Adding Optional 2 Stream and Set.of examples.

core-java-9/src/test/java/com/baeldung/java9/OptionalToStreamTest.java

@@ -0,0 +1,21 @@
+package com.baeldung.java9;
+
+import java.util.Optional;
+import java.util.stream.Stream;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+
+public class OptionalToStreamTest {
+    
+    @Test
+    public void testOptionalToStream(){
+        Optional<String> op = Optional.ofNullable("String value");
+        Stream<String> strOptionalStream = op.stream();
+        Stream<String> filteredStream = strOptionalStream.filter(
+               (str) -> { return str != null && str.startsWith("String"); }
+               );
+        assertEquals(1, filteredStream.count());
+        
+    }
+}

core-java-9/src/test/java/com/baeldung/java9/SetExamplesTest.java

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+package com.baeldung.java9;
+
+
+import java.util.Set;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class SetExamplesTest {
+
+    @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);
+    }
+}