Update "Java built-in Annotations" article

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/AnnotatedClass.java

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+package com.baeldung.annotations;
+
+import javax.annotation.Generated;
+
+@RetentionAnnotation
+@Generated("Avilable only on source code")
+public class AnnotatedClass {
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/RetentionAnnotation.java

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+package com.baeldung.annotations;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import static java.lang.annotation.ElementType.TYPE;
+
+@Target(TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface RetentionAnnotation {
+}

core-java-modules/core-java-annotations/src/test/java/com/baeldung/annotations/AnnotatedClassUnitTest.java

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+package com.baeldung.annotations;
+
+import org.junit.Test;
+
+import java.lang.annotation.Annotation;
+
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThat;
+
+public class AnnotatedClassUnitTest {
+
+    @Test
+    public void whenAnnotationRetentionPolicyRuntime_shouldAccess() {
+        AnnotatedClass anAnnotatedClass = new AnnotatedClass();
+        Annotation[] annotations = anAnnotatedClass.getClass().getAnnotations();
+        assertThat(annotations.length, is(1));
+    }
+}