diff --git a/lucene/benchmark/src/java/org/apache/lucene/benchmark/byTask/feeds/DemoHTMLParser.java b/lucene/benchmark/src/java/org/apache/lucene/benchmark/byTask/feeds/DemoHTMLParser.java
index a1e6a3c013f..79eafbc5415 100644
--- a/lucene/benchmark/src/java/org/apache/lucene/benchmark/byTask/feeds/DemoHTMLParser.java
+++ b/lucene/benchmark/src/java/org/apache/lucene/benchmark/byTask/feeds/DemoHTMLParser.java
@@ -145,21 +145,17 @@ public class DemoHTMLParser implements HTMLParser {
       // assign body text
       this.body = body.toString();
     }
-    
-    private static final Set<String> createElementNameSet(String... names) {
-      return Collections.unmodifiableSet(new HashSet<>(Arrays.asList(names)));
-    }
-    
+
     /** HTML elements that cause a line break (they are block-elements) */
-    static final Set<String> ENDLINE_ELEMENTS = createElementNameSet(
-      "p", "h1", "h2", "h3", "h4", "h5", "h6", "div", "ul", "ol", "dl",
-      "pre", "hr", "blockquote", "address", "fieldset", "table", "form",
-      "noscript", "li", "dt", "dd", "noframes", "br", "tr", "select", "option"
+    static final Set<String> ENDLINE_ELEMENTS = Set.of(
+        "p", "h1", "h2", "h3", "h4", "h5", "h6", "div", "ul", "ol", "dl",
+        "pre", "hr", "blockquote", "address", "fieldset", "table", "form",
+        "noscript", "li", "dt", "dd", "noframes", "br", "tr", "select", "option"
     );
 
     /** HTML elements with contents that are ignored */
-    static final Set<String> SUPPRESS_ELEMENTS = createElementNameSet(
-      "style", "script"
+    static final Set<String> SUPPRESS_ELEMENTS = Set.of(
+        "style", "script"
     );
   }
 
diff --git a/lucene/core/src/java/org/apache/lucene/index/FieldInfos.java b/lucene/core/src/java/org/apache/lucene/index/FieldInfos.java
index d9076d767d0..979a248f705 100644
--- a/lucene/core/src/java/org/apache/lucene/index/FieldInfos.java
+++ b/lucene/core/src/java/org/apache/lucene/index/FieldInfos.java
@@ -421,7 +421,7 @@ public class FieldInfos implements Iterable<FieldInfo> {
         return dvType == docValuesType.get(fieldName);
       }
     }
-    
+
     synchronized void clear() {
       numberToName.clear();
       nameToNumber.clear();
diff --git a/lucene/core/src/java/org/apache/lucene/store/FSDirectory.java b/lucene/core/src/java/org/apache/lucene/store/FSDirectory.java
index cbaafb2f86d..d20df51d3ee 100644
--- a/lucene/core/src/java/org/apache/lucene/store/FSDirectory.java
+++ b/lucene/core/src/java/org/apache/lucene/store/FSDirectory.java
@@ -428,7 +428,7 @@ public abstract class FSDirectory extends BaseDirectory {
     if (pendingDeletes.isEmpty()) {
       return Collections.emptySet();
     } else {
-      return Collections.unmodifiableSet(new HashSet<>(pendingDeletes));
+      return Set.copyOf(pendingDeletes);
     }
   }
 }
diff --git a/lucene/replicator/src/java/org/apache/lucene/replicator/nrt/PrimaryNode.java b/lucene/replicator/src/java/org/apache/lucene/replicator/nrt/PrimaryNode.java
index 6b90c7843e5..f96f6d23395 100644
--- a/lucene/replicator/src/java/org/apache/lucene/replicator/nrt/PrimaryNode.java
+++ b/lucene/replicator/src/java/org/apache/lucene/replicator/nrt/PrimaryNode.java
@@ -136,7 +136,7 @@ public abstract class PrimaryNode extends Node {
     message("top: now flushAndRefresh");
     Set<String> completedMergeFiles;
     synchronized(finishedMergedFiles) {
-      completedMergeFiles = Collections.unmodifiableSet(new HashSet<>(finishedMergedFiles));
+      completedMergeFiles = Set.copyOf(finishedMergedFiles);
     }
     mgr.maybeRefreshBlocking();
     boolean result = setCurrentInfos(completedMergeFiles);
diff --git a/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java b/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
index d6a875fcd9c..c0083b9167a 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
@@ -593,14 +593,13 @@ public abstract class LuceneTestCase extends Assert {
   private final static long STATIC_LEAK_THRESHOLD = 10 * 1024 * 1024;
 
   /** By-name list of ignored types like loggers etc. */
-  private final static Set<String> STATIC_LEAK_IGNORED_TYPES = Collections.unmodifiableSet(new HashSet<>(Arrays.asList(
+  private final static Set<String> STATIC_LEAK_IGNORED_TYPES = Set.of(
       "org.slf4j.Logger",
       "org.apache.solr.SolrLogFormatter",
-      "java.io.File", // Solr sometimes refers to this in a static way, but it has a "java.nio.fs.Path" inside 
+      "java.io.File", // Solr sometimes refers to this in a static way, but it has a "java.nio.fs.Path" inside
       Path.class.getName(), // causes problems because interface is implemented by hidden classes
       Class.class.getName(),
-      EnumSet.class.getName()
-  )));
+      EnumSet.class.getName());
 
   /**
    * This controls how suite-level rules are nested. It is important that _all_ rules declared