BAEL-3994: Add example of chaining methods returning Optionals (#9102)

* BAEL-3994: Add example of chaining methods returning Optionals

* BAEL-3994: Update

core-java-modules/core-java-optional/src/main/java/com/baeldung/orelseoptional/ItemsProvider.java

@@ -0,0 +1,21 @@
+package com.baeldung.orelseoptional;
+
+import java.util.Optional;
+
+public class ItemsProvider {
+
+    Optional<String> getEmptyItem() {
+        System.out.println("Returning an empty item");
+        return Optional.empty();
+    }
+
+    Optional<String> getNail() {
+        System.out.println("Returning a nail");
+        return Optional.of("nail");
+    }
+
+    Optional<String> getHammer() {
+        System.out.println("Returning a hammer");
+        return Optional.of("hammer");
+    }
+}

core-java-modules/core-java-optional/src/test/java/com/baeldung/orelseoptional/OrElseOptionalUnitTest.java

@@ -1,10 +1,10 @@
 package com.baeldung.orelseoptional;
 
-import static org.junit.Assert.assertEquals;
+import org.junit.Test;
 
 import java.util.Optional;
 
-import org.junit.Test;
+import static org.junit.Assert.assertEquals;
 
 public class OrElseOptionalUnitTest {
 
@@ -25,6 +25,28 @@ public class OrElseOptionalUnitTest {
         assertEquals(fallbackOptionalString, OptionalUtils.or(optionalString, fallbackOptionalString));
     }
 
+    @Test
+    public void givenTwoOptionalMethods_whenFirstEmpty_thenSecondEvaluated() {
+        ItemsProvider itemsProvider = new ItemsProvider();
+
+        Optional<String> item = itemsProvider.getEmptyItem()
+                .map(Optional::of)
+                .orElseGet(itemsProvider::getNail);
+
+        assertEquals(Optional.of("nail"), item);
+    }
+
+    @Test
+    public void givenTwoOptionalMethods_whenFirstNonEmpty_thenSecondNotEvaluated() {
+        ItemsProvider itemsProvider = new ItemsProvider();
+
+        Optional<String> item = itemsProvider.getNail()
+                .map(Optional::of)
+                .orElseGet(itemsProvider::getHammer);
+
+        assertEquals(Optional.of("nail"), item);
+    }
+
 //    Uncomment code when code base is compatible with Java 9
 //    @Test
 //    public void givenOptional_whenEmptyValue_thenCustomMessage() {