743f15c00d6 100644
--- a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/metric/model/MetricsPacket.java
+++ b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/metric/model/MetricsPacket.java
@@ -5,7 +5,6 @@ import ai.vespa.metricsproxy.metric.Metric;
 
 import java.time.Instant;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -14,7 +13,6 @@ import java.util.Objects;
 import java.util.Set;
 import java.util.function.Function;
 
-import static java.util.Collections.unmodifiableMap;
 import static java.util.stream.Collectors.joining;
 
 /**
@@ -42,13 +40,13 @@ public class MetricsPacket {
         this.statusMessage = statusMessage;
         this.timestamp = timestamp;
         this.service = service;
-        this.metrics = metrics;
-        this.dimensions = dimensions;
+        this.metrics = Map.copyOf(metrics);
+        this.dimensions = Map.copyOf(dimensions);
         this.consumers = Set.copyOf(consumers);
     }
 
-    public Map<MetricId, Number> metrics() { return unmodifiableMap(metrics); }
-    public Map<DimensionId, String> dimensions() { return unmodifiableMap(dimensions); }
+    public Map<MetricId, Number> metrics() { return metrics; }
+    public Map<DimensionId, String> dimensions() { return dimensions; }
     public Set<ConsumerId> consumers() { return consumers;}
 
     @Override
@@ -80,7 +78,7 @@ public class MetricsPacket {
         private long timestamp = 0L;
         private Map<MetricId, Number> metrics = new LinkedHashMap<>();
         private final Map<DimensionId, String> dimensions = new LinkedHashMap<>();
-        private Set<ConsumerId> consumers = Collections.emptySet();
+        private Set<ConsumerId> consumers = Set.of();
 
         public Builder(ServiceId service) {
             Objects.requireNonNull(service, "Service cannot be null.");
@@ -169,7 +167,7 @@ public class MetricsPacket {
             if ((extraConsumers != null) && !extraConsumers.isEmpty()) {
                 if (consumers.isEmpty()) {
                     if (extraConsumers.size() == 1) {
-                        consumers = Collections.singleton(extraConsumers.iterator().next());
+                        consumers = Set.of(extraConsumers.iterator().next());
                         return this;
                     }
                     consumers = new LinkedHashSet<>(extraConsumers.size());
diff --git a/orchestrator/src/main/java/com/yahoo/vespa/orchestrator/model/ClusterApiImpl.java b/orchestrator/src/main/java/com/yahoo/vespa/orchestrator/model/ClusterApiImpl.java
index d2638345f29..bf0de161f73 100644
--- a/orchestrator/src/main/java/com/yahoo/vespa/orchestrator/model/ClusterApiImpl.java
+++ b/orchestrator/src/main/java/com/yahoo/vespa/orchestrator/model/ClusterApiImpl.java
@@ -18,7 +18,6 @@ import com.yahoo.vespa.orchestrator.status.HostStatus;
 import java.time.Clock;
 import java.time.Duration;
 import java.time.Instant;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Optional;
@@ -83,8 +82,8 @@ class ClusterApiImpl implements ClusterApi {
                                 Collectors.groupingBy(
                                         instance -> nodeGroup.contains(instance.hostName()),
                                         Collectors.toSet()));
-        servicesInGroup = serviceInstancesByLocality.getOrDefault(true, Collections.emptySet());
-        servicesNotInGroup = serviceInstancesByLocality.getOrDefault(false, Collections.emptySet());
+        servicesInGroup = serviceInstancesByLocality.getOrDefault(true, Set.of());
+        servicesNotInGroup = serviceInstancesByLocality.getOrDefault(false, Set.of());
 
         int serviceInstances = serviceCluster.serviceInstances().size();
         if (clusterParams.size().isPresent() && serviceInstances < clusterParams.size().getAsInt()) {
diff --git a/vespa-athenz/src/test/java/com/yahoo/vespa/athenz/identityprovider/client/InstanceCsrGeneratorTest.java b/vespa-athenz/src/test/java/com/yahoo/vespa/athenz/identityprovider/client/InstanceCsrGeneratorTest.java
index 1f9ad2ced64..322e9ffaf82 100644
--- a/vespa-athenz/src/test/java/com/yahoo/vespa/athenz/identityprovider/client/InstanceCsrGeneratorTest.java
+++ b/vespa-athenz/src/test/java/com/yahoo/vespa/athenz/identityprovider/client/InstanceCsrGeneratorTest.java
@@ -12,7 +12,6 @@ import org.junit.jupiter.api.Test;
 
 import javax.security.auth.x500.X500Principal;
 import java.security.KeyPair;
-import java.util.Collections;
 import java.util.Set;
 
 import static com.yahoo.security.SubjectAlternativeName.Type.DNS;
@@ -36,7 +35,7 @@ public class InstanceCsrGeneratorTest {
         VespaUniqueInstanceId vespaUniqueInstanceId = VespaUniqueInstanceId.fromDottedString("0.default.default.foo-app.vespa.us-north-1.prod.node");
         KeyPair keyPair = KeyUtils.generateKeypair(KeyAlgorithm.RSA);
 
-        Pkcs10Csr csr = csrGenerator.generateInstanceCsr(service, vespaUniqueInstanceId, Collections.emptySet(), ClusterType.CONTAINER, keyPair);
+        Pkcs10Csr csr = csrGenerator.generateInstanceCsr(service, vespaUniqueInstanceId, Set.of(), ClusterType.CONTAINER, keyPair);
         assertEquals(new X500Principal(String.format("OU=%s, CN=%s", PROVIDER_SERVICE, ATHENZ_SERVICE)), csr.getSubject());
         var actualSans = Set.copyOf(csr.getSubjectAlternativeNames());
         var expectedSans = Set.of(
diff --git a/vespajlib/src/main/java/com/yahoo/collections/LazyMap.java b/vespajlib/src/main/java/com/yahoo/collections/LazyMap.java
index 9d0df495f9a..c979d746243 100644
--- a/vespajlib/src/main/java/com/yahoo/collections/LazyMap.java
+++ b/vespajlib/src/main/java/com/yahoo/collections/LazyMap.java
@@ -4,7 +4,6 @@ package com.yahoo.collections;
 import java.util.AbstractMap;
 import java.util.AbstractSet;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
@@ -129,7 +128,7 @@ public abstract class LazyMap<K, V> implements Map<K, V> {
 
         @Override
         public Set<Entry<K, V>> entrySet() {
-            return Collections.emptySet();
+            return Set.of();
         }
     }
 
diff --git a/vespajlib/src/test/java/com/yahoo/collections/LazySetTest.java b/vespajlib/src/test/java/com/yahoo/collections/LazySetTest.java
index ecefd891ca9..8450c7986ef 100644
--- a/vespajlib/src/test/java/com/yahoo/collections/LazySetTest.java
+++ b/vespajlib/src/test/java/com/yahoo/collections/LazySetTest.java
@@ -4,11 +4,11 @@ package com.yahoo.collections;
 import org.junit.Test;
 import org.mockito.Mockito;
 
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Iterator;
+import java.util.List;
 import java.util.NoSuchElementException;
 import java.util.Set;
 
@@ -26,25 +26,25 @@ public class LazySetTest {
 
     @Test
     public void requireThatInitialDelegateIsEmpty() {
-        LazySet<String> set = newLazySet(new HashSet<String>());
+        LazySet<String> set = newLazySet(new HashSet<>());
         assertEquals(LazySet.EmptySet.class, set.getDelegate().getClass());
     }
 
     @Test
     public void requireThatEmptySetAddUpgradesToSingletonSet() {
-        LazySet<String> set = newLazySet(new HashSet<String>());
+        LazySet<String> set = newLazySet(new HashSet<>());
         assertTrue(set.add("foo"));
         assertEquals(LazySet.SingletonSet.class, set.getDelegate().getClass());
 
-        set = newLazySet(new HashSet<String>());
-        assertTrue(set.addAll(Arrays.asList("foo")));
+        set = newLazySet(new HashSet<>());
+        assertTrue(set.addAll(List.of("foo")));
         assertEquals(LazySet.SingletonSet.class, set.getDelegate().getClass());
     }
 
     @Test
     public void requireThatEmptySetAddAllEmptySetDoesNotUpgradeToSingletonSet() {
-        LazySet<String> set = newLazySet(new HashSet<String>());
-        assertFalse(set.addAll(Collections.<String>emptySet()));
+        LazySet<String> set = newLazySet(new HashSet<>());
+        assertFalse(set.addAll(Set.of()));
         assertEquals(LazySet.EmptySet.class, set.getDelegate().getClass());
     }
 
@@ -52,7 +52,7 @@ public class LazySetTest {
     public void requireThatEmptySetAddAllUpgradesToFinalSet() {
         Set<String> delegate = new HashSet<>();
         LazySet<String> set = newLazySet(delegate);
-        assertTrue(set.addAll(Arrays.asList("foo", "bar")));
+        assertTrue(set.addAll(List.of("foo", "bar")));
         assertSame(delegate, set.getDelegate());
         assertEquals(2, delegate.size());
         assertTrue(delegate.contains("foo"));
@@ -76,7 +76,7 @@ public class LazySetTest {
     @Test
     public void requireThatSingletonSetAddAllEmptySetDoesNotUpgradeToFinalSet() {
         LazySet<String> set = newSingletonSet("foo");
-        assertFalse(set.addAll(Collections.<String>emptySet()));
+        assertFalse(set.addAll(Set.of()));
         assertEquals(LazySet.SingletonSet.class, set.getDelegate().getClass());
     }
 
@@ -102,7 +102,7 @@ public class LazySetTest {
     public void requireThatSingletonSetAddAllUpgradesToFinalSet() {
         Set<String> delegate = new HashSet<>();
         LazySet<String> set = newSingletonSet(delegate, "foo");
-        assertTrue(set.addAll(Arrays.asList("bar")));
+        assertTrue(set.addAll(List.of("bar")));
         assertSame(delegate, set.getDelegate());
         assertEquals(2, delegate.size());
         assertTrue(delegate.contains("foo"));
@@ -110,7 +110,7 @@ public class LazySetTest {
 
         delegate = new HashSet<>();
         set = newSingletonSet(delegate, "foo");
-        assertTrue(set.addAll(Arrays.asList("bar", "baz")));
+        assertTrue(set.addAll(List.of("bar", "baz")));
         assertSame(delegate, set.getDelegate());
         assertEquals(3, delegate.size());
         assertTrue(delegate.contains("foo"));
diff --git a/zkfacade/src/main/java/com/yahoo/vespa/curator/mock/MemoryFileSystem.java b/zkfacade/src/main/java/com/yahoo/vespa/curator/mock/MemoryFileSystem.java
index c4cc1541ca6..d05c8f11ad4 100644
--- a/zkfacade/src/main/java/com/yahoo/vespa/curator/mock/MemoryFileSystem.java
+++ b/zkfacade/src/main/java/com/yahoo/vespa/curator/mock/MemoryFileSystem.java
@@ -53,7 +53,7 @@ class MemoryFileSystem extends FileSystem {
 
     @Override
     public Iterable<Path> getRootDirectories() {
-        return Collections.singleton(Paths.get("/"));
+        return Set.of(Paths.get("/"));
     }
 
     @Override
@@ -63,7 +63,7 @@ class MemoryFileSystem extends FileSystem {
 
     @Override
     public Set<String> supportedFileAttributeViews() {
-        return Collections.emptySet();
+        return Set.of();
     }
 
     @Override