Add test for optional

Author: mperor

FirstSteps/src/test/java/pl/mperor/lab/java/lang/element/OptionalTest.java

@@ -0,0 +1,51 @@
+package pl.mperor.lab.java.lang.element;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+public class OptionalTest {
+
+    @Test
+    public void testOptionalImperatively() {
+        Assertions.assertFalse(SomeAPI.getNameById(0).isPresent());
+        // Please for(get), do not use get, instead use orElseThrow() / orElse("default")
+        Assertions.assertEquals("default", SomeAPI.getNameById(0).orElse("default"));
+        Assertions.assertEquals("some name", SomeAPI.getNameById(1).orElseThrow());
+    }
+
+    @Test
+    public void testOptionalFunctionally() {
+        SomeAPI.getNameById(1).ifPresentOrElse(
+                name -> Assertions.assertEquals("some name", name),
+                () -> Assertions.fail()
+        );
+    }
+
+    static class SomeAPI {
+
+        // 1. Return a reference if the value will always exist
+        // 2. Return an Optional<T> if the value may or may not exist
+        public static Optional<String> getNameById(long id) {
+            if (id == 0) {
+                return Optional.empty();
+            }
+
+            return Optional.of("some name");
+        }
+
+        // 3. Do not use Optional<T> for fields - overhead with little benefit
+        private String config;
+
+        // 4. Do not user Optional<T> for method parameters - user overloading instead
+        public void setConfig(String config) {
+            this.config = config;
+        }
+
+        public void setConfig() {
+            setConfig("default");
+        }
+    }
+
+}