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

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

@@ -0,0 +1,44 @@
+package com.baeldung.set;
+
+import com.google.common.collect.ImmutableSet;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+public class UnmodifiableSet {
+
+    public static void main(String[] args) {
+
+        Set<String> set = new HashSet<>();
+        set.add("Canada");
+        set.add("USA");
+
+        coreJDK(set);
+        guavaOf();
+        copyOf(set);
+        java9Of();
+    }
+
+    private static void java9Of() {
+        Set<String> immutable = Set.of("Canada", "USA");
+        System.out.println(immutable);
+    }
+
+    private static void guavaOf() {
+        Set<String> immutable = ImmutableSet.of("Canada", "USA");
+        System.out.println(immutable);
+    }
+
+    private static void copyOf(Set<String> set) {
+        Set<String> immutable = ImmutableSet.copyOf(set);
+        set.add("Costa Rica");
+        System.out.println(immutable);
+    }
+
+    private static void coreJDK(Set<String> set) {
+        Set<String> unmodifiableSet = Collections.unmodifiableSet(set);
+        set.add("Costa Rica");
+        System.out.println(unmodifiableSet);
+    }
+}

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

@@ -0,0 +1,39 @@
+package com.baeldung.set;
+
+import org.junit.Test;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+import static org.junit.Assert.assertEquals;
+
+public class SetExamplesUnitTest {
+
+    @Test
+    public void testUnmutableSet() {
+        Set<String> strKeySet = Set.of("key1", "key2", "key3");
+        try {
+            strKeySet.add("newKey");
+        } catch (UnsupportedOperationException uoe) {
+        }
+        assertEquals(strKeySet.size(), 3);
+    }
+
+    @Test
+    public void testArrayToSet() {
+        Integer[] intArray = new Integer[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
+        Set<Integer> intSet = Set.of(intArray);
+        assertEquals(intSet.size(), intArray.length);
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void testUnmodifiableSet() {
+        Set<String> set = new HashSet<>();
+        set.add("Canada");
+        set.add("USA");
+
+        Set<String> unmodifiableSet = Collections.unmodifiableSet(set);
+        unmodifiableSet.add("Costa Rica");
+    }
+}