code implemented

marker/src/main/java/App.java

@@ -2,5 +2,12 @@
  * Created by Alexis on 28-Apr-17.
  */
 public class App {
+  public static void main(String[] args) {
+    Guard guard = new Guard();
 
+    if (guard instanceof Permission) {
+      guard.enter();
+    }
+  }
 }
+

marker/src/main/java/Guard.java

@@ -0,0 +1,10 @@
+/**
+ * Created by Alexis on 29-Apr-17.
+ */
+public class Guard implements Permission {
+
+  protected static void enter() {
+    System.out.println("You can enter");
+  }
+
+}

marker/src/main/java/Permission.java

@@ -0,0 +1,7 @@
+/**
+ * Created by Alexis on 29-Apr-17.
+ * Interface without any methods
+ * Marker interface is based on that assumption
+ */
+public interface Permission {
+}