6.1 Not: Add another example for better understanding

Author: karimdevelops

src/boolean/not.md

@@ -13,3 +13,15 @@ So in this case, I have stuck to my calorie limit if there are _not_ Oreos in th
 | ---------------- | ------------------- |
 | false            | true                |
 | true             | false               |
+
+```java,no_run
+boolean isLoggedIn = false;
+boolean isGuest = !isLoggedIn;
+```
+
+Now in this case, if user is _not_ logged in he is a guest.
+
+| isLoggedIn | isGuest |
+| ---------- | ------- |
+| false      | true    |
+| true       | false   |