Compare and differentiate controllers extensions and custom controller. How are they similar? How are they extraordinary?

 Both consider custom code to be utilized, taking into consideration custom data sets and custom activities. The extension mainly uses the current information and activities inside a standard or custom controller.

The Custom controllers must contain all data and activities that should be executed by the page. The extension that mainly expands the standard controller takes into account all the pages which usually use those extensions to be used as a part of the standard button overrides, custom buttons,  and over declarative features.