Added Marker Annotation example (#148)

Added Marker Annotation example

core-java/annotation-processing/introduction-to-annotations/src/main/java/com/reflectoring/CSV.java

@@ -0,0 +1,11 @@
+package com.reflectoring;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface CSV {
+}

core-java/annotation-processing/introduction-to-annotations/src/main/java/com/reflectoring/TestMarkerAnnotation.java

@@ -0,0 +1,16 @@
+package com.reflectoring;
+
+public class TestMarkerAnnotation {
+
+    public static void main(String[] args) {
+
+        XYZClient client = new XYZClient();
+        Class clientClass = client.getClass();
+
+        if (clientClass.isAnnotationPresent(CSV.class)){
+            System.out.println("Write client data to CSV.");
+        } else {
+            System.out.println("Write client data to Excel file.");
+        }
+    }
+}

core-java/annotation-processing/introduction-to-annotations/src/main/java/com/reflectoring/XYZClient.java

@@ -0,0 +1,6 @@
+package com.reflectoring;
+
+@CSV
+public class XYZClient {
+
+}