docs: Explanation for Feature Toggle iluwatar#2230 Finished (iluwatar#2622)

* Added documentation for Feature Toggle design pattern

* Explanation for Feature Toggle Issue iluwatar#2230 finished, added intent, explanation, programmatic example, applicability and consequences

Author: Jack-Hodges

feature-toggle/README.md

@@ -10,10 +10,53 @@ tag:
 Feature Flag
 
 ## Intent
-Used to switch code execution paths based on properties or groupings. Allowing new features to be released, tested
-and rolled out. Allowing switching back to the older feature quickly if needed. It should be noted that this pattern,
-can easily introduce code complexity. There is also cause for concern that the old feature that the toggle is eventually
-going to phase out is never removed, causing redundant code smells and increased maintainability.
+A technique used in software development to control and manage the rollout of specific features or functionality in a 
+program without changing the code. It can act as an on/off switch for features depending on the status or properties of
+other values in the program. This is similar to A/B testing, where features are rolled out based on properties such as
+location or device. Implementing this design pattern can increase code complexity, and it is important to remember to
+remove redundant code if this design pattern is being used to phase out a system or feature.
+
+## Explanation
+Real-world Example
+> This design pattern works really well in any sort of development, in particular mobile development. Say you want to
+> introduce a feature such as dark mode, but you want to ensure that the feature works correctly and don't want to roll
+> out the feature to everyone immediately. You write in the code, and have it switched off as default. From here, it is
+> easy to turn on the code for specific users based on selection criteria, or randomly. This will also allow the feature
+> to be turned off easily without any drastic changes to the code, or any need for redeployment or updates.
+
+In plain words
+> Feature Toggle is a way to introduce new features gradually instead of deployment all at once.
+
+Wikipedia says
+> A feature toggle in software development provides an alternative to maintaining multiple feature branches in source 
+> code. A condition within the code enables or disables a feature during runtime. In agile settings the toggle is 
+> used in production, to switch on the feature on demand, for some or all the users.
+
+## Programmatic Example
+This example shows Java code that allows a feature to show when it is enabled by the developer, and when a user is a 
+Premium member of the application. This is useful for subscription locked features.
+```java
+public class FeatureToggleExample {
+    // Bool for feature enabled or disabled
+    private static boolean isNewFeatureEnabled = false;
+
+    public static void main(String[] args) {
+        boolean userIsPremium = true; // Example: Check if the user is a premium user
+
+        // Check if the new feature should be enabled for the user
+        if (userIsPremium && isNewFeatureEnabled) {
+            // User is premium and the new feature is enabled
+            showNewFeature();
+        }
+    }
+
+    private static void showNewFeature() {
+        // If user is allowed to see locked feature, this is where the code would go
+    }
+}
+```
+The code shows how simple it is to implement this design pattern, and the criteria can be further refined or broadened
+should the developers choose to do so.
 
 ## Class diagram
 ![alt text](./etc/feature-toggle.png "Feature Toggle")
@@ -24,7 +67,20 @@ Use the Feature Toggle pattern when
 * Giving different features to different users.
 * Rolling out a new feature incrementally.
 * Switching between development and production environments.
+* Quickly disable problematic features
+* External management of feature deployment
+* Ability to maintain multiple version releases of a feature
+* 'Hidden' deployment, releasing a feature in code for designated testing but not publicly making it available
+
+## Consequences
+Consequences involved with using the Feature Toggle pattern
+
+* Code complexity is increased
+* Testing of multiple states is harder and more time-consuming
+* Confusion between friends on why features are missing
+* Keeping documentation up to date with all features can be difficult 
 
 ## Credits
 
 * [Martin Fowler 29 October 2010 (2010-10-29).](http://martinfowler.com/bliki/FeatureToggle.html)
+* [Feature Toggle - Java Design Patterns](https://java-design-patterns.com/patterns/feature-toggle/)