BAEL-2682: Move java-immutable-set article to core-java-collections-set module (#9001)

core-java-modules/core-java-9/README.md

@@ -8,5 +8,4 @@ This module contains articles about Java 9 core features
 - [Introduction to Chronicle Queue](https://www.baeldung.com/java-chronicle-queue)
 - [Iterate Through a Range of Dates in Java](https://www.baeldung.com/java-iterate-date-range)
 - [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
-- [Immutable Set in Java](https://www.baeldung.com/java-immutable-set)
 - [Immutable ArrayList in Java](https://www.baeldung.com/java-immutable-list)

core-java-modules/core-java-collections-set/README.md

@@ -11,3 +11,4 @@ This module contains articles about the Java Set collection
 - [Guide to EnumSet](https://www.baeldung.com/java-enumset)
 - [Set Operations in Java](https://www.baeldung.com/java-set-operations)
 - [Copying Sets in Java](https://www.baeldung.com/java-copy-sets)
+- [Immutable Set in Java](https://www.baeldung.com/java-immutable-set)

core-java-modules/core-java-collections-set/src/main/java/com/baeldung/set/UnmodifiableSet.java

@@ -1,4 +1,4 @@
-package com.baeldung.java9.set;
+package com.baeldung.set;
 
 import com.google.common.collect.ImmutableSet;
 

core-java-modules/core-java-collections-set/src/test/java/com/baeldung/set/SetExamplesUnitTest.java

@@ -1,9 +1,10 @@
-package com.baeldung.java9;
+package com.baeldung.set;
+
+import org.junit.Test;
 
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
-import org.junit.Test;
 
 import static org.junit.Assert.assertEquals;